ALBERT

Description: Investing in the current reproduction requires diverting energy resources from other metabolic functions, which may compromise future reproduction and lifespan. To solve this trade-off, an individual may consider its labile state to decide how much to invest in current reproduction. We tested experimentally whether the “state quality” of male rock lizards influences their reproductive strategies. To improve the nutritional status of males before the mating season, we captured and supplemented experimental males (N = 20) with dietary vitamin D3 (an essential nutrient for lizards) and had a control group of males (N = 20). Then, we released all these males and females (N = 31) in a large semi-natural outdoor enclosure where lizards could interact and mate freely during the mating period. Activity levels of males did not vary between treatments, but supplemented males started fewer intrasexual agonistic interactions and made fewer mating advances to females. When the mating season ended, we incubated eggs laid by females to obtain the offspring and estimated the paternity of males using DNA microsatellites. Supplemented males sired fewer offspring than control males. These results suggest that vitamin D3 supplemented males used a low risk/less costly mating strategy to protect their assets (i.e., vitamin D reserves), but that still resulted in “some” current reproductive success, while likely increasing longevity and the expected future total reproductive success.

Description: New species can arise when female preferences and male sexual signals diverge across populations and thereby reduce mating between populations. Under this hypothesized mechanism for speciation, mate preferences and sexual signals should be correlated, but divergent, across populations. We evaluated this prediction using spadefoot toads (Spea multiplicata). We measured a sexually selected male signal (call rate) for which female preferences are known to vary across populations in response to the risk of hybridizing with another species. Contrary to expectation, we found no correlation between male call rate and female preferences across populations. We discuss possible mechanisms of this pattern, including the effect of gene flow from heterospecifics on male call rate. Our results suggest that, even when populations vary in mating traits, the independent evolution of female preferences and male sexual signals might impede reproductive isolation between populations.

Description: Synchronized male courtship signals are puzzling because males generally compete with each other for females. Male Austruca mjoebergi fiddler crabs wave in synchrony to attract females, but, all else being equal, females have a strong preference for “leader” males that can produce waves before other males (“followers”). So why do followers participate in synchrony? Here, we experimentally investigate three explanations for why followers might wave in synchrony: 1) followers obtain a small proportion of matings, 2) followers are more likely than a leader to attract females if they are positioned closer to her than is the leader, and 3) synchrony functions as a long-distance visual signal that attracts females so there is a net benefit to synchrony for all males. Using robotic male crabs, we found that females show a strong preference for leading males, but followers obtain a “better-than-nothing” proportion of mates. We also showed that closer proximity of a follower to the female did not affect her preference for leaders, although being a leader increased a male’s success when he was further from the female than were rival males. Finally, females were more likely to approach a distant group if there was a leader present, suggesting that followers do benefit from participating in synchrony.

Description: Decorating behavior is common in various animal taxa and serves a variety of functions from camouflage to communication. One predominant function cited for decoration is to avoid predators. Conspicuous, disc-like (discoid) silk decorations spun by orb-web Argiope juvenile spiders are hypothesized, among others, to defend spiders against visual predators by concealing spider outlines on the web, deflecting attacks, shielding them from view, or masquerading as bird-droppings. However, the direct evidence is limited for a specific mechanism by which discoid decorations may deter predators. Here we evaluate the mechanisms by which discoid decorations may defend Argiope juveniles against naïve chicks. Using visual modeling, we show that avian predators are able to distinguish spiders from discoid decorations. Using chick predation experiments, we found that the naïve chicks readily pecked any objects, ruling out the possibility of their neophobia. Significantly more chicks attacked spiders when they were exposed to chicks, regardless of whether their webs had discoid decorations, but few chicks attacked spiders when they were behind the decorations. We also found that significantly few chicks attacked decorations when spiders were absent or behind the decorations. We thus conclude that discoid decorations function to deter avian predators by shielding the spider from view or distracting, not by deflecting attacks, concealing the spider’s outline, or masquerading as bird-droppings. This study sheds light on the study of other similar anti-predator strategies, in a wide range of spider species and other animals that use decorating strategies.

Description: When individuals engage in fights with conspecifics over access to resources, injuries can occur. Most theoretical models suggest that the costs associated with these injuries should influence an individual’s decision to retreat from a fight. Thus, damage from intraspecific combat is frequently noted and quantified. However, the fitness-related costs associated with this damage are not. Quantifying the cost of fighting-related damage is important because most theoretical models assume that it is the cost associated with the damage (not the damage itself) that should influence an individual’s decision to retreat. Here, we quantified the cost of fighting-related injuries in the giant mesquite bug, Thasus neocalifornicus. We demonstrate that experimentally simulated fighting injuries result in metabolic costs and costs to flight performance. We also show that flight costs are more severe when the injuries are larger. Overall, our results provide empirical support for the fundamental assumption that damage acquired during intraspecific combat is costly.

Description: Group size can vary in relation to population density, habitat, and season. Habitat and season may also interact with population density and affect group size through varying foraging benefits of social aggregation in different ecological contexts. We tested the hypothesis that group size varies across ecological contexts, including population density, habitat type, and season, for woodland caribou (Rangifer tarandus) in ten herds over 25 years in Newfoundland, Canada. We predicted that group size would increase as a function of population density. Based on the foraging benefits of social aggregation, we predicted larger groups as habitat openness increased because open areas tend to have higher quality foraging resources. We predicted larger groups during winter when foraging resources are covered in snow because caribou and other social animals exploit social information about the location of foraging resources. In contrast to our prediction, group size decreased as a function of population density. In support of our prediction, group size was larger in winter than calving and summer, and we found that group size increased with habitat openness in some, but not all, cases. Patterns of animal grouping are context-dependent and the additive effect of different ecological contexts on variation in group size informs our understanding of the implicit trade-offs between competition, predation risk, and profitability of forage.

Description: Homophily by morphological and behavioral traits has been described in several species of vertebrates, but its functional consequences remain poorly studied. Homophily by plurally breeding females may improve direct fitness by enhancing reproductive success. Female mammals may exhibit phenotypical masculinization due to exposure to androgens during early development, a condition that is associated with maternal performance during subsequent breeding. Our goal was to assess whether female composition (in terms of masculinization) of plurally breeding groups influences female fitness in a natural population of degus (Octodon degus). We assessed if plurally breeding female degus assort themselves by anogenital distance (AGD), an accurate measure of masculinization level. We also quantified if homophily by AGD phenotype affects female reproductive success and the reproductive output of the group. Plurally breeding groups typically included similarly masculinized (i.e., long AGD) females or similarly feminized (short AGD) females, indicating a strong degree of homophily. Females weaned more offspring in plurally breeding groups with more masculinized females. Additionally, standardized variance in the number of offspring weaned decreased in plurally breeding groups with mostly masculinized females, indicating greater reproductive equality in these groups. We conclude that female degus organize into homophilic social groups of similar AGD, and that social groups of masculinized females exhibit a higher reproductive success.

Description: Elevated maternal glucocorticoid levels during gestation can lead to phenotypic changes in offspring via maternal effects. Although such effects have traditionally been considered maladaptive, maternally derived glucocorticoids may adaptively prepare offspring for their future environment depending upon the correlation between maternal and offspring environments. Nevertheless, relatively few studies test the effects of prenatal glucocorticoid exposure across multiple environments. We tested the potential for ecologically relevant increases in maternal glucocorticoids in the eastern fence lizard (Sceloporus undulatus) to induce adaptive phenotypic changes in offspring exposed to high or low densities of an invasive fire ant predator. Maternal treatment had limited effects on offspring morphology and behavior at hatching, but by 10 days of age, we found maternal treatment interacted with offspring environment to alter anti-predator behaviors. We did not detect differences in early-life survival based on maternal treatment or offspring environment. Opposing selection on anti-predator behaviors from historic and novel invasive predators may confound the potential of maternal glucocorticoids to adaptively influence offspring behavior. Our test of the phenotypic outcomes of transgenerational glucocorticoid effects across risk environments provides important insight into the context-specific nature of this phenomenon and the importance of understanding both current and historic evolutionary pressures.

Description: Breeding- and nest-site choice is a behavioral strategy often used to counter negative interactions. Site choices before breeding prevent costs of predation and competition but have been neglected in the context of brood parasitism. For hosts of brood parasites, the earlier brood parasitism is prevented in the breeding cycle the lower the future costs. Suitable nest-sites for cavity-nesting common redstarts (Phoenicurus phoenicurus), a host of the common cuckoo (Cuculus canorus), are a limited resource, but their cavity-nesting strategy could potentially deter predators and brood parasites. We altered the entrance size of breeding cavities and investigated redstart nest-site choice and its consequences to nest predation and brood parasitism risk, although accounting for potential interspecific competition for nest sites. We set-up paired nest-boxes and let redstarts choose between 7 cm and 5 cm entrance sizes. Additionally, we monitored occupancy rates in nest-boxes with 3 cm, 5 cm, and 7 cm entrance sizes and recorded brood parasitism and predation events. We found that redstarts preferred to breed in 5 cm entrance size cavities, where brood parasitism was eliminated but nest predation rates were comparable to 7 cm entrance size cavities. Only in 3 cm cavities both, brood parasitism and predation rates were reduced. In contrast to the other cavity-nesting species, redstart settlement was lowest in 3 cm entrance size cavities, potentially suggesting interspecific competition for small entrance size cavities. Nest-site choice based on entrance size could be a frontline defense strategy that redstarts use to reduce brood parasitism.

Description: Because sex ratios are a key factor regulating mating success and subsequent fitness both across and within species, there is widespread interest in how population-wide sex ratio imbalances affect marriage markets and the formation of families in human societies. Although most modern cities have more women than men and suffer from low fertility rates, the effects of female-biased sex ratios have garnered less attention than male-biased ratios. Here, we analyze how sex ratios are linked to marriages, reproductive histories, dispersal, and urbanization by taking advantage of a natural experiment in which an entire population was forcibly displaced during World War II to other local Finnish populations of varying sizes and sex ratios. Using a discrete time-event generalized linear mixed-effects model, and including factors that change across time, such as annual sex ratio, we show how sex ratios, reproduction, and migration are connected in a female-dominated environment. Young childless women migrated toward urban centers where work was available to women, and away from male-biased rural areas. In such areas where there were more females, women were less likely to start reproduction. Despite this constraint, women showed little flexibility in mate choice, with no evidence for an increase in partner age difference in female-biased areas. We propose that together these behaviors and conditions combine to generate an “urban fertility trap” which may have important consequences for our understanding of the fertility dynamics of today including the current fertility decline across the developed world.

Description: In response to environmental stimuli, including variation in the presence of conspecifics, genotypes show highly plastic responses in behavioral and physiological traits influencing reproduction. Although extensively documented in males, such female responses are rather less studied. We expect females to be highly responsive to environmental variation and to differentially allocate resources to increase offspring fitness, given the major contribution of mothers to offspring number, size, and developmental conditions. Using Drosophila melanogaster, we (a) manipulate exposure to conspecific females, which mothers could use to anticipate the number of potential mates and larval density, and; (b) test how this interacts with the spatial distribution of potential oviposition sites, with females from higher densities expected to prefer clustered resources that can support a larger number of larvae. We found that high density females were slower to start copulating and reduced their copulation duration, the opposite effect to that observed in males. There was a parallel, perhaps related, effect on egg production: females previously housed in groups laid fewer eggs than those housed in solitude. Resource patchiness also influenced oviposition behavior: females preferred aggregated substrate, which attracted more females to lay eggs. However, we found no interaction between prior housing conditions and resource patchiness, indicating that females did not perceive the value of different resource distributions differently when exposed to environments that could signal expected levels of larval competition. We show that, although exposure to consexual competition changes copulatory behaviors of females, the distribution of oviposition resources has a greater effect on oviposition decisions.

