Retention of acquired predator recognition among shy versus bold juvenile rainbow trout

Age-Related Changes in Survival Behaviour in Parasite-Free Hatchery-Reared Rainbow Trout (Oncorhynchus mykiss)

Millions of hatchery-reared Rainbow trout are currently released in Australian waters to support recreational fisheries objectives, yet many of these fish die soon after release. In addition, little is known whether these fish harbour parasites that can potentially threaten freshwater ecosystems and human health. Here, we tested the behaviour of hatchery-reared trout using six tank-based tests at six different ages to evaluate their chances of survival and then dissected fish to investigate parasite prevalence. At 7 weeks of age fish readily emerged from a hide and showed the greatest number of startle responses to predators. Behaviour around 25-29 weeks of age was relatively "shy", staying in shelter and avoiding open water. At around 37-41 weeks of age though, behaviour changed, with fish emerging from a hide more readily and exploring the environment. Interestingly, at 58 weeks of age fish were slower to initiate exploration, possibly indicating a return to "shyer" behaviour. All fish underwent thorough parasite examination, revealing no infections. We conclude that knowledge of the behaviour of hatchery-reared fish at different ages is useful for decisions around the timing of release that balance the needs of recreational fishers whilst managing the impact on freshwater ecosystem.

Early-life intraguild predation risk produces adaptive personalities in predatory mites

Animal personalities are defined by within-individual consistency, and consistent among-individual variation, in behavior across time and/or contexts. Here we hypothesized that brief early-life experience of intraguild predation (IGP) risk has enduring phenotypic effects on personality expression in boldness and aggressiveness in later life. We tested our hypothesis in predatory mites Phytoseiulus persimilis, which are IG predators with ontogenetic role reversals, i.e., they are potential IG prey during early life but IG predators as adults. Adult P. persimilis females, which had experienced IGP risk early in life or not, were subjected to three tests each for boldness and aggressiveness. IGP-experienced individuals were on average bolder and more aggressive. Boldness was moderately repeatable, aggressiveness was weakly repeatable. Strikingly, early-life IGP experience shifted the within-group personality composition toward consistently bold and aggressive personalities. Phenotypic adjustment of personality expression was adaptive, as indicated by the positive correlation between personality scores and egg production.

Environmentally relevant concentrations of triclocarban affect behaviour, learning, and brain gene expression in fish

Many chemicals spilled in aquatic ecosystems can interfere with cognitive abilities and brain functions that control fitness-related behaviour. Hence, their harmful potential may be substantially underestimated. Triclocarban (TCC), one of the most common aquatic contaminants, is known to disrupt hormonal activity, but the consequences of this action on behaviour and its underlying cognitive mechanisms are unclear. We tried to fill this knowledge gap by analysing behaviour, cognitive abilities, and brain gene expression in zebrafish larvae exposed to TCC sublethal concentrations. TCC exposure substantially decreased exploratory behaviour and response to stimulation, while it increased sociability. Additionally, TCC reduced the cognitive performance of zebrafish in a habituation learning task. In the brain of TCC-exposed zebrafish, we found upregulation of c-fos, a gene involved in neural activity, and downregulation of bdnf, a gene that influences behavioural and cognitive traits such as activity, learning, and memory. Overall, our experiments highlight consistent effects of non-lethal TCC concentrations on behaviour, cognitive abilities, and brain functioning in a teleost fish, suggesting critical fitness consequences of these compounds in aquatic ecosystems as well as the potential to affect human health.

Multiple benefits of juvenile play: A ground squirrel's perspective

Adaptive functions of play can vary across species, and also within species, reflecting behavioral ecology and evolutionary history. We evaluated juvenile play in Belding's ground squirrels (Urocitellus beldingi), a species for which field studies have assessed play behavior in the context of the squirrels' ecology and life history. Social play behavior in U. beldingi appears not to have the range of adaptive benefits related to social behavior apparent in species with more complex social organization. Play in juvenile U. beldingi improves general motor skill, which may translate to more proficient performance of behaviors during and beyond the juvenile period. Social play in juvenile squirrels is associated with refinement of temperament and behavior, promoting behavioral shifts toward less docile responses as well as more cautious behavior. Social play also influences behavior of juvenile squirrels in novel situations, fostering greater exploration and adaptability of responses. Important life events in U. beldingi such as the timing of natal dispersal and defense of maternal territories can be influenced by juvenile play.

