ALBERT

Description: The Australian continent is renowned for its idiosyncratic flora and fauna and high diversity of endemic taxa (e.g., Eucalyptus , marsupials, and monotremes; Braithwaite RW. 1990. Australia’s unique biota: implications for ecological processes. J Biogeogr. 17:347–354.). Given this diversity, it is perhaps not surprising that Australia is a coveted and productive field site for behavioral ecologists worldwide. The prevalence of some unusual animal behaviors is well documented, such as cooperative breeding in birds, low rates of herbivory, and high rates of pollination by vertebrates. However, other behavioral phenomena, especially those involving deception and exploitation, are also remarkably prevalent in some systems and still require comprehensive treatment. We examine 3 distinct forms of deception in entirely different taxa, cuckoos, crab spiders, and orchids, where there is strong evidence that deception is more prevalent in Australia than in other geographic regions. We offer several explanations addressing environmental conditions, evolutionary isolation, the prevalence of behavioral ecologists, and the research culture in Australia. The aim of this "Idea" paper is to draw attention to intriguing patterns of deception in a limited number of well-studied systems and to generate several testable predictions. It is not intended as a thorough review of all deceptive systems, but we hope to stimulate more research, a systematic review, and further testing in this area.

Description: Avian visual displays often target either conspecifics or heterospecifics, but few visual displays have been described where both conspecifics and heterospecifics are the intended receivers. In this study, combining observational and experimental approaches, we present evidence that a tail-raising display performed by the elegant trogon ( Trogon elegans ) is used in multiple contexts and is directed at conspecifics and heterospecifics. We observed tail-raising displays toward conspecifics in both intersexual and intrasexual contexts, as well as toward heterospecifics. Displays performed toward heterospecifics were directed at humans, monkeys, or birds of prey, all of which could have been perceived as potential predators. We experimentally tested the possible functions of tail-raising behavior in the presence of a predator by presenting elegant trogons with models of a natural predator and a nonthreatening control. Tail-raising displays were much more likely to occur when trogons were in the presence of a predator model (48% of trials) than a control model (6% of trials). The presence of conspecifics did not influence tail-raising propensity (conspecifics present: 44% of trials and conspecifics absent: 50% of trials). Our results suggest that tail raising in trogons is a multifunctional visual display that may function as an intersexual and intrasexual conspecific signal as well as a pursuit-deterrent signal directed at predators.

Description: Economic escape theory predicts flight initiation distance (FID, predator–prey distance when fleeing from an approaching predator begins), but currently cannot account for an observed increase in FID as alert distance (AD, predator–prey distance when a prey becomes alert to a predator), or its surrogate, starting distance (SD, predator–prey distance when approach begins) increases. The flush early and avoid the rush hypothesis suggests that FID increases as AD increases due to costs of monitoring the predator. However, the AD–FID relationship and the cost of monitoring have been questioned. Nevertheless, recent evidence shows that FID remains correlated with AD even when spontaneous movements are removed. We discuss possible effects of monitoring that might explain the AD–FID relationship and ways to improve understanding of the influence of spontaneous movements. We disentangle possible effects of 3 distinct phenomena associated with monitoring predators and incorporate them into escape theory. Cost of fleeing might increase as an attentional monitoring cost increases as duration of approach increases. Cost of not fleeing might increase as AD increases due to a physiological cost of monitoring and because assessed risk might increase as duration of approach increases. The attentional cost and effect on assessed risk occur in addition to the effect of decreasing distance in prey that do not account for duration of approach, while assessing costs of fleeing and not fleeing. Some of these effects may operate simultaneously. We describe research needed to better understand the flush early hypothesis and proposed costs associated with monitoring approaching predators.

Description: Strong selection against heterospecific sex signals, which includes both receivers and signallers, is considered to be the most significant causal factor in animal signal modification and is expected to prevent mate misinterpretation. Using a simultaneous choice bioassay, we tested the continued use of primordial sex signals in distantly related and geographically separated fish species, Pseudorasbora parva and Pimephales promelas . Here, we show that intraspecific selection pressures have not caused significant sex chemical signal differentiation between the 2 species and that mate attraction is likely due to a combination of common ancestry and an absence of divergence in allopatry. In the absence of mate discrimination among species, which have evolved for long periods of time in allopatry, reunification through species translocation could represent an overlooked risk of pheromone pollution.

Description: We examine cues used in assortative mating in a sympatric species flock of pupfishes ( Cyprinodon ) from San Salvador Island, The Bahamas. The species are morphologically, genetically, and ecologically distinct. We focus on 2 species, a generalist detritivore and a predator/scale-eater. Experiments show that premating isolation is based primarily on visual cues and is asymmetrical. It is well developed in the less abundant scale-eater but is much less well developed in the more abundant detritivore. Responses of detritivore females from 3 lakes to conspecific and scale-eater males suggest that abundance of the predator also affects development of premating isolating mechanisms in the prey species. These results highlight the importance of frequency-dependent selection and predators in the evolution of premating isolating mechanisms.

Description: We examined whether variation in group exploratory behavior was linked with variation in personality traits (boldness, activity, and sociability) in a population of feral guppies ( Poecilia reticulata ). A huge amount of variation was observed in dispersal tendency between shoals. Surprisingly, no significant correlations were found between group exploratory behavior and average group personality scores, which suggests that the movement of the shoal was not generated by group conformity. However, our analysis revealed correlations between group exploration and the activity score of the least active member of a group and the sociality index of the most social member of a group. These results indicate that a minority of key individuals with certain personality types can have substantial effects on group behavior. These results are discussed in the broader context of group decision making in social animals.

Description: Conspecific attraction is a form of social information use whereby individuals are attracted to the presence of conspecifics because they may indicate high-quality sites or resources. Conspecific attraction results in aggregation of individuals with similar needs and may therefore intensify competition, in particular, at high densities. Thus, the occurrence and strength of conspecific attraction may be dependent on density, but the effects of predicted intensity of future competition for resources on individual decisions have rarely been quantified. We studied realized early fecundity and oviposition site selection in the butterfly Pieris napi in relation to a density gradient of conspecific eggs on available host plants in an explicit laboratory experiment. Relying on conspecific assessment of host quality is expected to select for conspecific attraction, whereas competition avoidance is expected to select for avoidance of high conspecific densities. Presence of conspecific cues did not substantially affect realized fecundity as females exposed to an environment containing conspecific cues laid approximately equal number of eggs as females exposed to an environment lacking such cues. Instead, when females were able to choose among host plants with or without previously laid conspecific eggs, they preferred plants that already carried eggs in relation to egg-free host plants, independently of the initial egg density. Indeed, the maintenance of conspecific attraction, rather than avoidance, in P. napi implies that the possible benefits of conspecific attraction in oviposition site selection may outweigh the costs of competition in the wild.

Description: Innovative behaviors such as exploiting novel food sources can grant significant fitness benefits for animals, yet little is known about the mechanisms driving such phenomena, and the role of physiology is virtually unexplored in wild species. Two hypotheses predict opposing effects of physiological state on innovation success. On one hand, poor physiological condition may promote innovations by forcing individuals with poor competitive abilities to invent alternative solutions. On the other hand, superior physiological condition may ensure greater cognitive capacity and thereby better problem-solving and learning performance. To test these hypotheses, we studied the behavior of wild-caught house sparrows ( Passer domesticus ) in 4 novel tasks of food acquisition, one of which was presented to the birds in repeated trials, and we investigated the relationships of individual performance with relevant physiological traits. We found that problem-solving performance across the 4 tasks was moderately consistent within individuals. Birds with lower integrated levels of corticosterone, the main avian stress hormone, solved the most difficult task faster and were more efficient learners in the repeated task than birds with higher corticosterone levels. Birds with higher concentration of total glutathione, a key antioxidant, solved 2 relatively easy tasks faster, whereas birds with fewer coccidian parasites tended to solve the difficult task more quickly. Our results, thus, indicate that aspects of physiological state influence problem-solving performance in a context-dependent manner, and these effects on problem-solving capacity, probably including cognitive abilities, are more likely to drive individual innovation success than necessity due to poor condition.

Description: Trade-offs lie at the heart of behavioral ecology, with our ultimate understanding of many behaviors reliant on an assessment of both fitness benefits and costs. However, the rapidly expanding research literature on the impacts of anthropogenic noise (a recently recognized global pollutant) tends to focus on the benefits likely to be accrued by any resulting behavioral adaptations or plasticity. In particular, although studies investigating acoustic communication (the topic receiving the most attention to date) invariably discuss, and occasionally attempt to measure, the perceived benefits in terms of reduced masking that might arise from vocal adjustments by signalers, only rarely are the potential fitness costs even mentioned. The bias toward benefits prevents a full understanding of the consequences of anthropogenic noise, including the implications for population viability and community structure. Here, we argue for a greater consideration of fitness costs, outline a number of specific examples (reduced transmission distances, increased risk of predation/parasitism, altered energy budgets, loss of vital information), make suggestions about how to move forward, and showcase why a balanced view is as crucial in this field as any other aspect of behavioral ecology.

Description: There has been growing interest in the causes and consequences of different behavioral types within members of the same species. Male Siamese fighting fish consistently adopt 1 of 3 behavioral strategies (i.e., fighter, lover, or divider) when encountering a male and female conspecific simultaneously. These strategies may carry fitness consequences if female conspecifics attend to these differences and use them when selecting mates. To address this question, female Siamese fighting fish were repeatedly presented with video playback images of males expressing these strategies in a series of preference tests. Subjects were exposed to male stimuli both sequentially and simultaneously. The results suggest that females prefer males using the lover strategy and actively avoid fighter males. This avoidance is found regardless of whether the male stimuli are presented sequentially or simultaneously. Although presentation type did not affect expressed preference, it did influence strength of preference, with females attending more to the divider and lover behavioral types in the simultaneous presentations. This study highlights the importance of using multiple presentation formats when examining mate preference and demonstrates that male behavioral type may influence female choice. In addition, it is one of the first examinations of how male behavioral type may influence female mate choice and suggests that female choice may be a mechanism for generating and/or maintaining differences in behavioral type.

Description: Individual behavioral variation (aka behavioral types [BTs]) can alter the nature of species interactions. Here, we explore the performance consequences of behavioral variation in heterospecific dyads of the social spider Anelosimus studiosus and two of its most common inquilines ( Larinioides cornutus and Theridion murarium ). We determined the BTs of A. studiosus (docile vs. aggressive), determined the aggressiveness of their inquilines, and released dyads in the field for 40 days. We assessed the performance of A. studiosus and its inquilines using egg case mass and change in body mass, respectively. In the absence of inquilines, we found that aggressive A. studiosus outperformed dociles, however docile A. studiosus outperformed aggressives in the presence of inquilines. Aggression in T. murarium had a large effect on A. studiosus fecundity and its own performance, though this trend was not observed in L. cornutus . The performance of host and inquiline was simultaneously maximized when dyads were composed of opposing BTs: docile A. studiosus with aggressive T. murarium and vice versa. Thus, our data demonstrate bidirectional impacts of behavioral variation in a host–inquiline interaction and reveal that the traits that yield the greatest success in one species may depend on the representation of traits in another associated species.

Description: Contest behavior forms an important part of reproductive investment. Life-history theory predicts that as individuals age and their residual reproductive value decreases, they should increase investment in contest behavior. However, other factors such as social experience may also be important in determining age-related variation in contest behavior. To understand how selection acts on contest behavior over an individual’s lifetime, it is therefore important to tease apart the effects of age per se from other factors that may vary with age. Here, we independently manipulate male age and social experience to examine their effects on male contest behavior in the burying beetle Nicrophorus vespilloides . We found that social experience, but not age, influenced male contest behavior but that these changes in behavior did not alter contest outcomes. Male size (relative to his opponent) was overwhelmingly the most important factor determining contest outcome. Our results suggest that in systems with high variation in fighting ability among males, there may be little opportunity for selection to act on factors that influence contest outcomes by altering motivation to win.