Description: Birdsong is typically seen as a long-range signal functioning in mate attraction and territory defense. Among birds, the zebra finch is the prime model organism in bioacoustics, yet almost exclusively studied in the lab. In the wild, however, zebra finch song differs strikingly from songbirds commonly studied in the wild as zebra finch males sing most after mating and in the absence of territoriality. Using data from the wild, we here provide an ecological context for a wealth of laboratory studies. By integrating calibrated sound recordings, sound transmission experiments and social ecology of zebra finches in the wild with insights from hearing physiology we show that wild zebra finch song is a very short-range signal with an audible range of about nine meters and that even the louder distance calls do not carry much farther (up to about fourteen meters). These integrated findings provide an ecological context for the interpretation of laboratory studies of this species and indicate that the vocal communication distance of the main laboratory species for avian acoustics contrasts strikingly with songbirds that use their song as a long-range advertisement signal.

Description: In some species, sperm form coordinated groups that are hypothesized to improve their swimming performance in competitive contexts or to navigate through the viscous fluids of the female reproductive tract. Here we investigate sperm aggregation across closely related species of Peromyscus mice that naturally vary by mating system to test the predictions that sperm aggregates 1) are faster than solitary sperm in species that females mate multiply to aid cells in sperm competition, and 2) outperform solitary sperm cells in viscous environments. We find significant variation in the size of sperm aggregates, which negatively associates with relative testis mass, a proxy for sperm competition risk, suggesting that postcopulatory sexual selection has a stabilizing effect on sperm group size. Moreover, our results show that sperm aggregates are faster than solitary sperm in some, but not all, species, and this can vary by fluid viscosity. Of the two species that produce the largest and most frequent groups, we find that sperm aggregates from the promiscuous P. maniculatus are faster than solitary sperm in every experimentally viscous environment but aggregation provides no such kinematic advantage under these same conditions for the monogamous P. polionotus. The reduced performance of P. polionotus aggregates is associated with less efficient aggregate geometry and the inclusion of immotile or morphological abnormal sperm. Our cross-species comparison yields insight into the evolution of sperm social behaviors, provides evidence of extensive variation in the Peromyscus lineage, and reveals that differences in sperm aggregate quality associate with postcopulatory sexual selection.

Description: Dispersal is one of the key elements of species’ metapopulation dynamics and, hence, influences global conservation status. Furthermore, determining the geographic variation in magnitude and direction of dispersal throughout a species’ distribution may expand our understanding of the causes of population declines in species of conservation concern. For instance, western burrowing owl (Athene cunicularia hypugaea) populations have declined at the northern and eastern edge of their breeding distribution during the 20th century. In the same period, large areas of thornscrub that did not support breeding owls were converted to irrigated agriculture in the southern edge of the subspecies’ breeding distribution in northwestern Mexico. These farmlands now support some of the highest breeding densities of owls. We tested the hypothesis that owls that colonized this recently created habitat originated from declining migratory populations from the northern portion of the subspecies’ range. We used stable isotopes 2H, 13C, and 15N in owl feathers to infer breeding dispersal patterns throughout the subspecies’ breeding range. Populations near the northern edge of the subspecies’ breeding range had immigrants that dispersed over larger distances than immigrants at low and mid latitude populations. However, agricultural populations in northwestern Mexico disrupted this latitudinal pattern, attracting owls from more distant locations. We also found immigrants originated from further distances in declining populations than increasing populations. Stable isotopes provided no evidence of contemporaneous breeding dispersal from Canadian populations to northwestern Mexico but suggest that agricultural areas in the southern edge of the subspecies’ distribution have altered the continental dispersal pattern.

Description: Ambient noise can cause birds to adjust their songs to avoid masking. Most studies investigate responses to a single noise source (e.g., low-frequency traffic noise, or high-frequency insect noise). Here, we investigated the effects of both anthropogenic and insect noise on vocalizations of four common bird species in Hong Kong. Common Tailorbirds (Orthotomus sutorius) and Eurasian Tree Sparrows (Passer montanus) both sang at a higher frequency in urban areas compared to peri-urban areas. Red-whiskered Bulbuls (Pycnonotus jocosus) in urban areas shifted the only first note of their song upwards. Swinhoe’s White-eye (Zosterops simplex) vocalization changes were correlated with noise level, but did not differ between the peri-urban and urban populations. Insect noise caused the Eurasian Tree Sparrow to reduce both maximum, peak frequency, and overall bandwidth of vocalizations. Insect noise also led to a reduction in maximum frequency in Red-whiskered bulbuls. The presence of both urban noise and insect noise affected the sound of the Common Tailorbirds and Eurasian Tree Sparrows; in urban areas, they no longer increased their minimum song frequency when insect sounds were also present. These results highlight the complexity of the soundscape in urban areas. The presence of both high- and low-frequency ambient noise may make it difficult for urban birds to avoid signal masking while still maintaining their fitness in noisy cities.

Description: Studies of self-organizing groups like schools of fish or flocks of birds have sought to uncover the behavioral rules individuals use (local-level interactions) to coordinate their motion (global-level patterns). However, empirical studies tend to focus on short-term or one-off observations where coordination has already been established or describe transitions between different coordinated states. As a result, we have a poor understanding of how behavioral rules develop and are maintained in groups. Here, we study the emergence and repeatability of coordinated motion in shoals of stickleback fish (Gasterosteus aculeatus). Shoals were introduced to a simple environment, where their spatio-temporal position was deduced via video analysis. Using directional correlation between fish velocities and wavelet analysis of fish positions, we demonstrate how shoals that are initially uncoordinated in their motion quickly transition to a coordinated state with defined individual leader-follower roles. The identities of leaders and followers were repeatable across two trials, and coordination was reached more quickly during the second trial and by groups of fish with higher activity levels (tested before trials). The rapid emergence of coordinated motion and repeatability of social roles in stickleback fish shoals may act to reduce uncertainty of social interactions in the wild, where individuals live in a system with high fission-fusion dynamics and non-random patterns of association.

Description: Facultative sexual organisms must allocate resources to both asexual and sexual reproduction. Optimal patterns of investment in sex depend on the relative costs and benefits of each reproductive mode, and may consequently be context- and condition-dependent. Two proposed explanations for the observed variation in investment in sex among facultative sexual lineages invoke alternative condition-dependent scenarios. Under the fitness-associated sex hypothesis, sex is predicted when individuals are in poor condition or experience stressful environments. Under the resource-demanding sex hypothesis, sex is only affordable to individuals in good condition experiencing favourable environments. Direct tests of these contrasting hypotheses are rare; moreover, investment in different components of sexual reproduction responds differently to cues promoting sex, and may be subject to different energetic constraints. Using genotypes of facultative sexual Daphnia carinata that differ in their level of investment in sex, we manipulated resource availability while accounting for day length (a seasonal cue for sex) to evaluate these hypotheses. The sexual response to day length depended on resource availability: increased day lengths and reduced food availability increased the production of sexual eggs, and relative investment in males, in a manner consistent with the fitness-associated sex hypothesis. The pattern of condition-dependence was specific to each component of reproductive investment – while male production covaried with asexual fecundity across genotypes, increased sexual egg production was associated with reduced asexual reproduction. Our results suggest that investment in sex is determined largely by its context-dependent advantages, and that this investment is not moderated by immediate costs to asexual reproduction.

Description: During biotic invasions, native prey are abruptly exposed to novel predators and are faced with unprecedented predatory pressures. Under these circumstances, the lack of common evolutionary history may hamper predator recognition by native prey, undermining the expression of effective antipredator responses. Nonetheless, mechanisms allowing prey to overcome evolutionary naïveté exist. For instance, in naïve prey, history of coevolution with similar native predators or detection of general traits characterizing predators can favor the recognition of stimuli released by invasive predators. However, few studies have assessed how these mechanisms shape prey response at the community level. Here, we evaluated behavioral responses in naïve larvae of 13 amphibian species to chemical and visual cues associated with an invasive predator, the American red swamp crayfish (Procambarus clarkii). Moreover, we investigated how variation among species responses was related to their coexistence with similar native crayfish predators. Amphibian larvae altered their behavior in presence of visual stimuli of the alien crayfish, while chemical cues elicited feeble and contrasting behavioral shifts. Activity reduction was the most common and stronger response, whereas some species exhibited more heterogeneous strategies also involving distancing and rapid escape response. Interestingly, species sharing coevolutionary history with the native crayfish were able to finely tune their response to the invasive one, performing bursts to escape. These results suggest native prey can respond to invasive predators through recognition of generic risk cues (e.g., approaching large shapes), still the capability of modulating antipredator strategies may also depend on their coevolutionary history with similar native predators.

Description: Competition structures ecological communities. In carnivorans, competitive interactions are disproportionately costly to subordinate carnivores who must account for the risk of interspecific killing when foraging. Accordingly, missed opportunity costs for meso-carnivores imposed by risk can benefit the smallest-bodied competitors. However, the extent to which the risk perpetuates into spatial partitioning in hierarchically structured communities remains unknown. To determine how risk-avoidance behaviors shape the space-use of carnivore communities, we studied a simple community of carnivores in northern Patagonia, Argentina: pumas (Puma concolor; an apex carnivore), culpeo foxes (Lycalopex culpaeus; a meso-carnivore), and chilla foxes (Lycalopex griseus; a small carnivore). We used multi-species occupancy models to quantify the space use within the carnivore community and giving-up densities to understand the behaviors that structure space use. Notably, we applied an analytical framework that tests whether the actual or perceived risk of predation most strongly influences the space use of subordinate carnivores although accounting for their foraging and vigilance behaviors. We found that there was a dominance hierarchy from the apex carnivore through the meso-carnivore to the subordinate small carnivore, which was reflected in space. Although both meso- and small carnivores exhibited similar predator avoidance behavioral responses to apex carnivores, the habitat associations of apex carnivores only altered meso-carnivore space use. The biases in risk management we observed for meso-carnivores likely translates into stable co-existence of this community of competing carnivores. We believe our analytical framework can be extended to other communities to quantify the spatial-behavioral tradeoffs of risk.

Description: Interspecific territoriality has complex ecological and evolutionary consequences. Species that interact aggressively often exhibit spatial or temporal shifts in activity that reduce the frequency of costly encounters. We analyzed data collected over a 13-year period on 50 populations of rubyspot damselflies (Hetaerina spp.) to examine how rates of interspecific fighting covary with fine-scale habitat partitioning and to test for agonistic character displacement in microhabitat preferences. In most sympatric species, interspecific fights occur less frequently than expected based on the species’ relative densities. Incorporating measurements of spatial segregation and species discrimination into the calculation of expected frequencies accounted for most of the reduction in interspecific fighting (subtle differences in microhabitat preferences could account for the rest). In 23 of 25 sympatric population pairs, we found multivariate differences between species in territory microhabitat (perch height, stream width, current speed, and canopy cover). As predicted by the agonistic character displacement hypothesis, sympatric species that respond more aggressively to each other in direct encounters differ more in microhabitat use and have higher levels of spatial segregation. Previous work established that species with the lowest levels of interspecific fighting have diverged in territory signals and competitor recognition through agonistic character displacement. In the other species pairs, interspecific aggression appears to be maintained as an adaptive response to reproductive interference, but interspecific fighting is still costly. We now have robust evidence that evolved shifts in microhabitat preferences also reduce the frequency of interspecific fighting.

Description: Animals can encode information within acoustic signals, particularly, bird songs can be remarkably complex and can indicate individual identity and quality. Two main sets of hypotheses attempt to explain the evolution of increased birdsong complexity across large-scale geographic ranges: 1) larger acoustic space availability, and 2) greater sexual selection intensity, both of which would favor the evolution of more complex songs at higher latitudes, more seasonal and/or species-poor environments. However, few studies have assessed patterns of song complexity for birds with broad geographic ranges. Here, we determined patterns of song variation in the blue-black grassquit (Volatinia jacarina), considering metrics of song complexity, structure and performance. This Neotropical bird occurs from Mexico to Argentina and produces a monosyllabic song. Using recordings from online databases, we calculated song metrics, such as bandwidth, song rate, number of song components, and proportion of vibratos of this signal. We found that song features varied with latitude, climate seasonality, bird species richness, and hemisphere. However, contrary to theoretical predictions, complexity mostly decreased with latitude and greater seasonality, while it was positively correlated with bird species richness. Proportion of vibratos was positively correlated with latitude and seasonality, and may be a feature under sexual selection in this species. Overall, our results did not support the main hypotheses proposed as explanations for song complexity. Our findings also highlight that song complexity does not vary uniformly among songbirds and song parameters, and future studies encompassing more species should clarify patterns and drivers of song variation across broad geographic dimensions.

