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Preview: Behavioral Ecology - current issue

Behavioral Ecology Current Issue





Published: Thu, 05 Oct 2017 00:00:00 GMT

Last Build Date: Mon, 13 Nov 2017 02:43:36 GMT

 



Sex-specific phenotypes and metabolism-related gene expression in juvenile sticklebacks

2017-10-05

Abstract
To fully understand the evolution of sexual dimorphism, it is necessary to study how genetic and developmental systems function to generate sex-specific phenotype as well as sex-specific selection. Males and females show different patterns of energy storage and mitochondrial metabolism from early stages of life, and this may underlie sex-specific developmental pathway to shape both juvenile and adult phenotype. Here, we examined sex-specific relationships between juvenile morphology and behavior, and transcriptional profiles of 4 candidate genes related to mitochondrial function in the 3-spined stickleback. This study provides, for the first time to our knowledge, evidence for sex differences in melanin pigmentation and antipredator behavior as well as the expression of mitochondria-related genes in juvenile sticklebacks. Males were paler and bolder, and overexpressed genes involved in mitochondrial respiration and antioxidant enzymes compared to females. Relationships between phenotypic traits and gene expression were also sex-specific. In general, females showed stronger positive correlations between body size or pigmentation and the expression of genes involved in mitochondrial biogenesis and activity. In both sexes, more fearful individuals overexpressed those genes. Our results suggest that mitochondrial function may either facilitate or constrain sex-specific responses to selection on dimorphic phenotype, possibly generating intralocus sexual conflict on the transcriptional regulation of mito-nuclear genes during ontogeny. This study highlights that mitochondrial regulation plays an important role in the process of phenotypic differentiation between the 2 sexes from early stages of life before apparent sexual dimorphism appears.



Do personality and innovativeness influence competitive ability? An experimental test in the great tit

2017-09-25

Abstract
Competitive ability is a major determinant of fitness, yet why individuals vary in their ability to compete for resources remains unclear. Rather than simply reflecting inherent differences in the ability of individuals to reach an assumed optimum behavior, empirical evidence suggests that competitive ability may also reflect alternative strategies that arise because of correlations with other behaviors, such as innovativeness and personality. We examined experimentally how 2 behavioral traits—exploration of a novel environment (an index of the reactive-proactive personality axis) and performance in a novel lever pulling task (a measure of innovativeness)—were related to the outcomes of dyadic contests involving wild-caught great tits. Dyads were then allowed to compete freely at a feeder before being exposed to a novel string-pulling task. Although we found no significant relationship between exploration behavior or innovativeness in isolation and competitiveness, individuals that were less competitive were more likely to spontaneously perform the string-pulling behavior during the dyadic trials, the first direct experimental demonstration of competitive exclusion leading to innovation. Our results support the hypothesis that innovations provide a means for less competitive individuals to access resources in line with the “necessity drives innovation hypothesis”, and we discuss the functional significance of innovative behaviors in wild populations.



Cognition, personality, and stress in budgerigars, Melopsittacus undulatus

2017-09-25

Abstract
To study the fitness effects of individual variation in cognitive traits, it is paramount to understand whether traits such as personality and physiological stress influence cognitive performance. We first tested whether budgerigars showed both consistent personalities and cognitive performance across time and tasks. We tested object and food neophobia, and exploratory behavior. We measured cognitive performance in habituation, ability to solve foraging problems, spatial memory, and seed discrimination tasks. Budgerigars showed consistency in their neophobic tendencies and these tendencies were associated with their exploratory behavior. Birds were also consistent in how they performed in most of the cognitive tasks (temporal consistency), but were not consistent in their performance across tasks (context consistency). Neither corticosterone levels (baseline and stress-induced) showed a significant relationship with either cognitive or personality measures. Neophobic and exploratory tendencies determined the willingness of birds to engage only in the seed discrimination task. Such tendencies also had a significant effect on problem-solving ability. Our results suggest that consistent individual differences in cognitive performance along with consistent differences in personality could determine response to environmental change and therefore have important fitness consequences.