Description: Scatter hoarding is a common food-hoarding strategy of many granivores, known to significantly contribute to seed dispersal. Models of scatter hoarding typically hold that the spatial distribution of the scatter hoards made by birds and mammals result from a trade-off between the energetic cost of spacing caches and the increased risk of pilferage as cache densities increase. Here, we present evidence from 3 field experiments that eastern gray squirrels ( Sciurus carolinensis ) rely on an alternative strategy in which preferred food items are stored in open habitats, beyond tree crowns, where the probability of predation is higher but the risk of cache pilferage is also reduced (hereafter the habitat structure hypothesis). In the first 2 experiments, squirrels cached larger, more profitable acorns at significantly greater distances from canopy edges than smaller acorns, which were more often cached under trees. In the third experiment, in which we tested the effects of both tree canopy cover and cache density on pilferage rates, we found no effect of density on pilferage rates but significantly higher pilferage rates under canopy cover. Our results indicate that habitat heterogeneity, potentially as it relates to predation risks, influences the distribution of scatter-hoarded seeds, with more profitable seeds placed in more open vegetation beyond the shadow of parent plants. We suggest that this behavior may reflect a general strategy of other scatter-hoarding mammals and birds that likely increases the probability of dispersal and establishment of seeds.

Description: In biparental species, parents may be in conflict over how much they invest into their offspring. To understand this conflict, parental care needs to be accurately measured, something rarely done. Here, we quantitatively describe the outcome of parental conflict in terms of quality, amount, and timing of incubation throughout the 21-day incubation period in a population of semipalmated sandpipers ( Calidris pusilla ) breeding under continuous daylight in the high Arctic. Incubation quality, measured by egg temperature and incubation constancy, showed no marked difference between the sexes. The amount of incubation, measured as length of incubation bouts, was on average 51min longer per bout for females (11.5h) than for males (10.7h), at first glance suggesting that females invested more than males. However, this difference may have been offset by sex differences in the timing of incubation; females were more often off nest during the warmer period of the day, when foraging conditions were presumably better. Overall, the daily timing of incubation shifted over the incubation period (e.g., for female incubation from evening–night to night–morning) and over the season, but varied considerably among pairs. At one extreme, pairs shared the amount of incubation equally, but one parent always incubated during the colder part of the day; at the other extreme, pairs shifted the start of incubation bouts between days so that each parent experienced similar conditions across the incubation period. Our results highlight how the simultaneous consideration of different aspects of care across time allows sex-specific investment to be more accurately quantified.

Description: Natal dispersal is a major life-history trait, with important consequences for population dynamics and genetic structure. Successful dispersal depends on a complex blend of decisions at all main stages of the dispersal process: emigration, prospection for a site, and settling. Costs and benefits of such decisions are expected to depend on sex and on the ecological context, on individual physiological state, and on concomitant decisions by relatives, which affect competition with kin and inbreeding. We analyzed natal dispersal propensity (i.e., dispersing or not) and dispersal distance in the semicolonial barn swallow ( Hirundo rustica ) in relation to context-, phenotype-, and kin-dependent factors. Females had larger dispersal propensity and distance than males. Dispersal propensity of both sexes was negatively density dependent and was less likely from colonies (farms) with large number of livestock, which is important to barn swallow distribution. Dispersal propensity was larger among males ranking high in the body mass brood hierarchy and smaller among late-hatched females. Dispersal distance was larger for late-hatched males and for females that ranked high in the body mass brood hierarchy. Finally, both dispersal propensity and distance of males increased with the number of male siblings. We, thus, identified several context-, phenotype-, and kin-dependent components of dispersal decisions. Phenotype-dependent effects suggest that decisions of whether to disperse and of dispersal distance are different processes under control of sex-specific traits. Finally, male dispersal behavior suggests that kin selection favors males that reduce the risk of sib–sib mating competition, in a population with male-biased tertiary sex ratio.

Description: A growing body of research over the past decade indicates that interindividual variation in behavior can result from a variety of factors. Two important sources of this variation are behavioral plasticity (adaptive variation in behavior) and behavioral type (i.e., an individual with consistent behavioral differences across one or more situations). Although oviposition-site selection (OS) is widespread and affects both parents and offspring, it has been overlooked in the context of the behavioral type. Thus, we used the Texas field cricket ( Gryllus texensis ) to determine if OS could be integrated into the behavioral type paradigm and if a relevant environmental variable (food limitation) influences behavioral type. We found that behavioral type was consistent across contexts because individuals exhibiting riskier (bolder) behavior in a novel environment also exhibited riskier behavior during oviposition. Also, individuals traded off safety with food availability during oviposition—that is, fasted crickets were more likely to choose food over safety (shelter) when making an oviposition decision. Last, relative to fed crickets, those that were fasted oviposited fewer eggs during overnight trials in which food was available. By integrating a behavior tightly linked to multigenerational fitness with an established behavioral assay (behavior to novel stimuli), we show that behavioral type can be both consistent across contexts and plastic in response to a ubiquitous environmental factor (food limitation).

Description: The honesty of animal communication has long been disputed and continues to be largely associated with the "handicap principle," in which strategic costs are paid by signalers in order to maintain signal honesty. Recently, several manuscripts have forcefully made the point that costly signaling models do not require handicaps (realized signal costs) to be paid by signalers. The aim of the present manuscript is to reiterate, clarify, and develop some of those ideas. Although the message that handicaps are not necessary for honest signaling seems to have been readily accepted, the point that handicaps are also not sufficient for honest signaling has been less well understood by the communication community. I argue that the central separation should not be between "handicaps" and "other" mechanisms such as "indices" and "punishment of cheaters." Indices, for example, are in fact a trivial exemplar of costly signaling, in which the cost functions associated with exhibiting a greater level of signal of signal expression are simply infinite. I advocate that the essential distinction is between circumstances where there is alignment of interest between signaler and receiver and those where there is not. I reenforce the view that the current focus on measuring the realized costs of signals ("handicaps") is misplaced, as without further constraints the costly signaling paradigm makes no predictions about whether honest signalers pay strategic costs for giving their own signals. Rather, it only predicts potential costs for individuals giving dishonest signals—costs that are often not paid in an honest system.

Description: It is increasingly recognized that association patterns of most gregarious animals are nonrandom. However, nonrandom patterns can emerge in any population that exhibits spatial structure, even if individuals associate randomly. In species that lack clearly differentiated social relationships characteristic of socially complex mammals, space use patterns must be considered alongside association patterns in order to establish whether nonrandom association patterns are determined by underlying social structure or are merely an artifact of spatial structure. In this study, we simultaneously consider space use and association patterns for a wild population of reticulated giraffe. We examined whether the giraffe’s flexible fission–fusion association patterns were embedded in higher levels of social organization. We identified multilevel social organization in which individuals were members of social cliques. Cliques were embedded in larger subcommunities, which in turn were embedded in communities. The frequency with which 2 individuals were observed together was positively correlated with the extent to which their home range overlapped, implying an underlying role of shared space use in determining association patterns. However, membership in cliques and subcommunities was relatively unrelated to space use patterns for males. For females, space use played a much larger role in determining multitiered social organization, which is consistent with a matrilineal-based society characterized by female philopatry. Although giraffe social interactions are highly fluid in nature, it is apparent that association patterns in giraffe are not the result of random fission–fusion events but are embedded within a structured social network characterized by multiple levels of organization.

Description: In modeling resource choice, resources are commonly categorized as essential, complementary, or substitutable. Most models concerning nonsubstitutable resources have represented each resource as a set of identical options. In reality, nonsubstitutable resources often vary in quality. Biting insects require a bloodmeal host and an oviposition site for reproduction, and expected offspring yield from different hosts and sites varies dramatically. Because both of these resources are necessary, selection may exist for interdependent choice, or bloodfeeding decisions that depend on egglaying site distribution, and vice versa. For example, insects may be selected to feed on hosts near high-quality sites or to lay eggs in sites near high-quality hosts. These decisions may be influenced by resource distribution; some areas may have clusters of high-quality hosts or sites, but the co-occurrence of both resources may be uncommon. In this study, we demonstrate the selective advantage of interdependent choice in heterogeneous environments. A 2-patch model demonstrates that interdependent choice is advantageous when resource quality varies greatly, as threshold acceptable bloodmeal host quality differed most from in a completely random environment when oviposition site quality was highly variable, and with high movement costs. A dynamic state variable model extended this result, demonstrating that spatial correlation in quality between resources is sufficient to select for interdependent choice, and autocorrelation increases the effect of between-resource correlation on behavior. This model also demonstrates that the relationship between the resources influences optimal behavior; highly complementary resources are more likely to select for populations that exhibit interdependent choice.

Description: The intensity of color expression in animals plays a key role in social environments as a mechanism to signal individual capacities in competitive contests. Selective pressures for resource competition differ at different stages of life and between sexes; therefore, coloration is expected to vary between juveniles and adults and between males and females. Exploring the covariance between coloration and other traits may help to understand the functional significance of color and the action of natural selection on multivariate phenotypes. Melanin-based plumage coloration was investigated in the masked booby Sula dactylatra in relation to melanin concentration, sex, hormone levels, and shy–bold behavior of chicks close to fledging. Darker brown boobies showed higher levels of both eumelanin and pheomelanin concentration and lower body mass. Males behaved bolder than females and showed on average 8% larger brown patches. Bolder females had smaller brown patches. Bolder individuals also had lower levels of circulating testosterone, but no differences in corticosterone levels were found. Stronger phenotypic integration was observed in females than males. Our study suggests that juvenile melanic coloration may reflect behavioral strategies by sex, endocrine profiles, and body mass indicating the convergence of different adaptive functions in a given phenotype, this being more evident in females. Direction of correlations differed from those predicted under the pleiotropic idea for color-related traits. These results suggest the possibility that juvenile plumage acts as a signaling system in a social context within the age class and suggest that plumage coloration may indicate different behavioral strategies.

Description: Social dynamics, the emergent effects of interactions within structured groups, play a key role in shaping social phenotypes and fitness. We examined the potential positive and negative effects of social dynamics in simple groups, by creating social groups of harvester ant queens with 2 alternate nest-founding strategies, solitary versus cooperative. We compared social interactions, survival, and nest productivity of pairs containing queens from the cooperative founding population, the normally solitary founding population, or mixed pairs of the 2 types. Expressed social phenotypes of queens in pairs depended strongly on the lineage of the other queen. Two behaviors, aggression and brood care, showed simple social dynamical effects. Aggression escalated in pairs of normally solitary queens, whereas queens in cooperative pairs coordinated brood output, leading to more efficient worker production. These dynamics had context-based fitness consequences, such that cooperative queens gained a survival advantage in cooperative pairs, but neither type of queen experienced an advantage or disadvantage in "mixed" associations. The interplay between social dynamics and fitness in these associations provides an empirical example of social selection. It captures a likely scenario of the transition to and the early evolution of cooperative living, in which cooperative individuals interact with solitary individuals who lack a priori strategies for cooperation or cheating.

Description: The change in benefits of high socioeconomic status to fertility in humans during the demographic transition from high to low fertility has interested both demographers and evolutionary biologists. Evolutionary analyses add to demographic analyses by considering also males and status-related differential in male mating success, but they have been limited to time cross-sections and have not linked this differential to differentials in other determinants of male fertility. We use life-history records of males ( n = 3791) entering marriage market before (1810s–1880s) and during (1890s–1960s) the Finnish fertility transition to investigate associations between socioeconomic status and chance and timing of marriage, choice for spouse, and lifetime fertility. Low status invariantly brought a lower marriage chance throughout these 160 years, which partly explained why ever-married high-status men lost advantage at early marriage when the system of achieving a high status shifted from inheritance to self-effort. The loss, coupled with assortative mating by age, promoted disappearance of differential in wife’s age at marriage and thus, disappearance of differential in fertility between ever-married high- and low-status men in the Finnish fertility transition. Consequently, among all men (married and unmarried), status-related differential in lifetime fertility—not selection coefficient—declined over the transition. This study is among the first to show the interrelated dynamics of status-related differentials in male mating and reproductive traits; by doing so, it contributes to an evolutionary understanding of change of status–fertility relationship in human fertility transition and confirms continuing phenotypic selection on male status/wealth in modern societies.