Can we use antipredator behavior theory to predict wildlife responses to high-speed vehicles?

Animals seem to rely on antipredator behavior to avoid vehicle collisions. There is an extensive body of antipredator behavior theory that have been used to predict the distance/time animals should escape from predators. These models have also been used to guide empirical research on escape behavior from vehicles. However, little is known as to whether antipredator behavior models are appropriate to apply to an approaching high-speed vehicle scenario. We addressed this gap by (a) providing an overview of the main hypotheses and predictions of different antipredator behavior models via a literature review, (b) exploring whether these models can generate quantitative predictions on escape distance when parameterized with empirical data from the literature, and (c) evaluating their sensitivity to vehicle approach speed using a simulation approach wherein we assessed model performance based on changes in effect size with variations in the slope of the flight initiation distance (FID) vs. approach speed relationship. The slope of the FID vs. approach speed relationship was then related back to three different behavioral rules animals may rely on to avoid approaching threats: the spatial, temporal, or delayed margin of safety. We used literature on birds for goals (b) and (c). Our review considered the following eight models: the economic escape model, Blumstein's economic escape model, the optimal escape model, the perceptual limit hypothesis, the visual cue model, the flush early and avoid the rush (FEAR) hypothesis, the looming stimulus hypothesis, and the Bayesian model of escape behavior. We were able to generate quantitative predictions about escape distance with the last five models. However, we were only able to assess sensitivity to vehicle approach speed for the last three models. The FEAR hypothesis is most sensitive to high-speed vehicles when the species follows the spatial (FID remains constant as speed increases) and the temporal margin of safety (FID increases with an increase in speed) rules of escape. The looming stimulus effect hypothesis reached small to intermediate levels of sensitivity to high-speed vehicles when a species follows the delayed margin of safety (FID decreases with an increase in speed). The Bayesian optimal escape model reached intermediate levels of sensitivity to approach speed across all escape rules (spatial, temporal, delayed margins of safety) but only for larger (> 1 kg) species, but was not sensitive to speed for smaller species. Overall, no single antipredator behavior model could characterize all different types of escape responses relative to vehicle approach speed but some models showed some levels of sensitivity for certain rules of escape behavior. We derive some applied applications of our findings by suggesting the estimation of critical vehicle approach speeds for managing populations that are especially susceptible to road mortality. Overall, we recommend that new escape behavior models specifically tailored to high-speeds vehicles should be developed to better predict quantitatively the responses of animals to an increase in the frequency of cars, airplanes, drones, etc. they will face in the next decade.

Translational relevance of forward genetic screens in animal models for the study of psychiatric disease

Psychiatric disorders represent a significant burden in our societies. Despite the convincing evidence pointing at gene and gene-environment interaction contributions, the role of genetics in the etiology of psychiatric disease is still poorly understood. Forward genetic screens in animal models have helped elucidate causal links. Here we discuss the application of mutagenesis-based forward genetic approaches in common animal model species: two invertebrates, nematodes (Caenorhabditis elegans) and fruit flies (Drosophila sp.); and two vertebrates, zebrafish (Danio rerio) and mice (Mus musculus), in relation to psychiatric disease. We also discuss the use of large scale genomic studies in human populations. Despite the advances using data from human populations, animal models coupled with next-generation sequencing strategies are still needed. Although with its own limitations, zebrafish possess characteristics that make them especially well-suited to forward genetic studies exploring the etiology of psychiatric disorders.

Does the female seahorse still prefer her mating partner after a period of separation?