Description: In the last few decades, there has been much research regarding the importance of social prestige in shaping the social structure of small-scale societies. While recent studies show that social prestige may have important health consequences, little is known about the extent to which prestige translates into actual in-person interactions and proximity, even though the level of integration into such real-life social networks has been shown to have important health consequences. Here, we determine the extent to which two different domains of social prestige, popularity (being perceived as a friend by others), and hunting reputation (being perceived as a good hunter), translate into GPS-derived in- and out-of-camp proximity networks in a group of egalitarian hunter-gatherer men, the Hadza. We show that popularity and hunting reputation differ in the extent to which they are translated into time spent physically close to each other. Moreover, our findings suggest that in-camp proximity networks, which are commonly applied in studies of small-scale societies, do not show the full picture of Hadza men’s social preferences. While men are in camp, neither popularity nor hunting reputation is associated with being central in the proximity network; however, when out of camp, Hadza men who are popular are more integrated in the proximity networks while men with better hunting reputations are less integrated. Overall, our findings suggest that, to fully understand social preferences among hunter-gatherers, both in-camp and out-of-camp proximity networks should be considered.

Description: Sensitive periods are widespread in nature, but their evolution is not well understood. Recent mathematical modeling has illuminated the conditions favoring the evolution of sensitive periods early in ontogeny. However, sensitive periods also exist at later stages of ontogeny, such as adolescence. Here, we present a mathematical model that explores the conditions that favor sensitive periods at later developmental stages. In our model, organisms use environmental cues to incrementally construct a phenotype that matches their environment. Unlike in previous models, the reliability of cues varies across ontogeny. We use stochastic dynamic programming to compute optimal policies for a range of evolutionary ecologies and then simulate developmental trajectories to obtain mature phenotypes. We measure changes in plasticity across ontogeny using study paradigms inspired by empirical research: adoption and cross-fostering. Our results show that sensitive periods only evolve later in ontogeny if the reliability of cues increases across ontogeny. The onset, duration, and offset of sensitive periods—and the magnitude of plasticity—depend on the specific parameter settings. If the reliability of cues decreases across ontogeny, sensitive periods are favored only early in ontogeny. These results are robust across different paradigms suggesting that empirical findings might be comparable despite different experimental designs.

Description: Examining the social behaviors of solitary species can be challenging due to the rarity in which interactions occur and the large and often inaccessible areas which these animals inhabit. As shared space-use is a prerequisite for the expression of social behaviors, we can gain insights into the social environments of solitary species by examining the degree of spatial overlap between individuals. Over a 10-year period, we examined how spatial overlap amongst 105 estuarine crocodiles Crocodylus porosus was influenced by season, sex, and movement tactic. We discovered that crocodiles displayed highly consistent spatial overlaps with conspecifics between months and across years. Furthermore, male crocodiles that exhibited a greater degree of site fidelity displayed more stable social environments, while females and males that were less site-attached had more dynamic social environments with spatial overlaps between conspecifics peaking during the mating season. Our results demonstrate how long-term tracking of multiple individuals within the same population can be used to quantify the spatial structure and social environment of cryptic and solitary species.

Description: Disassortative mating in color-polymorphic raptors is a proposed mechanism for the maintenance of color polymorphism in populations. Selection for such a mating system may occur if there are fitness advantages of mating with a contrasting morph. In the black sparrowhawk (Accipiter melanoleucus), mixed-morph pairs may have a selective advantage because they produce offspring that have higher survival rates. Two hypotheses, which may explain the mechanism, are the “avoidance-image” and “complementarity” hypotheses. The first suggests that, within a predator’s territory, prey develop a search image for the more commonly encountered parental morph, for example, the male morph during incubation and brooding. Females of a contrasting morph to their partner would then have higher capture rates once they commence hunting in the later nestling phase. Thus, the “avoidance-image” hypothesis predicts higher provisioning rates for mixed-morph pairs. Alternatively, the “complementarity” hypothesis posits that different color morphs exploit different environmental conditions, allowing mixed-morph pairs to hunt under a wider range of conditions and predicts that food is delivered more consistently. We test these hypotheses using nest cameras to record prey delivery rates during the late nestling phase when both parents are hunting. We found support for the “complementarity” hypothesis, with mixed-morph pairs delivering food more consistently but not at a higher rate. This higher consistency in prey deliveries may explain the improved survival of the offspring of mixed-morph pairs and could, therefore, play a role in maintaining the stability of color polymorphism in this system.

Description: In species with long-term social relationships, the ability to recognize individuals after extended separation and the ability to discriminate between former social affiliates that have died and those that have left the group but may return are likely to be beneficial. Few studies, however, have investigated whether animals can make these discriminations. We presented acorn woodpeckers (Melanerpes formicivorus), a group-living, cooperatively breeding bird, with playbacks of current group members, former group members still living nearby, former group members that had died or left the study area, and familiar nongroup members. Subjects responded more quickly to the calls of nongroup members than to the calls of current group members or former group members still living in the study area but did not discriminate between nongroup members and former group members that had died or disappeared. This suggests that acorn woodpeckers can vocally recognize both current group members and former group members that have dispersed to nearby groups and that they either forget former group members that no longer live in the vicinity or classify them differently from former group members that still live nearby. This study suggests an important role for vocal recognition in maintaining valuable relationships with social affiliates postdispersal.

Description: Forming strong social bonds can lead to higher reproductive success, increased longevity, and/or increased infant survival in several mammal species. Given these adaptive benefits, understanding what determines partner preferences in social bonding is important. Maternal relatedness strongly predicts partner preference across many mammalian taxa. The role of paternal relatedness, however, has received relatively little attention, even though paternal and maternal kin share the same number of genes, and theoretically similar preferences would therefore be expected for paternal kin. Here, we investigate the role of maternal and paternal relatedness in female affiliation in Assamese macaques (Macaca assamensis), a species characterized by a relatively low male reproductive skew. We studied a wild population under natural conditions using extensive behavioral data and relatedness analyses based on pedigree reconstruction. We found stronger affiliative relationships and more time spent grooming between maternal kin and paternal half-sisters compared with nonkin, with no preference of maternal over paternal kin. Paternally related and nonrelated dyads did not form stronger relationships when they had less close maternal kin available, but we would need a bigger sample size to confirm this. As expected given the low reproductive skew, affiliative relationships between paternal half-sisters closer in age were not stronger than between paternal half-sisters with larger age differences, suggesting that the kin bias toward paternal kin was not mediated by age similarity. An alternative way through which paternal kin could get familiarized is mother- and/or father-mediated familiarity.

Description: In polygynous species, male reproductive success is predicted to be monopolized by a few dominant males. This prediction is often not supported, suggesting that ecological and alternative mating tactics influence siring success. The spatiotemporal distribution of individuals and the number of males competing for each receptive female are often overlooked because they are difficult to monitor in wild animals. We examined how spatial overlap of female–male pairs, the time spent by a male on the breeding site, number of competitors, and morphological traits influence siring probability in eastern gray kangaroos (Macropus giganteus). We compared home range overlap for 12 208 dam–male pairs and 295 known dam–sire pairs to define local competitive groups and to estimate every male’s opportunity to sire the young of each female. We compared models considering morphological traits relative to the entire population or to local competitive groups. Including local competition improved model performance because it estimated the intensity of competition and compared each male’s morphological traits to those of its competitive group. Regardless of size, males can increase their probability to sire a young by increasing their mating opportunity relative to the mother. We underline the importance of considering spatial structure to assess the intensity of competition in species where males cannot equally access all females in a population. The estimation of mating opportunity and intensity of local competition improves our understanding of how morphological traits affect siring success when each mating event involves a different set of competing males, a characteristic of most wild species.

Description: Individual niche specialization can have important consequences for competition, fitness, and, ultimately, population dynamics and ecological speciation. The temporal window and the level of daily activity are niche components that may vary with sex, breeding season, food supply, population density, and predator’s circadian rhythm. More recently, ecologists emphasized that traits such as dispersal and space use could depend on personality differences. Boldness and exploration have been shown to correlate with variation in foraging patterns, habitat use, and home range. Here, we assessed the link between exploration, measured from repeated novel environment tests, activity patterns, and temporal niche specialization in wild eastern chipmunks (Tamias striatus). Intrinsic differences in exploration should drive daily activity patterns through differences in energy requirements, space use, or the speed to access resources. We used collar-mounted accelerometers to assess whether individual exploration profiles predicted: 1) daily overall dynamic body acceleration, reflecting overall activity levels; 2) mean activity duration and the rate of activity sequences, reflecting the structure of daily activity; and 3) patterns of dawn and dusk activity, reflecting temporal niche differentiation. Exploration and overall activity levels were weakly related. However, both dawn activity and rate of activity sequences increased with the speed of exploration. Overall, activity patterns varied according to temporal variability in food conditions. This study emphasizes the role of intrinsic behavioral differences in activity patterns in a wild animal population. Future studies will help us understand how yearly seasonality in reproduction, food abundance, and population density modulate personality-dependent foraging patterns and temporal niche specialization.

Description: Species with genetically differentiated allopatric populations commonly differ in phenotypic traits due to drift and/or selection, which can be important drivers of reproductive isolation. Wedge-tailed sabrewing (Campylopterus curvipennis) is a species complex composed of three genetically and acoustically differentiated allopatric lineages that correspond to currently recognized subspecies in Mexico: C. c. curvipennis (Sierra Madre Oriental), C. c. pampa (Yucatán Peninsula), and C. c. excellens (Los Tuxtlas). Although excellens is taxonomically recognized as a distinct species, there is genetic evidence that lineages excellens and curvipennis have diverged from each other later than pampa. In this study, we experimentally tested C. c. curvipennis song recognition as a major factor in premating reproductive isolation for lineage recognition. To this end, we conducted a song playback experiment to test whether territorial males of one C. c. curvipennis lek discriminate among potential competitors based on male songs from the three lineages. Males of curvipennis responded more aggressively to songs of their own lineage and excellens, than to songs of the most divergent lineage pampa, as evidenced by significant differences in a variety of intensity and latency response variables. This indicate that the pampa male song does not represent a competitive threat as curvipennis and excellens songs, in which divergence and song recognition represent premating reproductive isolation between these isolated lineages. However, the acoustic limits between curvipennis and excellens might be attenuated by gene flow in case of secondary contact between them, despite the strong and relatively rapid divergence of their sexually selected song traits.

Description: Variation in animal material technology, such as tool use and nest construction, is thought to be caused, in part, by differences in the early-life socio-ecological environment—that is, who and what is around—but this developmental hypothesis remains unconfirmed. We used a tightly controlled developmental paradigm to determine whether adult and/or raw-material access in early life shape first-time nest construction in laboratory-bred zebra finches Taeniopygia guttata at sexual maturity. We found that juvenile access to both an unrelated adult and raw material of one color led to a majority preference (75%) by novice builders for this color of material over that for either natal-nest or novel-colored material, whereas a lack of juvenile access to both an unrelated adult and raw material led to a 4- and nearly 3-fold reduction in the speed at which novice builders initiated and completed nest construction, respectively. Contrary to expectation, neither the amount of time juveniles nor their adult groupmate spent handling the raw material appear to drive these early-life effects on zebra finches’ first-time nest construction, suggesting that adult presence might be sufficient to drive the development of animal material technology. Together these data show that the juvenile socio-ecological environment can trigger variation in at least two critical aspects of animal material technology (material preference and construction speed), revealing a potentially powerful developmental window for technological advancement. Thus, to understand selection on animal material technology, the early-life environment must be considered.

Description: Anthropogenic noise is an increasingly widespread pollutant, with a rapidly burgeoning literature demonstrating impacts on humans and other animals. However, most studies have simply considered if there is an effect of noise, examining the overall cohort response. Although substantial evidence exists for intraspecific variation in responses to other anthropogenic disturbances, this possibility has received relatively little experimental attention with respect to noise. Here, we used field-based playbacks with dwarf mongooses (Helogale parvula) to test how traffic noise affects vigilance behavior and to examine potential variation between individuals of different age class, sex, and dominance status. Foragers exhibited a stronger immediate reaction and increased their subsequent vigilance (both that on the ground and as a sentinel) in response to traffic-noise playback compared with ambient-sound playback. Traffic-noise playback also resulted in sentinels conducting longer bouts and being more likely to change post height or location than in ambient-sound playback. Moreover, there was evidence of variation in noise responses with respect to age class and dominance status but not sex. In traffic noise, foraging pups were more likely to flee and were slower to resume foraging than adults; they also tended to increase their vigilance more than adults. Dominants were more likely than subordinates to move post during sentinel bouts conducted in traffic-noise trials. Our findings suggest that the vigilance–foraging trade-off is affected by traffic noise but that individuals differ in how they respond. Future work should, therefore, consider intrapopulation response variation to understand fully the population-wide effects of this global pollutant.