Description: Animal (and human) societies characterized by dominance hierarchies invariably suffer from inequality. The rise of inequality has 3 main prerequisites: 1) a group in which inequality can emerge, 2) the existence of differences in payoff, and 3) a mechanism that initiates, accumulates, and propagates the differences. Hitherto, 2 kinds of models have been used to study the processes involved. In winner–loser models of inequality (typical in zoology), the 3 elements are independent. In division-of-labor models of inequality, the first 2 elements are linked, whereas the third is independent. In this article, we propose a new model, that of synchronized group action, in which all 3 elements are linked. Under these conditions, agent-based simulations of communal action in multilayered communities naturally give rise to endogenous status, emergent social stratification, and the rise of elite cliques. We show that our 3 emergent social phenomena (status, stratification, and elite formation) react to natural variations in merit (the capacity to influence others’ decisions). We also show that the group-level efficiency and inequality consequences of these emergent phenomena define a space for social institutions that optimize efficiency gain in some fitness-related respect, while controlling the loss of efficiency and equality in other respects.

Description: Recent theory and empirical studies of avian biparental systems suggest that animals resolve conflict over parental care via a process of behavioral negotiation or "rules for responding." Less is known, however, about whether negotiation over helping effort occurs in cooperatively breeding animal societies or whether behavioral negotiation requires a relatively large brain. In this study, we tested whether negotiation over help occurs in a social insect, the paper wasp Polistes dominulus , by recording individual responses to both observed and experimentally induced foraging returns by other group members. In our experiments, we manipulated food delivery to the nest in 2 ways: 1) by catching departing foragers and giving them larval food to take back to the nest and 2) by giving larval food directly to wasps on the nest, which they then fed to larvae, so increasing food delivery independently of helper effort. We found no evidence from Experiment 1 that helpers adjusted their own foraging effort according to the foraging effort of other group members. However, when food was provided directly to the nest, wasps did respond by reducing their own foraging effort. One interpretation of this result is that paper wasp helpers adjust their helping effort according to the level of offspring need rather than the work rate of other helpers. Negotiation based on indicators of demand rather than work rate is a likely mechanism to resolve conflict over investment in teams where helpers cannot observe each other’s work rate directly, as is commonly the case in insect and vertebrate societies.

Description: Theory predicts that a mother’s ability to produce high-quality offspring should influence whether she produces sons or daughters. We tested this hypothesis in house wrens ( Troglodytes aedon ) using a within-clutch design in which we induced females to produce more eggs (8–10 eggs) than they normally would (6 or 7 eggs) to determine whether maternal effort and the allocation of resources to supernumerary eggs (those laid beyond the usual number) influence the offspring sex ratio. At the clutch level, we predicted that high-quality females, as defined by their ability to produce supernumerary eggs in response to egg removal, would overproduce sons relative to females treated the same way but producing fewer eggs. At the level of the egg, we predicted that supernumerary eggs would more likely contain daughters than sons. As predicted, females producing extralarge clutches overproduced sons and those producing smaller clutches produced relatively more daughters. Last-laid eggs were also more likely to contain daughters than earlier-laid eggs although there was no difference in the mass of eggs containing males and females. These results suggest that mothers adjust the sex of their offspring strategically to maximize fitness.

Description: When individuals invest in a common good, an efficient outcome is hard to achieve, because each can free ride on others’ efforts. This problem can lead parents that raise their young together to reduce their investment in care, with negative consequences for offspring. Here, we present a mathematical model to show that a strategy of conditional cooperation, in which parents take turns feeding their young, can help to resolve this problem. To test this idea, we studied the behavior of great tit parents raising chicks together. We found that parents alternated visits to the nest more than would be expected by chance, speeding up their feeding rate after their partner had visited the chicks, but slowing down again once they had visited in turn. This effect was not mediated by visit-to-visit changes in offspring begging intensity, although females (but not males) were influenced by mean begging levels across broods. We conclude that conflict over parental investment in this species is partly ameliorated by a simple form of reciprocity.

Description: The frequency of extrapair paternity within populations has been hypothesized to be related to ecological and social factors, which in turn can determine the impact of extrapair paternity on the opportunity for sexual selection. Here, we use the blue tit Cyanistes caeruleus as study species to assess both issues. In particular, we analyze patterns of extrapair paternity in 12 nest-box plots that greatly vary in local population size, level of nest-box aggregation, and breeding density. We found a significant positive relationship between extrapair paternity rate and local population size. Within study plots, neither local breeding density nor synchrony had an effect on the occurrence of extrapair paternity. Most extrapair males engaged in extrapair copulations with neighbouring females, probably in order to avoid paternity losses. Individuals that travelled larger distances to gain extrapair paternity likely did so because the social females of most of them had not yet begun their fertile period and, thus, within-pair paternity was not at risk. Variance in male reproductive success was mostly produced by variance in within-pair success, which in turn was primarily influenced by mate quality. Extrapair success contributed substantially to variance in male reproductive success (26%), but its effect was smaller than expected. Bateman gradients showed positive slopes (β ss ) for both males and females. However, the lack of a positive covariance between within-pair and extrapair success suggests that the effect of extrapair paternity on the strength of sexual selection was limited. This fact can be explained by the spatial distribution of extrapair fertilizations, which points to the absence of directional female mating preferences in this study system and, thus, not leading to "big winners" and "big losers."

Description: The persistence of gynogenetic organisms is an evolutionary paradox. An ideal system for examining the persistence of gynogens is the unisexual–bisexual mating complex of the unisexual Amazon molly ( Poecilia formosa ), and the bisexual, parent species, the sailfin molly ( Poecilia latipinna ) and the Atlantic molly ( Poecilia mexicana ). Insight into the maintenance of this mating complex might be enhanced by taking a more holistic view of male and female behavior through a behavioral syndrome framework. In this study, we examined whether male mate choice is part of a behavioral syndrome. We quantified behaviors related to activity, boldness, exploration, and sociability in male sailfin mollies, as well as their mate preference for conspecific females or the all-female species of Amazon mollies. In addition, we explored the relationship between behavioral type and cortisol (a fish stress hormone) production in male sailfin mollies. We found evidence for behavioral correlations in male sailfin mollies, but individual behavioral type was not correlated with their mate preference or stress hormone production. However, we did find differences in preexperience cortisol production related to male boldness behaviors. The lack of correlation between behavioral types, mate preference, and stress hormone production emphasizes that the nature of behavioral–hormonal interactions is complex. In summary, neither individual traits nor the behavioral types found here are adequate to explain the maintenance of this unisexual–bisexual mating system.

Description: In some systems, organisms form or join groups mediated by certain recognition cues. However, it is predicted that variability in such cues cannot be maintained as positive, frequency-dependent selection favors the dominant cue (Crozier’s paradox). We utilize a simple analytical model of 2 groups as well as computer simulations to find conditions where the coexistence (polymorphism) of 2 distinct recognition cues is maintained. We assume a species that forms reproductive groups and the adoption of a newborn individual into a group depends on that individual’s genotype (recognition cue) in relation to the group’s profile. We investigate the role of 2 factors affecting the level of isolation between groups, namely group tolerance toward deviant genotypes and dispersal between groups. Results from the analytical model show that high tolerance or high dispersal lead to the global fixation of a single genotype, whereas low group tolerance and low dispersal promote the globally stable coexistence of different genotypes. Interestingly, coexistence can only be global, with a different genotype dominating each group, or local, with 2 genotypes coexisting in one group, depending on the degree of tolerance and dispersal. Local coexistence, however, does not persist, when dispersal is allowed to evolve. In this case, low dispersal evolves, which stabilizes global coexistence but reduces local coexistence. If we expand the number of groups and assume spatially limited dispersal, global coexistence becomes a more likely outcome even under conditions where it was impossible in the 2-group system.

Description: Anthropogenic (man-made) noise has changed the acoustic environment both on land and underwater and is now recognized as a pollutant of international concern. Increasing numbers of studies are assessing how noise pollution affects animals across a range of scales, from individuals to communities, but the topic receiving the most research attention has been acoustic communication. Although there is now an extensive literature on how signalers might avoid potential masking from anthropogenic noise, the vast majority of the work has been conducted on birds and marine mammals. Fish represent more than half of all vertebrate species, are a valuable and increasingly utilized model taxa for understanding behavior, and provide the primary source of protein for 〉1 billion people and the principal livelihoods for hunderds of millions. Assessing the impacts of noise on fish is therefore of clear biological, ecological, and societal importance. Here, we begin by indicating why acoustic communication in fish is likely to be impacted by anthropogenic noise. We then use studies from other taxa to outline 5 main ways in which animals can alter their acoustic signaling behavior when there is potential masking due to anthropogenic noise and assess evidence of evolutionary adaptation and behavioral plasticity in response to abiotic and biotic noise sources to consider whether such changes are feasible in fish. Finally, we suggest directions for future study of fish acoustic behavior in this context and highlight why such research may allow important advances in our general understanding of the impact of this global pollutant.

Description: Many animals use reliable indicators of upcoming events such as antagonistic interactions to prepare themselves. In group-living animals, not only the cue perceiving individuals are involved in mobilization, but the entire group can use this information. In this study, we analyze whether social insects, which perceive reliable information on an upcoming social parasite attack, can use this knowledge to better defend their colony. We focus on the interaction between the ant Temnothorax longispinosus and the slave-making ant Protomognathus americanus , which conducts destructive raids on host colonies to steal their brood. As a behavioral defense, host colonies show aggression, which has a constitutive and inducible component: earlier studies demonstrated both behavioral consistency and an increase in aggression after slavemaker contact. Here, we analyze the fitness benefits of aggression in the context of slave raids. Aggression only facilitated host colony defense if the hosts were informed about a pending slave raid: slavemaker scouts were not only less likely to enter forewarned host colonies, but more aggressive colonies who previously encountered a slavemaker saved a higher fraction of their brood. We thus demonstrate that the fitness costs of raids depend on an interaction between the collective defense abilities and reliable information on impending dangers.

Description: It is well established that artificial night lighting can influence animal orientation, but there is less information about its effects on other behaviors. Previous work suggested that light pollution can affect both seasonal and daily patterns of behavior. The aim of our study was to investigate the effects of artificial night lighting and daytime traffic noise on the timing of dawn and dusk singing in 6 common songbirds. We recorded singing behavior in 11 nonurban plots: 2 plots with light, but no noise, 3 with light and noise pollution, 3 with noise, but no light, and 3 undisturbed forests. Our results show that artificial night lighting, but not noise, leads to an earlier start of dawn singing in 5 out of 6 species, ranging on average from 10min for the song thrush to 20min for the robin and the great tit. This effect was strongest at higher light intensities. We further show that dusk song is also affected: 3 species continued dusk singing for longer in lighted areas, but the effect was smaller than that observed for dawn song (from about 8min for the blackbird to 14min for the great tit). For all species, onset and cessation of singing changed relative to sunrise and sunset with the progress of the season. Rain delayed the onset of singing at dawn and advanced the cessation at dusk. We discuss the implications of our findings in the context of sexual selection.

Description: Dietary access to carotenoids is expected to determine the strength of carotenoid-based signal expression and potentially to maintain signal honesty. Species that display carotenoid-based yellow, orange, or red plumage are therefore expected to forage selectively for carotenoid-rich foods when they are depositing these pigments during molt, but whether they actually do so is unknown. We set out to address this in the hihi ( Notiomystis cincta ), a New Zealand passerine where males, but not females, display yellow carotenoid-based plumage. We measured circulating carotenoid concentrations in male and female hihi during breeding and molt, determined the nutritional content of common foods in the hihi diet, and conducted feeding observations of male and female hihi during molt. We found that although male and female hihi do not differ significantly in plasma carotenoid concentration, male hihi have a greater proportion of carotenoid-rich foods in their diet than do females. This is a consequence of a greater fruit and lower invertebrate intake than females and an avoidance of low-carotenoid content fruit. By combining behavioral observations with quantification of circulating carotenoids, we present evidence that colorful birds forage to maximize carotenoid intake, a conclusion we would not have drawn had we examined plasma carotenoids alone.

