ALBERT

Description: Wood biophysical properties and the dynamics of water storage discharge and refilling were studied in the trunk of canopy tree species with diverse life history and functional traits in subtropical forests of northeast Argentina. Multiple techniques assessing capacitance and storage capacity were used simultaneously to improve our understanding of the functional significance of internal water sources in trunks of large trees. Sapwood capacitances of 10 tree species were characterized using pressure–volume relationships of sapwood samples obtained from the trunk. Frequency domain reflectometry was used to continuously monitor the volumetric water content in the main stems. Simultaneous sap flow measurements on branches and at the base of the tree trunk, as well as diurnal variations in trunk contraction and expansion, were used as additional measures of stem water storage use and refilling dynamics. All evidence indicates that tree trunk internal water storage contributes from 6 to 28% of the daily water budget of large trees depending on the species. The contribution of stored water in stems of trees to total daily transpiration was greater for deciduous species, which exhibited higher capacitance and lower sapwood density. A linear relationship across species was observed between wood density and growth rates with the higher wood density species (mostly evergreen) associated with lower growth rates and the lower wood density species (mostly deciduous) associated with higher growth rates. The large sapwood capacitance in deciduous species may help to avoid catastrophic embolism in xylem conduits. This may be a low-cost adaptation to avoid water deficits during peak water use at midday and under temporary drought periods and will contribute to higher growth rates in deciduous tree species compared with evergreen ones. Large capacitance appears to have a central role in the rapid growth patterns of deciduous species facilitating rapid canopy access as these species are less shade tolerant than evergreen species.

Description: Nuclear magnetic resonance (NMR) and NMR imaging (magnetic resonance imaging) offer the possibility to quantitatively and non-invasively measure the presence and movement of water. Unfortunately, traditional NMR hardware is expensive, poorly suited for plants, and because of its bulk and complexity, not suitable for use in the field. But does it need to be? We here explore how novel, small-scale portable NMR devices can be used as a flow sensor to directly measure xylem sap flow in a poplar tree ( Populus nigra L.), or in a dendrometer-like fashion to measure dynamic changes in the absolute water content of fruit or stems. For the latter purpose we monitored the diurnal pattern of growth, expansion and shrinkage in a model fruit (bean pod, Phaseolus vulgaris L.) and in the stem of an oak tree ( Quercus robur L.). We compared changes in absolute stem water content, as measured by the NMR sensor, against stem diameter variations as measured by a set of conventional point dendrometers, to test how well the sensitivities of the two methods compare and to investigate how well diurnal changes in trunk absolute water content correlate with the concomitant diurnal variations in stem diameter. Our results confirm the existence of a strong correlation between the two parameters, but also suggest that dynamic changes in oak stem water content could be larger than is apparent on the basis of the stem diameter variation alone.

Description: While natural spatial temperature gradients between measurement needles have been thoroughly investigated for continuous heat-based sap flow methods, little attention has been given to how natural changes in stem temperature impact heat pulse-based methods through temporal rather than spatial effects. By modelling the theoretical equation for both an ideal instantaneous pulse and a step pulse and applying a finite element model which included actual needle dimensions and wound effects, the influence of a varying stem temperature on heat pulse-based methods was investigated. It was shown that the heat ratio (HR) method was influenced, while for the compensation heat pulse and T max methods changes in stem temperatures of up to 0.002 °C s –1 did not lead to significantly different results. For the HR method, rising stem temperatures during measurements led to lower heat pulse velocity values, while decreasing stem temperatures led to both higher and lower heat pulse velocities, and to imaginary results for high flows. These errors of up to 40% can easily be prevented by including a temperature correction in the data analysis procedure, calculating the slope of the natural temperature change based on the measured temperatures before application of the heat pulse. Results of a greenhouse and outdoor experiment on Pinus pinea L. show the influence of this correction on low and average sap flux densities.

Description: The control of plant transpiration by stomata under water stress and recovery conditions is of paramount importance for plant performance and survival. Although both chemical and hydraulic signals emitted within a plant are considered to play a major role in controlling stomatal dynamics, they have rarely been assessed together. The aims of this study were to evaluate (i) the dynamics of chemical and hydraulic signals at leaf, stem and root level, and (ii) their effect on the regulation of stomatal conductance ( g s ) during water stress and recovery. Measurements of g s , water potential, abscisic acid (ABA) content and loss of hydraulic functioning at leaf, stem and root level were conducted during a water stress and recovery period imposed on 1-year-old olive plants ( Olea europaea L.). Results showed a strong hydraulic segmentation in olive plants, with higher hydraulic functioning losses in roots and leaves than in stems. The dynamics of hydraulic conductance of roots and leaves observed as water stress developed could explain both a protection of the hydraulic functionality of larger organs of the plant (i.e., branches, etc.) and a role in the down-regulation of g s . On the other hand, ABA also increased, showing a similar pattern to g s dynamics, and thus its effect on g s in response to water stress cannot be ruled out. However, neither hydraulic nor non-hydraulic factors were able to explain the delay in the full recovery of g s after soil water availability was restored.

Description: For isohydric trees mid-day water uptake is stable and depends on soil water status, reflected in pre-dawn leaf water potential ( pd ) and mid-day stem water potential ( md ), tree hydraulic conductance and a more-or-less constant leaf water potential ( l ) for much of the day, maintained by the stomata. Stabilization of l can be represented by a linear relationship between canopy resistance ( R c ) and vapor pressure deficit ( D ), and the slope ( B D ) is proportional to the steady-state water uptake. By analyzing sap flow (SF), meteorological and md measurements during a series of wetting and drying ( D / W ) cycles in a nectarine orchard, we found that for the range of md relevant for irrigated orchards the slope of the relationship of R c to D , B D is a linear function of md . R c was simulated using the above relationships, and its changes in the morning and evening were simulated using a rectangular hyperbolic relationship between leaf conductance and photosynthetic irradiance, fitted to leaf-level measurements. The latter was integrated with one-leaf, two-leaf and integrative radiation models, and the latter gave the best results. Simulated R c was used in the Penman–Monteith equation to simulate tree transpiration, which was validated by comparing with SF from a separate data set. The model gave accurate estimates of diurnal and daily total tree transpiration for the range of md s used in regular and deficit irrigation. Diurnal changes in tree water content were determined from the difference between simulated transpiration and measured SF . Changes in water content caused a time lag of 90–105 min between transpiration and SF for md between –0.8 and –1.55 MPa, and water depletion reached 3 l h –1 before noon. Estimated mean diurnal changes in water content were 5.5 l day –1  tree –1 at md of –0.9 MPa and increased to 12.5 l day –1  tree –1 at –1.45 MPa, equivalent to 6.5 and 16.5% of daily tree water use, respectively. Sixteen percent of the dynamic water volume was in the leaves. Inversion of the model shows that md can be predicted from D and R c , which may have some importance for irrigation management to maintain target values of md . That relationship will be explored in future research.

Description: Cooperative breeding occurs in several major animal phyla, predominantly in arthropods and chordates. A number of comparative analyses have focused on understanding the evolution of cooperative breeding, yielding mixed, inconclusive, and often phyla-specific findings. We argue that much of this ambiguity results from an erroneous classification of social systems into noncooperatively and cooperatively breeding species. The shortcomings of this assumption are apparent among birds where noncooperative species constitute a heterogeneous group: some species are clearly non–family living, with offspring dispersing at or shortly after nutritional independency, whereas other species form persistent family groups through offspring delaying their dispersal substantially beyond independency. Here, we propose an objective, life history–based criterion classifying noncooperative bird species into non–family living and family living species. We demonstrate that by using the family time (the time offspring remain with its parent/s beyond independence) and body size–scaled reproductive investment, we are able to differentiate 2 groups with contrasting life histories. Our classification matches seasonal environmental variation experienced by different species: family living species postpone dispersal beyond the onset of less favorable autumn conditions. We discuss the consequences of this new social system classification for evolutionary and ecological research, potentially allowing solutions to some of the most intriguing riddles in the evolutionary history of birds—and cooperative behavior itself.

Description: Humans have brought about unprecedented changes to environments worldwide. For many species, behavioral adjustments represent the first response to altered conditions. In this review, we consider the pivotal role that behavior plays in determining the fate of species under human-induced environmental change and highlight key research priorities. In particular, we discuss the importance of behavioral plasticity and whether adaptive plastic responses are sufficient in keeping pace with changing conditions. We then examine the interplay between individual behavioral responses and population processes and consider the many ways in which changes in behavior can affect ecosystem function and stability. Lastly, we turn to the evolutionary consequences of anthropogenic change and consider the impact of altered behaviors on the evolutionary process and whether behavior can facilitate or hinder adaptation to environmental change.

Description: Non-native species can serve as a prey resource for native predators. Yet because there is often no shared evolutionary history between the predator and prey, individuals within a predator population may vary greatly in their willingness to consume a recently introduced, yet profitable prey. Here, we measured individual variation in diet, behavior, and demographic traits of the native predatory mud crab, Panopeus herbstii , and evaluated how these traits influenced an individual’s consumption of a recently introduced, non-native crab, Petrolisthes armatus , using both simultaneous and no-choice assays. These same individual predatory mud crabs were also assayed to quantify their antipredator reaction and exploratory behavior. Results indicated significant variation in the diets of individual predators with 45% specializing on native mussels, 14% specializing on non-native Petrolisthes , and the remainder eating multiple prey species. When given a choice of alternative prey, individual Panopeus predators that consumed a larger proportion of Petrolisthes were female, smaller, and more likely to flee in response to predators. When given no choice of alternative prey, Petrolisthes was consumed more frequently by Panopeus that were female and less exploratory. We suggest that individuals that more readily consume non-native Petrolisthes may be attempting to reduce competition with conspecifics that are larger, more aggressive, exploratory, and male. Our results suggest that at least initially following invasion, adoption of a non-native prey species into the diet of a native predator may not occur universally within the population. Such nonuniform predation pressure could contribute to the non-native prey’s release from natural enemies.

Description: In socially monogamous species, in which both sexes provide essential parental care, males as well as females are expected to be choosy. Whereas hundreds of studies have examined monogamy in biparental birds, only several such studies exist in fish. We examined mate choice in the biparental, colonial cichlid fish Neolamprologus caudopunctatus in Lake Tanganyika, Zambia. We genotyped more than 350 individuals at 11 microsatellite loci to investigate their mating system. We found no extrapair paternity, identifying this biparental fish as genetically monogamous. Breeders paired randomly according to their genetic similarity, suggesting a lack of selection against inbreeding avoidance. We further found that breeders paired assortatively by body size, a criterion of quality in fish, suggesting mutual mate choice. In a subsequent mate preference test in an aquarium setup, females showed a strong preference for male size by laying eggs near the larger of 2 males in 13 of 14 trials.

Description: Demographic variation, such as changes in population size, affects group-living conditions and thus creates new opportunities for individuals to interact socially. To understand how this variation in the social environment affects social structure, we used social network analysis to explore affiliative behaviors of nonpup (i.e., 1 year or older), female, yellow-bellied marmots ( Marmota flaviventris ). We examined 4 social attributes (outdegree, indegree, closeness centrality, and betweenness centrality) to measure social plasticity in response to group size variation. We found that, in response to increases in group size, individuals established fewer social connections than possible, which suggests that marmots experience constraints on sociality. Similarly, closeness and betweenness centrality decreased as group size increased, suggesting that females are expected to lose influence over other members of the group as group size increases, and there are substantial constraints on marmots transmitting information to others in large groups. Our results also suggest that group-level responses, such as behavioral plasticity, can be explained by individual-level mechanisms that evaluate the costs and benefits of sociality. Interestingly, the mechanistic basis of these group-level responses may, at times, follow patterns expected by chance. We propose that further research is necessary to uncover the mechanisms underlying the individual-level behavioral response. Like group size effects studied in other domains, formally considering group size effects on social structure may shed novel light on the constraints on sociality.