Description: Theoretical models of animal contests such as the Hawk-Dove game predict that variation in fighting behavior will persist due to mixed evolutionarily stable strategies (ESS) under certain conditions. However, the genetic basis for this variation is poorly understood and a mixed ESS for fighting can be interpreted in more than one way. Specifically, we do not know whether variation in aggression within a population arises from among-individual differences in fixed strategy (determined by an individual’s genotype—direct genetic effects [DGEs]), or from within-individual variation in strategy across contests. Furthermore, as suggested by developments of the original Hawk-Dove model, within-individual variation in strategy may be dependent on the phenotype and thus genotype of the opponent (indirect genetic effects—IGEs). Here we test for the effect of DGEs and IGEs during fights in the beadlet sea anemone Actinia equina. By exploiting the unusual reproductive system of sea anemones, combined with new molecular data, we investigate the role of both additive (DGE + IGE) and non-additive (DGE × IGE) genetic effects on fighting parameters, the latter of which have been hypothesized but never tested for explicitly. We find evidence for heritable variation in fighting ability and that fight duration increases with relatedness. Fighting success is influenced additively by DGEs and IGEs but we found no evidence for non-additive IGEs. These results indicate that variation in fighting behavior is driven by additive indirect genetic effects (DGE + IGE), and support a core assumption of contest theory that strategies are fixed by DGEs.

Description: Socially monogamous females regularly mate with males outside the pair bond. The prevailing explanation for this behavior is that females gain genetic benefits resulting from increased fitness of extra-pair offspring. Furthermore, because of the risk of reduced paternal care in response to cuckoldry, females are expected to seek extra-pair copulations when they can rear offspring with little help from their social partner (“constrained female” hypothesis). We tested these hypotheses and analyzed variation in paternal care in the Afrotropical, facultative cooperative breeding placid greenbul (Phyllastrephus placidus). Overall, approximately 50% of the offspring resulted from extra-pair (and extra-group) mating. Identified extra-pair males were in most cases neighboring dominant males, yet never within-group subordinates. As predicted by the constrained female hypothesis, the occurrence of extra-pair paternity (EPP) increased with the number of cooperative helpers (and not with total group size). However, dominant males did not adjust their food provisioning rates in response to EPP. Although extra-pair males were more strongly related to the dominant female and less heterozygous than the latter’s social mate, this did not result in more inbred extra-pair offspring, likely because identified extra-pair males were not representative of the extra-pair male population. While earlier studies on EPP mainly focused on male genetic quality, results from this study provide evidence that female’s social context may affect extra-pair strategies too.

Description: Why females pair with already mated males and the mechanisms behind variation in such polygynous events within and across populations and years remain open questions. Here, we used a 19-year data set from a pied flycatcher (Ficedula hypoleuca) population to investigate, through local networks of breeding pairs, the socio-ecological factors related to the probability of being involved in a polygynous event in both sexes. Then, we examined how the breeding contexts experienced by individuals shaped the spatial and temporal separation between broods of polygamous males. The probability of polygyny decreased with the distance between nests. Indeed, secondary females were often close neighbors of primary females, although the distance between both nests increased slightly with increasing synchrony between them. The probability of polygyny was also related to the breeding time of individuals because early breeding males were more likely to become polygynous with late-breeding females. Throughout the season, there was substantial variation in the temporal separation between primary and secondary broods, and this separation was, in turn, related to the breeding asynchrony of the polygamous males (in the primary nest) relative to the neighbors. Polygynous males that bred late relative to their neighbors had a short time window to attract a second female and, thus, the breeding interval between their primary and secondary broods was reduced. Overall, the spatial proximity between polygynous males’ broods and, if the opportunity existed, their temporal staggering are compatible with a male strategy to maximize paternity and reduce the costs of caring for two broods, though the effect of female’s interest, either primary or secondary, cannot be fully ruled out. We highlight that a comprehensive assessment of the breeding contexts faced by individuals is essential to understand mating decisions and reconcile the discrepancies raised by previous work on social polygyny.

Description: Sexual size dimorphism is biased toward males in most mammalian species. The most common explanation is precopulatory intramale sexual selection. Large males win fights and mate more frequently. In artiodactyls, previous tests of this hypothesis consisted of interspecific correlations of sexual dimorphism with group size as a surrogate for the intensity of sexual selection (Is). However, group size is not a proper measure of sexual selection for several reasons as is largely recognized in other mammalian taxa. I conducted an interspecific test on the role of sexual selection in the evolution of sexual dimorphism using the variance in genetic paternity as a proxy for the Is. I reviewed the literature and found 17 studies that allowed estimating Is= V/(W2), where V and W are the variance and mean number of offspring per male, respectively. A phylogenetic generalized least squares analysis indicated that dimorphism (Wm/Wf) showed a significant positive regression with the intensity of sexual selection but not group size (multiple r2= 0.40; F3,17= 12.78, P = 0.002). This result suggests that sexual selection may have played a role in the evolution of sexual size dimorphism in Artiodactyla. An alternative hypothesis based on natural selection is discussed.

Description: Generalist invasive predators consume prey at different trophic levels and generate drastic changes in local communities. However, the long-term effects of predation may be reduced by eco-evolutionary responses of native populations. The capacity of prey species distributed across the trophic network to develop antipredator responses may determine the ecosystem potential to buffer against the invader. The African clawed frog is a major invader on several continents. Because of its large size, generalist diet, and aquatic lifestyle, we predicted the development of antipredator responses in prey species at different trophic levels. We tested for behavioral shifts between populations within and outside the invasive range in the herbivorous snail Physella acuta and the predatory heteropteran, the backswimmer Notonecta glauca. We detected antipredator responses in both prey species. In sympatry, P. acuta stayed higher in the water column, while N. glauca spent more time swimming underwater and less time surfacing when the predator cues were present. In allopatry, P. acuta dived deeper and N. glauca spent more time surfacing and stayed longer still underwater. In both species, sympatric populations showed evidence of olfactory recognition of the frog. Our results show that the introduction of a top predator like Xenopus laevis in the pond ecosystem drives behavioral antipredator responses in species across the trophic network. Eco-evolutionary processes may allow some degree of long-term resilience of pond communities to the invasion of X. laevis.

Description: Carotenoid-based traits commonly act as condition-dependent signals of quality to both males and females. Such colors are typically quantified using summary metrics (e.g., redness) derived by partitioning measured reflectance spectra into blocks. However, perceived coloration is a product of the whole spectrum. Recently, new methods have quantified a range of environmental factors and their impact on reflection data at narrow wavebands across the whole spectrum. Using this approach, we modeled the reflectance of red integumentary eye combs displayed by male black grouse (Lyrurus tetrix) as a function of ornament size and variables related to male quality. We investigated the strength and direction of effect sizes of variables at each waveband. The strongest effect on the spectra came from eye comb size, with a negative effect in the red part of the spectrum and a positive effect in ultraviolet reflectance. Plasma carotenoid concentration and body mass were also related to reflectance variance in differing directions across the entire spectra. Comparisons of yearlings and adults showed that the effects were similar but stronger on adult reflectance spectra. These findings suggest that reflectance in different parts of the spectrum is indicative of differing components of quality. This method also allows a more accurate understanding of how biologically relevant variables may interact to produce perceived coloration and multicomponent signals and where the strongest biological effects are found.

Description: Extrapair paternity should contribute to sexual selection by increasing the number of potential mates available to each individual. Potential copulation partners are, however, limited by their proximity. Spatial constraints may therefore reduce the impact of extrapair paternity on sexual selection. We tested the effect of spatial constraints on sexual selection by simulating extrapair copulations for 15 species of socially monogamous songbirds with varying rates of extrapair paternity. We compared four metrics of sexual selection between simulated populations without spatial constraints and populations where extrapair copulations were restricted to first- and second-order neighbors. Counter to predictions, sexual selection as measured by the Bateman gradient (the association between the number of copulation partners and offspring produced) increased under spatial constraints. In these conditions, repeated extrapair copulations between the same individuals led to more offspring per copulation partner. In contrast, spatial constraints did somewhat reduce sexual selection—as measured by the opportunity for selection, s’max, and the selection gradient on male quality—when the association between simulated male quality scores and copulation success (e.g., female preferences or male–male competition) was strong. Sexual selection remained strong overall in those populations even under spatial constraints. Spatial constraints did not substantially reduce sexual selection when the association between male quality and copulation success was moderate or weak. Thus, spatial constraints on extrapair copulations are insufficient to explain the absence of strong selection on male traits in many species.

Description: Natal dispersal is a crucial life-history trait that affects both individual fitness and population structure, yet drivers of variation in dispersal probability and distance are difficult to study in wild populations. In cooperatively breeding species, individuals typically delay dispersal beyond their first breeding season and remain on the natal territory as nonbreeders, which prolongs social dynamics that can affect dispersal decisions. Using a 35-year data set covering almost 600 dispersal events in the cooperatively breeding Florida scrub-jay (Aphelocoma coerulescens), we examined the environmental and social parameters that predict dispersal probability over time and distance. In both sexes, dispersal probability increased with age, which, in turn, was negatively correlated with dispersal distance. In males, individuals occupying low-quality natal territories and living with a stepfather had an increased probability of dispersal. Older and more dominant males were more likely to inherit their natal territory. In females, which generally disperse earlier and farther than males, socially subordinate jays dispersed farther than dominant ones. Overall, jays that delayed dispersal the longest were more likely to attain breeding status near their natal territory, which was previously found to be associated with increased survival and lifetime fitness. Our results suggest that social dynamics and environmental factors on the natal territory affect delayed dispersal patterns differently for the two sexes in this cooperative breeder.

Description: Metabarcoding of prey DNA from fecal samples can be used to design behavioral experiments to study the foraging behavior and sensory ecology of predators. The frog-eating bat, Trachops cirrhosus, eavesdrops on the mating calls of its anuran prey. We captured wild T. cirrhosus and identified prey remains in the bats’ fecal samples using DNA metabarcoding of two gene regions (CO1 and 16S). Bats were preying on frogs previously unknown in their diet, such as species in the genus Pristimantis, which occurred in 29% of T. cirrhosus samples. Twenty-three percent of samples also contained DNA of Anolis lizards. We additionally report apparently rare predation events on hummingbirds and heterospecific bats. We used results from metabarcoding to design acoustic and 3D model stimuli to present to bats in behavioral experiments. We show predatory responses by T. cirrhosus to the calls of the frog Pristimantis taeniatus and to the rustling sounds of anoles moving through leaf-litter, as well as attacks on a stuffed hummingbird and a plastic anole model. The combination of species-specific dietary information from metabarcoding analyses with behavioral responses to prey cues provides a unique window into the foraging ecology of predators that are difficult to observe in the wild.

Description: Asymmetry of the brain and behavior (lateralization) is widespread in the animal kingdom and could be particularly advantageous for gregarious organisms. Here, we investigate the possibility that lateralized behaviors affect the structure of foraging flocks. Phalaropes (Scolopacidae: Phalaropus) are highly aquatic shorebirds and the only vertebrates that spin on the water to feed, often in large flocks. There is anecdotal evidence that individuals spin in a single direction and that those spinning counter the majority are usually found at the periphery of a flock. Although such phenotypic segregation may reduce interference among socially foraging birds, its extent and underlying mechanism remain unexplored. Using over 900 spinning bouts from freely available video repositories, we find support for individual, but not population, lateralization of spinning in the three phalarope species. Although spinning direction was not determined by the position occupied within a flock (periphery vs. core), nearest neighbors were more likely to spin in the same direction; moreover, they were three times less likely to interfere with each other when aligning spinning direction. Our results indicate that a simple rule (keep foraging with similarly lateralized individuals) can generate self-organized interactions among flockmates, resulting in groups phenotypically assorted.