Description: Consistent between-individual differences in behavior have been demonstrated in an array of species from diverse taxa, and variation in boldness may be associated with variation in aggressiveness. However, little is known about how boldness is linked with the ability to win fights (resource holding potential) or about how the experience of fighting may alter subsequent boldness. Animal contests often involve role asymmetries, where the 2 opponents fight in different ways. Here, we investigate boldness before and after fighting in attacking and defending hermit crabs during contests over the ownership of gastropod shells. Although prefight boldness did not influence the chance of winning for attackers, successful defenders had longer startle responses (less bold) than those that gave up. Postfight changes in boldness also differed between roles. For defenders, there was a significant decline in consistency of startle responses after fighting, coupled with outcome-dependent plasticity in mean boldness. Furthermore, postfight boldness in defenders varied with the intensity of agonistic behavior inflicted on them by attackers. In contrast, boldness in attackers was stable across the before- and after-fighting situations. Links between internal state and agonistic behavior are known to vary between roles in asymmetric contests. It now appears that similar role-specific links are present between aggression and animal personality.

Description: The ability to adjust behavioral responses to environmental cues probably contributes to an individual’s ability to persist in unfamiliar habitats. One behavior, how an individual responds to novelty, influences the acquisition of resources (e.g., novel foods) and identification of stressors, but it may also increase exposure to risks. Here, using house sparrows ( Passer domesticus ) recently introduced to Kenya, we tested how range expansion influenced individuals’ responses to novel foods and objects. We predicted that range edge birds would be less averse to novelty than birds at the site of introduction and that this effect would be more pronounced for novel foods than novel non-nutritional items. We also expected range edge individuals to be more sensitive to changes in the environment and therefore more apt to adjust their behavior in response to different cues; in other words, individuals at the range edge would have a more flexible behavioral repertoire than individuals at the site of introduction. As predicted, individuals at the range edge ate novel foods faster than those from established areas; however, latency to touch novel objects did not vary across the range. Individuals throughout the range were variable in their response to novelty, but there was no indication that individual flexibility was greater at the range edge. Although many novel items might be useful to introduced organisms, novel foods are likely more valuable, and therefore individuals should be most apt to risk the potential costs associated with novelty for a high nutritional payoff.

Description: Courtship signals are expected to be consistent within but vary between males of different qualities. Such traits are, therefore, predicted to exhibit high repeatability. However, studies have shown that courtship behaviors vary greatly in their within-individual repeatability, resulting in substantial variation in their ability to reflect male quality. This has implications for the evolution of female mate choice and courtship communication, as low levels of repeatability may reflect courtship signals that do not provide accurate quality information to females. In this article, we tested whether male courtship shuddering in the tropical orb-web spider, Argiope radon , influences female mate choice. We also tested whether male shudder performance reflects male phenotypic condition and is repeatable. We found that male shudder performance and condition predicted female latency to move onto the mating thread, a measure of mate preference. Aspects of male shudder performance were positively correlated with male body condition. Further, we found surprisingly high levels of repeatability in male courtship shuddering, ranking among the highest levels recorded to date for courtship behavior. We suggest that male courtship shuddering functions as an important indicator of male quality, with strong potential to respond to selection.

Description: Condition-dependent mate choice is thought to affect the strength and direction of sexual selection. Although there is ample evidence of this from studies that experimentally manipulate female condition, few studies to date have examined condition dependence of natural mate choice wherein females interact with a pool of available males. We examined mate assessment by free-living Pavo cristatus peafowl, focusing on 3 measures of the choosing female’s condition: mass condition (scaled mass index), ectoparasite load, and white blood cell (WBC) count. Females with greater mass condition were more active on peacock leks, approaching and visiting males more often, and spending more time near the males they visited. Condition did not affect the total number of males visited or the probability that a female would visit a male that she had already approached. Peacock mating success is strongly correlated with the iridescent colors of the eyespots on their train, suggesting that color signals are a major focus of female choice. Here, we show that females in better condition (higher mass condition and lower WBC count) allocate a greater proportion of their visit time to the most iridescent males displaying on leks. Our results provide evidence of strong condition-dependent effects on female mate assessment and choice in the absence of experimentally induced stress. We suggest that condition-dependent mate choice may help maintain variation in sexually selected male color traits.

Description: Secondary sexual traits in males are recognized as having arisen in order to gain access to reproductive opportunities, through their effects on the outcome of male–male competition and female choice. The phenotype-linked fertility hypothesis proposes that ejaculate quality is honestly advertised via secondary sexual traits. Alternatively, if males have limited resources to allocate to both pre- and postcopulatory traits, males possessing attractive phenotypic or behavioral traits may produce poorer quality ejaculates. Sperm competition theory also predicts that the female phenotype will influence ejaculate quality, with males increasing investment as female attractiveness increases. However, the extent to which the male and female phenotypes interact in affecting ejaculate quality has not been widely studied. Here, we examine how male and female phenotypes influence ejaculate quality in humans. Eighty-one men, for whom we had a composite measure of overall male mate value, produced a semen sample in response to images of either highly attractive or less attractive women. We found a significant relationship between male mate value and ejaculate quality that was context dependent. Sperm motility and concentration increased with male mate value but only when men viewed images of highly attractive women. Context dependence may contribute, in part, to the often conflicting patterns of variation found in studies that test the phenotype-linked fertility hypothesis.

Description: Bird flocks are characteristic of environments worldwide, and there is a rich literature investigating the purported costs and benefits for attendant species. Few studies, however, have investigated the potential sources of individual variation in flocking behavior. We hypothesized that flocking propensity would vary among individuals as a function of intrinsic, environmental, and social characteristics, as well as flock-joining opportunities as a function of home range size and number of flocks present. We tracked wedge-billed woodcreepers ( Glyphorynchus spirurus ) using radiotelemetry from January–February, 2011 and January–March, 2012 at Tiputini Biodiversity Station in eastern Ecuador. Individual home ranges overlapped a mean of 2.6 (0.2 standard error [SE]) individuals by a mean of 44% (0.09 SE) per overlapping individual. Flocking propensity was 32% in 2011 and 20% in 2012, with considerable individual variation (2–35%). Expected flocking propensity was 45% based on average home range size and number of flocks in the study area; assuming that dominant individuals excluded subordinates in areas of home range overlap reduced the predicted value to 35%. Individual flocking propensity was positively correlated with body condition, frequency of aggressive behavior, and probability of joining a flock given presence, and negatively correlated with number of overlapping conspecifics. Our results suggest that woodcreepers compete for access to flocks within areas of home range overlap, which results in limited opportunities for some individuals to join flocks. The costs and benefits of group behavior may, therefore, vary among individuals within a species.

Description: There is growing empirical support for teaching in nonhuman animals. To unravel the evolutionary dynamics of teaching, we need to understand its costs and benefits. In superb fairy-wrens ( Malurus cyaneus ), females teach their embryos by calling to them: embryos learn a vocal password, and hatchlings incorporate the learned vocal password into their begging calls to solicit parental feeding. The more a female teaches (higher call rate), the better the embryos learn (greater call similarity), leading to more food provisioning by parents. Given these direct benefits, we would expect all female fairy-wrens to call often to maximize embryonic learning in their genetic progeny, yet they do not. Teaching the password carries a severe cost: nest predation was higher at both natural and artificial nests that had more incubation calls. At artificial nests, predation was 8-fold higher for high incubation call rate (30 calls per hour) and 5-fold higher for low incubation call rate (15 calls per hour) compared with nests without any incubation calls. At natural nests, nests that were depredated during incubation had higher incubation call rate (18.3 calls per hour) than nests that survived (11.4 calls per hour). Mother fairy-wrens must trade-off the costs of calling and the benefits of learning to optimize fitness benefits of teaching.

Description: Dispersal is a potentially risky behavior that has several important implications for demography. Dispersal may be measured directly through behavioral observations or indirectly using genetic analyses. The direct approach is accurate but labor-intensive, whereas the indirect approach depends on population subdivision to infer dispersal events. Here, we combine field studies of behavior and natural selection in an island lizard ( Anolis sagrei ) to provide direct estimates of sex-specific dispersal and then compare these estimates to measures of population subdivision at both nuclear (biparental inheritance) and mitochondrial (uniparental inheritance) genetic markers. Juvenile males dispersed 4 times further than juvenile females. Natural selection acted against long-distance dispersal in females, but we measured no such selection on dispersal distance in males. Despite strong evidence for sex-biased dispersal accompanied by selection, we detected no population genetic signature of dispersal at either nuclear or mitochondrial loci. In closed populations, such as those occurring on small islands, repeated dispersal events may have important demographic consequences and yet produce no population genetic signature owing to continuous admixture of genotypes.

Description: Many animals use volatile chemicals to detect and locate their food, but they frequently have to cope with a large variation in volatile blends associated with food. It has often been suggested that they do this by learning the association between odors and the presence of food. Indeed, associative learning was demonstrated for a range of animals under laboratory conditions and individuals usually take seconds to hours to modify their behavior. However, it is poorly understood at which timescale field populations and communities of animal species respond. We studied this by exposing egg batches of arthropod herbivores, half of which were combined with a volatile, to a community of natural enemies in the field. We used mint oil as a volatile blend, which we showed not to be attractive in the laboratory for 2 predators that commonly occur in the field. The predation of egg batches with volatiles in the field was initially slightly lower than that of batches without volatiles, indicating that the odor was not innately attractive to the natural enemies. However, relative to the controls, the predation of eggs associated with volatiles increased significantly over a period of 4–5 days. This suggests that individuals in the community of natural enemies associated the presence of eggs with the volatiles. We observed 3 different types of predation, indicating that various groups of predator species were responsible for predation in the field. Our results show that communities of animals rapidly associate volatiles with food in the field.

Description: Both predators and parasites can elicit behavioral and physiological responses in prey and hosts, respectively. These responses may involve the reallocation of resources and may thus limit each other. We investigated the effects of concurrent pre-laying exposure of great tit females ( Parus major ) to both a simulated predation risk and a nest-based ectoparasite, the hen flea ( Ceratophyllus gallinae ), on nestling growth and development. We manipulated perceived predation risk using models and vocalizations of sparrowhawks ( Accipiter nisus ). At the start of incubation, we swapped whole clutches between treated and untreated nests to separate pre-laying maternal effects from posthatching effects. Since costs and benefits of maternal responses to parasites need to be assessed under parasite pressure, we infested half of the rearing nests with hen fleas. Parasites had negative effects on mass gain and wing growth, both via maternal effects and via direct exposure of nestlings, whereas maternal predation risk had no significant effect. The interaction between predator and parasite treatments was not significant and, thus, suggests the absence of a trade-off between the 2 stressors operating at the level of maternal effects. Alternatively, the complexity of the design, despite a relatively large sample size, may have limited the power for detection of this expected trade-off.

Description: Premature loss of offspring decreases direct fitness of parents. In gregarious mammals, both ecological and social variables impact offspring survival and may interact with each other in this regard. Although a number of studies have investigated factors influencing offspring loss in mammals, we still know very little on how different factors interact with one another. We therefore investigated fetal and infant mortality in 3 large groups of wild crested macaques ( Macaca nigra ) over a period of up to 5 years by including potential social causes such as maternal dominance rank, male immigration, between group encounters, and ecological conditions such as rainfall in a multivariate survival analysis using Cox proportional hazards model. Infant but not fetal survival was most impaired after a recent takeover of the alpha-male position by an immigrant male. Furthermore, infant survival probability increased when there was an increase in number of group adult females and rainfall. Fetal survival probability also increased with an increase of these 2 factors, but more in high-ranking than low-ranking females. Fetal survival, unlike that of infants, was also improved by an increase of intergroup encounter rates. Our study thus stresses the importance of survival analyses using a multivariate approach and encompassing more than a single offspring stage to investigate the determinants of female direct fitness. We further provide evidence for fitness costs and benefits of group living, possibly deriving from high pressures of both within- and between-group competition, in a wild primate population.