Description: Postcopulatory variation in reproductive success is fundamental for sexual selection. Because evolutionary change is impossible without a heritable basis for variation, the study of postcopulatory variation has mainly focused on genetic differences between males, that is, the effect of sperm competition or differential female responses toward male genotypes (cryptic female choice). The role of environmental components in shaping postcopulatory variation in reproductive success is well known, for example, in the form of damaging lifestyle effects on sperm, but their effect on eliciting female responses has rarely been tested, as has its relative significance compared with male genotypic effects. Here we provide such a test in bedbugs, a species where cryptic female choice has been hypothesized to be directed toward specific sperm genotypes. We measured female transcriptomic responses after experimentally controlling the male genetic and environmental component of the ejaculate. For identical female genetic background and identical male age at mating, we analyzed female gene expression in response to insemination with sperm of 3 different inbred populations (genotypes), each exposed to 1 of 2 environmental treatments (sperm storage duration in the male). Females responded mainly to environmental variation: 〉15 times more genes were differentially expressed, including stress response genes, compared with male genotypic variation. Our results suggest that postcopulatory natural selection exists and plays a significant role in the evolution and diversification of reproductive traits. Our results add complexity to testing the cryptic female choice hypothesis and show that nongenetic ejaculate effects are an important but underappreciated source of variation in biology.

Description: Heterospecific eavesdropping on alarm calls is well documented, but less is known about the factors influencing asymmetry in the reliability of heterospecific alarm calls. Partial overlap of predators between heterospecifics has been hypothesized as 1 possible mechanism driving asymmetric eavesdropping. We tested the responses of common mynas ( Acridotheres tristis ) and red-vented bulbuls ( Pycnonotus cafer ) to reciprocal playbacks of alarm and social calls by measuring changes from baseline in the rates of fly-bys near the speaker and in rates of singing. We found an asymmetric communication network between bulbuls and mynas: bulbuls only responded to conspecific alarm calls, whereas mynas responded to both bulbul and conspecific alarm calls. This communication asymmetry may be due to a partial overlap in predators between species. Mynas were observed to spend time in both trees and on the ground and may be susceptible to both aerial and ground predators. We observed bulbuls primarily in trees and therefore may be susceptible primarily to aerial predators. If this is the case, then the alarm calls of mynas are less reliable to bulbuls compared with the reliability of alarm calls of bulbuls to mynas. However, further studies into the predators of each species are necessary before drawing a definitive conclusion. Our study demonstrates a differential responsiveness of 1 species on the alarm calls from another species for predator information and underscores the importance in considering heterospecific communication networks in the removal of species from a community.

Description: Allonursing, the nursing of another female’s offspring, is assumed to impose a substantial energetic cost given the high cost of lactation to mothers. However, these costs have not been quantified. In cooperatively breeding mammals where helpers contribute to lactation, they might be expected to modify their behavior to mitigate these potential costs. Here, we show that overnight weight loss during lactation did not differ between allonurses and controls. However, meerkat helpers that allonursed do not gain weight over a reproductive bout as non-allonursing subordinate females did, suggesting that allonurses may incur some cost. Allonurses may mitigate the costs by increasing foraging effort during lactation. Allonurses do not, as expected, reduce investment in other cooperative behaviors during lactation. We suggest that the increase in cooperative behavior, including allonursing, may serve a social function, but further work is needed to confirm this hypothesis.

Description: The adrenocortical stress response may divert energy away from sexual ornamentation, such that ornaments signal exposure or resistance to physiological stress. Alternatively, steroid glucocorticoids released via the stress response may support ornament development by stimulating foraging and metabolism. The relationship between glucocorticoids and ornamentation may vary with ornament type and across age and sex classes that experience different resource allocation tradeoffs. In yellow warblers ( Setophaga petechia ), we conducted the first study to simultaneously assess whether relationships between corticosterone (the primary avian glucocorticoid) and ornamentation depend on sexual pigment type, age, and sex. We quantified carotenoid- and phaeomelanin-based pigmentation using spectrometry, and assayed corticosterone in feathers (CORT f ) to derive an integrative metric of corticosterone levels during molt. Yellow warblers with lower carotenoid hue (lambda R50) had higher CORT f , suggesting that carotenoid hue may signal stress during molt across age and sex classes. Carotenoid chroma also negatively correlated with CORT f . However, this correlation was absent in older males, seemingly because these males display more saturated carotenoid pigmentation, and thus less variance in carotenoid chroma. Young males with higher CORT f also tended to have poorer quality tertial feathers, indicating poor condition at molt. Phaeomelanin-based pigmentation was largely unrelated to CORT f , suggesting that pleiotropic effects do not link phaeomelanogenesis and CORT release. Finally, CORT f was repeatable across years within individuals. Thus, carotenoid- and phaeomelanin-based pigmentation communicate nonequivalent information about physiological stress, with carotenoid pigmentation having the potential to signal stable differences in stress levels that could affect fitness.

Description: Animal populations are currently under pressure from multiple factors that include human land use and climate change. They may compensate for such effects by reducing, either by habituation or by natural selection, the distance at which they flee from humans (i.e., flight initiation distance), and this adaptation may improve their population trends. We analyzed population trends of common breeding birds in relation to flight initiation distance and geographical location (latitude, longitude, and marginality of the breeding distribution) across European countries from Finland in the north to Spain in the south while also considering other potential predictors of trends like farmland habitat, migration, body size, and brain size. We found evidence of farmland, migratory, and smaller-sized species showing stronger population declines. In contrast, there was no significant effect of relative brain size on population trends. We did not find evidence for main effects of flight initiation distance and geographical location on trends after accounting for confounding and interactive effects; instead, flight initiation distance and location interacted to generate complex spatial patterns of population trends. Trends were more positive for fearful populations northward, westward, and (marginally) toward the center of distribution areas and more negative for fearless populations toward the south, east, and the margins of distribution ranges. These findings suggest that it is important to consider differences in population trends among countries, but also interaction effects among factors, because such interactions can enhance or compensate for negative effects of other factors on population trends.

Description: Sociality is associated with a variety of costs and benefits, one of which can be to increase the likelihood of individuals solving novel problems. Several hypotheses explaining why groups show higher innovative problem-solving efficiencies than individuals alone have been proposed including the sharing of antipredator vigilance and the pool-of-competence effect, whereby larger groups containing a more diverse range of individuals are more likely to contain individuals with the skills necessary to solve the particular problem at hand. Interference between group members may cause groups to have lower problem solving abilities, however. Using a simulation approach, we model the shape of the relationship between group-level problem-solving probability and group size across a range of facilitation and inhibition scenarios, various population distributions of problem solving, and a task requiring 1 action or 2 actions to be solved. Simulations showed that both sharing of antipredator vigilance and the addition of competent individuals to an existing group lead to positive relationships between group-level problem solving and group size that reach 100% solving probability, whereas interference effects generate group-solving probabilities that rise to a maximum and decrease again, generating a group size for which problem solving is maximized. In contrast, both inhibition and facilitation scenarios generate identical patterns of individual efficiencies. Our results have important implications for our ability to understand the mechanisms that underpin group-size effects on problem solving in nonhumans.

Description: Although personality has been well studied in a wide range of species, relatively few studies have assessed if behavior in standardized captive tests is predictive of behavior in the wild. We captured wild zebra finches around 2 breeding colonies and assayed their exploratory behavior with a novel environment test. The birds’ foraging behavior in the wild was also measured with the use of a passive integrated transponder tag system to monitor their use of feeders that were periodically moved around the colonies to assess exploratory behavior and sociality. During the same period, individuals’ reproductive success was monitored at the nest-boxes being used in this area. We found that our measures of sociality, wild, and captive exploration were repeatable, but contrary to our predictions, exploration in the novel environment test was not significantly correlated with exploration of feeders in the wild. We failed to find a predicted negative relationship between exploration and sociality, instead finding a significant positive correlation between exploration in the novel environment and sociality. Finally, we found little evidence that any of our measured personality traits influenced reproductive success at the colony, either individually or when the interactions between the personalities of both members of the pair were taken into account. The only exception was that highly exploratory males (assayed with wild feeder behavior) were more likely to make breeding attempts than less exploratory males. Our results suggest that researchers should use caution when using tests such as the classic novel environment test to make inferences about personality in wild populations.

Description: Life-history theory predicts a trade-off for allocation of limited resources to reproduction and self-maintenance; however, many of the underlying physiological mechanisms remain elusive. There is growing evidence for oxidative stress to play an essential role in this trade-off because some by-products from the immune system and from normal metabolism generate reactive oxygen species that can cause oxidative damage. We manipulated reproductive effort of male and female great tits shortly before reproduction by clipping feathers of either the male or female parent of pairs of known age, given that parental effort may differ between the sexes and change over the lifetime of an individual. We quantified the effect of the treatment on morphological, physiological, behavioral, and reproductive traits. We found that feather clipping led to a decrease in parental body mass and to a reduced clutch size. Nestlings raised by clipped fathers showed reduced body mass although feeding rate was equally high between clipped and control individuals. In contrast to our predictions, we found that the feather clipping did not affect oxidative status. However, independently of the treatment, adult males had higher antioxidant capacity than females and older males showed higher oxidative damage compared with yearlings. Thus, our results suggest that the self-maintenance was prioritized over reproduction. It suggests that males are more susceptible to increased workload than females and thus more likely to reduce allocation of resources to reproduction.

Description: In conspecific brood parasitism, some females ("parasites") lay eggs in nests of other females of the same species ("hosts"). This reproductive tactic is particularly common in waterfowl, in which studies suggest that parasites are often related to the host. Here, we test the hypothesis that hosts may discriminate and reject unrelated parasites. Based on observations and 〉4100h of digital video film, we analyze behavioral interactions at 65 nests of High Arctic common eiders during the laying sequence. We also estimate parasitism and host–parasite relatedness by albumen fingerprinting of 975 eggs from 232 nests. Among the video-filmed nests in which interactions were recorded during the egg-laying period, 11 had eggs from 2 females. At 8 of these 11 nests, there was overt female aggression and significantly lower host–parasite relatedness (mean coefficient of relationship r = –0.40) than in the nests with tolerant or no interactions ( r = 0.91). The results demonstrate active female kin discrimination in common eiders, used against nonrelatives that try to lay eggs in the nest. Other females trying to access the nest were often prevented from doing so: in 65% of 34 such attempts, the sitting female rejected the intruder. Brood "parasitism" in eiders and other waterfowl is complex, ranging from violent female conflict and parasitic exploitation of the host’s parental care to nest takeover and potential kin selection favoring acceptance of related parasites. These and other aspects of female sociality in eiders are discussed; in some respects, they may resemble certain long-lived matriarchal mammals.

Description: In social mammals, condition and health are important determinants of the ability of males to achieve high dominance rank. Measures of individual condition are also predicted to affect male fitness via female preference for high-quality mates. We examined intermale variation in phenotypic quality (immune function and oxidative stress) in relation to male dominance status and mating success in a species with prominent female choice and a lack of male–female sexual coercion, the rhesus macaque ( Macaca mulatta ). We quantified immunity via 2 functional assays of innate immune response (bacteria killing assay and hemolytic complement assay) and measured oxidative stress via a lipid peroxidation assay in 15 adult males from 1 social group of macaques on Cayo Santiago, Puerto Rico. We then observed these males throughout the mating season to test the prediction that males in better condition achieved higher mating success. Males with more robust innate immune response and lower oxidative damage mated with a greater number of potentially fertile females. Male dominance rank, however, also correlated with our measures of quality. Higher-ranking males had more robust functional innate immune response and lower levels of oxidative damage. After accounting for rank, male quality was no longer correlated with mating success. These results demonstrate a potentially important role of male phenotypic quality in the mating system of a long-lived, group-living primate. What are the exact behavioral mechanisms via which sexual selection may operate on traits related to immunocompetence and resistance to oxidative damage in this species, however, remains an open question.