Description: A widespread hypothesis for the ontogeny of behavior and decision-making is the early-exploration-later-canalization hypothesis. It postulates that juveniles are more exploratory and adults more consistent in their behavior. In addition, it is often assumed that naïve juveniles could overcome the costs of individual experience building by copying more the decisions of others than adults (early-conformism-later-self-defining hypothesis). Here, we compare the central place foraging movements of adults and postfledging juveniles in their first flights around the colony before dispersal and migration in two sympatric species of tropical seabirds: red-footed boobies and great frigatebirds. Using GPS records of individual movements, we analyzed the foraging directions of seabirds from the colony across successive trips. Juveniles of both species showed significant within-individual consistency in foraging direction but at lower levels than adults. Juveniles leaving the colony within the same time window showed significant but low between-individual resemblance in foraging direction at levels similar to adults. In both species, homing efficiency was lower in juveniles than in adults. Juvenile foraging directions were initially influenced by wind conditions, particularly in low wing loading frigatebirds. Wind conditions progressively lost influence on juvenile foraging directions during their first weeks of flights. In contrast, within-individual consistency, between-individual resemblance, and homing efficiency did not show signs of progression in juveniles. Our results support the early-exploration-later-canalization hypothesis but not the early-conformism-later-self-defining hypothesis. Relaxed constraints on self-feeding efficiency could favor high variability in postfledging tropical seabirds. Our simple approach could be applied to further test these hypotheses by comparing strategies across a wide range of central place foragers.

Description: Navigating social relationships frequently rests on the ability to recognize familiar individuals using phenotypic characteristics. Across diverse taxa, animals vary in their capacities for social recognition, but the ecological and social sources of selection for recognition are often unclear. In a comparative study of two closely related species of poison frogs, we identified a species difference in social recognition of territory neighbors and investigated potential sources of selection underlying this difference. In response to acoustic playbacks, male golden rocket frogs (Anomaloglossus beebei) recognized the calls of neighbors and displayed a “dear enemy effect” by responding less aggressively to neighbors’ calls than strangers’ calls. In contrast, male Kai rocket frogs (Anomaloglossus kaiei) were equally aggressive to the calls of neighbors and strangers. This species difference in behavior is associated with key differences in reproductive ecology and characteristics of territories. Golden rocket frogs defend reproductive resources in the form of bromeliads, which is expected to create a threat asymmetry between neighbors and strangers favoring decreased aggression to neighbors. In contrast, Kai rocket frogs do not defend reproductive resources. Further, compared with Kai rocket frog territories, golden rocket frog territories occur at higher densities and are defended for longer periods of time, creating a more complex social environment with more opportunities for repeated but unnecessary aggression between neighbors, which should favor the ability to recognize and exhibit less aggression toward neighbors. These results suggest that differences in reproductive ecology can drive changes in social structure that select for social recognition.

Description: The development of numerical methods for inferring social ranks has resulted in an overwhelming array of options to choose from. Previous work has established the validity of these methods through the use of simulated datasets, by determining whether a given ranking method can accurately reproduce the dominance hierarchy known to exist in the data. Here, we offer a complementary approach that assesses the reliability of calculated dominance hierarchies by asking whether the calculated rank order produced by a given method accurately predicts the outcome of a subsequent contest between two opponents. Our method uses a data-splitting “training–testing” approach, and we demonstrate its application to real-world data from wild vervet monkeys (Chlorocebus pygerythrus) collected over 3 years. We assessed the reliability of seven methods plus six analytical variants. In our study system, all 13 methods tested performed well at predicting future aggressive outcomes, despite some differences in the inferred rank order produced. When we split the dataset with a 6-month training period and a variable testing dataset, all methods predicted aggressive outcomes correctly for the subsequent 10 months. Beyond this 10-month cut-off, the reliability of predictions decreased, reflecting shifts in the demographic composition of the group. We also demonstrate how a data-splitting approach provides researchers not only with a means of determining the most reliable method for their dataset but also allows them to assess how rank reliability changes among age–sex classes in a social group, and so tailor their choice of method to the specific attributes of their study system.

Description: In cooperatively breeding species, nonbreeding individuals provide alloparental care and help in territory maintenance and defense. Antipredator behaviors of subordinates can enhance offspring survival, which may provide direct and indirect fitness benefits to all group members. Helping abilities and involved costs and benefits, risks, and outside options (e.g., breeding independently) usually diverge between group members, which calls for status-specific differentiated behavioral responses. Such role differentiation within groups may generate task-specific division of labor, as exemplified by eusocial animals. In vertebrates, little is known about such task differentiation among group members. We show how breeders and helpers of the cooperatively breeding cichlid Neolamprologus savoryi partition predator defense depending on intruder type and the presence of dependent young. In the field, we experimentally simulated intrusions by different fish species posing a risk either specifically to eggs, young, or adults. We used intrusions by harmless algae eaters as a control. Breeders defended most when dependent young were present, while helper investment hinged mainly on their body size and on the potential threat posed by the respective intruders. Breeders and helpers partitioned defense tasks primarily when dependent young were exposed to immediate risk, with breeders investing most in antipredator defense, while helpers increased guarding and care in the breeding chamber. Breeders’ defense likely benefits helpers as well, as it was especially enhanced in the treatment where helpers were also at risk. These findings illustrate that in a highly social fish different group members exhibit fine-tuned behavioral responses in dependence of ecological and reproductive parameter variation.

Description: In response to the reduction in fitness associated with sperm competition, males are expected to evolve tactics that hinder female remating. For example, females often display a postmating reduction in their sexual receptivity that has been shown to be mediated by proteins contained in a male’s seminal fluid (sfps). However, although there has been comprehensive research on sfps in genetically well-characterized species, few nonmodel species have been studied in such detail. We initially confirm that female Australian field crickets, Teleogryllus oceanicus, do display a significant reduction in their mate-searching behavior 24 h after mating. This effect was still apparent 3 days after mating but was entirely absent after 1 week. We then attempted to identify the sfps that might play a role in inducing this behavioral response. We identified two proteins, ToSfp022 and ToSfp011, that were associated with the alteration in female postmating behavior. The knockdown of both proteins resulted in mated females that displayed a significant increase in their mate-searching behaviors compared with females mated to males having the full compliment of seminal fluid proteins in their ejaculate. Our results indicate that the female refractory period in T. oceanicus likely reflects a sperm competition avoidance tactic by males, achieved through the action of male seminal fluid proteins.

Description: Should females prefer older males as mates? Male survival to old age might indicate the presence of fitness-enhancing genes that increase offspring fitness. However, many correlational studies show that mating with older males can lower female fecundity and even reduce offspring fitness due to epigenetic or germline mutation effects. One problem in quantifying female choice based on male age is that age is usually confounded with mating history. This begs a question: Do females choose males based on their age or their mating history? The answer requires an experimental approach, but few such studies exist. Here, we test if experimentally induced variation in the mating history of old and young males (12-week difference in postmaturity age) affects female choice in the eastern mosquitofish (Gambusia holbrooki). To vary mating history, adult males were either allowed to freely mate with females for 3 weeks or they only had visual contact with females. Immediately thereafter, we ran four-choice mating trials, using association time, to test the effects of male age and mating history (2 × 2 design) on male attractiveness. Females did not show a clear preference for males based on either characteristic. This was not due to a lack of female choice: females spent significantly more time with larger males. In addition, female choice was significantly repeatable across four trials: twice as a virgin and twice as a nonvirgin. Finally, female mating status (virgin or nonvirgin) did not affect her choice of mate, although virgin females spent significantly more time associating with test males.

Description: Animals, including humans, must make sense of information, bombarding them from the enviroment, quickly and effectively. Categorical perception is one such process, and the evidence for it is increasing. We argue that the next step in the research of category-based decision making should be to study wild animals in the field and in behavioral contexts that have strong fitness-relevant impacts. We illustrate this point by the promise of categorical perception in the rejection of foreign egg colors by American robins (Turdus migratorius).

Description: Conflicts in animals are usually resolved based on asymmetries, where contest winners are often those that value a resource the most and/or those who have the greatest potential to retain it. In parasitoid wasps, contests between females determine which individual exploits hosts for offspring production. Previous studies on solitary parasitoids rarely considered the role of biotic factors generating phenotypic variation that could influence the strength of asymmetries. Some parasitoid species parasitize host species of various sizes, producing offspring that vary considerably in size and potentially fighting ability. In this study, we reared the egg endoparasitoid Telenomus podisi (Hymenoptera: Scelionidae) on two host species to measure the effect of body size on contest resolution and how it interacts with ownership and resource value (RV) asymmetries. Our results showed that ownership status best predicts the final contest outcome when similar-sized wasps fight over hosts. The frequency and outcomes of individual fights structuring contests were better explained by the difference in the number of eggs laid in the hosts by each female at a given time. When contestants varied in body size, larger intruders frequently dislodged small owners regardless of ownership and RV asymmetries. These results imply that body size is an important factor to consider in solitary parasitoid contests and that it can overshadow the effects of other asymmetries. Our study suggests that host community diversity could have a direct effect on parasitoid contests and that biotic communities, through their effects on animal phenotypes, may play an underrated role in contest resolution.

Description: Sunlight is the ultimate source of most visual signals. Theory predicts strong selection for its effective use during communication, with functional links between signal designs and display behaviors a likely result. This is particularly true for iridescent structural colors, whose moment-to-moment appearance bears a heightened sensitivity to the position of signalers, receivers, and the sun. Here, we experimentally tested this prediction using Lispe cana, a muscid fly in which males present their structurally colored faces and wings to females during ground-based sexual displays. In field-based assays, we found that males actively bias the orientation of their displays toward the solar azimuth under conditions of full sunlight and do so across the entire day. This bias breaks down, however, when the sun is naturally concealed by heavy cloud or experimentally obscured. Our modeling of the appearance of male signals revealed clear benefits for the salience of male ornaments, with a roughly 4-fold increase in subjective luminance achievable through accurate display orientation. These findings offer fine-scale, causal evidence for the active control of sexual displays to enhance the appearance of iridescent signals. More broadly, they speak to predicted coevolution between dynamic signal designs and presentation behaviors, and support arguments for a richer appreciation of the fluidity of visual communication.

Description: Many vocalizing animals produce the discrete elements of their acoustic signals in a specific sequential order, but we know little about the biological relevance of this ordering. For that, we must characterize the degree by which individuals differ in how they organize their signals sequentially and relate these differences to variation in quality and fitness. In this study, we fulfilled these tasks in male collared flycatchers (Ficedula albicollis). We characterized the sequential order of syllables with a network analysis approach and studied the consistency of network variables on distinct time scales (within day, between days, and between years), and assessed their relationship with such quality indicators like age, body condition, arrival date, and fitness related proxies like survival to the next year and pairing success. We found that the syllables were associated nonrandomly with one another and both the frequency differences of consecutive syllables and the number of motif types were higher in the original than in randomized syllable sequences. Average degree and small-worldness showed considerable among-individual differences and decreasing repeatability with increasing time scale. Furthermore, we found relationships between male age and average degree among and within individuals. Accordingly, older males produce syllable sequences by using common syllables less often than younger individuals. However, the network variables showed no relationship with fitness-related variables. In conclusion, the sequential organization of birdsong has the potential to encode individual-specific characteristics, which thus could be used as signal in social interactions and thus potentially could be subject to sexual selection.

Description: The global trend of urbanization is creating novel challenges for many animal species. Studies investigating behavioral differences between rural and urban populations often report a general increase in risk-taking behaviors in urban populations. According to the most common energy management model (the performance model), behaviors that increase access to resources, such as aggression and boldness, and behaviors that consume net energy, like locomotion and stress responses, are both positively correlated to resting metabolic rate (RMR). Thus, we expect urban populations to not only exhibit a higher level of risk-taking behavior but also a higher RMR. However, these interactions remain poorly investigated. Our main goal was to analyze the relationship between RMR and risk-taking behaviors in the greater white-toothed shrew (Crocidura russula) in rural versus urban populations. Trapped shrews were brought to captivity where we measured RMR, boldness, and exploration rate three times in each individual. Our findings revealed that urban shrews were indeed bolder and more exploratory, but contrary to our expectations, their RMR was lower than that of rural shrews. This is likely explained by differences in the environmental conditions of these two habitats, such as higher ambient temperatures and/or lower prey availability in cities. When looking at each population separately, this relationship remained similar: urban shrews with a higher RMR were less bold, and rural shrews with a higher RMR showed a lower exploration rate. We conclude that the energetic strategy of C. russula is dependent on the environmental and observational context and cannot be explained by the performance model.