Description: Recent ecological and evolutionary research emphasizes the importance of adaptive trait integration. For instance, antipredator defenses are built up of several morphological and behavioral components in many species, yet their functional relationships are still poorly documented. Using field-collected freshwater crustaceans Gammarus fossarum in a within-subject design, we investigated the flexibility and consistency of refuge use, photophobia, and exploration behavior as well as their associations, quantified both when predation risk was absent or artificially simulated. In agreement with the "threat-sensitivity" hypothesis, both refuge use and photophobia increased under predation risk, whereas exploration behavior did not vary. For all behaviors, individuals exhibited low but significant consistency between risk treatments. However, intraindividual variability did not vary with weight or between sexes. Finally, a positive relationship between photophobia and refuge use was observed only under predation risk in females, whereas it was found in both risk treatments in males. Our findings demonstrate that predation risk may promote behavioral flexibility and behavioral correlations, or syndromes, in wild populations, and call for an integrative study of antipredator mechanisms where the evolution of each dimension has to be examined in combination with all others. Additional phenotypic traits should be included in future studies to better characterize the multidimensionality of antipredator defense and the functional relationships among traits. The survival consequence of behavioral correlations between risk-sensitive traits also remains to be estimated in mortality selection experiments.

Description: Feathers are inhabited by numerous bacteria, some of them being able to degrade feathers, and thus potentially alter thermoregulation and visual communication. To limit the negative effects of feather bacteria on fitness, birds have therefore evolved antimicrobial defense mechanisms, including preening feathers with secretions of the preen gland. However, whether feather bacteria can alter feather condition and color signaling in vivo, and thus whether birds adjust their investment in preening according to feather bacterial load, has barely been investigated. Here, we experimentally decreased and increased feather bacterial load on captive feral pigeons Columba livia and investigated the effects on plumage characteristics and investment in preening. We found that birds of both sexes had a plumage in higher condition and invested less in preen secretion quantity and preening behavior when feather bacterial load was lower. It suggests that preen secretions may be used by pigeons to limit feather degradation by bacteria, but as they are probably costly to produce, their quantity is adjusted depending on feather bacteria load. Birds with lower bacteria load on feathers had brighter iridescent neck feathers, suggesting that feather bacteria may play an important role in the evolution of the signaling function of iridescent color in pigeons. Altogether, our study provides the first experimental evidence for in vivo effects of feather bacteria on plumage degradation and coloration and suggests that preening is an inducible antibacterial defense.

Description: A preference to mate with novel partners has been shown for both males and females in a range of taxa. Preferences for novel mates may result from direct recognition of previous sexual partners, or from other cues that predict this, such as familiarity. Costs and benefits of mating with multiple mates differ for males and females. Despite this, few studies have tested whether the sexes differ in their preferences for novel mates. Here, we investigated whether males and/or females showed preferences for novel mates and whether this differed depending on the type of experience with a familiar mate (i.e., previously allowed to mate or allowed visual and olfactory exposure only) in the eastern mosquitofish ( Gambusia holbrooki ). We show that mosquitofish prefer to associate with novel fish and that there was no significant difference between the sexes in the strength of this preference if the choosing fish had previously had an opportunity to mate. In contrast, males and females that had not recently mated and were familiar due solely to visual and olfactory contact did not have a preference for novel mates. Our results suggest that there are likely to be benefits of mating with multiple partners for both males and females.

Description: Kinship is a key factor that can influence the fitness benefits associated with social behaviors through the operation of kin selection. A species’ patterns of dispersal, and resulting fine-scale spatial genetic structure, can mediate kin selection by altering both the capacity for kin cooperation and the intensity of kin competition. In this study, we used proximity logger collars and multilocus genotypes to investigate how genetic relatedness influences the associations of mountain brushtail possums ( Trichosurus cunninghami ) in the context of fine-scale spatial genetic structure. We found distinct differences between diurnal and nocturnal associations. Diurnal (den-sharing) associations occurred within a small subset of mainly male–female dyads, whose members were socially pair-bonded. In contrast, nocturnal associations occurred between multiple individuals of both sexes. Spatial proximity was an important factor influencing the nocturnal encounter rate. Further, proximity was associated with relatedness between individuals, a pattern that was stronger among females than males. After proximity was accounted for, we found that possums who shared a mitochondrial haplotype associated more often and for longer during nocturnal activity. By comparison, autosomal nuclear relatedness metrics did not explain associations. This is likely to represent, in part, mother–offspring associations but may also indicate a general preference for associating with familiar individuals. Females also associated for longer than did males, which may be attributed to a combination of kin preference and differences between the sexes in genetic structuring. Thus, this study demonstrates the way social behaviors may be shaped by how kin selection and fine-scale spatial genetic structure interact.

Description: When approached by a predator, prey make economic decisions between remaining where they are and obtaining benefits from their current activity or leaving and enhancing their safety. The "flush early and avoid the rush" hypothesis suggests that animals that flee to escape approaching threats flee soon after they become alert to an approaching predator so as to reduce any costs incurred by ongoing monitoring of the predator. This hypothesis has been supported by several studies, but some researchers argue the relationship may be partially or entirely a consequence of bouts of spontaneous vigilance and/or bouts of spontaneous locomotion (vigilance or locomotion that occur when the animal is unaffected by a predator), rather than an economic decision related to the approaching predator. If this were true, spontaneous vigilance might incorrectly be recorded as alert distance (predator–prey distance when the prey becomes aware of and begins to monitor the predator) and spontaneous locomotion might be incorrectly recorded as flight initiation distance (predator–prey distance when escape begins). To evaluate these potential effects, we recorded the intervals between bouts of spontaneous vigilance and locomotion by yellow-bellied marmots ( Marmota flaviventris ). We used these baseline rates to conduct a series of alert distance–flight initiation distance regressions after removing potentially spurious observations recorded as alert distance or flight initiation distance. Although spontaneous vigilance and spontaneous locomotion may lead to artifactual increases in flight initiation distance as alert distance increases, the fundamental relationship remains after effects of spontaneous movements have been removed, supporting the flush early and avoid the rush hypothesis. We tested a key challenge of the "flush early and avoid the rush" (FEAR) hypothesis; our results provide strong support for the hypothesis.

Description: An important problem facing organisms in a heterogeneous environment is how to redistribute resources to where they are required. This is particularly complex in social insect societies as resources have to be moved both from the environment into the nest and between individuals within the nest. Polydomous ant colonies are split between multiple spatially separated, but socially connected, nests. Whether, and how, resources are redistributed between nests in polydomous colonies is unknown. We analyzed the nest networks of the facultatively polydomous wood ant Formica lugubris . Our results indicate that resource redistribution in polydomous F. lugubris colonies is organized at the local level between neighboring nests and not at the colony level. We found that internest trails connecting nests that differed more in their amount of foraging were stronger than trails between nests with more equal foraging activity. This indicates that resources are being exchanged directly from nests with a foraging excess to nests that require resources. In contrast, we found no significant relationships between nest properties, such as size and amount of foraging, and network measures such as centrality and connectedness. This indicates an absence of a colony-level resource exchange. This is a clear example of a complex behavior emerging as a result of local interactions between parts of a system.

Description: The nonreproductive helpers of many arthropod, bird and mammal species are a perennial puzzle for evolutionary biologists. Theory and evidence suggests that helping is favored by high relatedness between social partners and by certain ecological factors. I suggest that the availability of information on reproductive value may be another important factor predicting whether helping evolves. Using simple models, I show that conditional helping strategies, in which individuals assess the reproductive value of themselves and their relatives and then help conditionally, evolve more easily than unconditional helping strategies. The models also identify conditions that cause parent–offspring conflict over helping strategy and produce predictions regarding the evolution of honest signaling and parental effects. Crucially, the evolution of facultative helping can select for specialization in helping, which in turn selects for more frequent helping, creating positive feedback. Facultative helping might thereby act as stepping-stone to advanced forms of obligate helping.

Description: The ability to discriminate information quality from multiple social partners may be essential to animals that use social cues in deciding when, where, and what to eat. This may be particularly important in species that rely on ephemeral and widely dispersed resources. We show that tent-making bats, Uroderma bilobatum , socially acquire preferences for novel foods through interactions with roostmates both in captivity and in natural roosts and that these food cues can influence roostmates’ decisions at least for several days. More importantly, these bats can distinguish between the quality and information content of 2 different cues that are brought back to their roost. Inexperienced individuals prefer food that has been consumed by a roostmate to food whose odor is present only on the fur of a roostmate that has eaten sugar water. The ability of bats to discriminate odors on breath and fur may allow them to select the most informative cues about the presence or renewed availability of dispersed resources. This selectivity may help stabilize roosts as information centers for the social acquisition of updated information on unpredictable and widely distributed food items.

Description: Environmental differences can cause reproductive isolation to evolve. Distinct habitats can be particularly important for the evolution of genetically based sexual isolation, which occurs when divergent preferences and mating traits reduce mating between species. Yet, we know little about environmental effects on the potentially plastic expression, and thus the current maintenance, of sexual isolation. This is especially intriguing in the context of reverse speciation, where previously isolated taxa begin hybridizing and merge. Environmental change could weaken reproductive isolation underlain by plastic traits even before any genetic change occurs. Here, we examine how differences in mating habitats affect the expression of both female discrimination between species and male traits that underlie sexual isolation. We used 2 species pairs of threespine stickleback fish ( Gasterosteus spp.): an intact species pair and a formerly distinct but now hybridizing species pair, where habitat change presumably triggered reverse speciation. The expression of female discrimination was fairly insensitive to habitat, despite the central importance of habitat differences to the initial evolution of sexual isolation. Only the ecotype being subsumed by hybridization showed habitat sensitivity, suggesting this plasticity may have contributed to reverse speciation either as a cause or consequence of gene flow. Also, we found plasticity in male courtship across habitats that could further erode sexual isolation. Thus, environmental differences may play different roles in the genetic evolution versus plastic maintenance of sexual isolation, with implications for the forward versus reverse processes of speciation.

Description: During agonistic contests, males may assess the relative differences between their own and their opponent’s resource-holding potential or simply persist in a contest according to an internal threshold. Game theory models such as the sequential assessment model, energetic war of attrition, and the cumulative assessment model were developed to place assessment strategy in an evolutionary framework. Distinguishing between these models requires one to document contest structure and test predictions of the relationship between the size of the contestants and contest duration and probability of escalation. This study focused on the escalating fighting behavior and competitive assessment strategy of the New Zealand giraffe weevil ( Lasiorhynchus barbicornis ). Aggressive fighting occurred frequently between males of all sizes, and body length (which included rostrum length) was an important predictor of contest outcome. Contest duration was negatively related to body length difference and the size of the winning male and showed a nonsignificant positive relationship with loser size. The probability of fight escalation showed a significant negative relationship with body length difference, a positive relationship with loser size, and a nonsignificant negative relationship with winner size. Contests were also found to escalate, but not de-escalate, and behavioral matching did not occur during all phases. Male behavior during contests was therefore most consistent with mutual assessment under the sequential assessment model.