Description: Pollinators have the capability of discriminating a wide variety of floral cues in order to identify rewarding flowers. However, little is known about how possible ecological or functional implications of horizontal and vertical positioning of flowers affect pollinator decision making. Flowers are commonly either arranged horizontally in meadows or vertically in inflorescences and blooming trees or bushes. Using bumblebees ( Bombus terrestris ), we here investigate if these 2 different foraging scenarios affect decision-making accuracy using an operant learning paradigm. Training foragers to feeders arranged either horizontally or vertically but bearing identical color or pattern cues, we found a highly significant and consistent difference in feeder choice accuracy. Bees presented with horizontally arranged feeders achieved accuracies of more than 90% by the end of the training. In contrast, bees foraging on vertically arranged feeders largely disregarded the feeder cues and accuracies remained well below 70%. Apart from feeder arrangement (horizontal, vertical) neither cue type (color, pattern), feeder display orientation (horizontal, vertical) nor vertical feeder distribution contributed significantly to choice accuracy. Training bees successively on vertical, horizontal, and vertical feeder arrays revealed that individual bees are capable of discriminating the presented feeder cues with high precision on the horizontal plane but did not use the acquired knowledge on subsequently presented vertically arranged feeders. Our results indicate that the spatial arrangement of flowers has marked effects on the foraging strategy employed by a generalist pollinator. We discuss the broader implications of foragers selectively allocating attention to focus on or disregard environmental information depending on spatial context.

Description: As for other pollinators, hummingbirds have been classified as trapliners, that is, foragers that repeat the order in which they will revisit several locations. Although the study of hummingbird foraging behavior is extensive, there has been no direct evidence for the repeatability of hummingbird traplines. Here, we show that male territorial rufous hummingbirds repeated the order in which they visited artificial flowers in an array, which we increased one by one from 2 to 5 flowers. Despite the large number of possible routes that the birds could have flown around the flower arrays, the birds flew only a very small subset of routes and those routes were most often the shortest distance routes around the flowers. To our knowledge, this is the first quantitative evidence that hummingbirds do develop traplines when foraging.

Description: Animals may perceive humans as a form of predatory threat, a disturbance, triggering behavioral changes together with the activation of physiological stress responses. These adaptive responses may allow individuals to cope with stressful stimuli, but a repeated or long-term exposure to disturbances may have detrimental individual- and population-level effects. We studied the effects of human activities, particularly hunting, on the behavior and physiological status of a near-threatened nongame steppe bird, the little bustard. Using a semiexperimental approach, we compared before, during, and after weekends: 1) the type and intensity of human activities and 2) the behavior and 3) physiological stress (fecal corticosterone metabolites) of wintering birds. Higher rates of human activity, in particular those related to hunting, occurred during weekends and caused indirect disturbance effects on birds. Little bustards spent more time vigilant and flying during weekends, and more time foraging in the mornings after weekend, possibly to compensate for increased energy expenditure during weekends. We also found increased physiological stress levels during weekends, as shown by higher fecal glucocorticoid metabolite concentrations. Increased corticosterone metabolite levels were associated with the highest levels of hunting-related disturbances. Little bustard showed marked behavioral and physiological (stress hormones) responses to human activities that peaked during weekends, in particular hunting. The long-term effect of this particular activity carried out during weekends from autumn throughout winter might adversely impact wintering populations of this nongame endangered species, potentially counteracting conservation efforts conducted on local as well as foreign breeding populations.

Description: Urbanization involves dramatic environmental alterations, which can limit survival and reproduction of organisms and contribute to loss of biodiversity. One such alteration is anthropogenic noise, which biases natural ambient noise spectra toward low frequencies where it may interfere with acoustic communication among birds. Because vocalizing at higher frequencies could prevent masking by noise, it has been hypothesized that species with higher song frequencies should be less affected by urbanization. Indeed, evidence is accumulating that urban birds often vocalize at higher frequency than nonurban birds. However, the extent to which singing frequency affects their success in cities is less clear. We tested this hypothesis with a comprehensive phylogenetic Bayesian analysis comparing song frequency of songbirds from 5 continents with 4 measures of success in urbanized environments. Tolerance to urbanization was not associated with dominant or minimum song frequencies, regardless of the metric used to quantify urban success and the intensity of the urban alterations. Although song frequency was related to habitat preferences and body size of the species, none of these factors explained the lack of association with urban success. Singing high may be beneficial for signal perception under noisy conditions, but these high frequencies are apparently no guarantee for the success of bird species in urbanized environments.

Description: Activity patterns have profound implications on primates’ morphology, physiology, and behavior and have likely driven their diversification. The last common ancestor of extant primates has been traditionally considered nocturnal although this notion has been recently debated due to emerging contradictory evidence. Previous studies underestimated the role of cathemerality (i.e., the ability to remain active throughout a 24-h cycle) by simplifying primate activity to the diurnal–nocturnal dichotomy. We estimated the evolutionary trajectories of activity patterns in primates and investigated how these may have influenced their diversification rates. We used a comprehensive data set to test multiple evolutionary hypotheses, following a robust Bayesian framework by using 5000 calibrated phylogenetic trees to account for phylogenetic uncertainty. Our results support a nocturnal ancestor that has shifted to diurnality in the Simiformes, has retained nocturnality in Lorisiformes and most Lemuriformes, and shifted to cathemerality in the ancestor of Lemuridae. The diversification of activity patterns in primates seems to have mainly arose by speciation rather than shifts between activity patterns, suggesting a low flexibility of diurnal and nocturnal patterns and the key importance of cathemeral activity as transitional state to shift between more specialized activity patterns. A cathemeral activity seems to appear well before diurnality in Malagasy lemurs, suggesting an ancient origin of this trait on the island and rejecting the hypothesis of a recent transition. The present research contributes to further disentangle the adaptive role of activity patterns in primate evolution.

Description: Many animals communicate through acoustic signaling, and "acoustic space" may be viewed as a limited resource that organisms compete for. If acoustic signals overlap, the information in them is masked, so there should be selection toward strategies that reduce signal overlap. The extent to which animals are able to partition acoustic space in acoustically diverse habitats such as tropical forests is poorly known. Here, we demonstrate that a single cicada species plays a major role in the frequency and timing of acoustic communication in a neotropical wet forest bird community. Using an automated acoustic monitor, we found that cicadas vary the timing of their signals throughout the day and that the frequency range and timing of bird vocalizations closely track these signals. Birds significantly avoid temporal overlap with cicadas by reducing and often shutting down vocalizations at the onset of cicada signals that utilize the same frequency range. When birds do vocalize at the same time as cicadas, the vocalizations primarily occur at nonoverlapping frequencies with cicada signals. Our results greatly improve our understanding of the community dynamics of acoustic signaling and reveal how patterns in biotic noise shape the frequency and timing of bird vocalizations in tropical forests.

Description: Surface ice in rivers and lakes buffers the thermal environment and provides overhead cover, protecting aquatic animals from terrestrial predators. We tested if surface ice influenced the behavior (swimming activity, aggressive encounters, and number of food items eaten) and stress level (coloration of eyes and body) of stream-living brown trout Salmo trutta at temperatures of 3–4 °C in indoor experimental flumes. We hypothesized that an individual’s resting metabolic rate (RMR, as measured by resting ventilation rate) would affect winter behavior. Therefore, groups of 4 trout, consisting of individuals with high, low, or mixed (2 individuals each) RMR, were exposed to experimental conditions with or without ice cover. Ice cover reduced stress responses, as evaluated by body coloration. Also, trout in low RMR groups had a paler body color than those in both mixed and high RMR groups. Trout increased their swimming activity under ice cover, with the highest activity found in high RMR groups. Ice cover increased the number of aggressive encounters but did not influence the number of drifting food items taken by each group. In mixed RMR groups, however, single individuals were better able to monopolize food than in the other groups. As the presence of surface ice increases the activity level and reduces stress in stream-living trout, ice cover should influence their energy budgets and production. The results should be viewed in light of ongoing global warming that reduces the duration of ice cover, especially at high latitudes and altitudes.

Description: In recent years, considerable research interest in behavioral ecology has focused on characterizing and understanding individual differences in behavior that are consistent over time and across contexts, termed animal "personalities," and correlations between various behaviors across contexts, termed behavioral syndromes. Although there is some evidence that differences in personality among individuals within populations can be genetically based and adaptive, when and how individual personality differences emerge in a population is not well understood, but of considerable general interest. Here, using juveniles of the convict cichlid ( Amatitlania siquia ) as a model system, we investigated in the laboratory whether individuals consistently differ in their personalities and whether behavioral syndromes are apparent at an early developmental stage and, if so, whether distinct personality traits are heritable. Under standardized laboratory conditions and using sibling analysis, we quantified interindividual differences in their boldness behavior under potential predation threat and their exploratory activity in a novel environment, 2 ecologically important behaviors, as our focal personality traits and estimated their respective repeatability and heritability. We report for the first time consistent (repeatable) and heritable individual differences in boldness and exploratory behaviors, and a boldness–exploration behavioral syndrome, in young convict cichlids. Bolder fish were more exploratory than relatively timid ones. These results provide novel evidence for the emergence in early life history of consistent individual differences in personality traits and behavioral syndromes in this species and suggest that genetic variation for boldness and exploratory behaviors, and thus potential for selection on these traits, exists in our study population.

Description: Many animals search for potential mates or prey using a perch-and-sally strategy. The success of such a strategy will depend on factors that affect the observer’s ability to detect a passing resource item. Intrinsic factors (e.g., eye structure and physiology) have received much recent attention, but less is known about effects on object detection in nature and extrinsic factors such as size, coloration, and speed of a passing object and the background against which the object is viewed. Here, we examine how background affects the detection of butterfly models by perched males of the butterfly Asterocampa leilia in the field. We test the hypothesis that male choice of perch site in nature will influence the contrast between the object and background against which it is viewed and that this will influence success in detecting the object. We also test the effect of contrast by manipulating the brightness of the object and presenting butterfly models of different reflectance (ranging from black to white). We found an effect of model luminance, with dark models being most likely to elicit a response regardless of background. Further, there was an effect of background type with models viewed against blue sky eliciting the highest response. Perceived luminance contrast correlates to behavior; highly contrasting objects are more frequently detected. This study expands our understanding of visual system performance and has implications for our understanding of the behavior and evolutionary ecology of perching species.

Description: Theory suggests that consistent individual differences in activity are linked to life history where high activity is associated with rapid growth, high dispersal tendency, and low survival (the pace-of-life syndrome hypothesis). We addressed this influential hypothesis by combining behavioral studies with fine-scale positional scoring in nature, estimating how individual movement strategies in brown trout ( Salmo trutta ) associate with fitness correlates (growth and survival) in the wild. Initial dispersal in the wild was positively related to the laboratory activity. Moreover, the growth of individuals with high laboratory activity decreased with increasing home range size, whereas the growth of individuals with lower laboratory activity increased slightly with increasing home range size. Survival in the wild was not associated with laboratory activity. Our results do not support the original pace-of-life syndrome hypothesis. As an alternative explanation, we suggest that the growth of individuals adopting a high-activity strategy is more sensitive to variation in resource abundance (indicated by home range size) than the fitness individuals adopting a more passive strategy.

Description: The study of adaptive individual behavior ("animal personality") focuses on whether individuals differ consistently in (suites of correlated) behavior(s) and whether individual-level behavior is under selection. Evidence for selection acting on personality is biased toward species where behavioral and life-history information can readily be collected in the wild, such as ungulates and passerine birds. Here, we report estimates of repeatability and syndrome structure for behaviors that an insect (field cricket; Gryllus campestris ) expresses in the wild. We used mark-recapture models to estimate personality-related survival and encounter probability and focused on a life-history phase where all individuals could readily be sampled (the nymphal stage). As proxies for risky behaviors, we assayed maximum distance from burrow, flight initiation distance, and emergence time after disturbance; all behaviors were repeatable, but there was no evidence for strong syndrome structure. Flight initiation distance alone predicted both daily survival and encounter probability: bolder individuals were more easily observed but had a shorter life span. Individuals were also somewhat repeatable in the habitat temperature under which they were assayed. Such environment repeatability can lead to upward biases in estimates of repeatability in behavior; this was not the case. Behavioral assays were, however, conducted around the subject’s personal burrow, which could induce pseudorepeatability if burrow characteristics affected behavior. Follow-up translocation experiments allowed us to distinguish individual and burrow identity effects and provided conclusive evidence for individual repeatability of flight initiation distance. Our findings, therefore, forcefully demonstrate that personality variation exists in wild insects and that it is associated with components of fitness.