Selfish partners: resource partitioning in male coalitions of Asiatic lions

2017-09-25

Abstract
Behavioral plasticity within species is adaptive which directs survival traits to take multiple pathways under varying conditions. Male–male cooperation is an evolutionary strategy often exhibiting an array of alternatives between and within species. African male lions coalesce to safeguard territories and mate acquisition. Unique to these coalitions is lack of strict hierarchies between partners, who have similar resource securities possibly because of many mating opportunities within large female groups. Skewed mating and feeding rights have only been documented in large coalitions where males were related. However, smaller modal prey coupled with less simultaneous mating opportunities for male Asiatic lions in Gir forests, India would likely result in a different coalition structure. Observations on mating events (n = 127) and feeding incidents (n = 44) were made on 11 male coalitions and 9 female prides in Gir, to assess resource distribution within and among different sized male coalitions. Information from 39 males was used to estimate annual tenure-holding probabilities. Single males had smaller tenures and appropriated fewer matings than coalition males. Pronounced dominance hierarchies were observed within coalitions, with one partner getting more than 70% of all matings and 47% more food. Competition between coalition partners at kills increased with decline in prey size, increase in coalition size and the appetite states of the males. However, immediate subordinates in coalitions had higher reproductive fitness than single males. Declining benefits to partners with increasing coalition size, with individuals below the immediate subordinates having fitness comparable to single males, suggest to an optimal coalition size of 2 lions. Lions under different competitive selection in Gir show behavioral plasticity to form hierarchical coalitions, wherein partners utilize resources asymmetrically, yet coalesce for personal gains.



Change in sex pheromone expression by nutritional shift in male cockroaches

2017-09-12

Abstract
Environmental conditions during sexual maturation impact sexual signal expression, but little is known about how individual histories of changing environmental conditions affect the intensity of male sexual advertisement. We investigated the effects of shifting dietary nutrient composition (protein vs. carbohydrates) in male Nauphoeta cinerea cockroaches on consumption, final lipid reserves, and sex pheromone levels subsequent to completing sexual maturation on a specific diet, at high and low concentration of dietary nutrients. Consumption, lipid reserves, and sex pheromone levels were highly affected by dietary nutrient composition with higher values on carbohydrate-biased diet, and males had significantly higher and lower levels of consumption, lipid reserves, and sex pheromones when shifted to a carbohydrate-biased and a protein-biased diet, respectively, compared with males maintained on either initial diet throughout the experiment. Males shifted to a carbohydrate-biased diet at high nutrient concentration fully recouped their sex pheromone levels, attaining levels that were not significantly lower than those in males maintained on carbohydrate-biased diet at high nutrient concentration throughout the experiment. Our study shows that male sexual display in N. cinerea is plastic and highly affected by present as well as previous dietary conditions. Signaling of adaptive quality through male sex pheromones can therefore vary dynamically within the early adult life of a male in response to the nutritional composition of food that is available to ingest. This contrasts morphological sexual traits in arthropods that are affected during development and are fixed at adulthood.



Is male rhesus macaque facial coloration under intrasexual selection?

2017-09-11

Abstract
Exaggerated male traits can evolve under intra- or intersexual selection, but it remains less clear how often both mechanisms act together on trait evolution. While the males of many anthropoid primate species exhibit colorful signals that appear to be badges of status under intrasexual selection, the red facial coloration of male rhesus macaques (Macaca mulatta) appears to have evolved primarily under intersexual selection and female mate choice. Nonetheless, experiments show that red color is salient to males, raising the question of whether the signal may also be under intrasexual selection. Here, we examine whether males express this signal more strongly in competitive contexts. Facial images were collected on all 15 adult males of a free-ranging social group during the peak of the mating season, and coloration was quantified using visual models. Results show that males more similar in facial redness were more likely to interact aggressively than more dissimilar ones, suggesting that color may be involved in the assessment of rivals. Furthermore, males exhibited darker coloration on days they were observed copulating, and dominance rank predicted facial redness only on copulating days, suggesting that coloration may also advertise motivation to defend a mate. Male rhesus macaque facial coloration may thus mediate agonistic interactions with rivals during competition over reproductive opportunities, such that it is under both inter- and intrasexual selection. However, color differences were small, raising perceptibility questions. It remains possible that color variation reflects differences in male condition, which in turn alter investment towards male–male competition and mating effort.