Description: Humans and human infrastructure are known to alter the relationship between predators and prey, typically by directly or indirectly shielding one of the species from the other. In addition to these overt changes to animals’ behavior, observers may have more subtle impacts on animals’ foraging decisions. However, the anthropogenic alteration of risk-taking behavior has rarely been acknowledged or quantified, particularly in behavioral ecological studies reliant on habituated animals. We tested the magnitude of the "human shield effect" experimentally on 2 groups of samango monkeys, Cercopithecus mitis erythrarcus , at a site with high natural predator density and no human hunting pressure. In general, giving-up densities—the density of food remaining in a patch when a forager leaves—were greatest at ground level (0.1 m) relative to 3 tree canopy levels (2.5, 5, and 7.5 m), highlighting a strong vertical axis of fear. When human followers were present, however, giving-up densities were reduced at all 4 heights; furthermore, for 1 group, the vertical axis disappeared in the presence of observers. Our results suggest that human observers lower monkeys’ perceived risk of terrestrial predators and, thereby, affect their foraging decisions at or near ground level. These results have significant implications for future studies of responses to predation risk based on habituation and observational methods.

Description: Foraging requirements and predation risk shape activity patterns and temporal behavior patterns widely across taxa. Although this has been extensively studied in small mammals, the influence of predation and prey acquisition on the activity and behavior of large carnivores has received little attention. The diurnal activity described as typical for cheetahs ( Acinonyx jubatus ) has been explained in terms of their avoidance of antagonistic interactions with other larger predators. However, a recent study revealed that cheetahs are frequently active at night, especially during periods of full moon. Being both predator and "prey" in an environment with comparatively high densities of larger and competitively dominant nocturnal predator species, we investigated whether cheetah nocturnal behavior could be explained by favorable conditions for 1) predator avoidance or 2) prey acquisition. We used a data set of continuously recorded behavior created using machine-learning techniques on behavioral data collected in the field to transform recorded 2D activity values from radio-collars into 3 distinct behavioral states (feeding, moving, and resting). We found that 32.5% of cheetah feeding behavior occurred at night and that, in the dry season, nocturnal feeding behavior was positively correlated with moonlight intensity. Our results suggest that nocturnal and circalunar behavior of cheetahs is driven by optimal hunting conditions, outweighing the risks of encountering other predators. Using novel methodology, the results provide new insights into the temporal distribution of behavior, contributing to our understanding of the importance of moonlight and season on the behavior patterns of diurnal species.

Description: In many social species, individuals make group decisions to coordinate their actions. Despite the importance of group decisions for successful group living, few studies investigated how wild animals make group decisions in situations where group members have conflicting interests. This lack of empirical data is most evident for animal groups that regularly split into subgroups for some time. In groups with high fission–fusion dynamics, individuals can avoid group decisions that are not in their interest without foregoing benefits from being social. Here, we compare group decision making about communal day roosts in 2 syntopic bat species with a similar ecology and life history but a different fission–fusion behavior of their colonies. Daily roost monitoring during 3 breeding seasons showed that Bechstein’s bats formed subgroups 5 times more often than brown long-eared bats although both species occupied a similar number of bat boxes per colony and year. Bechstein’s bats were also significantly faster in discovering newly installed boxes and explored them further away from their established roosting areas compared with brown long-eared bats. In a field experiment where we created a conflict of interests among colony members where to roost, brown long-eared bats always achieved a colony-wide consensus about communal roosts. On the contrary, in Bechstein’s bats, individuals with conflicting interests often formed subgroups in different roosts according to their individual interests instead of reaching a consensus on a single communal roost. Our findings show that even ecologically similar species can use different group decision-making rules for solving an identical coordination problem.

Description: Maternal allocation shapes offspring phenotype by being tailored to parental phenotype and offspring sex. Because melanogenesis and immunity have partly common genetic control, maternal effects via egg immune factors and parental melanization may covary. Here, we tested whether barn swallows Hirundo rustica allocated antibodies against a novel antigen to their eggs according to embryo sex depending on maternal melanin-based coloration while controlling for paternal tail ornamentation. Egg antibody concentration increased with maternal plumage darkness in broods with relatively more females, whereas it decreased in broods with relatively more males. Thus, darker females allocated more antibodies to their eggs when offspring sex ratio was female biased, whereas paler females allocated more antibodies to the eggs when offspring sex ratio was male biased. These effects were independent of laying order. Our results are compatible with the hypotheses that maternal allocation to sons depends on their reproductive value as predicted by heritable melanin-based coloration and with the hypothesis of differential susceptibility of pheomelanic daughters to parasitism. These effects may depend on pleiotropy of the genes that control melanogenesis and immunity, which may differentially act on investment in self-maintenance and maternal effects. This study is the first study in vertebrates of the association between maternal effects on either sex via egg quality and parental melanization. The links between the genetic control of melanogenesis and of major fitness traits like immunity and the role of maternal effects in reproductive strategies prompt for more studies of the covariation between parental coloration and maternal sex-dependent allocation via egg quality.

Description: The presence of several clonal lineages within a single aphid colony raises the possibility for conflict between clones over safer positions within multiclonal colonies. To study the effect of relatedness on group dynamics, we manipulated the clonal composition of pea aphid groups (2 pure clonal groups and 1 mixed group) under laboratory conditions and allowed the individuals to cluster together freely on a leaf. We found variation between the clones in both the speed at which individuals joined the group and the aggregation level, where mixed colonies showed intermediates. Experimental and simulation results showed a nonrandom distribution of aphids in mixed colonies between the center and the periphery area, suggesting that one of the clones exhibits selfish herd behavior. In a second set of experiments, aphid groups were exposed to a single parasitoid female. Interestingly, we found that aphids from pure colonies were more likely to react by falling from the plant than individuals in mixed colonies. Our results revealed unexpected kin recognition abilities by nonsocial aphids, which make aphid colony dynamics more complex than previously thought.

Description: In typically outbreeding species, females can avoid a reduction in offspring fitness by choosing unrelated sires. However, the kin selection model of mate choice suggests that it may be adaptive to mate with relatives to gain inclusive fitness benefits, especially in lekking species. Several studies have shown that females tend to mate with relatives, but the detailed behavioral data necessary to determine whether this reflects an active preference is difficult to acquire. We test the hypotheses that females actively preferred or avoided relatives in mate choice in satin bowerbirds ( Ptilonorhynchus violaceus ), a lekking species in which comprehensive observations of natural mate choice were obtained using automated video cameras positioned at bowers. We identified specific males that were sampled by individual females and assessed whether relatedness influenced their acceptance or rejection as mates. We found no consistent effect of relatedness on mate choice across years or among multiple stages of mate choice. In 2 of 6 years, females copulated with relatives at or above the half-sibling level significantly more often than expected, but this was attributed to females searching for mates in areas populated by relatives, and not to an active preference for relatives. Furthermore, we found no evidence for inbreeding avoidance through mate choice discrimination or sex-biased dispersal.

Description: The sexy-sperm hypothesis proposes that polyandrous females will have a selective advantage over monandrous females as their sons will be sired by males with competitively superior sperm and will inherit this trait. Although the good-sperm hypothesis also predicts that offspring will be sired by males with competitively superior sperm, it additionally assumes a positive correlation between offspring sperm quality and the general viability of both sons and daughters. We examined the potential for sexy-sperm and good-sperm processes by exploring the effect of polyandry on offspring sperm quality and immunocompetence in the field cricket, Teleogryllus oceanicus , a species in which sperm viability predicts sperm competitive ability. In the parental generation, females were mated monandrously or polyandrously, where each female received 3 matings. We reared the resultant offspring through to maturity and assayed approximately 10 offspring per family for both sperm viability and immunity. We found that male offspring from polyandrous mothers had higher sperm viability, but that this was not phenotypically associated with male or female offspring condition, as measured by either immune function or ability to survive a bacterial infection. Thus, our data are consistent with a sexy-sperm, but not a good-sperm model in explaining the evolution of polyandry in this species.

Description: Testosterone is a key hormone for the development of secondary sexual characters and dimorphisms in behavior and morphology of male vertebrates. Because females often express detectable levels of testosterone, testosterone has been suggested to also play a role in the modulation of secondary sexual traits in females. Previous comparative analyses in birds and fish demonstrated a relationship between male-to-female testosterone ratios and the degree of sexual dimorphism. Furthermore, female maximum testosterone was related to mating system and coloniality. Here, we reevaluate these previous ideas using phylogenetic analyses and effect size measures for the relationship between birds’ male-to-female maximum testosterone levels. Further, we investigate the seasonal androgen response of female birds (the difference from baseline to maximum testosterone), which in males is strongly related to mating system. We could not confirm a relationship between male-to-female testosterone, maximum female testosterone, or the seasonal androgen response of females with any life-history parameter. We conclude that the expectation that testosterone regulates traits in females in a similar manner as in males should be reconsidered. This expectation may be partially due to hormone manipulation studies using pharmacological doses of testosterone that had similar effects in females than in males but may be of limited importance for the physiological range of testosterone concentrations occurring within ecological and evolutionary contexts. Thus, the assumption that circulating testosterone should covary with ecologically relevant secondary sexual traits in females may be misleading: selection pressures on females differ from those on males and females may regulate behavior differently.

Description: Increased predation risk is one of the greatest costs associated with sexual signaling. Studies have shown that individuals often adjust their signaling behavior in the presence of predators with consequences for current reproductive opportunities. Predation risk, however, can vary over time and is rarely (if ever) constant. Despite this, surprisingly little is known about how recent exposure to a predator might influence an individual’s subsequent signaling behavior. Here, we set out to determine how a previous encounter with a piscivorous predator affected courtship behavior in a freshwater fish, the desert goby, Chlamydogobius eremius . We tested male courtship before and after manipulating their perception of risk. We found that male gobies previously exposed to a predatory fish, the spangled perch, Leiopotherapon unicolor, took longer to initiate courtship and subsequently spent less time courting females. Such males, instead, spent more time taking refuge in their nests. In contrast, unexposed control male gobies and males that were exposed to a nonpredatory fish, the Lake Eyre Hardyhead, Craterocephalus eyresii, did not alter their courtship behavior. Our results suggest that male courtship behavior is not only sensitive to the immediate presence of a predator but can persist even after the predatory threat has abated.

Description: The design of brains, sense organs, or immune systems is an impressive product of natural selection, far ahead of human engineering capability. But what if behavior is less well adapted? A bird’s perfect eye is useless if it fails to avoid a stalking cat. If we fail in choosing a partner with complementary immunogenes, our ability to detect major histocompatibility complex–dependent body odors is worthless. Besides being able to detect all available prey items, the diet that maximizes net energy gain must be chosen. Individuals that are selected naturally will be those best able to avoid predators, choose mates, select food, and so on. Those with less perfect behavior produce fewer offspring, and their genotypes will disappear. Ecology is the stage on which the fittest have behaved most successfully. Thus, their strategies prevail today. Behavioral ecology is about the optimal design of behavior.

Description: Here, we argue that behavioral ecologists can do even more than we have done to facilitate new, interdisciplinary collaborations. Our argument is a general one, but we focus on how to do this with winner and loser effects. We develop a new, general model of winner and loser effects as the outcome of flexible decisions about how much to invest in competition and discuss the model’s implications for overall levels of conflict within a species. Finally, we argue that winner and loser effects is a topic ripe for fostering collaborations with researchers in cultural anthropology and sports psychology.

Description: Female reproductive status can have strong selective effects on male mating strategies due to the threat of sperm competition, which may explain why males prefer virgin over mated females. However, in mating systems with female multiple mating rates and mating plugs, males should not only respond to the risk but also to the level of sperm competition and should be sensitive to the interference from mating plugs. In the orb-web spider Argiope keyserlingi , females possess paired sperm-storage organs facilitating separate sperm storage from different males. Males are limited to 2 copulations due to mutilation of their paired genitals (pedipalps). By conducting binary choice experiments, we tested whether males of different mating status can distinguish between females that mated with 1 or 2 males and whether single-mated males discriminate between single-mated females with matched or unmatched virgin genital openings. Furthermore, we investigated whether males adapt their mating strategies to the intensity of sperm competition by providing males with varying qualities of females in their immediate vicinity. Our results demonstrated that males are sensitive to the level of sperm competition and preferred single-mated females over double-mated females. However, they failed to identify single-mated females whose virgin genital opening matched their unused pedipalp, which is required due to their fixed ipsilateral insemination. Surprisingly, males never mated twice with the same female independently of the quality of surrounding females. This suggests that the benefits from searching and mating with a different female are greater than the benefits of monopolizing the female by mating twice with her.