For species showing sexual monogamy, once one male and one female form a mating pair bond, they will be faithful to each other in subsequent breeding events. However, if their pair bond is broken for some reason, do they continue to prefer their partner when they come together again for mating? In other words, can the broken pair bond of sexually monogamous species be repaired? This is an interesting question but not yet well answered. To address this question, in the present study we used the lined seahorse (Hippocampus erectus), a typical sexually monogamous species, to study the partner preference of a female individual who experienced a complete separation followed by a reunion with her partner. Our main findings are as follows: (i) The female seahorse no longer prefers her partner after a separation, whether it is a former partner or a recent partner. No preference for partner-males may indicate that the broken pair bond cannot be repaired. (ii) The female seahorse maintains sexual fidelity to her partner in the absence of separation. However, once the health of her partner decreases, the female will switch mate, and her courtship with the new partner can take place during the pregnancy of her original partner. The first finding may provide insight into whether monogamous species still have an opportunity to reselect a new partner in the future to correct their poor choice once they have mated with a low-quality partner. The answer is that they can still gain an opportunity as long as the pair bonds with their current partners are broken. The second finding may reveal the conditions and timing at which a female seahorse switches her mate. These findings help us better understand the mating system of the seahorse H. erectus.

Npas4a expression in the teleost forebrain is associated with stress coping style differences in fear learning

Learning to anticipate potentially dangerous contexts is an adaptive behavioral response to coping with stressors. An animal's stress coping style (e.g. proactive-reactive axis) is known to influence how it encodes salient events. However, the neural and molecular mechanisms underlying these stress coping style differences in learning are unknown. Further, while a number of neuroplasticity-related genes have been associated with alternative stress coping styles, it is unclear if these genes may bias the development of conditioned behavioral responses to stressful stimuli, and if so, which brain regions are involved. Here, we trained adult zebrafish to associate a naturally aversive olfactory cue with a given context. Next, we investigated if expression of two neural plasticity and neurotransmission-related genes (npas4a and gabbr1a) were associated with the contextual fear conditioning differences between proactive and reactive stress coping styles. Reactive zebrafish developed a stronger conditioned fear response and showed significantly higher npas4a expression in the medial and lateral zones of the dorsal telencephalon (Dm, Dl), and the supracommissural nucleus of the ventral telencephalon (Vs). Our findings suggest that the expression of activity-dependent genes like npas4a may be differentially expressed across several interconnected forebrain regions in response to fearful stimuli and promote biases in fear learning among different stress coping styles.

Intraspecific variation in inhibitory motor control in guppies, Poecilia reticulata

Inhibitory control (IC) is the ability to overcome impulsive or prepotent but ineffective responses in favour of more appropriate behaviours. The ability to inhibit internal predispositions or external temptations is vital in coping with a complex and variable world. Traditionally viewed as cognitively demanding and a main component of executive functioning and self-control, IC was historically examined in only a few species of birds and mammals but recently a number of studies has shown that a much wider range of taxa rely on IC. Furthermore, there is growing evidence that inhibitory abilities may vary within species at the population and individual levels owing to genetic and environmental factors. Here we use a detour-reaching task, a standard paradigm to measure motor inhibition in nonhuman animals, to quantify patterns of interindividual variation in IC in wild-descendant female guppies, Poecilia reticulata. We found that female guppies displayed inhibitory performances that were, on average, half as successful as the performances reported previously for other strains of guppies tested in similar experimental conditions. Moreover, we showed consistent individual variation in the ability to inhibit inappropriate behaviours. Our results contribute to the understanding of the evolution of fish cognition and suggest that IC may show considerable variation among populations within a species. Such variation in IC abilities might contribute to individual differences in other cognitive functions such as spatial learning, quantity discrimination or reversal learning.

An escape theory model for directionally moving prey and an experimental test in juvenile Chinook salmon

Prey evaluate risk and make decisions based on the balance between the costs of predation and those of engaging in antipredator behaviour. Economic escape theory has been valuable in understanding the responses of stationary prey under predation risk; however, current models are not applicable for directionally moving prey.