Description: Social network analysis is a suite of approaches for exploring relational data. Two approaches commonly used to analyze animal social network data are permutation-based tests of significance and exponential random graph models. However, the performance of these approaches when analyzing different types of network data has not been simultaneously evaluated. Here we test both approaches to determine their performance when analyzing a range of biologically realistic simulated animal social networks. We examined the false positive and false negative error rate of an effect of a two-level explanatory variable (e.g., sex) on the number and combined strength of an individual’s network connections. We measured error rates for two types of simulated data collection methods in a range of network structures, and with/without a confounding effect and missing observations. Both methods performed consistently well in networks of dyadic interactions, and worse on networks constructed using observations of individuals in groups. Exponential random graph models had a marginally lower rate of false positives than permutations in most cases. Phenotypic assortativity had a large influence on the false positive rate, and a smaller effect on the false negative rate for both methods in all network types. Aspects of within- and between-group network structure influenced error rates, but not to the same extent. In "grouping event-based" networks, increased sampling effort marginally decreased rates of false negatives, but increased rates of false positives for both analysis methods. These results provide guidelines for biologists analyzing and interpreting their own network data using these methods.

Description: Triadic awareness, or knowledge of the relationships between others, is essential to navigating many complex social interactions. While some animals maintain relationships with former group members post-dispersal, recognizing cross-group relationships between others may be more cognitively challenging than simply recognizing relationships between members of a single group because there is typically much less opportunity to observe interactions between individuals that do not live together. We presented acorn woodpeckers (Melanerpes formicivorus), a highly social species, with playback stimuli consisting of a simulated chorus between two different individuals, a behavior that only occurs naturally between social affiliates. Subjects were expected to respond less rapidly if they perceived the callers as having an affiliative relationship. Females responded more rapidly to a pair of callers that never co-occurred in the same social group, and responded less rapidly to callers that were members of the same social group at the time of the experiment and to callers that last lived in the same group before the subject had hatched. This suggests that female acorn woodpeckers can infer the existence of relationships between conspecifics that live in separate groups by observing them interact after the conspecifics in question no longer live in the same group as each other. This study provides experimental evidence that nonhuman animals may recognize relationships between third parties that no longer live together and emphasizes the potential importance of social knowledge about distant social affiliates.

Description: Offspring of many animals beg for food from parents. Begging is often costly, and offspring should seek to reduce such costs to maximize their returns on begging. Whenever multiple adults provide care for a joint brood, as in species where multiple females breed communally, offspring should beg toward the parent that provisions the most food. Here, we investigate whether larvae spend more time begging toward larger females in the burying beetle Nicrophorus vespilloides. Prior work on this species shows that larger females provision more food than smaller ones, suggesting that larvae would benefit by preferentially begging toward larger females. To test for such a preference, we provided experimental broods with a simultaneous choice between two dead females: a smaller and a larger one. Larvae spent more time begging toward larger females. We next examined the behavioral mechanism for why larvae begged more toward larger females. Larvae spent more time in close contact with larger females over smaller ones, whereas there was no evidence that larvae begged more when in close contact with larger females. Thus, larvae begged more toward the larger female simply as a consequence of spending more time close to larger females. Our findings have important implications for our understanding of parent–offspring communication by showing that offspring can choose between parents based on parental attributes, such as body size, reflecting how much food parents are likely to provision.

Description: Multiple phenotypic traits often interact with each other to determine an individual’s fitness. Behavioral and extended phenotypic traits, such as architectural constructions, can contribute to fitness in an integrated way. The goal of this study was to understand how the interaction between behavioral and extended phenotypic traits can affect foraging success. We tested this question using black widow spiders, where spiders that are aggressive in a foraging context tend to build more gumfooted silk lines that aid in prey capture, while non-aggressive spiders build webs with fewer gumfooted lines. We repeatedly assessed behavior and web structure to quantify relationships between these traits, and then allowed spiders to forage for live prey on their own web or the web of a conspecific that differed in structure. Thus, we assessed how varying combinations of behavior and web structure affect foraging success, and if correlational selection might act on them. We confirmed that aggressiveness and number of gumfooted lines are positively correlated and found that capture success increased with both aggressiveness and the number of gumfooted lines. Yet, we did not find any evidence for correlational selection: aggressiveness and number of gumfooted lines appeared to affect foraging success independently of each other. These findings highlight that a correlation between traits that contribute towards the same ecological function does not necessarily imply correlational selection. Taking advantage of the experimental convenience afforded by extended phenotypic traits can provide insight into the functional consequences of phenotypic variation within and between individuals.

Description: The environment that parents experience can influence their reproductive output and their offspring’s fitness via parental effects. Perceived predation risk can affect both parent and offspring phenotype, but it remains unclear to what extent offspring behavioral traits are affected when the mother is exposed to predation risk. This is particularly unclear in live-bearing species where maternal effects could occur during embryogenesis. Here, using a half-sib design to control for paternal effects, we experimentally exposed females of a live-bearing fish, the guppy (Poecilia reticulata), to visual predator cues and conspecific alarm cues during their gestation. Females exposed to predation risk cues increased their antipredator behaviors throughout the entire treatment. Offspring of mothers exposed to the predation stimuli exhibited more pronounced exploratory behavior, but did not show any significant differences in their schooling behavior, compared to controls. Thus, while maternally perceived risk affected offspring’s exploration during early stages of life, offspring’s schooling behavior could be influenced more by direct environmental experience rather than via maternal cues. Our results suggest a rather limited role in predator-induced maternal effects on the behavior of juvenile guppies.

Description: Across populations, animals that inhabit areas with high anthropogenic noise produce vocalizations that differ from those inhabiting less noisy environments. Such patterns may be due to individuals rapidly adjusting their songs in response to changing noise, but individual variation is seldom explored. Therefore, we tested the hypothesis that male house wrens (Troglodytes aedon) immediately adjust their songs according to changing noise and that social context further modifies responses. We recorded songs, quantified noise, and defined social context within pairs as female fertile status and between males as number of conspecific neighbors. We used a reaction-norm approach to compare song trait intercepts (between-male effects) and slopes (within-male effects) as a function of noise. Individuals immediately adjusted song duration in response to changing noise. How they achieved adjustments varied: some sang shorter and others longer songs with greater noise, and individuals varied in the extent to which they adjusted song duration. Variation in song duration could be affected by competition as between-male noise levels interacted with number of neighbors to affect syllable duration. Neither within- nor between-male noise effects were detected for frequency traits. Rather, males with fertile mates sang lower-frequency songs and increased peak frequency with more neighbors. Among males, social context but not noise affected song frequency, whereas temporal structure varied between and within individuals depending on noise and social factors. Not all males adjusted signals the same way in response to noise, and selection could favor different levels of variation according to noise.

Description: Territorial animals are expected to adjust their response to intruders according to the perceived threat level. One of the factors that drives threat level is the identity of the intruder. The dear enemy phenomenon theory postulates that individuals should respond with lower intensity to neighbors, already possessing a territory, than to strangers that may fight to evict them. In social species, the hierarchical status of the intruder might also mediate this response. Such behavioral adjustments presuppose a capacity to discriminate between individuals posing different threat levels. Here, we tested the behavioral response of Alpine marmots to territorial intrusions in a wild population. We compared both dominant females’ and males’ responses to scents from neighbor and stranger dominant males (dear enemy phenomenon) and to dominant and subordinate stranger males (social status-specific response). In addition, we tested for any covariance between male scents and social status. We showed that female and male dominant marmots do not adjust the intensity of their behavioral responses to whether the intruder’s territory is bordering or not (neighbors or strangers) or to the intruder’s social status, even though dominant and subordinate males are thought to pose different threats and social status is encoded in scents. Thus, we did not find support for the dear enemy phenomenon and conclude instead that, in dominant Alpine marmots, no intruder should enter a foreign territory. Research taking a more holistic approach of the evolution and maintenance of territoriality is required to understand the flexibility of responses to intruders in group-living species.

Description: Eavesdropping on community members has immediate and clear benefits. However, little is known regarding its importance for the organization of cross-taxa community structure. Furthermore, the possibility that eavesdropping could allow species to coexist with a predator and access risky foraging habitat, thereby expanding their realized niche, has been little considered. Kalahari tree skinks (Trachylepis spilogaster) associate with sociable weaver (Philetairus socius) colonies as do African pygmy falcons (Polihierax semitorquatus), a predator of skinks and weavers. We undertook observational and experimental tests to determine if skinks eavesdrop on sociable weavers to mitigate any increase in predation threat that associating with weaver colonies may bring. Observations reveal that skinks use information from weavers to determine when predators are nearby; skinks were more active, more likely to forage in riskier habitats, and initiated flight from predators earlier in the presence of weavers compared with when weavers were absent. Playback of weaver alarm calls caused skinks to increase vigilance and flee, confirming that skinks eavesdrop on weavers. Furthermore, skinks at sociable weaver colonies were more likely to flee than skinks at noncolony trees, suggesting that learning is mechanistically important for eavesdropping behavior. Overall, it appears that eavesdropping allows skinks at colony trees to gain an early warning signal of potential predators, expand their realized niche, and join communities, whose predators may otherwise exclude them.

Description: The juvenile period is a challenging life-history stage, especially in species with a high degree of fission–fusion dynamics, such as bottlenose dolphins, where maternal protection is virtually absent. Here, we examined how juvenile male and female bottlenose dolphins navigate this vulnerable period. Specifically, we examined their grouping patterns, activity budget, network dynamics, and social associations in the absence of adults. We found that juveniles live in highly dynamic groups, with group composition changing every 10 min on average. Groups were generally segregated by sex, and segregation was driven by same-sex preference rather than opposite-sex avoidance. Juveniles formed strong associations with select individuals, especially kin and same-sex partners, and both sexes formed cliques with their preferred partners. Sex-specific strategies in the juvenile period reflected adult reproductive strategies, in which the exploration of potential social partners may be more important for males (which form long-term alliances in adulthood) than females (which preferentially associate with kin in adulthood). Females spent more time alone and were more focused on foraging than males, but still formed close same-sex associations, especially with kin. Males cast a wider social net than females, with strong same-sex associations and many male associates. Males engaged in more affiliative behavior than females. These results are consistent with the social bonds and skills hypothesis and suggest that delayed sexual maturity in species with relational social complexity may allow individuals to assess potential associates and explore a complex social landscape without the risks associated with sexual maturity (e.g., adult reproductive competition; inbreeding).

Description: Mixed-species flocks are a key facilitative interaction for tropical birds. Forest fragmentation leads to species loss and spatial turnover in these flocks, yet it is unknown how these changes to composition influence within-flock species interactions. We used network analysis to characterize flocking interactions along a fragment-size gradient in the Colombian Western Andes. We asked 1) how patch size, edge density, and vegetation structure explained network measures indicative of flock cohesion, 2) whether changes were driven by flocking species turnover or changes to the frequency of species co-occurrence, and 3) whether nuclear species, those that maintain flock stability and cohesion, changed in importance across the gradient. We constructed weighted social networks from flock compositions observed on 500-m transects, and then calculated global network measures and the centrality of six nuclear species. Patch size and edge density did not correlate with interspecific co-occurrence patterns, but interaction strength increased with canopy height. Flocks contained numerous, weak interactions, and there were no flock subtypes, suggesting flock composition was dynamic and unstructured. Several redundant nuclear species were present and varied in importance based on ecological conditions. A chlorospingus (Passerellidae) was most central in old-growth forest, whereas several tanager (Thraupidae) species became more central in smaller fragments and disturbed forest. When partitioning network dissimilarity, we found that 66% of dissimilarity resulted from species turnover, whereas only 34% resulted from changes to species co-occurrence. This finding suggests that coherence of flocking behavior itself is maintained even as extensive species turnover occurs from continuous forest to small fragments.