Description: For many animal taxa, group-living is a strategy where the cohesion provided by groups confers fitness benefits to individuals. Bats are highly gregarious with many species living in groups with complex social structures. During the summer, many temperate species are sexually segregated among roosts where females have been found to exhibit dynamic social structures and males remain understudied. We studied the group dynamics of little brown and northern Myotis bats ( Myotis lucifugus and Myotis septentrionalis ) during autumn swarming, a period for which social interactions are largely unknown. Using capture–mark–recapture surveys, we characterized the occurrence and frequency of age and sex groups occurring at swarms. Within a night, young-of-the-year associated more often with other bats than did adult males and females. Further, they associated more often with other young-of-the-year than adults. We found no evidence to support the maternal guidance hypothesis predicting that there would be associations between mother–offspring pairs. Adult male and female bats associated less frequently with each other and were captured alone most often. When males were captured in groups, these groups were more likely to be composed of multiple males and in M. lucifugus , males had preferred male associates they grouped with over multiple nights. Groups formed during the autumn swarming season may represent cohort groups of young bats learning of the location of sites and groups of males that are potentially cooperating to secure more mating opportunities.

Description: Offspring transmit signals to parents to communicate their resource demands. Parents interpret these signals and should adjust provisioning efforts to meet offspring demands but only to the point at which the benefits of enhanced offspring quality stops exceeding the increased costs to future reproduction. We investigated both proximate behavioral mechanisms in these interactions and ultimate-level decisions for total parental investment in streaked shearwaters Calonectris leucomelas by recording begging calls, monitoring parental attendance, and altering states of chicks by supplementing food. In our study, chicks seemed to honestly communicate satiety and body condition via begging. The parents, however, did not downwardly adjust feeding rates, meal sizes delivered to chicks, and total investment in nests in which chicks were regularly supplementary-fed partial meals. But on nights when both parents visited the nest, the second-arriving parents recognized that chicks had already received a full meal because they reduced the food they gave to chicks and also lengthened their subsequent foraging trip. Our findings therefore suggest that although chick begging appeared to reflect need, parents only responded to variation in begging that indicated that chicks had already received a full meal. In a simulation, we show that this strategy prevents parents from exceeding the optimal amount of parental investment. Their insensitivity to slightly reduced begging after partial meals caused them to exceed optimal investment in supplementary-fed nests, suggesting that parental investment is largely regulated by responses to feeding rate of the other parent rather than being fine-tuned to cues about body condition of chicks.

Description: Animals respond to approaching predators by taking flight at a distance that optimizes the costs and benefits of such flight. Previous studies have shown that urban populations of birds have shorter flight initiation distances than rural populations of the same species, that this difference is partly explained by differences in the community of predators, and that a longer history of urbanization implies a greater reduction in flight initiation distance in urban populations. The use of birdfeeders may be an additional factor reducing flight initiation distance not only in cities but also elsewhere by among other effects increasing body condition, increasing availability and reliability of food, and hence reducing the relative cost of flight. Here, we tested the prediction that urban habitats and presence of feeders independently accounted for reductions in flight initiation distance using extensive samples from different cities in Poland. We found independent significant effects of urban habitat and presence of feeders on flight initiation distance. These findings suggest that different factors have contributed to the "tameness" of urban birds.

Description: The expected quality of paternal behavior can influence female mating decisions and determine male mating success. We evaluated the importance of oviposition site quality, male body size, parental status (presence vs. absence of eggs under males’ protection), and time invested in care (less vs. more than 1 month) for male mating success in the harvestman Iporangaia pustulosa . The chances of acquiring a clutch are relatively small for noncaring males but increase nearly 4 times once males start caring for eggs. After 1 month of caring, the chances of acquiring an additional clutch show a marked decline, probably because the cumulative energetic costs imposed by paternal care decreases males’ attractiveness or their ability to replenish gametes throughout the caring period. Therefore, male mating success seems to be affected by a combination of presence of eggs and body condition while caring. Because the presence of eggs increases male attractiveness, we also conducted a field experiment removing caring males from their broods and expected that noncaring males would adopt unattended broods as a deceptive strategy to acquire matings. However, noncaring males cannibalized eggs and no brood adoption was recorded. Because well-fed males stay stationary on the vegetation waiting for mating opportunities, unattended broods may have been found more often by vagrant and poorly fed males. We argue that detailed comprehension of the costs and the benefits of paternal activities, as well as the direct benefits of female preference, is fundamental to better understand the interaction between male care and female mate choice.

Description: Sex allocation theory predicts that parents should bias offspring sex according to the costs and benefits associated with producing either sex in a given context. Accurately interpreting sex-ratio biases, therefore, requires a precise identification of these selective pressures. However, such information is generally lacking. This may partly explain the inconsistency in reported sex allocation patterns, especially in vertebrates. We present data from a long-term feeding experiment in black-legged kittiwakes ( Rissa tridactyla ) that allowed us to increase investment capacity for some breeding pairs. Previous findings showed that these pairs then overproduced sons compared with control parents. Here, our aim was to test the underlying assumptions of the 2 appropriate sex allocation models for our context: the "cost of reproduction hypothesis" and the "Trivers–Willard hypothesis." The former assumes a sex difference in rearing costs, whereas the latter assumes a difference in fitness returns. 1) Independent of feeding treatment, rearing sons was energetically more demanding for parents (as revealed by higher energy expenditure and higher baseline corticosterone levels) than rearing daughters, thereby corroborating the underlying assumption of the "cost of reproduction hypothesis." 2) Evidence supporting the assumptions of the "Trivers–Willard hypothesis" was less convincing. Overall, our results suggest that drivers of parental sex allocation decisions are probably more related to offspring sex-specific energetic costs than to their future reproductive success in our study species. Assessing the adaptive value of sex-ratio biases requires precise investigation of the assumptions underlying theoretical models, particularly as long as the mechanisms involved in sex-ratio manipulation remain largely unknown.

Description: In social groups, hierarchies are the fundamental organizational unit and integral to the structure of social groups. For many social fishes, rank is determined by body size and conflict over rank is resolved via aggressive threats from dominants and growth restraint by subordinates. However, this balance may be offset by an alteration of abiotic factors, such as elevated temperature expected from climate change, which could thereby disrupt the usual mechanisms of conflict resolution. Here, we determined the effect of elevated temperature on hierarchy structure, stability, and conflict resolution in the Eastern mosquitofish, Gambusia holbrooki . Body size was significantly related to dominance rank, and aggression was more commonly directed toward subordinates and was heightened between individuals of adjacent rank, demonstrating that conflict over rank occurs in size-based hierarchies. Temperature did not affect overall levels or directionality/adjacency of aggression but substantially altered subordinate growth patterns. In only the high-temperature groups, growth rates of subordinates decreased as the size ratio between themselves and their immediate dominant approached 1.0, whereas growth rates of dominants were unaffected. This unique finding suggests that only under high temperatures, subordinates may adopt growth regulation to resolve conflict, when the costs of conflict with dominants are greater. This provides the first causal link between abiotic stressors and changes to hierarchical structure and functioning, providing a springboard for further research into implications of temperature-dependent subordinate growth alteration at higher levels of ecological organization.

Description: Mate choice is an important evolutionary process influencing a vast array of traits and ecological processes. Although the study of mate choice has proved to be hugely popular, the number of ways in which mate choice can be described is complex and a bewildering array of terminology has developed. The author begins by summarizing some examples of the range of terms used to describe choice that expose this complexity. The author then shows how the information conveyed by different mate choice descriptors can be better understood by comparison to null expectations, that is, the expected variation in a trait when mate choice is not expressed. This comparison is important because many traits that might be affected by mate choice, such as mating rate, mate search effort, and responsiveness, also vary in non-choosy individuals. This is in contrast to other traits, such as the slope of a preference function and mate assessment effort, for which null expectations are predictable. By understanding the null expectation for a trait, its utility as a descriptor of mate choice can be gauged. From this basis, the author suggests an alternative approach to the description of mate choice based upon a principle of describing variation in both "what" is preferred and "by how much" it is preferred. Crucially, the author describes how this approach might apply to a wide range of preference function shapes, thus aiding comparisons across taxa. Finally, the author considers how an improved appreciation of the way mate choice is described can inform future research.

Description: Understanding how organisms respond to any environment requires a full characterization of how the environment varies over time and space. A rapidly growing literature on the influence of anthropogenic noise on wildlife, and in particular animal communication, has yet to fully describe this variation. Point measurements of amplitude, often separated in time and space from animal observations, and qualitative descriptions of noise inadequately capture variation, a bias that may limit deeper understanding of noise effects on wildlife. We suggest that a greater focus on temporal and spatial heterogeneity in noise amplitude, as well as additional properties of noise, including onset, consistency, regularity, and frequency range, is critical for continued advancement in this emerging field. Recordings of noise using calibrated systems allow researchers to measure a suite of noise properties simultaneously with animal observations. Not only will such an approach improve quantification of single metrics of noise, the noise data collected may then be analyzed in a multivariate framework, which will help us understand the full range of behavioral and physiological adjustments animals may make and their broader implications for wildlife health and conservation.

Description: Artificial light at night is an increasing threat for ecological processes. Previous work has highlighted the effects of nighttime light on individuals and on higher levels of biological organization, such as community ecology and ecosystem functioning. Here, we focus on the effects of artificial light at night on social interactions and group dynamics. We discuss 4 main ways of how light pollution is expected to alter social interactions and group dynamics. First, light at night can alter the activity patterns of individuals and this is predicted to affect the social network structure of populations, which in turn affects the transfer of information and diseases. Second, changes in activity patterns and disrupted biological rhythms are expected to reduce behavioral synchrony in social processes such as reproduction, migration, and dispersal. Third, increased light at night is expected to affect the communication between individuals; primarily, it will increase the opportunities for visual social information transfer. Last, artificial nighttime light is expected to lower social competence, with subsequent negative effects on aggressive interactions and group coordination. Throughout the article, we propose testable hypotheses and identify suitable study species, and we hope that this article inspires future research on the effects of bright nights on social interactions and group dynamics.

Description: Quantifying the shape and strength of mating preferences is a vital component of the study of sexual selection and reproductive isolation, but the influence of experimental design on these estimates is unclear. Mating preferences may be tested using either no-choice or choice designs, and these tests may result in different estimates of preference strength. However, previous studies testing for this difference have given mixed results. To quantify the difference in the strength of mating preferences obtained using the 2 designs, we performed a meta-analysis of 38 studies on 40 species in which both experimental designs were used to test for preferences in a single species/trait/sex combination. We found that mating preferences were significantly stronger when tested using a choice design compared with a no-choice design. We suggest that this difference is due to the increased cost of rejecting partners in no-choice tests; if individuals perceive they are unlikely to remate in a no-choice situation they will be more likely to mate randomly. Importantly the use of choice tests in species in which mates are primarily encountered sequentially in the wild may lead to mating preferences being significantly overestimated. Furthermore, this pattern was seen for female mate choice but not for male mate choice, and for intraspecific choice but not for interspecies or interpopulation mate discrimination. Our study thus highlights the fact that the strength of mating preferences, and thus sexual selection, can vary significantly between experimental designs and across different social and ecological contexts.

Description: Traditional views of sexual selection view males as the indiscriminate sex, competing for access to choosy females. It is increasingly recognized that mating can also be costly for males and they are therefore likely to exhibit choice in order to maximize their reproductive success. Stalk-eyed flies are model species in sexual selection studies. Males are sperm limited and constrained in the number of matings they are able to partake in. In addition, variation in female fecundity has been shown to correlate positively with female eyespan, so eyespan size could provide males with a reliable signal of female reproductive value. We examined male mate preference in the wild in the stalk-eyed fly, Teleopsis dalmanni . In addition, we set up experiments in the laboratory allowing males a choice between females that varied in 1) eyespan (a proxy for fecundity) and/or 2) fecundity (manipulated through diet). We found that males exhibited preference for large eyespan females, both in the wild and laboratory studies. As well as using female eyespan as a mating cue, males were also able to assess female fecundity directly. Changes in fecundity among large eyespan females caused corresponding changes in male mate preference, whereas changes in the fecundity of small eyespan females had limited effect on their attractiveness. These results show that male mate preferences are a prevalent feature of a canonical example of female mate choice sexual selection and that males use multiple cues when they assess females as potential mates.