Here we present an extension of existing escape theory that predicts how much predation risk is perceived by directionally moving prey. Perceived risk is measured by the extent antipredator behaviour causes a change in travel speed (the distance to a destination divided by the total time to reach that destination). Cryptic or cautious antipredator behaviour slows travel speed, while prey may also speed up to reduce predator–prey overlap. Next, we applied the sensitization hypothesis to our model, which predicts that prey with more predator experience should engage in more antipredator behaviour, which leads to a larger change in travel speed under predation risk. We then compared the qualitative predictions of our model to the results of a behavioural assay with juvenile Chinook salmon Oncorhynchus tshawytscha that varied in their past predator experience.

We timed salmon swimming downstream through a mesh enclosure in the river with and without predator cues present to measure their reaction to a predator. Hatchery salmon had the least predator experience, followed by wild salmon captured upstream (wild‐upstream) and wild‐salmon captured downstream (wild‐downstream).

Both wild salmon groups slowed down in response to predator cues, whereas hatchery salmon did not change travel speed. The magnitude of reaction to predator cues by salmon group followed the gradient of previous predator experience, supporting the sensitization hypothesis.

Moving animals are conspicuous and vulnerable to predators. Here we provide a novel conceptual framework for understanding how directionally moving prey perceive risk and make antipredator decisions. Our study extends the scope of economic escape theory and improves general understanding of non‐lethal effects of predators on moving prey.

Personality traits covary with individual differences in inhibitory abilities in 2 species of fish

In a number of animal species, individuals differ in their ability to solve cognitive tasks. However, the mechanisms underlying this variability remain unclear. It has been proposed that individual differences in cognition may be related to individual differences in behavior (i.e., personality); a hypothesis that has received mixed support. In this study, we investigated whether personality correlates with the cognitive ability that allows inhibiting behavior in 2 teleost fish species, the zebrafish Danio rerio and the guppy Poecilia reticulata. In both species, individuals that were bolder in a standard personality assay, the open-field test, showed greater inhibitory abilities in the tube task, which required them to inhibit foraging behavior toward live prey sealed into a transparent tube. This finding reveals a relationship between boldness and inhibitory abilities in fish and lends support to the hypothesis of a link between personality and cognition. Moreover, this study suggests that species separated by a relatively large phylogenetic distance may show the same link between personality and cognition, when tested on the same tasks.

Hypoxia but not shy-bold phenotype mediates thermal preferences in a threatened freshwater fish, Notropis percobromus

For ectothermic animals, ambient temperature strongly influences developmental growth rate and individual fitness. While many ectotherms live in environments that are spatially hetero-thermal, the coupling between behavioural phenotypes (e.g., shy or bold behaviour) and thermal preferences remains uncertain. Relative to shy counterparts, bolder phenotypes may exert higher preference for ambient temperatures that are closer to their thermal optimum, thereby accelerating development. In addition, ectotherms should select colder temperatures in low oxygen conditions (hypoxia) according to the oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis. Using wild caught carmine shiner (Notropis percobromus), this study examined thermoregulatory behaviour in individuals exhibiting consistent behavioural phenotypes along the shy-bold continuum and between ecologically relevant normal oxygen concentration (normoxic) and hypoxic treatments. Furthermore, the behaviour observed in the laboratory was compared to environmental data from the natal stream. Results demonstrated that individual shy-bold behavioural phenotype was consistent before and after a simulated aerial predator attack, indicating consistency of behaviour across situations. Individual preferred and avoidance temperatures varied substantially, but were unrelated to shy-bold behavioural phenotypes. In contrast, individual preferred and maximum avoidance temperatures were significantly reduced in hypoxia, consistent with the OCLTT hypothesis. These findings might indicate suppressed development rates in hypoxia, not only by the limited oxygen for aerobic metabolism, but also by the preference for colder water in hypoxia. Furthermore, the tolerated thermal ranges were reduced in hypoxia. Using test conditions confirmed by field data, our study demonstrates the strong influence of oxygen availability on thermoregulatory behaviours and preferences in aquatic environments.