Description: The black-headed duck (Heteronetta atricapilla) of South America is the only known avian obligate brood parasite with precocial offspring. In Argentina, it relies on two species of coots as primary hosts, which typically reject 35–65% of duck eggs. We show that environmentally driven increases in host egg rejection behavior lead to substantial reductions in the reproductive success of the brood parasite. Episodes of flooding and vegetation loss caused dramatic shifts in host egg-rejection behavior, resulting in rejection (85–95%) of almost all duck eggs. Coots respond to fluctuating water levels by building up their nest, raising their own eggs but leaving duck eggs behind. Coots can apparently recognize parasitic duck eggs, but large-scale rejection is triggered only when hosts must actively make a choice. We use a simple population model to illustrate the unique demographic challenges that black-headed ducks face with their parasitic lifestyle and to explore the potential impact of environmentally induced escalation of egg rejection. Using the best available estimates for key vital rates, we show that obligate parasitism may provide a demographically precarious existence for black-headed ducks, even under benign environmental conditions. Environmentally mediated increases in egg rejection rates by hosts could impact significantly the viability of this enigmatic species of brood parasitic duck. Our results demonstrate that egg rejection rates are not fixed properties of host populations or individuals but are strongly influenced by social and ecological factors. Shifts in these environmental drivers could have important and unforeseen demographic consequences for brood parasites.

Description: Cobreeding, which occurs when multiple females breed together, is likely to be associated with uncertainty over maternity of offspring in a joint brood, preventing females from directing resources towards their own offspring. Cobreeding females may respond to such uncertainty by shifting their investment towards the stages of offspring development when they are certain of maternity and away from those stages where uncertainty is greater. Here we examined how uncertainty of maternity influences investment decisions of cobreeding females by comparing cobreeding females and females breeding alone in the burying beetle, Nicrophorus vespilloides. In this species, females sometimes breed together on a single carcass but females cannot recognize their own offspring. We found that cobreeding females shifted investment towards the egg stage of offspring development by laying more and larger eggs than females breeding alone. Furthermore, cobreeding females reduced their investment to post-hatching care of larvae by spending less time providing care than females breeding alone. We show that females respond to the presence of another female by shifting allocation towards egg laying and away from post-hatching care, thereby directing resources to their own offspring. Our results demonstrate that responses to parentage uncertainty are not restricted to males, but that, unlike males, females respond by shifting their investment to different components of reproduction within a single breeding attempt. Such flexibility may allow females to cope with maternity uncertainly as well as a variety of other social or physical challenges.

Description: To understand the evolution of cognitive abilities, we need to understand both how selection acts upon them and their genetic (co)variance structure. Recent work suggests that there are fitness consequences for free-living individuals with particular cognitive abilities. However, our current understanding of the heritability of these abilities is restricted to domesticated species subjected to artificial selection. We investigated genetic variance for, and genetic correlations among four cognitive abilities: inhibitory control, visual and spatial discrimination, and spatial ability, measured on 〉450 pheasants, Phasianus colchicus, over four generations. Pheasants were reared in captivity but bred from adults that lived in the wild and hence, were subject to selection on survival. Pheasant chicks are precocial and were reared without parents, enabling us to standardize environmental and parental care effects. We constructed a pedigree based on 15 microsatellite loci and implemented animal models to estimate heritability. We found moderate heritabilities for discrimination learning and inhibitory control (h2 = 0.17–0.23) but heritability for spatial ability was low (h2 = 0.09). Genetic correlations among-traits were largely positive but characterized by high uncertainty and were not statistically significant. Principle component analysis of the genetic correlation matrix estimate revealed a leading component that explained 69% of the variation, broadly in line with expectations under a general intelligence model of cognition. However, this pattern was not apparent in the phenotypic correlation structure which was more consistent with a modular view of animal cognition. Our findings highlight that the expression of cognitive traits is influenced by environmental factors which masks the underlying genetic structure.

Description: Direct pathogen and parasite transmission is fundamentally driven by a population’s contact network structure and its demographic composition and is further modulated by pathogen life-history traits. Importantly, populations are most often concurrently exposed to a suite of pathogens, which is rarely investigated, because contact networks are typically inferred from spatial proximity only. Here, we use 5 years of detailed observations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) that distinguish between four different types of social contact. We investigate how demography (sex and age) affects these different social behaviors. Three of the four social behaviors can be used as a proxy for understanding key routes of direct pathogen transmission (sexual contact, skin contact, and aerosol contact of respiratory vapor above the water surface). We quantify the demography-dependent network connectedness, representing the risk of exposure associated with the three pathogen transmission routes, and quantify coexposure risks and relate them to individual sociability. Our results suggest demography-driven disease risk in bottlenose dolphins, with males at greater risk than females, and transmission route-dependent implications for different age classes. We hypothesize that male alliance formation and the divergent reproductive strategies in males and females drive the demography-dependent connectedness and, hence, exposure risk to pathogens. Our study provides evidence for the risk of coexposure to pathogens transmitted along different transmission routes and that they relate to individual sociability. Hence, our results highlight the importance of a multibehavioral approach for a more complete understanding of the overall pathogen transmission risk in animal populations, as well as the cumulative costs of sociality.

Description: Trust can transform conflicting interests into cooperation. But how can individuals know when to trust others? Here, I develop the theory that reputation building may signal cooperative intent, or “trustworthiness.” I model a simple representation of this theory in which individuals 1) optionally invest in a reputation by performing costly helpful behavior (“signaling”); 2) optionally use others’ reputations when choosing a partner; and 3) optionally cooperate with that partner. In evolutionary simulations, high levels of reputation building, of choosing partners based on reputation, and of cooperation within partnerships emerged. Costly helping behavior evolved into an honest signal of trustworthiness when it was adaptive for cooperators, relative to defectors, to invest in the long-term benefits of a reputation for helping. I show using game theory that this occurs when cooperators gain larger marginal benefits from investing in signaling than do defectors. This happens without the usual costly signaling assumption that individuals are of two “types,” which differ in quality. Signaling of trustworthiness may help explain phenomena such as philanthropy, pro-sociality, collective action, punishment, and advertising in humans and may be particularly applicable to courtship in other animals.

Description: Microhabitat choice of nest sites is an important maternal effect that influences the survival and development of embryos in oviparous species. Embryos of many species display a high degree of plasticity in response to developmental environments, which places maternal nesting behavior under strong selective pressure, particularly in temporally changing environments. Nesting behavior varies widely across taxa that exhibit diverse reproductive strategies. The brown anole (Anolis sagrei), for example, lays one egg every 7–10 days across an extended reproductive season from April to October. This aspect of their reproduction provides an opportunity to examine temporal shifts in nesting behavior and its consequences on egg survival and offspring development under seasonally changing climatic conditions. We conducted a two-part study to quantify temporal variation in maternal nesting behavior and its effect on development of A. sagrei embryos. First, we measured nest micro-environments over the nesting season. Second, we “planted” eggs across the landscape at our field site to examine the influence of nest conditions on egg survival and hatchling phenotypes. We also incubated eggs inside chambers in the field to decouple effects of nest moisture from those of other environmental variables (e.g., temperature). Females chose nest sites with higher moisture and lower temperatures relative to what was generally available across the landscape during the nesting season. In addition, eggs exposed to relatively cool temperatures had higher hatching success, and high nest moisture increased egg survival and body condition of hatchlings. Overall, we provide evidence in the field that maternal nesting behavior facilitates offspring survival.

Description: Reproduction in cooperative animal groups is often dominated by one or a few individuals, with the remaining group members relegated to nonreproductive helping roles. This reproductive skew can evolve if helpers receive fitness benefits such as potential future inheritance of the breeding position, but the mechanisms by which inheritance is determined are not well resolved. Polistes paper wasps form highly reproductively skewed groups and inheritance of the breeding position is likely to play a key role in the maintenance of this social structure, making them excellent models for the processes by which simple societies are maintained. Reproductive succession is thought to be determined via an age-based convention in some Polistes species, but there is also evidence for contest-based succession systems in which the replacement queen uses physical aggression to overpower and thereby subordinate her nestmates. Here, we provide evidence that queen succession in colonies of the European paper wasp Polistes dominula is determined via convention rather than contest, with little disruption to the colony’s social functioning. We use queen removal experiments and fine-scale behavioral analyses to confirm that age is a strong predictor of succession, and that behavioral responses to queen removal are restricted to the oldest individuals rather than being experienced equally across the group. We provide the most comprehensive and detailed experimental analysis on the dynamics of breeder succession in a cooperatively breeding invertebrate to date, thereby shedding light on the mechanisms by which animal societies are able to maintain cohesion in the face of within-group conflict.

Description: Predation fear is a unifying theme across vertebrate taxa. Here, we explored how the frequency and duration of predation risk affects postrisk fear behavior in Trinidadian guppies. We first exposed individuals to visual cues of potential predators for 3 days, either frequently (6×/day) or infrequently (1×/day). Each exposure lasted for either a relatively brief (5 min) or long (30 min) duration, whereas a control group consisted of no risk exposures. One day later, we quantified guppy behavior. All background risk treatments induced a fear response toward a novel odor (i.e., neophobia), and individuals previously exposed to frequent bouts of brief risk showed elevated baseline fear. Although neophobic responses were initially similar across risk treatments (1 day later), retention of this response differed. After 8 days, only individuals previously exposed to brief bouts of risk (both frequent and infrequent) maintained neophobic responses, whereas their initially higher level of baseline fear remained elevated but was no longer significantly different from the control. These results increase our understanding of temporal factors that affect the intensity and retention of fear that persists after risk exposure, which may have applications across vertebrates in relation to problems with fearful phenotypes.

Description: Animals employing acoustic signals, such as birds, must effectively communicate over both background noise and potentially attenuating objects in the environment. To surmount these obstacles, animals evolve species-specific acoustic signals that do not overlap with sources of interference (such as songs of close relatives), and issue these songs from locations that maximize transmission. In multispecies assemblages of birds, the acoustic resource may thus be interspecifically partitioned along multiple axes, including song perch height and signal space. However, very few such studies have focused on open habitats, where differences in sound transmission patterns and limited availability of song perches may drive competition across multiple axes within signal space. Here, we demonstrate acoustic signal space partitioning in four sympatric species of wren-warbler (Cisticolidae, Prinia), in an Indian dry deciduous scrub-grassland habitat. We found that the breeding songs of the four species partition acoustic signal space, resulting in interspecific community organization. Within each species’ signal space, we uncovered different intraspecific patterns in note diversity. Two species partition intraspecific signal space into multiple note types, whereas the other two vary note repetition rate to different extents. Finally, we found that the four species also partition song perch heights, thus exhibiting acoustic niche separation along multiple axes. We hypothesize that divergent song perch heights may be driven by competition for higher singing perches or other ecological factors rather than signal propagation. Acoustic signal partitioning along multiple axes may therefore arise from a combination of diverse ecological processes.

Description: Lures are deceptive strategies that exploit sensory biases in prey, usually mimicking a prey’s mate or food item. Several predators exploit plant–pollinator systems, where visual signals are an essential part of interspecific interactions. Many diurnal, and even nocturnal, orb-web spiders present conspicuous body coloration or bright color patches. These bright colors are regarded as color-based lures that exploit biases present in insect visual systems, possibly mimicking flower colors. The prey attraction hypothesis was proposed more than 20 years ago to explain orb-web spider coloration. Although most data gathered so far has corroborated the predictions of the prey attraction hypothesis, there are several studies that refute these predictions. We conducted a multilevel phylogenetic meta-analysis to assess the magnitude of the effect of conspicuous orb-web spider body coloration on prey attraction. We found a positive effect in favor of the prey attraction hypothesis; however, there was substantial heterogeneity between studies. Experimental designs comparing conspicuous spiders to painted spiders or empty webs did not explain between-studies heterogeneity. The lack of theoretical explanation behind the prey attraction hypothesis makes it challenging to address which components influence prey attraction. Future studies could evaluate whether color is part of a multicomponent signal and test alternative hypotheses for the evolution of spider colors, such as predator avoidance and thermoregulation.