Description: To study biologically relevant variation in visual signals, these need to be assessed in relation to the sensory abilities of receivers. For the study of colors, reflectance spectrometry has been the method of choice, but analyses of reflectance spectra present challenges that hamper our understanding of color variation. Among these are computing meaningful color variables and interpreting their biological relevance. Here, we suggest how to overcome the limitations of commonly used approaches. We describe how to use psychophysical visual models to assess chromatic variation in the visual space of animals. This approach consists of 1) obtaining cone quantum catches from reflectance spectra, 2) transforming these into visual space coordinates where Euclidean distances reflect perceptual distances, 3) summarizing variation in visual space using principal component analysis (PCA) maintaining original perceptual units, and 4) interpreting the axes of chromatic variation (PC) based on their loadings and relative and absolute levels of chromatic variation. We illustrate this approach by comparing it to traditional color indices (hue and saturation) and PCA computed directly on reflectance spectra, using 2 examples: 1) determining the biological relevance of correlations between bill coloration and male quality in mallards and 2) assessing the success of experimental color manipulations in blue tits. In both cases, re-analyzing the data suggests different interpretations. This approach provides a simple way of objectively summarizing chromatic variation and interpreting the magnitude of biologically relevant effects. We provide R scripts to carry out computations and recommendations on how to report results to make data comparable between studies.

Description: The ability of an organism to detect threats is fundamental to mounting a successful defense and this is particularly important when resisting parasites. Early detection of parasites allows for initiation of defense mechanisms, which are vital in mitigating the cost of infection and are likely to be especially important in social species, particularly those whose life history makes parasite pressure more significant. However, understanding the relative strength of behavioral responses in different species and situations is still limited. Here, we test the response of individual ants to fungal parasites in 3 different contexts, for 4 ant species with differing life histories. We found that ants from all 4 species were able to detect fungi on their food, environment, and nest mates and initiate avoidance or upregulate grooming behaviors accordingly to minimize the threat to themselves and the colony. Individuals avoided fungal-contaminated surfaces and increased grooming levels in response to fungal-contaminated nest mates. Ants from all species responded qualitatively in a similar way although the species differed quantitatively in some respects that may relate to life-history differences. The results show that ants of multiple species are capable of recognizing fungal threats in various contexts. The recognition of parasite threats may play an important role in enabling ant colonies to deal with the ever-present threat from disease.

Description: Different populations of a host species subject to variable patterns of selection due to cuckoo parasitism provide an optimal situation for studying natural selection and coevolution in action. We compared egg appearance and egg-rejection behavior of 2 common cuckoo ( Cuculus canorus ) hosts, the ashy-throated parrotbill ( Paradoxornis alphonsianus ) and the vinous-throated parrotbill ( Paradoxornis webbianus ) between mainland China and Taiwan population that have been segregated for 2–3 million years. Avian visual modeling showed that the mainland host population under strong selection from brood parasitism has evolved polymorphic eggs, while the island host population released from brood parasitism has maintained the original monomorphic egg phenotype. Furthermore, experiments indicated that under such long historical segregation, egg rejection in the island population decayed dramatically in the absence of cuckoo parasitism. This study provides strong evidence that egg-rejection ability can be dramatically deficient in host populations without brood parasitism compared to parasitized ones. The results further enhance our understanding of changes in egg-rejection behavior in birds without the selection pressure of brood parasitism for an extended period of time.

Description: In scramble competition polygyny, male and female mobility may be under strong selection as a result of fitness effects of searching for reproductive resources such as mates, oviposition sites, or resources for egg production. We analyzed the relationship between mating frequency, mobility, and body size in males and females of the chrysomelid beetle Leptinotarsa undecimlineata . We obtained a detailed data set of movement and mating frequency of an entire population (1037 adults) over a full reproductive season using individual tagging and direct behavioral observations. Unlike previous studies, we found a negative relationship between mobility and mating success for both sexes. Size was positively correlated to mating frequency in females, but negatively in males. High male mobility may be the result, and not a cause, of low mating success in scramble mating polygynies where rejected or displaced males switch plants more often searching for mating opportunities. More mobile females may be looking for competition-free oviposition substrate and thus experiencing fewer sexual encounters.

Description: Few biological examples of cooperation seem to precisely fit the assumptions of an iterated prisoner’s dilemma. In an attempt to increase biological validity, one model altered the assumption that cooperating is an all-or-nothing decision to a situation where benefits are a function of interaction duration, which in turn is a function of the levels of cooperation. A potential application involves pairs of cleaner fish coinspecting a client fish. In this mutualism, clients visit cleaners to have ectoparasites removed but a conflict of interest exists, as cleaners prefer to eat client mucus, which constitutes cheating. As large clients often flee in response to a cleaner cheating, pair inspections lead to a dilemma: the cheater obtains the benefit while both cleaners share the cost of the client leaving. The model predicts that pairs of cleaners behave more cooperatively toward reef fish clients than when inspecting alone, to entice clients to profit from the increased parasite removal rate and keep interaction duration almost constant. Here, we present field experiments that first replicate results that pairs behave indeed more cooperatively than when inspecting alone and second show that levels of cooperation quantitatively predict the duration of cleaning interactions. We also found that several additional variables may affect the duration of cleaning interactions, such as a client’s willingness to interact with a cleaner, identity of interaction terminator, and the presence of bystanders. In conclusion, introducing benefits as a function of interaction duration into the prisoner’s dilemma framework provides a biologically relevant framework to study cooperation.

Description: Anthropogenic noise is a major pollutant for organisms that live in urban areas. City birds modify their songs in ways that can increase their communication potential in spite of noise. However, these changes cannot prevent song masking by the extremely loud noises to which some urban bird populations are exposed. Here, we show that birds near a major airport advance their dawn singing time, thus reducing overlap with periods of intense aircraft noise. This modification was stronger in species whose normal singing time was relatively late, those which overlapped the most with aircraft noise. Although suggestive of a causal relationship, this pattern does not allow us to tell apart the effect of aircraft noise from that of other variables that may correlate with dawn singing time. In order to control for such potentially confounding variables, we replicated the study in several airports at different latitudes in Spain and Germany. The results show that indeed the overlap of song chorus with aircraft noise was the key factor that influenced time advancement. Aircraft traffic time was the main predictor of song advancement: across Europe, those bird populations whose singing time overlapped the most with aircraft traffic were those that advanced their song timing to a higher extent. Our results exemplify how behavioral plasticity may allow the survival of avian populations in areas of high noise pollution. However, such an adaptation likely involves departing from optimal singing times, leading to higher energetic costs and amplifying between-species differences in competitive ability and resilience.

Description: Sexual selection theory suggests that males benefit more than females from multiple mates and that sexual selection is weak in monogamous mating systems. However, little research on sexual selection has been conducted simultaneously in men and women, and we lack a detailed understanding of the socioecological factors that can influence it. Here, we examined the effects of wealth and sex on 2 distinct episodes of human sexual selection (marry once and remarry) in historical Norwegian populations with imposed monogamy, where remarriage was only possible after widowhood. We quantified sexual selection using the Bateman gradient. We also examined the underlying proximate factors that might influence the odds of remarriage and reproduction after widowhood. We found that the intensity of sexual selection corresponds well with Bateman gradients measured in other monogamous populations and was stronger for those who married once than for those who remarried. The selection gradients on "marry once" were affected by neither sex nor wealth. However, when we measured the gradients on "remarry," sexual selection was stronger on wealthy men and women compared with those who were poor. Remarriage age was the most important underlying factor explaining how widows increased reproductive success. For widowers, it was to remarry a younger woman than themselves. In conclusion, we show that sexual selection can operate on both sexes in a monogamous population and suggest that under certain circumstances (when very wealthy), women can benefit as much as men can by remarriage.

Description: Paired individuals are expected to leave their current partner for newly encountered ones of higher quality. In such cases, animals should therefore be able to compare the quality of their current partner to the quality of a new prospective mate next to the couple. We tested this prediction in Gammarus pulex , an amphipod species where paired males have been described to switch females before copulation. Contrary to expectations, a majority of males remained paired to their current female when presented to an unpaired female of higher quality. In fact, males did not seem to compare the quality of the 2 females before switching. They rather based their decision on the quality of their current female only, switching when it was of low quality. We suggest that mate switching functions as a male mate choice strategy under strong competition for female access in G. pulex . Unpaired males may first randomly pair with a female to gather information about its quality as a mate before switching for a new female when the expected quality of unpaired females in the population exceeds that of their current partner.

Description: Advancements in GPS radiotelemetry allow collection of vast data for a variety of species including those for which direct observations are typically not feasible. Predicting behavior from telemetry data is possible, but telemetry fix rate can influence inferences, and animal behavior itself can affect fix success. We use multinomial regression to predict behavior from GPS radiocollar data field validated with behavioral state information. Our study organism was a facultative carnivore, the grizzly bear ( Ursus arctos ) ( n = 10) from a threatened population in Alberta, Canada, monitored during 2008–2010. Models using GPS cluster parameters alone successfully predicted ungulate consumption, whereas bear bedding was sufficiently identified by models that included site-level information. Predicting more complex behaviors required models incorporating both cluster parameters and habitat characteristics. No model reliably predicted vegetation feeding, probably because this activity is shorter than the time required for cluster formation. Models built using infrequent fix rates underestimated all behaviors, with bear presence at ungulate carcass sites least sensitive to fix rate variability. Behavior influenced fix success, with highest fix acquisition occurring when bears fed on vegetation. Placing predictions into a conservation context, we show that grizzly bears modify their behavior as they move through a landscape with complex human-activity patterns on reclaimed open-pit mines, foothill, and mountain regions. The modeling approach we tested needs further applications across species and ecosystems including behavioral monitoring, quantifying activity budgeting, and identifying areas/habitats important for specific behaviors that may warrant conservation.

Description: "Ecosystem engineering" describes habitat alteration by an organism that affects another organism; such nontrophic interactions between organisms are a current focus in ecological research. Our study quantifies the actual impact an ecosystem engineer can have on another species by using a previously identified model system—peccaries and rainforest frogs. In a 4-year experiment, we simulated the impact of peccaries on a population of Allobates femoralis (Dendrobatidae) by installing an array of artificial pools to mimic a forest patch modified by peccaries. The data were analyzed using a gradual before-after control-impact (gBACI) model. Following the supplementation, population size almost doubled as a result of increased autochthonous recruitment driven by a higher per-capita reproduction of males and a higher proportion of reproducing females. The effect was evenly distributed across the population. The differential response of males and females reflects the reproductive behavior of A. femoralis , as only the males use the aquatic sites for tadpole deposition. Our study shows that management and conservation must consider nontrophic relationships and that human "ecosystem engineering" can play a vital role in efforts against the "global amphibian decline."

Description: Particularly in species with biparental care and low levels of extrapair paternity, sexual traits that honestly indicate phenotypic and genetic quality are expected. We investigated in the brown booby, Sula leucogaster , whether gular color displayed by males during courtship is related to direct or indirect benefits to females. We performed a cross-fostering experiment in order to identify the relative contribution of parental care and genetic effects on offspring condition. We found that rearing father gular color was positively related to parental care (offspring attendance and provisioning) and chick body mass increase, whereas the genetic father gular color was related to chick structural growth. Contrary to expectations, females paired to more colorful males laid smaller eggs and did not increase parental care. Interestingly, chicks from genetic mothers with more colorful gulars and chicks that hatched from larger eggs "begged" at higher rates to mothers than to fathers. Overall, the results suggest that male gular color may provide females with reliable information on mate genetic quality and parenting abilities.

Description: Females often mate with multiple males even when a single mating is sufficient to fertilize their eggs. Remating can lead to direct and indirect benefits for females, but these benefits trade-off against the potential costs associated with polyandry. There is a growing understanding that not all males are equal in their ability to deliver sperm to the site of fertilization. Such differences can arise both from environmental (e.g., mating history) and intrinsic (genetic) sources of variation. Most studies that investigate female fitness control male mating history to overcome such effects, but this control may bias interpretations of the benefits of polyandry. Here, we tried to avoid overestimating the benefits of polyandry that might accrue from mating repeatedly with virgin males. To do this, we quantified 6 components of fitness in female bruchid beetles, Callosobruchus maculatus , that were mated between 1 and 4 times to males with unknown mating histories, either in isolation or with rival males present. As copulation number increased, fecundity, offspring production, and egg-to-adult survival declined. In contrast to these short-term costs, the probability that a female remained completely infertile was highest at 1 copulation, and geometric mean fitness peaked after 3 copulations. Pericopulatory harassment by males did not affect female productivity. There was a significant interaction between this harassment and copulation number on longevity such that harassed females mating 2 or 3 times, and females mating twice in isolation, died soonest. Our results suggest that females may be selected to mate multiply despite short-term costs to fitness.