Contextual fear learning and memory differ between stress coping styles in zebrafish

Animals frequently overcome stressors and the ability to learn and recall these salient experiences is essential to an individual’s survival. As part of an animal’s stress coping style, behavioral and physiological responses to stressors are often consistent across contexts and time. However, we are only beginning to understand how cognitive traits can be biased by different coping styles. Here we investigate learning and memory differences in zebrafish (Danio rerio) displaying proactive and reactive stress coping styles. We assessed learning rate and memory duration using an associative fear conditioning paradigm that trained zebrafish to associate a context with exposure to a natural olfactory alarm cue. Our results show that both proactive and reactive zebrafish learn and remember this fearful association. However, we note significant interaction effects between stress coping style and cognition. Zebrafish with the reactive stress coping style acquired the fear memory at a significantly faster rate than proactive fish. While both stress coping styles showed equal memory recall one day post-conditioning, reactive zebrafish showed significantly stronger recall of the conditioned context relative to proactive fish four days post-conditioning. Through understanding how stress coping strategies promote biases in processing salient information, we gain insight into mechanisms that can constrain adaptive behavioral responses.

Memory retention capacity using two different training methods, appetitive and aversive learning, in juvenile red sea bream Chrysophrys major

Memory retention based on appetitive and aversive learning was studied in juvenile red sea bream Chrysophrys major. The fish were individually trained via appetitive and aversive learning. In general, they retained appetitive memories for 30 days, but not for 60 days. Conversely, aversive memory endured for 1 day, but not for 3 days or longer. Analyses at the individual level revealed that some fish retained appetitive memories for 60 days, whereas others lost it within 3 days; this suggests considerable variability in memory retention capacity among individual fish. The memory duration for aversive learning was remarkably short, which should be considered when releasing trained fish into the wild for stock enhancement. Furthermore, the high inter-individual variability suggests that evaluating memory retention capacity through group experiments might lead to overestimation of fishes' ability.

Consistent individual differences in associative learning speed are not linked to boldness in female Atlantic mollies

Recent studies on consistent individual differences in behavioural tendencies (animal personality) raised the question of whether individual differences in cognitive abilities can be linked to certain personality types. We tested female Atlantic mollies (Poecilia mexicana) in two different classical conditioning experiments. For the first time, we provide evidence for highly consistent individual differences in associative learning speed in fish. We characterized the same individuals for boldness in two experimental situations (latency to emerge from shelter and freezing time after a simulated predator attack) and found high behavioural repeatability. When we tested for a potential correlation between associative learning speed and boldness, however, there was no evidence for a link between them. Our study design included several steps to avoid typical pitfalls of disadvantaging shy individuals during learning tests. We caution that other experimental studies may have suffered from erroneous interpretations due to a more cautious coping style of shy individuals in the respective setup used to assess learning.

Why and how the early-life environment affects development of coping behaviours

Understanding the ways in which individuals cope with threats, respond to challenges, make use of opportunities and mediate the harmful effects of their surroundings is important for predicting their ability to function in a rapidly changing world. Perhaps one of the most essential drivers of coping behaviour of adults is the environment experienced during their early-life development. Although the study of coping, defined as behaviours displayed in response to environmental challenges, has a long and rich research history in biology, recent literature has repeatedly pointed out that the processes through which coping behaviours develop in individuals are still largely unknown. In this review, we make a move towards integrating ultimate and proximate lines of coping behaviour research. After broadly defining coping behaviours (1), we review why, from an evolutionary perspective, the development of coping has become tightly linked to the early-life environment (2), which relevant developmental processes are most important in creating coping behaviours adjusted to the early-life environment (3), which influences have been shown to impact those developmental processes (4) and what the adaptive significance of intergenerational transmission of coping behaviours is, in the context of behavioural adaptations to a fast changing world (5). Important concepts such as effects of parents, habitat, nutrition, social group and stress are discussed using examples from empirical studies on mammals, fish, birds and other animals. In the discussion, we address important problems that arise when studying the development of coping behaviours and suggest solutions.