Description: To understand how variation in warning displays evolves and is maintained, we need to understand not only how perceivers of these traits select color and toxicity but also the sources of the genetic and phenotypic variation exposed to selection by them. We studied these aspects in the wood tiger moth Arctia plantaginis, which has two locally co-occurring male color morphs in Europe: yellow and white. When threatened, both morphs produce defensive secretions from their abdomen and from thoracic glands. Abdominal fluid has shown to be more important against invertebrate predators than avian predators, and the defensive secretion of the yellow morph is more effective against ants. Here, we focused on the morph-linked reproductive costs of secretion of the abdominal fluid and quantified the proportion of phenotypic and genetic variation in it. We hypothesized that, if yellow males pay higher reproductive costs for their more effective aposematic display, the subsequent higher mating success of white males could offer one explanation for the maintenance of the polymorphism. We first found that the heritable variation in the quantity of abdominal secretion was very low (h2 = 0.006) and the quantity of defensive secretion was not dependent on the male morph. Second, deploying the abdominal defensive secretion decreased the reproductive output of both color morphs equally. This suggests that potential costs of pigment production and chemical defense against invertebrates are not linked in A. plantaginis. Furthermore, our results indicate that environmentally induced variation in chemical defense can alter an individual’s fitness significantly.

Description: Communication often happens in noisy environments where interference from the ambient noise and other signalers may reduce the effectiveness of signals which may lead to more conflict between interacting individuals. Signalers may also evolve behaviors to interfere with signals of opponents, for example, by temporally overlapping them with their own, such as the song overlapping behavior that is seen in some songbirds during aggressive interactions. Song overlapping has been proposed to be a signal of aggressive intent, but few studies directly examined the association between song overlapping and aggressive behaviors of the sender. In the present paper, we examined whether song overlapping and ambient noise are associated positively with aggressive behaviors. We carried out simulated territorial intrusions in a population of great tits (Parus major) living in an urban–rural gradient to assess signaling and aggressive behaviors. Song overlapping was associated negatively with aggressive behaviors males displayed against a simulated intruder. This result is inconsistent with the hypothesis that song overlapping is an aggressive signal in this species. Ambient noise levels were associated positively with aggressive behaviors but did not correlate with song rate, song duration, or song overlapping. Great tits in noisy urban habitats may display higher levels of aggressive behaviors due to either interference of noise in aggressive communication or another indirect effect of noise.

Description: Repeatable behaviors (i.e., animal personality) are pervasive in the animal kingdom and various mechanisms have been proposed to explain their existence. Genetic and nongenetic mechanisms, which can be equally important, predict correlations between behavior and body mass on different levels (e.g., genetic and environmental) of variation. We investigated multilevel relationships between body mass measured on weeks 1, 2, and 3 and three behavioral responses to handling, measured on week 3, which form a behavioral syndrome in wild blue tit nestlings. Using 7 years of data and quantitative genetic models, we find that all behaviors and body mass on week 3 are heritable (h2 = 0.18–0.23) and genetically correlated, whereas earlier body masses are not heritable. We also find evidence for environmental correlations between body masses and behaviors. Interestingly, these environmental correlations have different signs for early and late body masses. Altogether, these findings indicate genetic integration between body mass and behavior and illustrate the impacts of early environmental factors and environmentally mediated growth trajectory on behaviors expressed later in life. This study, therefore, suggests that the relationship between personality and body mass in developing individuals is due to various underlying mechanisms, which can have opposing effects. Future research on the link between behavior and body mass would benefit from considering these multiple mechanisms simultaneously.

Description: Many sexually selected ornaments and weapons are elaborations of an animal’s outer body surface, including long feathers, colorful skin, and rigid outgrowths. The time and energy required to keep these traits clean, attractive, and in good condition for signaling may represent an important but understudied cost of bearing a sexually selected trait. Male fiddler crabs possess an enlarged and brightly colored claw that is used both as a weapon to fight with rival males and also as an ornament to court females. Here, we demonstrate that males benefit from grooming because females prefer males with clean claws over dirty claws but also that the time spent grooming detracts from the amount of time available for courting females. Males, therefore, face a temporal trade-off between attracting the attention of females and maintaining a clean claw. Our study provides rare evidence of the importance of grooming for mediating sexual interactions in an invertebrate, indicating that sexual selection has likely shaped the evolution of self-maintenance behaviors across a broad range of taxa.

Description: Despite the important role that population density plays in ecological and evolutionary processes, studies of solitary species that occur at low densities remain scarce. In the context of mating systems, density is expected to influence the ability of males to find and monopolize mates, in turn, influencing variance in lifetime mating/reproductive success and the opportunity for selection. Herein, we investigate variance in male lifetime mating success (LMS), lifetime reproductive success (LRS), and the mating system of a sexually dimorphic carnivore that occurs at low densities, the polar bear (Ursus maritimus). Across 17 cohorts, born from 1975 to 1991, male LMS ranged from 0 to10 mates and LRS from 0 to 14 cubs; 40% of known-age males were not known to have reproduced. The opportunity for sexual selection (Is = 1.66, range = 0.60–4.99) and selection (I = 1.76, range: 0.65–4.89) were low compared to species with similar levels of sexual size dimorphism. Skew in male LRS was also low but significant for most cohorts indicating nonrandom reproductive success. Age-specific reproductive success was biased toward males from 11 to 17 years of age, with variation in fecundity (54%) but not longevity (10%) playing an important role in male reproduction. Our results support a growing body of evidence that suggests that male-biased size dimorphism and polygynous mating systems need not be associated with high variance in male mating and/or reproductive success.

Description: Many animals make contingent decisions, such as when and where to feed, as trade-offs between growth and risk when these vary not only with activity and location but also 1) in cycles such as the daily light cycle and 2) with feedbacks due to competition. Theory can assume an individual decides whether and where to feed, at any point in the light cycle and under any new conditions, by predicting future conditions and maximizing an approximate measure of future fitness. We develop four such theories for stream trout and evaluate them by their ability to reproduce, in an individual-based model, seven patterns observed in real trout. The patterns concern how feeding in four circadian phases—dawn, day, dusk, and night—varies with predation risk, food availability, temperature, trout density, physical habitat, day length, and circadian cycles in food availability. We found that theory must consider the full circadian cycle: decisions at one phase must consider what happens in other phases. Three theories that do so could reproduce almost all the patterns, and their ability to let individuals adapt decisions over time produced higher average fitness than any fixed behavior cycle. Because individuals could adapt by selecting among habitat patches as well as activity, multiple behaviors produced similar fitness. Our most successful theories base selection of habitat and activity at each phase on memory of survival probabilities and growth rates experienced 1) in the three previous phases of the current day or 2) in each phase of several previous days.

Description: In some socially monogamous birds, territories sometimes occur in aggregations. The “hidden lek” hypothesis suggests that territorial aggregations might be explained by males establishing territories near successful males (“hotshot” model) or by females preferring to mate in large clusters (“female preference” model). In both scenarios, clusters would provide more opportunities for finding mates and achieving extrapair copulations. Our study tests predictions of these two models in the blue-black grassquit (Volatinia jacarina). Males of this species migrate to their breeding grounds, establish territories within clusters, and initiate courtship displays. These displays consist of vertical leaps synchronized with vocalizations, or only the latter without leaps. The “hotshot” model predicts that: 1) earlier-arriving males would establish territories more centrally within clusters; 2) earlier or centrally positioned males would produce more elaborate displays; and 3) these same males would achieve higher success via within and extrapair fertilizations. The “female preference” model predicts that: 4) pairing success and 5) per-capita extrapair fertilizations would increase with cluster size. We found that earlier-arriving males executed higher leaps and longer songs, but there was no relationship between these traits and male position within clusters. We also found that earlier-arriving males were more likely to obtain extrapair fertilizations. However, we found little evidence that cluster size related to overall or per-capita breeding success. Considered together, our data provide partial validation of the hotshot model of hidden leks and expand on prior findings in this species by showing that females benefit by choosing males leaping higher and settling earlier in clusters.

Description: Polyandry (multiple mating by females) is a central challenge for understanding the evolution of eusociality. Several hypotheses have been proposed to explain its observed benefits in eusocial Hymenoptera, one of which, the parasite–pathogen hypothesis (PPH), posits that high genotypic variance among workers for disease resistance prevents catastrophic colony collapse. We tested the PPH in the polyandrous wasp Vespula shidai. We infected isolated workers with the entomopathogenic fungus Beauveria bassiana and quantified their survival in the laboratory. Additionally, we conducted a paternity analysis of the workers using nine microsatellite loci to investigate the relationship between survival and the matriline and patriline membership of the workers. As predicted by the PPH, nestmate workers of different patrilines showed differential resistance to B. bassiana. We also demonstrated variation in virulence among strains of B. bassiana. Our results are the first to directly support the PPH in eusocial wasps and suggest that similar evolutionary pressures drove the convergent origin and maintenance of polyandry in ants, bees, and wasps.

Description: Sexual segregation has important ecological implications, but its initial development in early life stages is poorly understood. We investigated the roles of size dimorphism, social behavior, and predation risk on the ontogeny of sexual segregation in Antarctic fur seal, Arctocephalus gazella, pups at South Georgia. Beaches and water provide opportunities for pup social interaction and learning (through play and swimming) but increased risk of injury and death (from other seals, predatory birds, and harsh weather), whereas tussock grass provides shelter from these risks but less developmental opportunities. One hundred pups were sexed and weighed, 50 on the beach and 50 in tussock grass, in January, February, and March annually from 1989 to 2018. Additionally, 19 male and 16 female pups were GPS-tracked during lactation from December 2012. Analysis of pup counts and habitat use of GPS-tracked pups suggested that females had a slightly higher association with tussock grass habitats and males with beach habitats. GPS-tracked pups traveled progressively further at sea as they developed, and males traveled further than females toward the end of lactation. These sex differences may reflect contrasting drivers of pup behavior: males being more risk prone to gain social skills and lean muscle mass and females being more risk averse to improve chances of survival, ultimately driven by their different reproductive roles. We conclude that sex differences in habitat use can develop in a highly polygynous species prior to the onset of major sexual size dimorphism, which hints that these sex differences will increasingly diverge in later life.

Description: Mate-choice copying is a form of social learning in which an individual’s choice of mate is influenced by the apparent choices of other individuals of the same sex and has been observed in more than 20 species across a broad taxonomic range. Though fitness benefits of copying have proven difficult to measure, theory suggests that copying should not be beneficial for all species or contexts. However, the factors influencing the evolution and expression of copying have proven difficult to resolve. We systematically searched the literature for studies of mate-choice copying in nonhuman animals and, then, performed a phylogenetically controlled meta-analysis to explore which factors influence the expression of copying across species. Across 58 published studies in 23 species, we find strong evidence that animals copy the mate choice of others. The strength of copying was significantly influenced by taxonomic group; however, sample size limitations mean it is difficult to draw firm conclusions regarding copying in mammals and arthropods. The strength of copying was also influenced by experimental design: copying was stronger when choosers were tested before and after witnessing a conspecific’s mate choice compared to when choosers with social information were compared to choosers without. Importantly, we did not detect any difference in the strength of copying between males and females or in relation to the rate of multiple mating. Our search also highlights that more empirical work is needed to investigate copying in a broader range of species, especially those with differing mating systems and levels of reproductive investment.

Description: While the importance of kin discrimination, that is, kin recognition and subsequent differential treatment of kin and nonkin, is well established for kin-directed cooperation or altruism, the role of kin discrimination in the context of kin competition and kin avoidance is largely unexplored. Theory predicts that individuals avoiding competition with kin should be favored by natural selection due to indirect fitness benefits. Using an experimental approach, we investigated whether the presence of same-sex kin affects avoidance and explorative behavior in subadult Pelvicachromis taeniatus, a West African cichlid fish with strong intrasexual competition in both sexes. Pelvicachromis taeniatus is capable of recognizing kin using phenotype matching and shows kin discrimination in diverse contexts. When exposed to a same-sex conspecific, both males and females tended to interact less with the related opponent. Moreover, individuals explored a novel environment faster after exposure to kin than to nonkin. This effect was more pronounced in females. Individuals avoiding the proximity of same-sex relatives may reduce kin competition over resources such as mating partners or food.