A case for considering individual variation in diel activity patterns

2017-09-11

Abstract
There is a growing recognition of the role of individual variation in patterns emerging at higher levels of biological organization. Despite the importance of the temporal configuration of ecological processes and patterns, intraspecific individual variation in diel activity patterns is almost never accounted for in behavioral studies at the population level. We used individual-based monitoring data from 98 GPS-collared brown bears in Scandinavia to estimate diel activity patterns before the fall hunting season. We extracted 7 activity measures related to timing and regularity of activity from individual activity profiles. We then used multivariate analysis to test for the existence of distinct activity tactics and their environmental determinants, followed by generalized linear regression to estimate the extent of within-individual repeatability of activity tactics. We detected 4 distinct activity tactics, with a high degree of individual fidelity to a given tactic. Demographic factors, availability of key foraging habitat, and human disturbance were important determinants of activity tactics. Younger individuals and those with higher bear and road densities within their home range were more nocturnal and more likely to rest during the day. Good foraging habitat and increasing age led to more diurnal activity patterns and nocturnal resting periods. We did not find evidence of diel activity tactics influencing survival during the subsequent hunting season. We conclude that individual variation in activity deserves greater attention than it currently receives, as it may help account for individual heterogeneity in fitness and could facilitate within-population niche partitioning that can have population- or community-level consequences.



Social information use and social learning in non-grouping fishes

2017-09-11

Abstract
Although it is natural to expect that group-living animals will utilize social learning, the expectation for non-grouping species is less clear. Only a few studies have explored the relationship between sociality and social learning. Here we presented 4 non-grouping fish species, fifteenspine sticklebacks (Spinachia spinachia), bullhead sculpins (Cottus gobio), stone loach (Barbatula barbatula) and juvenile European flounders (Platichthys flesus) with social information provided by groups of a shoal-forming heterospecific, the threespine stickleback (Gasterosteus aculeatus). Using a binary choice procedure we allowed individual test subjects to select between simulated prey patches. Although the test subjects could not sample the patches directly they were able to use information generated by the heterospecific demonstrators to select the “richer” of the 2 patches. For comparison we also recorded social information use in 2 shoaling species, threespine, and ninespine sticklebacks (Pungitius pungitius). We saw evidence of social information use and social learning in all 6 species, with no differences seen between social and non-grouping species. We argue that social learning is not likely to be restricted to group-living species, since many solitary species too are regularly exposed to social stimuli from both conspecifics and heterospecifics, and can benefit from using social information. We suggest that researchers have much to learn about the sensory, perceptive, and cognitive mechanisms underlying social learning, and the extent to which these vary (if at all) between grouping and non-grouping species.



Predation risk drives the expression of mobbing across bird species

2017-09-09

Abstract
Many species approach predators to harass and drive them away, even though mobbing a predator can be deadly. However, not all species display this behavior, and those that do can exhibit different behaviors while mobbing different predators. Here we experimentally assessed the role of social and ecological traits on the expression of mobbing behavior in a bird community in SE Brazil (n = 157 species). We exposed birds to models of two morphologically similar diurnal owls that pose different risks, and assessed which species engaged in mobbing. Among those that mobbed, we evaluated how they adjusted their mobbing behavior depending on the predator type. We tested the hypothesis that only species that are at risk and can afford to mob engage in this antipredator behavior. We found that species that engaged in mobbing are in the body mass range of potential prey, forage in the understory or in the canopy, and form flocks. A species’ social system did not influence its mobbing behavior. Furthermore, species that engaged in mobbing formed larger mobbing assemblages when facing a high-risk predator, but mobbed more intensely when facing a low-risk predator. Our findings support our predictions, namely that the expression of mobbing is limited by its costs.