Personality and the retention of neophobic predator avoidance in wild caught Trinidadian guppies

Neophobic predator avoidance allows prey to reduce the risk of predation but is costly in terms of reduced foraging or courtship opportunities if the novel cues do not represent an actual threat. Consequently, neophobic responses to novel cues should wane with repeated exposures in the absence of an actual threat. We tested the prediction that individual personality traits shape the retention of neophobic predator avoidance in wild-caught guppies. Using extinction trials, we demonstrate that personality (measured as latency to escape or approach a novel object) did not influence the initial response of wild-caught Trinidadian guppies to a novel odour; bolder and shyer guppies both exhibited similarly strong avoidance responses. However, after several exposures, shyer guppies maintain an avoidance response, and bolder guppies no longer respond. Our results highlight the complex nature of the antipredator algorithm of prey, whereby past experience, acute risk, and individual tactics shape neophobic predator avoidance patterns.

Personality and Cognition: Sociability Negatively Predicts Shoal Size Discrimination Performance in Guppies

Evidence from a growing number of organisms suggests that individuals show consistent performance differences in cognitive tasks. According to empirical and theoretical studies, these cognitive differences might be at least partially related to personality. We tested this hypothesis in the guppy, Poecilia reticulata, by comparing individuals with different degree of sociability in the discrimination of shoals formed by a different number of conspecifics. We found that individual guppies show repeatability of sociability as expected for personality traits. Furthermore, individuals with higher sociability showed poorer shoal size discrimination performance and were less efficient in choosing the larger shoal compared to individuals with low sociability. As choosing the larger shoal is an important strategy of defense against predators for guppies, we discuss this relationship between personality and cognition in the light of its fitness consequences.

Individual differences in cognition among teleost fishes

Individual differences in cognitive abilities have been thoroughly investigated in humans and to a lesser extent in other mammals. Despite the growing interest in studying cognition in other taxonomic groups, data on individual differences are scarce for non-mammalian species. Here, we review the literature on individual differences in cognitive abilities in teleost fishes. Relatively few studies have directly addressed this topic and have provided evidence of consistent and heritable individual variation in cognitive abilities in fish. We found much more evidence of individual cognitive differences in other research areas, namely sex differences, personality differences, cerebral lateralisation and comparison between populations. Altogether, these studies suggest that individual differences in cognition are as common in fish as in warm-blooded vertebrates. Based on the example of research on mammals, we suggest directions for future investigation in fish.

Predator recognition learning in rainbow darters Etheostoma caeruleum: specific learning and neophobia

This study investigated whether rainbow darters Etheostoma caeruleum can learn to recognize unfamiliar predators through the process of classical conditioning. Etheostoma caeruleum were conditioned by exposing them simultaneously to their chemical alarm cues (a known fright stimulus) and either chemical cues from larval ringed salamanders Ambystoma annulatum (unfamiliar predator) or to a blank water cue (control). Conditioning could result in either specific learning of the A. annulatum cue or increased wariness in response to any novel cue (neophobia). To distinguish between these possibilities, E. caeruleum in both groups were exposed to either A. annulatum cues alone or to chemical cues from western rat snakes Pantherophis obsoletus (novel cue) 2 days after conditioning. Treatment (A. annulatum-conditioned) E. caeruleum, but not control E. caeruleum, showed a fright response when they were exposed to both the conditioned (A. annulatum) and novel (P. obsoletus) cues, indicating increased sensitivity to new stimuli. When E. caeruleum were retested after an additional 32 days, however, the fright response occurred only following exposure to the conditioned (A. annulatum) stimulus, indicating that specific learning of the A. annulatum cue had been retained whereas the neophobia to novel stimuli was temporary.