Description: In the context of global warming, investigating how animals buffer against the hottest conditions is a crucial issue. We focused on habitat selection in a French Mediterranean mouflon population during 2010–2012 summers. Using locations and temperatures recorded on GPS-collared individuals, we assessed thermal cover provided by different habitats and analyzed sex- and scale-specific habitat selection and its thermal consequences for mouflon. At the home range scale, females ( n = 26) avoided unsafe plateaux and selected steep refuges, trading off thermal cover with better conditions for lamb survival. Larger males ( n = 18), not constrained by young rearing and expected to respond more strongly than smaller females to hot conditions, rather selected forests on plateaux providing thermal cover. In terms of movements, both sexes selected forests during hottest days. Males also took advantage of food and thermal cover provided by moorlands on plateaux until twilight, whereas females traded off food and thermal cover with refuges. Thermal cover significantly influenced habitat selection when temperature at the closest weather station exceeded 17.1 °C (95% confidence interval = 14.9–19.7) in males and 15.5 °C (95% confidence interval = 13.9–16.5) in females. Above these thresholds, ambient temperatures experienced by mouflon increased more slowly than temperatures at the weather station (males: 0.77 °C [95% confidence interval = 0.74–0.79] per 1 °C rise at the weather station, females: 0.75 °C [95% confidence interval = 0.73–0.76]) and more slowly than below these thresholds (males: 0.89 °C [95% confidence interval = 0.85–0.93], females: 0.94 °C [95% confidence interval = 0.89–0.98]). These findings suggested that habitat selection contributes to buffer mouflon against summer conditions but raised questions on energetic and fitness costs in areas where summer temperatures are predicted to increase further.

Description: Numerous animals are known to assess the resource holding potential of their opponents using conventional signals and other correlates of resource holding potential. Although body and weapon size generally correlate with resource holding potential and are often presumed to be visually evaluated in animal contests, no one has demonstrated visual assessment of opponent size while controlling for all potential correlates of size. To this end, we presented male Lyssomanes viridis jumping spiders with computer-animated opponents 1) of 3 different overall sizes and 2) with different weapon and nonweapon appendages elongated by the amount that would normally accompany a 20% increase in body size. Male L. viridis have strikingly colored, exaggerated chelicerae and forelegs, which are used as weapons in contests, and the forelegs are waved during visual agonistic displays. We scored 4 levels of escalation in males’ responses to animations. Using generalized linear mixed modeling, we assessed the relative predictive power of the following variables on escalation intensity: 1) focal male size, 2) animated opponent size, and 3) the difference in size between the focal male and his animated opponent. When we presented males with animations scaled to different sizes, we found that size difference was the best predictor of escalation intensity, followed by opponent size. The effect of opponent size disappeared when size difference was included in the same model. Focal male size did not significantly predict escalation intensity. This suggests that males employ a mutual assessment strategy. Surprisingly, males did not respond differently to animations with versus without elongated weaponry.

Description: The evolution of conspicuous begging displays has been suggested as the outcome of a conflict where offspring attempt to manipulate food allocation beyond the parental optimum. One resolution for the conflict arises via costs of begging, and oxidative stress has been proposed as a major mechanism for causing begging-induced costs. Although begging can be a physically demanding activity, the evidence for causing oxidative stress is scarce. Great tit ( Parus major ) parents provide food at the nest mostly from 2 different locations, which in consequence relaxes nestling competition. Here, we manipulated nestling competition by forcing parents to feed from a single location and supplemented half of the nestlings in each brood with vitamin E to test if this major antioxidant can alleviate a potential oxidative cost of begging. The design increases the cost of begging without altering parental feeding rates. Begging intensity was significantly higher when parents fed from a single location. Body mass and antioxidant capacity were not affected by the increase in begging, but oxidative damage was lower in females of the increased begging group compared with those in the control group, independent of vitamin E supplementation. The results suggest that oxidative stress is rather a minor cost of begging. Vitamin E–supplemented nestlings had a higher probability to fledge, which underlines the important role of vitamin E during development, although this might not be due to its role as an antioxidant.

Description: Brain size varies dramatically among vertebrates, and selection for increased cognitive abilities is thought to be the key force underlying the evolution of a large brain. Indeed, numerous comparative studies suggest positive relationships between cognitively demanding aspects of behavior and brain size controlled for body size. However, experimental evidence for the link between relative brain size and cognitive ability is surprisingly scarce and to date stems from a single study on brain size selected guppies ( Poecilia reticulata ), where large-brained females were shown to outperform small-brained females in a numerical learning assay. Because the results were inconclusive for males in that study, we here use a more ecologically relevant test of male cognitive ability to investigate whether or not a relatively larger brain increases cognitive ability also in males. We compared mate search ability of these artificially selected large- and small-brained males in a maze and found that large-brained males were faster at learning to find a female in a maze. Large-brained males decreased the time spent navigating the maze faster than small-brained males and were nearly twice as fast through the maze after 2 weeks of training. Our results support that relatively larger brains are better also for males in some contexts, which further substantiates that variation in vertebrate brain size is generated through the balance between energetic costs and cognitive benefits.

Description: Although many studies have examined precopulatory female choice, it is increasingly clear that females may choose paternity after copulation with multiple males. Such cryptic female choice may be more common in species where females have limited precopulatory choice. We tested for cryptic female choice in the monarch butterfly ( Danaus plexippus ), which has a male-coerced mating dynamic. We used a mating design consisting of female pairs mated to the same 2 males. Using microsatellite markers, we determined P2, the proportion of offspring fathered by the second male. In 3 treatments, we varied the relatedness of females and males and calculated P2 repeatability of the 2 females in a replicate. Assuming cryptic female choice, we predicted more repeatable P2 values for genetically related female pairs than unrelated pairs. Additionally, we predicted that females should favor paternity by unrelated males over brothers to avoid potential inbreeding depression. Our results revealed no P2 repeatability differences between treatments and no differences in paternity of brothers and unrelated males. These results suggest monarchs do not employ cryptic female choice and do not avoid inbreeding postmating. Moreover, we did not find significant sperm precedence; neither first nor second male obtained higher paternity. However, our results suggested that interactions between male and female lineages may slightly affect offspring paternity, suggesting genetic compatibilities may affect sexual selection in this species. We also found a bimodal paternity distribution, confirming that monarchs follow the lepidopteran pattern of paternity, despite precopulatory behavioral differences.

Description: Sea otters are well-known tool users, employing objects such as rocks or shells to break open hard-shelled invertebrate prey. However, little is known about how the frequency of tool use varies among sea otter populations and the factors that drive these differences. We examined 17 years of observational data on prey capture and tool use from 8 sea otter populations ranging from southern California to the Aleutian Islands in Alaska. There were significant differences in the diets of these populations as well as variation in the frequency of tool use. Sea otters at Amchitka Island, Alaska, used tools on less than 1% of dives that resulted in the capture of prey compared with approximately 16% in Monterey, California. The percentage of individuals in the population that used tools ranged from 10% to 93%. In all populations, marine snails and thick-shelled bivalves were most likely to be associated with tool use, whereas soft-bodied prey items such as worms and sea stars were the least likely. The probability that a tool would be used on a given prey type varied across populations. The morphology of the prey item being handled and the prevalence of various types of prey in local diets were major ecological drivers of tool use: together they accounted for about 64% of the variation in tool-use frequency among populations. The remaining variation may be related to changes in the relative costs and benefits to an individual otter of learning to use tools effectively under differing ecological circumstances.

Description: Aposematic species use conspicuous "warning" signals to communicate unprofitability to potential predators. Although warning signals are classic examples of communication systems that evolved by natural selection, they can also function in the context of sexual communication and are therefore particularly useful for investigating conspicuous trait evolution under multifarious selection. To test whether aposematic signals also serve to mediate intrasexual disputes, we observed males from a highly territorial poison frog species ( Oophaga pumilio ) in their native territories and in experimental dyadic contests to assess the influences of body characteristics such as warning signal brightness and body size on the outcomes of territorial interactions. We report here that although neither male size (snout–vent length) nor mass significantly predicted male aggressiveness (latency to call) in dyadic contests, a male’s dorsal brightness was a significant predictor of willingness to initiate aggressive interactions, with brighter males exhibiting a shorter latency to call than duller males. Furthermore, brightness asymmetries between males predicted the outcomes of contests such that asymmetries were smaller in escalated aggression trials (where both males called), and brighter males were more likely to be the sole aggressor in trials with large asymmetries. These tests, combined with previous work, provide evidence that warning coloration has been co-opted as an agonistic indicator trait in this aposematic amphibian and reveal the potential evolutionary lability of conspicuous traits that arise through natural selection.

Description: Although personality has been documented in numerous animals and characters, research into personality-dependent spatial ecology has focused on dispersal. Indeed, few authors have investigated the role of other important spatial traits such as home range, movement distance, vertical activity, and site fidelity, and it is not clear whether these behaviors are correlated with dispersal. In this study, we investigated individual differences in home range, dispersal from release, vertical activity, movement distance, and site fidelity of 44 wild burbot Lota lota over 2 years, using an acoustic telemetry array and a Bayesian mixed modeling framework. We tested whether the spatial behaviors met the following criteria for personality-dependent behavior: repeatability, cross-contextual consistency, and an absence of pseudo-repeatability associated with spatial context choice. We then tested for between-individual correlations among spatial behaviors, indicative of a behavioral syndrome. Our results documented repeatable, cross-contextually consistent, personality-dependent home range, movement, dispersal from release, and site fidelity. In contrast, behavioral differences in vertical activity were inconsistent across sampling years and may have been a product of habitat heterogeneity. Our data indicate a spatial behavioral syndrome occurred independently from dispersal from release, with behavioral types ranging from "resident" individuals with small home ranges, high site fidelity, and minimal movement to "mobile" individuals with large home ranges, high movement rates, and little site fidelity. Our findings suggest animal personality can play a key role in shaping the space use of individuals, and this diversity in spatial behaviors may be too complex to be captured by often used simple linear measures of dispersal.

Description: A longstanding hypothesis in evolutionary biology is that trade-offs between natural and sexual selection often underlie the diversification of sexual signals in the wild. A classic example of this "selection trade-off hypothesis" proposes that males evolve elaborate and conspicuous ornamentation in low-risk environments where female preferences dominate selection on sexual traits, but they evolve muted and relatively cryptic sexual traits in high-risk environments where selection from predators acts against conspicuous sexual traits and female preferences potentially weaken or reverse. However, little direct empirical evidence supports this notion. Using the model system of Bahamas mosquitofish ( Gambusia hubbsi )—where males have recently evolved greater orange coloration in their dorsal fins in blue holes lacking predatory fish relative to populations with fish predators—we tested this hypothesis using fish replicas differing only in dorsal-fin color. Specifically, we employed plastic fish models in a combination of field and lab experiments to directly examine conspicuity to predators and female preferences for dorsal-fin color. We found that orange-shifted dorsal fins resembling the color exhibited in predator-free populations appeared more conspicuous to predatory bigmouth sleepers ( Gobiomorus dormitor ) that are evolutionarily naive to mosquitofish. Wild-caught female mosquitofish preferred the orange-shifted dorsal-fin model during dichotomous choice tests; evolutionary history with predators did not affect female preferences. Similar mate-choice trials with lab-born virgin females also found preferences for the orange-shifted dorsal-fin model and revealed significant genetic variation for female preferences. Our study provides direct empirical evidence documenting a trade-off between natural and sexual selection in a colorful sexual signal.