No effect of elevated carbon dioxide on reproductive behaviors in the three-spined stickleback

2017-08-30

Abstract
Ocean acidification, the reduction in ocean pH resulting from anthropogenic emissions of carbon dioxide (CO2), has been predicted to alter the behavior of fishes. During experimental exposure to CO2 concentrations projected for the year 2100 (~1000 µatm), fish have been reported to display disturbances in activity, learning, behavioral lateralization, and even attraction to predator cues. Reproductive behaviors have received far less attention, despite an intensive research effort on ocean acidification and its ecological importance. Here, we investigate whether elevated levels of CO2 affect reproduction in breeding pairs of the three-spined stickleback, Gasterosteus aculeatus, a model species in behavioral, evolutionary ecology, and environmental toxicology. We found that males under both present day levels (400 µatm) and future levels (1000 µatm) of CO2 developed normal sexual ornaments, pursued normal nest building activities, exhibited similar levels of courtship behaviors and displacement fanning, and had the same mating probability. Moreover, fanning behavior during the paternal care period followed what is expected for the species for males from both treatments, and there was no effect of treatment on the numbers of offspring produced. This study is the first to investigate the effect of elevated CO2 on the complete breeding cycle in detail, studying an array of highly fitness-relevant traits. Our study showing surprising resilience of fish reproduction is an important contribution in order to realistically predict the impacts of future ocean acidification.



Host nest site choice depends on risk of cuckoo parasitism in magpie hosts

2017-08-30

Abstract
Avian brood parasites impose large fitness costs on their hosts and, thus, brood parasitism has selected for an array of host defensive mechanisms to avoid them. So far most studies have focused on antiparasite defenses operating at the egg and chick stages and neglected defenses that may work prior to parasite egg deposition. Here, we experimentally explore the possibility that hosts, as part of a front-line defense, might minimize parasitism costs through informed nest site choice based on perceived risk of cuckoo parasitism. We conducted a large-scale manipulation of visual and auditory cues potentially informing on the risk of great spotted cuckoo Clamator glandarius parasitism during the nest site choice period of the magpie Pica pica host to investigate its effect on host’s nest settlement and individual year to year site fidelity. Early breeding magpies preferentially placed their nests in safe areas (i.e., in sites of low perceived risk of parasitism), and, this effect diluted with time elapsed since risk of parasitism was manipulated. Site fidelity of individual magpies decreased with risk of cuckoo parasitism, for those that were not parasitized in the previous year. Our results constitute the first strong evidence showing that hosts can minimize the costs of cuckoo parasitism through informed nest-site choice, calling for future consideration of defenses potentially operating prior to parasite egg deposition to achieve a better understanding of cuckoo-host coevolution.



Antipredator escape distances of common and threatened birds

2017-08-30

Abstract
Most animals keep a safe distance from humans and other potential predators, forcing animals to trade foraging and other critical behaviors against flight with potentially negative consequences for population trends if energy budgets are consistently negative. Animals can adapt to human proximity through habituation or microevolution, and island, domesticated and urbanized animals have all reduced their threshold of fear compared to controls. We tested whether a common cause of threat status is susceptibility to human proximity. We did so by estimating whether 48 pairs of closely related bird species differing in their threat status consistently had longer flight initiation distances (FID, the distance at which the individual takes flight from an approaching human) in the more threatened species. We estimated threat status by relying on existing categorization of threat status by the European Union. Threatened species had consistently longer FID than their closely related species in both parametric and nonparametric tests. Common species were indeed more often recorded during field work while recording FID than were threatened species, the difference being almost 2-fold. This result provides a link between antipredator behavior, human proximity, threat status, and abundance.



Aposematism in the burying beetle? Dual function of anal fluid in parental care and chemical defense

2017-08-22

Abstract
Burying beetles (Nicrophorus vespilloides) bear distinctive and variable orange-black patterning on their elytra and produce an anal exudate from their abdomen when threatened. During breeding, the anal exudates contribute to the antimicrobial defense of the breeding resource. We investigated whether the anal exudates also provide a responsive chemical defense, which is advertised to potential avian predators by the beetle’s orange and black elytral markings. We found that that the orange-black elytral markings of the burying beetle are highly conspicuous for avian predators against range of backgrounds, by using computer simulations. Using bioassays with wood ants, we also showed that the burying beetle’s anal exudates are aversive to potential predators. From these results, and other evidence in the literature, we conclude that the evidence for aposematism in the burying beetle is as strong as the evidence for many other classically aposematic species, such as defended Hymenopterans, ladybirds, or poisonous frogs. Nevertheless, we also report unexpectedly high levels of individual variation in coloration and chemical defenses, as well as sex differences. We suggest that this variation might be partly due to conflicting selection pressures, particularly on the dual function of the exudates, and partly to nutritional differences in the developmental environment. The ecology of the burying beetles (Nicrophorus spp.) differs markedly from better-studied aposematic insects. This genus thus offers new potential for understanding the evolution of aposematism in general.