Description: Mate choice is known as an important behavior allowing females to choose the best mate to increase their reproductive success. To estimate male quality, females can use multiple traits. Among those, recent studies have shown that male personality traits could play an important role in mate choice as they are often linked to major life-history traits and can be heritable. However, because the relationships between life-history traits and personality traits are context dependent, females are expected to choose male personality types according to the mating context. In this study on common lizards ( Zootoca vivipara ), we examined the role of personality traits in female mate choice and mating behavior after experimentally manipulating the predation risk experienced by females prior to mating. We showed that females not exposed to predator cues preferred males with high-activity level, a heritable behavior. When females are exposed to predator cues prior to mating, this preference was reversed. High-activity levels generally increase competitive abilities and survival but could be detrimental when predators are present. Our results suggest that female common lizards choose males based on their personality types and can modify their preferences according to their environmental context in order to produce offspring that are better adapted to their environment.

Description: Predators alter prey dynamics by direct killing and through the costs of antipredator responses or risk effects. Antipredator behavior includes proactive responses to long-term variation in risk (e.g., grouping patterns) and reactive responses to short-term variation in risk (e.g., intense vigilance). In a 3-year field study, we measured variation in antipredator responses and the foraging costs of these responses for 5 ungulates (zebra, wildebeest, Grant’s gazelle, impala, and giraffe) that comprised more than 90% of the prey community available to the 2 locally dominant predators, lions and spotted hyenas. Using a model-selection approach, we examined how vigilance and group size responded to attributes of the predator, prey, and environment. We found that 1) the strength of antipredator responses was affected by attributes of the predator, prey, and environment in which they met; 2) grouping and vigilance were complementary responses; 3) grouping was a proactive response to the use of dangerous habitats, whereas vigilance was a reactive response to finer cues about predation risk; 4) increased vigilance caused a large reduction in foraging for some species (but not all); and 5) there was no clear relationship between direct predation rates and the foraging costs of antipredator responses. Broadly, our results show that antipredator responses and their costs vary in a complex manner among prey species, the predators they face, and the environment in which they meet.

Description: The cost of reproduction hypothesis predicts that the level of reproductive investment to current reproduction is constrained by an individual’s future reproductive potential or residual reproductive value. Therefore, age, or differences between young and old individuals in residual reproductive value, is expected to influence reproductive investment. However, recent theoretical work suggests that residual reproductive value is also influenced by an individual’s state or condition which may in part be determined by prior reproductive experience. We evaluated the reproductive investment of same-aged female burying beetles ( Nicrophorus orbicollis ) to determine how prior reproductive experience affects current reproduction. Consistent with previous research, females reproducing on low-quality carcasses allocated more to future reproduction by producing smaller offspring and gaining more mass than females on high-quality carcasses. When prior experience was manipulated, females that initially reproduced on a low-quality resource exhibited an accentuated response to a high-quality carcass by producing significantly larger broods of offspring compared with control females reproducing on high-quality carcasses. Conversely, females that initially reproduced on a high-quality carcass and were subsequently presented a low-quality carcass exhibited a decrease in offspring size and an increase in female mass change, indicative of a switch in allocation from current to future reproduction. The change in carcass quality resulted either in terminal investment or reproductive restraint, dependent on prior experience. Our results combined with those of previous papers demonstrate that the level of reproductive investment in burying beetles is influenced by both age and prior reproductive experience.

Description: Noise can be problematic for acoustically communicating organisms due to the masking effect it has on acoustic signals. Rapid expansion of human populations, accompanied by noise that comes with industrialization and motorized transportation, poses a threat for many acoustically communicating species. Although a significant amount of effort has been made exploring the responses of organisms inhabiting marine and terrestrial environments to elevated noise levels, relatively little has been directed toward organisms inhabiting small, lotic, freshwater systems. The aim of this study was to determine what effect elevated noise levels have on acoustic signals and inter-fish distance during sound production in the Blacktail Shiner, Cyprinella venusta . We hypothesized, based on the behaviors of other vocal organisms, that C. venusta would compensate for elevated noise levels by decreasing distance between sender and receiver, increasing signal amplitude (Lombard effect), or by changing temporal patterns to increase call redundancy. Using an experimental approach, we found that C. venusta altered several acoustic components under noisy conditions. Most notably, spectral levels of acoustic signals were increased in background noise, indicating presence of the Lombard effect in fishes. Inter-fish distance was typically not different between noisy and quiet conditions, although one circumstance did show a significantly smaller inter-fish distance under noisy conditions.

Description: Kin are generally expected to behave more cooperatively with their relatives than with unrelated individuals, and this cooperative behavior may result in positive effects on fitness. Such kin effects are likely to be modified by resource availability: in contexts of resource stress, cooperation among kin may disappear or weaken as more energy is required for investment in self. We use the Generations and Gender Survey, a large, multinational demographic survey, to test the following: firstly, how kin availability measures (parental survival status and coresidence with parents) affect measures of women’s fitness (timing of first birth, total fertility, and probability of childlessness); and, secondly, whether wealth (an indicator of resource stress or abundance) modifies kin effects in a high-income, low-fertility setting. We find differing effects of survival status of, and coresidence with, parents on fertility outcomes. Having a living mother tends to be correlated with higher fitness: women with living mothers have earlier first births, and mothers’ death in early life is correlated with a higher probability of childlessness. Fathers’ survival has no effect on any outcome. Coresidence with parents, on the other hand, delays first births and results in lower total fertility and higher probability of childlessness. We additionally find that the negative effects of coresidence on reproductive outcomes are exaggerated for poor women. Our results speak of the role of environment in modifying the relationship between kin and fertility.

Description: In species that live in one-male/multi-female groups, resident males have more access to females than do bachelor males and should have a within-group reproductive advantage. We used a genetic analysis of 13 microsatellite loci to assign paternity to 111 offspring born over 10 years in 8 groups of wild blue monkeys. Resident males sired a maximum of 61% of the offspring conceived in their groups, indicating that despite their greater access to females, residents lost a substantial number of offspring to outsiders. A resident was less likely to sire an offspring when multiple females were in conceptive estrus, suggesting that it is difficult to monitor many fertile females simultaneously. Moreover, multiple estrous females likely attract competitor males, whose presence also decreased the probability that a resident sired an offspring. The negative effect of intruders on resident siring success may occur because females prefer competitors or because an increase in the number of intruders increases the challenge of effective mate guarding by a resident, leading him to miss rare mating opportunities. Tenure length did not affect resident siring success. Identifying the factors affecting patterns of paternity within species will help us to better understand the considerable variation in resident male siring success that occurs in one-male groups.

Description: Active and risk-taking behavior may bring animals into contact with predators but can also result in frequent encounters with parasites and vectors via the exploration of risky or diverse habitats. Therefore, we predicted that antipredator behavior, here measured as escape behavior when captured by a human, would correlate with risk of parasite infection at the interspecific level with bolder species having more parasites than risk-averse species. Here we tested whether species with more active escape behavior also tended to have high prevalence of blood parasites, specifically hemosporidian parasites. Focusing on effect sizes we found that escape behavior was intermediately and positively related to prevalence of infection with Haemoproteus and Leucocytozoon , whereas that was not the case for the more virulent Plasmodium . Species that were habitat generalists and hence encountered a greater diversity of habitats had higher prevalence of blood parasites than specialists. In addition, some components of escape behavior were correlated at an intermediate magnitude with habitat exploration, as reflected by the relative frequency of feeding innovations, and coloniality. We failed to find considerable patterns of correlations between most of the behavioral variables and flight initiation distance, another commonly used antipredator behavior. Therefore, behavioral responses to an approaching predator and to being caught by a human likely represent 2 independent axes of antipredator behavior that do not evolve in concert. These findings are consistent with the hypothesis that escape behavior is related to risk of infection with blood parasites partially mediated by the effect of habitat generalism.

Description: Sociality and cooperative rearing may have evolved to increase direct fitness when conditions are challenging to reproduction and/or to reduce environmentally induced variance in fecundity. Examination of these hypotheses comes mostly from studies on singularly breeding birds where reproduction is monopolized by a male–female adult pair. Instead, little is known about plurally breeding species where most group members breed and rear their offspring communally. We used data from an 8-year field study to explore the relationship between the ecology and per capita offspring production and survival (2 components of reproductive success and direct fitness) of the plurally breeding rodent Octodon degus . We determined how mean and variance in food abundance, precipitation levels, degu density, soil hardness, predation risk, and thermal conditions modulated the effects of group size and number of breeding females (potential for breeding cooperation) on reproductive success. The effect of number of females per group on the per capita number of offspring produced was more positive during years with lower mean food and degu density. More positive effects of group size (on per capita number of offspring produced and on per capita surviving offspring) and of the number of females (on per capita number of offspring produced) occurred during years with decreasing mean precipitation levels. Thus, the hypothesis that group living and communal rearing are more beneficial (or less costly) under low mean habitat conditions is supported. In contrast, the social effects on reproductive success seem insensitive to variance in ecological conditions.

Description: The cost of behavioral thermoregulation is well recognized in the posthatching stage of ectothermic vertebrates. However, thermoregulatory behavior was discovered only recently in turtle embryos, and the cost of this interesting behavior remains unknown. We manipulated the intensity of thermoregulatory behavior in turtle embryos ( Pelodiscus sinensis ) and determined the hatching success, body mass, and righting response to assess the energetic cost associated with this behavior. Hatchlings from embryos that had experienced intensive behavioral thermoregulation were smaller and contained less energy than those from the control group, which indicates that behavioral thermoregulation by turtle embryos incurs energetic costs. Nonetheless, the smaller hatchings did not exhibit a lower hatching success or a slower righting response, suggesting that the cost incurred by behavioral thermoregulation is relatively low in turtle embryos.

Description: Pollinators often sequentially visit 1 flower type while bypassing other equally rewarding flower types, behavior known as flower constancy. One explanation for flower constancy is that pollinators use the search image of a specific flower type to efficiently find flowers because they are often cryptic. The so-called search image hypothesis predicts that temporal specialization to 1 flower type by an individual pollinator declines as flower conspicuousness increases because if flowers are conspicuous, pollinators can divide their attention among different flower types. To test this prediction, we investigated visitation sequences of individual bumble bees ( Bombus ignitus ) to a patch of blue and yellow artificial flowers. We used different flower sizes and interflower distances as independent determinants of flower visual size and noisiness of the background and, thus, of flower crypsis. Flower color selectivity and flower search time decreased and subsequently increased with visual size of the nearest flowers, with a minimum of approximately 15° of the visual angle. Within-bout constancy, measured as the tendency of flying to the same flower types in succession compared with the expectation of a given flower selectivity within a bout, increased with visual size of the nearest flowers. Flower selectivity and within-bout constancy did not differ among arrays that shared the same floral visual angle, indicating that visual size, rather than flight distance or flower size itself, had a substantial effect on flower choices. Our results suggest that flower visual size and background noisiness affect flower crypsis and constancy, providing support for the search image hypothesis.

Description: The fitness consequences of extreme competitive interactions such as cannibalism are often governed by the environment because the costs and benefits of such behaviors depend on the ecological and social context of the participants. However, most studies of context-dependent cannibalism are conducted under extreme circumstances or examine only a single environmental context, conditions that are unlikely to exist in natural populations. In this study, we tested the effect of multiple environmental contexts on the frequency of cannibalism in forked fungus beetle larvae ( Bolitotherus cornutus ), which develop in 1 of 3 different fungus species. We paired larvae in laboratory trials and measured the effect of 1) ecological context (the 3 fungi) and 2) the relatedness of the paired larvae on the frequency of cannibalism. We found a strong effect of ecological context on cannibalism: larvae in 1 fungus cannibalized nearly twice as often as larvae in the other two. We did not detect an effect of relatedness on cannibalism in the 1 species of fungus in which trials were conducted. Cannibalism conferred benefits in the form of accelerated growth rates in all measured traits relative to noncannibals. However, contrary to most studies, cannibalism was most common in the highest quality fungus, contradicting the hypothesis that cannibalism occurs in poor environments to compensate for resource deficiencies. We discuss alternative mechanisms that may drive the ecological context dependence of cannibalism in B. cornutus and emphasize the importance of studying context-dependent behavior in naturally occurring environments.