Description: Over the last century, expanding urbanization has led to a strong increase in the levels of background noise. This noise pollution has been shown to negatively affect wildlife (e.g., reduced species diversity and density, reduced breeding success), especially birds. Most research addressing the effects of anthropogenic noise has focused on avian communication and, to date, very little is known regarding the impact of chronic noise exposure on nonvocal behavior such as antipredator behavior. Here, we exposed free-living house sparrows ( Passer domesticus ) breeding in nest-boxes to either a playback of traffic noise (disturbed birds) or the rural background noise of the study site (no playback: control birds) during their first breeding attempt. We tested whether one of the female’s antipredator behaviors (i.e., flushing distance) was affected by exposure to chronic noise and investigated the impact of chronic noise on reproductive performances. Disturbed females flushed more rapidly than controls, suggesting that birds may compensate for reduced ability to detect predators with increased vigilance. However, we found no significant effect of exposure to chronic noise on reproductive performances. Our findings show, for the first time, that chronic noise exposure can affect the antipredator behavior of a breeding bird.

Description: Animals change the strategy that they use to select breeding sites at the spatial scales of habitat, patch, and microhabitat. In this regard, breeding site fidelity is expected to vary according to environmental predictability, which, in turn, is expected to differ between each spatial scale. However, whether or not animals change their degree of site fidelity at different spatial scales remains unclear. We captured and released males of the terrestrial frog Pseudophryne bibronii into alternative patches within a breeding habitat and determined the extent to which site fidelity influenced individual nest-site choice. We found that males tended to return to their original patch rather than resettle in an alternative patch. However, males were unlikely to return to their original nest sites within the patch. We suggest that site fidelity in this species may be scale dependent because information from previous breeding seasons can predict the quality of patches, but not nest sites. This behavioral variation is consistent with a hypothetical relationship between spatial scale and environmental predictability, which may have important implications for decision-making processes that extend over multiple spatial scales.

Description: Predation represents the primary cause of mortality for both nestling and fledgling birds and is often greatest in the days immediately before and after nest departure. Due to the selective pressures of such high mortality rates, behaviors likely evolved to increase the survival of young. Among altricial species, fledging often occurs in the morning with most nestlings leaving within 6h of sunrise. However, why nestlings tend to fledge in the morning and whether this strategy is a response to predation risk is unknown. We investigated how the time of day when fledging began and how rapidly broodmates fledged were influenced by nest predation rates and nest site features that affect nest predation risk. We video recorded 477 fledging events at 202 nests of 17 species. Nestlings occupying nests with greater predation risk initiated fledging earlier in the day than those at safer nests. Similarly, broodmates in riskier nests fledged over a shorter period of time than broodmates in safer nests. Our findings support the hypothesis that predation risk influences the time of day when fledging occurs. By fledging earlier and more quickly, young in high risk nests presumably decrease their chances of being depredated in the nest, whereas those occupying safer nests are likely under reduced pressure to fledge as early and quickly as possible. These results indicate that nestlings preparing to fledge likely face more complex situations than currently understood, and the timing of nest departure is an important decision made in an effort to maximize fledgling fitness.

Description: Emitting alarm calls may directly benefit individuals if callers have an increased chance of surviving, if calling increases the caller’s status, or if calling functions through reciprocity. Although previous studies have examined the costs and benefits of alarm calling, few have examined how an individual’s social position can influence the propensity to emit calls. An individual’s position in its social network may vary and individuals differ in the strength and degree to which they are connected to others. We hypothesized that this variation could influence the rate at which individuals emit calls. We examined how various social attributes (degree centrality, closeness centrality, eigenvector centrality, strength, and embeddedness) were related to the likelihood that yellow-bellied marmots ( Marmota flaviventris ) emitted calls. To do so, we first defined 2 principle components—"popularity" and "relationship strength"—and used generalized linear mixed effects models to explain both the natural rate of alarm calling and the rate of trap-induced calling. We found that the natural rate of alarm calling increased for marmots that were less popular (i.e., involved in fewer connections with other marmots) and that the rate of trap-induced calling increased for marmots involved in weaker relationships. These findings refute the reciprocity hypothesis. However, less popular marmots could be seeking to enhance their social status by calling, or they could be deterring predators without the aid of others. Similarly, marmots in traps are faced with an imminent personal threat. Thus, marmots in weaker relationships that cannot rely on other marmots may call to deter predators.

Description: The ability of animals to discriminate between individuals or groups of individuals (e.g., kin or nonkin) is an important component of many hypotheses proposed to explain the evolution of cooperation and benefits of group living. Previous studies in mammalian systems have demonstrated the use of vocal cues in individual recognition and discrimination. However, there are few such studies in birds. Previous avian studies have largely examined discrimination between different categories of individuals (e.g., mate vs. nonmate, offspring vs. non-offspring) while discrimination between individuals of the same category remain largely unexplored. Previous work has demonstrated that the contact calls of free-living apostlebirds ( Struthidea cinerea ) are individually distinct. Here, we demonstrate that apostlebirds can differentiate between the calls of other individuals of the same social group using vocal cues alone. These findings are biologically relevant as apostlebirds live in complex fission–fusion societies where social groups vary in size, sex ratio, number of breeders, and composition of related and unrelated members.

Description: The evolutionary loss of sexual signals is taxonomically widespread and quite common. These signals are often important not only in mate choice but also in male competition for territories and females; yet, male competition has rarely been investigated in the context of signal loss. We asked whether the loss of red throat color in three-spine stickleback ( Gasterosteus aculeatus ), an ancestral signal important in both male competition and mate choice, is accompanied by changes to intrasexual selection. Several freshwater stickleback populations have lost the red throat, and instead develop black breeding coloration. Previous work demonstrated that sensory drive is likely responsible. We conducted trials that mimic contact between ancestral (red) and derived (black) types during territory and nest establishment under conditions mimicking the 2 water color environments (clear and red-shifted, respectively) where they are found. We found that the allocation of competition behaviors depends on male breeding color, but not water color or the interaction of the 2. Although the total number of aggressive behaviors did not vary between color types, black males directed more aggression toward red males. Assessing each male competition behavior separately revealed that this pattern was largely driven by black fish biasing "charges" toward opposite type males. Agonistic behavior between types may strengthen divergence in resource or habitat use between populations of males with and without the ancestral sexual signal.

Description: Many studies have attempted to account for variation in male reproductive success by quantifying a single trait such as an ornament or a behavior, but male reproductive performance may be determined by a number of interacting traits. Although developmental nutrition is often a major determinant of adult body size and secondary sexual trait expression, other factors—such as residual shape variation and prior experience—may also exert independent effects on male reproductive success. Here, we studied how male sexual-trait expression, as manipulated by larval diet quality, and experience in direct male–male competition, affected male reproductive success in the sexually dimorphic neriid fly Telostylinus angusticollis . Among competing males matched by body size, individuals with relatively longer antennae (used as weapons) were more likely to win and also achieved matings faster. Unexpectedly, males reared on a poor larval diet and those that had previously lost in male–male combat appeared to invest more in some aspects of reproduction as indicated by a longer mating duration and a higher subsequent egg-hatching rate. Our findings demonstrate the complexity of male reproductive success, indicating that male developmental nutrition as well as morphological variation, and prior adult competitive experience interact in a complex manner to influence overall reproductive performance.

Description: The importance of between-group competition in the social evolution of animal societies is controversial, particularly with respect to understanding the origins and maintenance of cooperation in our own species. Among primates, aggressive between-group encounters are often rare or strikingly absent, a phenomenon that in some species has been ascribed to the presence of collective action problems. Here, we report on a series of comparative tests that show that the intensity of between-group contest competition is indeed lower in species that experience a collective action problem while controlling for predictions from an "ideal gas" model of animal encounters and general species’ ecology. Species that do not succumb to the collective action problem are either cooperative breeders, are characterized by philopatry of the dominant sex, or live in relatively small groups with few individuals of this dominant sex. This implies that collective action problems are averted either through shared genes and benefits or a by-product mutualism in which the territorial behavior of some privileged individuals is not affected by the behavior of others. We conclude that across the primate taxon, the intensity of between-group competition is predominantly constrained by a social dilemma among group members, rather than ecological conditions, and that the collective action problem is thus an important selective pressure in the evolution of primate (including human) cooperation and sociality.

Description: The development of preferences for males with sexual ornaments is still not well understood. Therefore, we investigated whether the use of public information in mate-choice copying can explain the development of mate preferences for a novel phenotype in male and female zebra finches ( Taeniopygia guttata castanotis ). In a binary choice situation, birds could choose between 2 conspecifics of the opposite sex of 2 different phenotypes: an unadorned phenotype and an adorned phenotype with a red feather on the forehead, simulating the novel phenotype. When no public information was provided, females and males spent a similar amount of time in front of individuals of both phenotypes. After observing a single, unadorned individual and a pair with 1 adorned partner for 2h, females and males could choose between other individuals of both phenotypes in 2 consecutive mate-choice tests. Females spent significantly more time in front of males of the adorned phenotype after the observation period than before the observation period. This shows that females copied and generalized the mate choice of other females for males of the new phenotype. In contrast to females, males did not copy the mate choice of other males. Results from controls provided no alternative explanation for the change in mate choice in females. Our study shows that sexes differ in using public information in mate-choice decisions and that mate-choice copying is a meaningful mechanism for the cultural inheritance of mate preferences in female zebra finches.

Description: Shelters are a key component of animal population ecology, as they provide protection from predators and promote visual isolation among competitors. From a behavioral perspective, how shelter availability affects the way individuals allocate their activity in space has been extensively documented. However, how shelters affect the distribution of activity in time (i.e., diel activity) has been less studied in natural conditions. Here, we report results from a field study that used stream enclosures with either high or low shelter availability and stream-dwelling juvenile Arctic charr as a model species. We collected repeated measurements of individual activity 8 times a day (every 3h) for six 24-h periods during a span of 9 days. In shelter-limited enclosures, fish were more active, became diurnal, and were active over a wider span of time each day, compared with fish with access to abundant shelters. In addition, fish were more aggregated and attacked prey over shorter distances and at lower rate when shelters were limited. Body mass did not affect individual activity rates, but smaller individuals extended their activity over longer periods, possibly as a result of interference competition, and were more isolated. Growth rates were similar across treatments and were positively correlated with individual activity rates and the average distance to the nearest competitor. However, additional nonmeasured effects on fitness may occur, such as increased predation risk associated with daytime feeding and extended activity in shelter-limited conditions.

Description: Animals rely on their acoustic environments to gain information regarding predator threats and social opportunities. However, because individuals have limited attention, focusing on a particular aspect of their acoustic environment may affect their ability to allocate attention elsewhere. Some previous studies support the distracted prey hypothesis, which suggests that animals may be distracted by any stimuli, inhibiting their ability to detect approaching predators. In this study, we further tested the distracted prey hypothesis by employing playback experiments to simultaneously examine the relative effects of 3 types of noises—anthropogenic sounds, conspecific nonalarm sounds, and heterospecific nonalarm sounds—as distractors for common mynas ( Acridotheres tristis ). We used 3 different stimuli: motorcycle noise, social common myna calls, and social red-vented bulbul ( Pycnonotus cafer ) calls. We first examined myna response to each stimulus by measuring time allocation to various behaviors immediately before and during broadcasting the 3 playbacks. We then studied how these stimuli affected their antipredator behavior by measuring the distance at which they fled from an approaching predator (flight initiation distance). We found that mynas responded to all 3 stimuli by delaying their return to relaxed behavior following the playbacks compared with a silent treatment. In contrast to the distracted prey hypothesis, we found that mynas fled at greater distances when hearing red-vented bulbul social vocalizations than during our silent treatment. This suggests that rather than distracting, some social vocalizations may enhance prey vigilance and lead to earlier flight.

Description: Coevolved species should avoid competition through resource partitioning, but human-induced alteration of plant/animal communities may facilitate the onset of competitive interactions. In herbivores, access to high-quality forage in the warm months, that is, during nursing and weaning, influences growth and survival of offspring. In turn, resource exploitation by a reintroduced, superior competitor should affect offspring survival of the inferior one, by decreasing foraging efficiency and diet quality of mothers and young. We assessed the negative effects of reintroduced red deer Cervus elaphus on grassland, on foraging behavior of female Apennine chamois Rupicapra pyrenaica ornata (July–October 2012–2013) and on winter survival of chamois kids, across 3 study sites with different deer densities (great/intermediate/extremely low). The size of bare soil patches was positively associated with deer density and, in areas with deer, it increased throughout July–October. The volume of nutritious plants (i.e., legumes) in the diet of female chamois was lower and decreased faster between summer and autumn, in areas with deer than in that with an extremely low deer density. Feeding intensity (bite rate) of female chamois was significantly lower and their food searching (step rate) was greater in areas with deer. Chamois kids showed a significantly greater winter mortality, with a lower proportion of younger individuals, in areas with deer than in that with an extremely low deer density. In human-altered ecosystems, unpredictable consequences can follow interspecific interactions within restored animal communities. In turn, patterns of ecological relationships among ecosystem components may be modified, with an increase of the potential for competitive interactions.