Control of signaling alignment during the dynamic courtship display of a jumping spider

2017-08-22

Abstract
During communication, alignment between signals and sensors can be critical. Signals are often best perceived from specific angles, and sensory systems can also exhibit strong directional biases. However, we know little about how animals establish and maintain such signaling alignment during communication. To investigate this, we characterized the spatial dynamics of visual courtship signaling in the jumping spider Habronattus pyrrithrix. The male performs forward-facing displays involving complex color and movement patterns, with distinct long- and short-range phases. The female views displays with 2 distinct eye types and can only perceive colors and fine patterns of male displays when they are presented in her frontal field of view. Whether and how courtship interactions produce such alignment between male display and female field of view is unknown. We recorded relative positions and orientations of both actors throughout courtship and established the role of each sex in maintaining signaling alignment. Males always oriented their displays toward the female. However, when females were free to move, male displays were consistently aligned with female principal eyes only during short-range courtship. When female position was fixed, signaling alignment consistently occurred during both phases, suggesting that female movement reduces communication efficacy. When female models were experimentally rotated to face away during courtship, males rarely repositioned themselves to re-align their display. However, males were more likely to present certain display elements after females turned to face them. Thus, although signaling alignment is a function of both sexes, males appear to rely on female behavior for effective communication.



Fighting over food unites the birds of North America in a continental dominance hierarchy

2017-08-22

Abstract
Members of different species often engage in aggressive contests over resources. This series of aggressive contests between species may result in an interspecific dominance hierarchy. Such hierarchies are of interest because they could be used to address a variety of research questions, for example, do similarly ranked species tend to avoid each other in time or space, and what will happen when such species come into contact as climates change? Here, we propose a method for creating a continental-scale hierarchy, and we make initial analyses based on this hierarchy. Leveraging the existing network of citizen scientists from Project FeederWatch, we collected the data with which to create a continent-spanning interspecific dominance hierarchy that included species that do not currently have overlapping geographic distributions. We quantified the extent of intransitivities (rock-paper-scissors relationships) in the hierarchy, as intransitivities can promote local species’ coexistence. Overall, the hierarchy was nearly linear, and largely predicted by body mass, although there were clade-specific deviations from the average mass–dominance relationship. Warblers and orioles, for instance, were more dominant than expected based on their body mass, while buntings, grosbeaks, and doves were less dominant than expected. Intransitive relationships were rare. Few interactions were reported between close relatives and ecological competitors like Mountain and Black-capped Chickadees, as such species often have only marginally overlapping geographic distributions, restricting opportunity for observation. Yet, these species’ ranks—emergent properties of the network—were often in agreement with targeted studies of dominance relationships between them.



Fat and happy in the city: Eastern chipmunks in urban environments

2017-08-22

Abstract
Cities are rapidly expanding, and wildlife may experience different selection pressures in urban environments when compared to natural habitats. Phenotypic differences between urban and natural populations may occur because of the altered urban environment. Behavior, the activity of the hypothalamic-pituitary-adrenal (HPA) axis and body condition can be expected to differ between urban and natural habitats. We used the eastern chipmunk (Tamias striatus) to test for differences in behavior assayed from an open field test, hair and fecal cortisol concentrations, and body condition (size-corrected body mass), predicting that urban chipmunks would exhibit more exploratory behavior, higher cortisol concentrations, and higher body condition, than their counterparts from natural habitats. We sampled eastern chipmunks in 2 urban areas paired with natural habitats and subjected adult chipmunks to an open field test, collected hair and fecal samples for the determination of cortisol concentrations, and measured body size and body mass to estimate body condition. Eastern chipmunks in urban habitats had significantly different behavior, tending toward reduced locomotion and grooming, and greater latency, than their counterparts from natural habitats. Urban chipmunks also had lower fecal cortisol concentrations than those from natural habitats, and female chipmunks were in better body condition when captured in urban habitats. These results suggest that urban habitats may be relatively benign for urban chipmunks, perhaps because of reduced need for exploration and the availability of anthropogenic food subsidies associated with urban environments.