Retention of neophobic predator recognition in juvenile convict cichlids: effects of background risk and recent experience

Exposure to conditions of elevated predation risk, even for relatively short periods, has been shown to induce neophobic responses to novel predators. Such phenotypically plastic responses should allow prey to exhibit costly anti-predator behaviour to novel cues only in situations where the risk of predation is high. While there is evidence that the level of background risk shapes the strength of induced neophobia, we know little about how long neophobic responses are retained. Here we exposed juvenile convict cichlids (Amatitlania nigrofasciata) to three background levels of short-term background risk and then tested their responses to novel predator odours. Cichlids exposed to low risk did not show neophobic responses, while those exposed to intermediate and high risk did. Using extinction trials, we demonstrate that the retention of neophobic responses is greater among cichlids exposed to high versus intermediate predation risk conditions. Moreover, we found much longer retention of the neophobic responses when cichlids were tested a single time compared to when they were tested repeatedly in the extinction trials. This work supports the prediction that neophobic responses to specific odours are relatively long lasting but can quickly wane if the cues are experienced repeatedly without them being associated with risk. It is clear that background level of risk and the frequency of exposure to novel cues are crucial factors in determining the retention of risk-related information among prey.

Does Environmental Heterogeneity Promote Cognitive Abilities?

In the context of global change the possible loss of biodiversity has been identified as a major concern. Biodiversity could be seriously threatened as a direct consequence of changes in availability of food, changing thermal conditions, and loss and fragmentation of habitat. Considering the magnitude of global change, an understanding of the mechanisms involved in coping with a changing environment is urgent. We explore the hypothesis that species and individuals experiencing highly variable environments are more likely to develop a wider range of responses to handle the different and unpredictable conditions imposed by global change. In the case of vertebrates, the responses to the challenges imposed by unpredictable perturbations ultimately are linked to cognitive abilities allowing the solving of problems, and the maximization of energy intake. Our models were hummingbirds, which offer a particularly compelling group in which to examine the functional and mechanistic links between behavioral and energetic strategies in individuals experiencing different degrees of social and environmental heterogeneity.

Studying the evolutionary ecology of cognition in the wild: a review of practical and conceptual challenges

Cognition is defined as the processes by which animals collect, retain and use information from their environment to guide their behaviour. Thus cognition is essential in a wide range of behaviours, including foraging, avoiding predators and mating. Despite this pivotal role, the evolutionary processes shaping variation in cognitive performance among individuals in wild populations remain very poorly understood. Selection experiments in captivity suggest that cognitive traits can have substantial heritability and can undergo rapid evolution. However only a handful of studies have attempted to explore how cognition influences life-history variation and fitness in the wild, and direct evidence for the action of natural or sexual selection on cognition is still lacking, reasons for which are diverse. Here we review the current literature with a view to: (i) highlighting the key practical and conceptual challenges faced by the field; (ii) describing how to define and measure cognitive traits in natural populations, and suggesting which species, populations and cognitive traits might be examined to greatest effect; emphasis is placed on selecting traits that are linked to functional behaviour; (iii) discussing how to deal with confounding factors such as personality and motivation in field as well as captive studies; (iv) describing how to measure and interpret relationships between cognitive performance, functional behaviour and fitness, offering some suggestions as to when and what kind of selection might be predicted; and (v) showing how an evolutionary ecological framework, more generally, along with innovative technologies has the potential to revolutionise the study of cognition in the wild. We conclude that the evolutionary ecology of cognition in wild populations is a rapidly expanding interdisciplinary field providing many opportunities for advancing the understanding of how cognitive abilities have evolved.

Cognitive ecology in hummingbirds: the role of sexual dimorphism and its anatomical correlates on memory

In scatter-hoarding species, several behavioral and neuroanatomical adaptations allow them to store and retrieve thousands of food items per year. Nectarivorous animals face a similar scenario having to remember quality, location and replenishment schedules of several nectar sources. In the green-backed firecrown hummingbird (Sephanoides sephanoides), males are territorial and have the ability to accurately keep track of nectar characteristics of their defended food sources. In contrast, females display an opportunistic strategy, performing rapid intrusions into males territories. In response, males behave aggressively during the non-reproductive season. In addition, females have higher energetic demands due to higher thermoregulatory costs and travel times. The natural scenario of this species led us to compared cognitive abilities and hippocampal size between males and females. Males were able to remember nectar location and renewal rates significantly better than females. However, the hippocampal formation was significantly larger in females than males. We discuss these findings in terms of sexually dimorphic use of spatial resources and variable patterns of brain dimorphisms in birds.