Description: Personality and behavioral syndromes are of significant interest to a wide range of biological disciplines. Recent research using network analysis techniques has revealed widespread variation among individuals in sociability, which is a major axis of personality that creates the social microenvironment in which individuals express all other behaviors. We investigated the relationship between sociability and boldness, another fundamental personality axis, using a wild population of eastern grey kangaroos ( Macropus giganteus ) tested in their natural environment. We studied 2 dimensions of sociability (grouping behavior and association patterns). Over 2 years we found significant within-individual consistency and interindividual variation in the foraging group sizes of 171 females. Network analysis comparisons of 103 females between the years, using HWIG (an association index that controls for gregariousness), showed that individuals were also highly consistent in their social network measures. We tested the boldness of 51 of these females 6–21 times each over 18 months, using flight initiation distance tests; individuals were also highly consistent in this measure of personality. Shy females had significantly larger mean foraging group sizes. After controlling for gregariousness and space use, shy females had fewer preferred associates than bolder females. Therefore, boldness can have an important influence on the size and composition of foraging groups and thus social networks, in wild mammals.

Description: Deciduous forests are characterized by the production of seed crops that may vary dramatically among years. In response to these pulsed resources, rodent populations grow rapidly, which may have crucial consequences for entire forest communities, including songbirds. It has been hypothesized that in response to these rodent outbreaks, the wood warbler Phylloscopus sibilatrix may exhibit nomadic behavior to avoid nest predation. We used data from the Polish Common Breeding Bird Survey and search query time series from Google Trends as indices of rodent numbers to investigate whether wood warbler respond to rodent outbreaks at a broad spatial scale. Additionally, we investigated whether population fluctuations of Eurasian Jay Garrulus glandarius , the important predator of wood warbler nests, negatively correlated with wood warbler densities and how rodent outbreaks may have affected the outcome of interactions between those species. Results suggested that in years with low rodent abundance, wood warblers avoided settling in areas with high densities of jays. However, when rodent abundance increased in response to masting, wood warblers switched settling strategy and exhibited nomadic behavior. Moreover, this phenomenon acts at a broad geographical scale, which is a unique feature for European forest-dwelling insectivorous. We proposed the hypothesis that wood warblers perceive different predators as unequal and exhibit a risk sensitive antipredator behavior in their habitat selection process. Such a sophisticated mechanism of avoiding predators would suggest that wood warblers are able to acquire information about predation risk, for example, by assessing rodent abundance and use this information to adjust settlement decisions appropriately.

Description: Predators shape the behavior and distribution of prey organisms, driving their evolution and environmental impact. We studied relationships between interspecific competition and predation risk in Ponto-Caspian invasive gammarid crustaceans: Pontogammarus robustoides and Dikerogammarus villosus . We hypothesized that a stronger competitor D. villosus would displace P. robustoides from a preferred habitat, but the frequency of this displacement would be reduced in the presence of a higher fish predator, the racer goby. We studied gammarid preferences for stone or sand substrata in 24-h pairwise-choice tests in single-species or mixed-species treatments, at 2 densities (12 or 24 individuals per tank), in the presence or absence of a predator. D. villosus displaced P. robustoides from the stone habitat, even at the low density. As P. robustoides tested separately preferred stones at both densities, its displacement resulted from active avoidance of a stronger competitor even when the substratum was not actually a limited resource. The presence of a predator reduced the number of instances of displacement of P. robustoides by D. villosus , allowing the weaker species to stay on its preferred substratum. Nevertheless, the presence of D. villosus still increased fish predation on P. robustoides . The presence of a predator modifies relationships between prey organisms, allowing a weaker competitor to stay in its preferred habitat. Thus, antipredator responses of prey organisms may have cascading effects on the functioning of the community, affecting habitat choice and competition among species.

Description: Drought-related tree die-off episodes have been observed in all vegetated continents. Despite much research effort, however, the multiple interactions between carbon starvation, hydraulic failure and biotic agents in driving tree mortality under field conditions are still not well understood. We analysed the seasonal variability of non-structural carbohydrates (NSCs) in four organs (leaves, branches, trunk and roots), the vulnerability to embolism in roots and branches, native embolism (percentage loss of hydraulic conductivity (PLC)) in branches and the presence of root rot pathogens in defoliated and non-defoliated individuals in a declining Scots pine ( Pinus sylvestris L.) population in the NE Iberian Peninsula in 2012, which included a particularly dry and warm summer. No differences were observed between defoliated and non-defoliated pines in hydraulic parameters, except for a higher vulnerability to embolism at pressures below –2 MPa in roots of defoliated pines. No differences were found between defoliation classes in branch PLC. Total NSC (TNSC, soluble sugars plus starch) values decreased during drought, particularly in leaves. Defoliation reduced TNSC levels across tree organs, especially just before (June) and during (August) drought. Root rot infection by the fungal pathogen Onnia P. Karst spp. was detected but it did not appear to be associated to tree defoliation. However, Onnia infection was associated with reduced leaf-specific hydraulic conductivity and sapwood depth, and thus contributed to hydraulic impairment, especially in defoliated pines. Infection was also associated with virtually depleted root starch reserves during and after drought in defoliated pines. Moreover, defoliated and infected trees tended to show lower basal area increment. Overall, our results show the intertwined nature of physiological mechanisms leading to drought-induced mortality and the inherent difficulty of isolating their contribution under field conditions.

Description: Non-structural carbohydrates (NSCs) are critical to maintain plant metabolism under stressful environmental conditions, but we do not fully understand how NSC allocation and utilization from storage varies with stress. While it has become established that storage allocation is unlikely to be a mere overflow process, very little empirical evidence has been produced to support this view, at least not for trees. Here we present the results of an intensively monitored experimental manipulation of whole-tree carbon (C) balance (young Picea abies (L.) H Karst.) using reduced atmospheric [CO 2 ] and drought to reduce C sources. We measured specific C storage pools (glucose, fructose, sucrose, starch) over 21 weeks and converted concentration measurement into fluxes into and out of the storage pool. Continuous labeling ( 13 C) allowed us to track C allocation to biomass and non-structural C pools. Net C fluxes into the storage pool occurred mainly when the C balance was positive. Storage pools increased during periods of positive C gain and were reduced under negative C gain. 13 C data showed that C was allocated to storage pools independent of the net flux and even under severe C limitation. Allocation to below-ground tissues was strongest in control trees followed by trees experiencing drought followed by those grown under low [CO 2 ]. Our data suggest that NSC storage has, under the conditions of our experimental manipulation (e.g., strong progressive drought, no above-ground growth), a high allocation priority and cannot be considered an overflow process. While these results also suggest active storage allocation, definitive proof of active plant control of storage in woody plants requires studies involving molecular tools.

Description: This study quantified the effect of soil warming on sap flow density ( Q s ) of Pinus cembra L. at the treeline in the Central Tyrolean Alps. To enhance soil temperature we installed a transparent roof construction above the forest floor around six trees. Six other trees served as controls in the absence of any manipulation. Roofing enhanced growing season mean soil temperature by 1.6, 1.3 and 1.0 °C at 5, 10 and 20 cm soil depth, respectively, while soil water availability was not affected. Sap flow density (using Granier-type thermal dissipation probes) and environmental parameters were monitored throughout three growing seasons. During the first year of treatment, no warming effect was detected on Q s . However, soil warming caused Q s to increase significantly by 11 and 19% above levels in control trees during the second and third year, respectively. This effect appeared to result from warming-induced root production, a reduction in viscosity and perhaps an increase also in root hydraulic conductivity. Hardly affected were leaf-level net CO 2 uptake rate and conductance for water vapour, so that water-use efficiency stayed unchanged as confirmed by needle 13 C analysis. We conclude that tree water loss will increase with soil warming, which may alter the water balance within the treeline ecotone of the Central Austrian Alps in a future warming environment.

Description: Process-based models that link seasonally varying environmental signals to morphological features within tree rings are essential tools to predict tree growth response and commercially important wood quality traits under future climate scenarios. This study evaluated model portrayal of radial growth and wood anatomy observations within a mature maritime pine ( Pinus pinaster (L.) Aït.) stand exposed to seasonal droughts. Intra-annual variations in tracheid anatomy and wood density were identified through image analysis and X-ray densitometry on stem cores covering the growth period 1999–2010. A cambial growth model was integrated with modelled plant water status and sugar availability from the soil–plant–atmosphere transfer model MuSICA to generate estimates of cell number, cell volume, cell mass and wood density on a weekly time step. The model successfully predicted inter-annual variations in cell number, ring width and maximum wood density. The model was also able to predict the occurrence of special anatomical features such as intra-annual density fluctuations (IADFs) in growth rings. Since cell wall thickness remained surprisingly constant within and between growth rings, variations in wood density were primarily the result of variations in lumen diameter, both in the model and anatomical data. In the model, changes in plant water status were identified as the main driver of the IADFs through a direct effect on cell volume. The anatomy data also revealed that a trade-off existed between hydraulic safety and hydraulic efficiency. Although a simplified description of cambial physiology is presented, this integrated modelling approach shows potential value for identifying universal patterns of tree-ring growth and anatomical features over a broad climatic gradient.

Description: Selecting plantation species to balance water use and production requires accurate models for predicting how species will tolerate and respond to environmental conditions. Although interspecific variation in water use occurs, species-specific parameters are rarely incorporated into physiologically based models because often the appropriate species parameters are lacking. To determine the physiological control over water use in Eucalyptus , five stands of Eucalyptus species growing in a common garden were measured for sap flux rates and their stomatal response to vapour pressure deficit ( D ) was assessed. Maximal canopy conductance and whole-canopy stomatal sensitivity to D and reduced water availability were lower in species originating from more arid climates of origin than those from humid climates. Species from humid climates showed a larger decline in maximal sap flux density ( J Smax ) with reduced water availability, and a lower D at which stomatal closure occurred than species from more arid climates, implying larger sensitivity to water availability and D in these species. We observed significant ( P  〈 0.05) correlations of species climate of origin with mean vessel diameter ( R 2  = 0.90), stomatal sensitivity to D ( R 2  = 0.83) and the size of the decline in J Smax to restricted water availability ( R 2  = 0.94). Thus aridity of climate of origin appears to have a selective role in constraining water-use response among the five Eucalyptus plantation species. These relationships emphasize that within this congeneric group of species, climate aridity constrains water use. These relationships have implications for species choices for tree plantation success against drought-induced losses and the ability to manage Eucalyptus plantations against projected changes in water availability and evaporation in the future.

Description: Mixtures can be more productive than monocultures and may therefore use more water, which may make them more susceptible to droughts. The species interactions that influence growth, transpiration and water-use efficiency (WUE, tree growth per unit transpiration) within a given mixture vary with intra- and inter-annual climatic variability, stand density and tree size, but these effects remain poorly quantified. These relationships were examined in mixtures and monocultures of Eucalyptus globulus Labill. and Acacia mearnsii de Wildeman. Growth and transpiration were measured between ages 14 and 15 years. All E. globulus trees in mixture that were growing faster than similar sized trees in monocultures had higher WUE, while trees with similar growth rates had similar WUE. By the age of 14 years A. mearnsii trees were beginning to senesce and there were no longer any relationships between tree size and growth or WUE. The relationship between transpiration and tree size did not differ between treatments for either species, so stand-level increases in transpiration simply reflected the larger mean tree size in mixtures. Increasing neighbourhood basal area increased the complementarity effect on E. globulus growth and transpiration. The complementarity effect also varied throughout the year, but this was not related to the climatic seasonality. This study shows that stand-level responses can be the net effect of a much wider range of individual tree-level responses, but at both levels, if growth has not increased for a given species, it appears unlikely that there will be differences in transpiration or WUE for that species. Growth data may provide a useful initial indication of whether mixtures have higher transpiration or WUE, and which species and tree sizes contribute to this effect.