Social plasticity in choosiness in green tree frogs, Hyla cinerea

2017-08-22

Abstract
Mate choice is an important driver of the evolution of sexual traits and can promote divergence and speciation. Understanding the underlying variation in mate choice decisions is crucial to understand variation in the strength and direction of sexual selection. We explored whether variation in the social environment influences mate choice decisions and focus on the aspect of mate choice termed choosiness (i.e. the effort invested in mate assessment and acquisition). Using call playbacks, we manipulated the social environment female green tree frogs would experience as they entered a chorus, and then we conducted two-choice playback trials to assess whether females exhibited social plasticity in choosiness. We explored social plasticity at 2 levels: in one experiment, we manipulated the presence or absence of preferred (attractive) and less preferred (unattractive) conspecific males (i.e. intraspecific context), and in the other experiment, we manipulated the presence or absence of preferred (conspecific) and less preferred closely related heterospecific males (i.e. interspecific context). We found that in the intraspecific context, the presence of attractive males increased choosiness, while absence of attractive males reduced choosiness. In the interspecific context, choosiness remained stable in most treatments, but was lowered when females experienced a mixture of conspecific and heterospecific calls. We discuss the effect of social plasticity in choosiness on mate choice decisions and highlight its evolutionary consequences.



Melanin in a changing world: brown trout coloration reflects alternative reproductive strategies in variable environments

2017-08-12

Abstract
Melanins are the most widespread pigments in animals but their adaptive significance remains elusive. Recent studies suggest that intraspecific variation in melanin-based coloration reflects individual genetic-based alternative strategies to cope with environment variability, which could be crucial for their responses to climate changes. However, empirical evidence is still scarce. In this study, we tested how skin coloration in natural populations of brown trout Salmo trutta fario would reflect alternative reproductive strategies in different environments. We experimentally manipulated the flow regime (constant vs. variable) in artificial streams and compared the reproductive investment (body mass and plasma triglyceride variations), innate immunity (variations in plasma peroxidase and lysozyme activity) and reproductive success (number of mates and offspring) of differently colored brown trout over 2 reproductive seasons. Results show that darker males had a higher reproductive investment, but similar immune variations during reproduction compared to paler males. In addition, this reproductive investment was higher in variable environments. However, this did not translate into a higher reproductive success in variable environments, as darker males had a similar number of mates and offspring compared to their paler counterparts under a variable water flow. Since climate change will likely lead to an increased flow variability in the next decades, this suggests that darker brown trout could incur a higher energetic cost of reproduction and could be more impacted by climate changes than their paler counterparts. This highlights the need to take into account intraspecific variability to better forecast the response of natural populations to climate changes.



Provisioning tactics of great tits ( Parus major ) in response to long-term brood size manipulations differ across years

2017-06-15

Abstract
Parents provisioning their offspring can adopt different tactics to meet increases in offspring demand. In this study, we experimentally manipulated brood demand in free living great tits (Parus major) via brood size manipulations and compared the tactics adopted by parents in 2 successive years (2010 and 2011) with very different ecological conditions. In 2011, temperatures were warmer, there were fewer days with precipitation, and caterpillars (the preferred prey of great tits) made up a significantly larger proportion of the diet. In this “good” year, parents responded to experimental increases in brood demand by decreasing mean inter-visit intervals (IVIs) and reducing prey selectivity, which produced equal average long-term delivery of food to nestlings across the brood size treatments. In 2010, there was no evidence for effects of brood size manipulations on mean IVIs or prey selectivity. Consequently, nestlings from enlarged broods experienced significantly lower long-term average delivery rates compared with nestlings from reduced broods. In this “bad” year, parents also exhibited changes in the variance in inter-visit intervals (IVIs) as a function of treatment that were consistent with variance-sensitive foraging theory: variance in IVIs tended to be lowest for reduced broods and highest for enlarged broods. Importantly, this pattern differed significantly from that observed in the “good” year. We therefore found some support for variance-sensitive provisioning in the year with more challenging ecological conditions. Taken together, our results show that variation in brood demand can result in markedly different parental foraging tactics depending on ecological conditions.