Description: Female mate choice decisions, which influence sexual selection, involve complex interactions between the 2 sexes and the environment. Theoretical models predict that male movement and spacing in the field should influence female sampling tactics, and in turn, females should drive the evolution of male movement and spacing to sample them optimally. Theoretically, simultaneous sampling of males using the best-of-n or comparative Bayes strategy should yield maximum mating benefits to females. We examined the ecological context of female mate sampling based on acoustic signals in the tree cricket Oecanthus henryi to determine whether the conditions for such optimal strategies were met in the field. These strategies involve recall of the quality and location of individual males, which in turn requires male positions to be stable within a night. Calling males rarely moved within a night, potentially enabling female sampling strategies that require recall. To examine the possibility of simultaneous acoustic sampling of males, we estimated male acoustic active spaces using information on male spacing, call transmission, and female hearing threshold. Males were found to be spaced far apart, and active space overlap was rare. We then examined female sampling scenarios by studying female spacing relative to male acoustic active spaces. Only 15% of sampled females could hear multiple males, suggesting that simultaneous mate sampling is rare in the field. Moreover, the relatively large distances between calling males suggest high search costs, which may favor threshold strategies that do not require memory.

Description: The degree of polygyny is predicted to influence the strength of direct male–male competition, leading to a high variance in male lifetime reproductive success and to reproduction limited to the prime period of adulthood. Here, we explore the variance in male lifetime reproductive success and reproductive time in an anthropoid primate forming multimale–multifemale groups. Males of this species form dominance hierarchies, which are expected to skew reproduction toward few high-ranking males. At the same time, however, females mate with multiple males (polygynandry), which should limit the degree of polygyny. Using 20 years of genetic and demographic data, we calculated lifetime reproductive success for the free-ranging rhesus macaque ( Macaca mulatta ) population of Cayo Santiago for subjects that died naturally or reached senescence. Our results show that 1) male lifetime reproductive success was significantly skewed (range: 0–47 offspring; males reproducing below average: 62.8%; nonbreeders: 17.4%), 2) variance in male lifetime reproductive success was 5 times larger than in females, and 3) male lifetime reproductive success was more influenced by variation in fecundity (60%) than longevity (25%), suggesting that some direct male–male competition takes place. However, the opportunity for selection (i.e., standardized variance in male lifetime reproductive success) is low compared with that in other large mammal species characterized by a high degree of polygyny. Moreover, male reproductive life extended much beyond the prime period, showing that physical strength was not required to acquire mates. We conclude that rhesus macaques exhibit a moderate degree of polygyny and, therefore, low levels of direct male–male competition for fertile females, despite the fact that males form linear dominance hierarchies.

Description: Animal sexual signals have been well studied in the context of mate attraction, but less attention has focused on the function of signals produced at other times of the year. Despite decades of research on bird song, we still do not know why many migratory songbirds also sing intensely on their wintering grounds. It has long been assumed that winter song is used to defend individual feeding territories; however, this assumption has never been tested. I studied willow warblers ( Phylloscopus trochilus ) that regularly sing on their African wintering grounds to test this supposition using a combination of behavioral experiments and radio telemetry. Contrary to expectations for individual territory defense, I found that individuals foraged in conspecific groups with fluid group membership, moved itinerantly from site to site rather than remaining in stable territories, and were highly aggressive toward model presentations combined with song playback, but in groups rather than individually. These results suggest a puzzling alternative function for winter song—singing for group territory defense—where territories are short term and group membership is not fixed. This work highlights the scarcity of our knowledge on the nonbreeding behavior of Palearctic–African songbirds and the unexpected complexity of avian social organization during this period of the annual cycle.

Description: The contribution of bacterial fermentation to the production of vertebrate scent signals has long been suspected, but there is still relatively little information about the factors driving variation in microbial composition in animal scent secretions. Our study subject, the meerkat ( Suricata suricatta ), is a social mongoose that lives in territorial, family groups and relies heavily on scent for social communication. Unusually in mammalian research, extensive life-history data exist for multiple groups inhabiting the same ecosystem, allowing for a study of both individual variation and group differences in the host’s microbial communities. Using a culture-independent sampling technique, we explored the relationship between a signaler’s sex, age/dominance, genotype or group membership, and the microbiota of its anal scent secretions. We found differences in the microbiota of males and females, but only after the animals had reached sexual maturity. Although bacterial communities in meerkat scent secretions were not more similar between kin than between nonkin, they were more similar between members of the same group than between members of different groups. Collectively, these results are consistent with a potential role for reproductive hormones in determining a host’s bacterial assemblages, as well as an influence of sociality (such as intragroup allo-marking behavior) and/or microhabitat in the acquisition of bacterial assemblages. This study provides a key starting point for understanding the role of microbes in the variation of scent composition in mammals.

Description: In many species, females have evolved behavioral strategies to reduce the risk of infanticide. For instance, polyandry can create paternity confusion that inhibits males from killing offspring they could have sired. Here, the authors propose that females could socially obtain the same benefits by nesting communally. Singly sired litters could be perceived as a large multiply sired litter once pooled together in a single nest. Long-term data from a wild house mouse population showed that monandrous litters (singly sired) were more common in communal than in solitary nests and 85% of them were raised with litters sired by different males hence becoming effectively polyandrous (multiply sired). These socially polyandrous litters had significantly higher offspring survival than genetically or socially monandrous litters and reached a similar survival to that of multiply sired litters raised in solitary or communal nests. Furthermore, the number of sires within nests significantly improved offspring survival whereas the number of mothers did not. These results suggest that the survival benefits associated with communal nesting are driven by polyandry and not communal defense. This socially mediated polyandry was as efficient as multiple paternity in preventing infanticide, and may also occur in other infanticidal and polytocous species where the caring parent exhibits social behavior.

Description: The extent to which animal vocalizations convey specific information about events in the environment is subject to continued debate. The alarm-calls of vervet monkeys have played a pivotal role in this debate as they represent the classic example of a predator-specific call production system combined with a set of equally specific responses by receivers. Here, we revisit the vervet alarm-calling system, and assess the hypothesis that these acoustically distinct calls trigger context- and predator-appropriate behavior. We investigated responses in 2 groups of free-ranging vervet monkeys ( Chlorocebus pygerythrus ) to both natural encounters with predators and experimental presentations of aerial and terrestrial predator alarm calls. Our results show that the modal natural and experimental response was not to initiate escape behavior, either immediately or in the 10s following an alarm call, but to look at the sound source. When monkeys did take evasive action, contextually inappropriate behavior (i.e., behavior that was not appropriate for evading the specific predator type) was as likely to occur as contextually appropriate behavior. The distance at which calls were heard was negatively correlated with the probability of evasive action. Larger group size, and the greater mean distance at which natural calls were heard, may explain why our animals displayed less predator-appropriate evasion or vigilance than expected. We conclude that the broader social and ecological framework in which calls occur, rather than a simple contextually regular linkage between call types and specific predators, shapes animals’ responses to calls in this species.

Description: In biparental species, conflict between the sexes is expected when optimal levels of parental care differ between males and females. We studied food provisioning in house wrens ( Troglodytes aedon ) to test whether male provisioning is more strongly affected than female provisioning by brood size, because this should influence the marginal return on a male’s investment. To test this, we created broods of reduced and enlarged size, and found that per-nestling food delivery varied more strongly for males than for females in association with brood size and nestling age; males delivered more food per nestling to enlarged broods, and less to small broods, as nestlings grew and approached asymptotic size. Although parents delivered a greater amount of prey to larger broods, the amount of food per nestling was initially higher for nestlings in small broods, and the amount of food delivered early in nestling development, particularly by males, affected offspring body mass, survival to fledging, and recruitment to the breeding population. However, provisioning rates were negatively associated with prey size, suggesting a trade-off between prey quantity and size. Finally, parents provisioning at a high rate to broods of reduced size were less likely to return to breed, suggesting that they assessed the low return on their investment and dispersed. Although potential for sexual conflict in house wrens remains, our data suggest that its resolution does not involve negotiation over provisioning, possibly because selection for offspring viability favors heavy investment by both parents.

Description: Factors affecting social group size in mammals are relatively well studied for females, but less is known about determinants of group size for males, particularly in species that live in sexually segregated groups. Male grouping patterns are thought to be driven more by spatial and temporal dispersion of mating opportunities than by food resources or predation risk. We evaluated the influence of 3 factors on male group sizes and number of males in mixed-sex groups in African elephants; forage availability (using Normalized Difference Vegetation Index, a satellite-based indicator of primary productivity), anthropogenic mortality risk (using distance of elephants from a protected area center), and mating opportunities (using the number of males in mixed-sex groups with and without estrous females). Using zero-truncated negative binomial regressions and a model-selection approach, we found that male elephants occurred in larger groups where primary productivity was higher and where they were further from a protected area center. However, we found an interaction between primary productivity and anthropogenic mortality risk: at low primary productivity, elephants formed larger groups further away from a protected area center, but did less so at higher primary productivity. This pattern suggests that male elephants are sensitive to seasonal variation in potential anthropogenic mortality risk, by remaining in smaller groups when risk is low, but forming larger groups when risk is high. Mating opportunities also led to an increase in male numbers in mixed-sex groups, but its relative influence on male grouping was less important because mating opportunities were rare.

Description: Animals with parental care defend their offspring with an intensity reflecting parental investment. Parental investment theory predicts that parents should take risks relative to their residual reproductive value. Therefore, parental defense should change consistently with age reaching a peak at middle age, and it should vary consistently with age at start and end of reproduction. We recorded the intensity of parental defense of offspring in 410 female goshawks Accipiter gentilis throughout their lives, ranging from timid females that barely approached a human intruder at the nest to aggressive females that physically attacked the human. Females were consistent in their level of defense throughout life, and aggressive females were mated to aggressive males. Investment in reproduction as reflected by laying date, clutch size, and brood size showed a bell-shaped relationship with age. Females that started to breed at a young age were less aggressive than females that started late. Likewise, females that finished reproduction at a young age behaved less aggressively than females that finished at an old age. The intensity of defense of offspring peaked at an intermediate age followed by a decrease into old age and senescence. Females that started to breed early during the season were more aggressive than late breeders. These findings are consistent with the hypothesis that the intensity of parental defense of their offspring reflects parental investment and patterns of aging.

Description: The behavioral decisions of migratory songbirds during migration stopovers can markedly influence the pace, efficiency, and success of migration. An individual’s fuel stores are considered in theory to directly dictate subsequent stopover behavior (e.g., extent of foraging or vigilance, when to depart), although such decisions at stopover must also consider atmospheric factors (e.g., wind, precipitation) that influence the energetic costs of migration. We conducted the first study to date that directly manipulated the fuel stores of newly arrived songbirds at a stopover site, evaluated their effect on movement behavior and departure decisions, and assessed how atmospheric factors mediated these behavioral decisions. Hermit thrushes ( Catharus guttatus ) captured during fall migration at a southern New England, USA, offshore island stopover site and subsequently released with increased fuel stores moved less and made more tortuous movements, were more likely to depart on a given night and regularly resumed migration earlier and in a seasonally appropriate direction relative to individuals released with little change in fuel stores. The importance of fuel stores in modifying behavioral decisions increased throughout the migration period, presumably in response to declining food abundance. Precipitation suppressed migrant movements during stopover and precluded departure. Migrants departed in light winds with little respect to wind direction. The pervasive influence of fuel stores on migrant stopover behavior underscores the central role of fuel acquisition in the dynamics, speed, and success of migration, as well as the importance of quality stopover sites to migratory birds.