Experience in aggressive contests often affects behaviour during, and the outcome of, later contests. This review discusses evidence for, variations in, and consequences of such effects. Generally, prior winning experiences increase, and prior losing experiences decrease, the probability of winning in later contests, reflecting modifications of expected fighting ability. We examine differences in the methodologies used to study experience effects, and the relative importance and persistence of winning and losing experiences within and across taxa. We review the voluminous, but somewhat disconnected, literature on the neuroendocrine mechanisms that mediate experience effects. Most studies focus on only one of a number of possible mechanisms without providing a comprehensive view of how these mechanisms are integrated into overt behaviour. More carefully controlled work on the mechanisms underlying experience effects is needed before firm conclusions can be drawn. Behavioural changes during contests that relate to prior experience fall into two general categories. Losing experiences decrease willingness to engage in a contest while winning experiences increase willingness to escalate a contest. As expected from the sequential assessment model of contest behaviour, experiences become less important to outcomes of contests that escalate to physical fighting.A limited number of studies indicate that integration of multiple experiences can influence current contest behaviour. Details of multiple experience integration for any species are virtually unknown. We propose a simple additive model for this integration of multiple experiences into an individual's expected fighting ability. The model accounts for different magnitudes of experience effects and the possible decline in experience effects over time. Predicting contest outcomes based on prior experiences requires an algorithm that translates experience differences into contest outcomes. We propose two general types of model, one based solely on individual differences in integrated multiple experiences and the other based on the probability contests reach the escalated phase. The difference models include four algorithms reflecting possible decision rules that convert the perceived fighting abilities of two rivals into their probabilities of winning. The second type of algorithm focuses on how experience influences the probability that a subsequent contest will escalate and the fact that escalated contests may not be influenced by prior experience. Neither type of algorithm has been systematically investigated.Finally, we review models for the formation of dominance hierarchies that assume that prior experience influences contest outcome. Numerous models have reached varied conclusions depending on which factors examined in this review are included. We know relatively little about the importance of and variation in experience effects in nature and how they influence the dynamics of aggressive interactions in social groups and random assemblages of individuals. Resear...

Social interactions are central to most animals and have a fundamental impact upon the phenotype of an individual. Social behavior (social interactions among conspecifics) represents a central challenge to the integration of the functional and mechanistic bases of complex behavior. Traditionally, studies of proximate and ultimate elements of social behavior have been conducted by distinct groups of researchers, with little communication across perceived disciplinary boundaries. However, recent technological advances, coupled with increased recognition of the substantial variation in mechanisms underlying social interactions, should compel investigators from divergent disciplines to pursue more integrative analyses of social behavior. We propose an integrative conceptual framework intended to guide researchers towards a comprehensive understanding of the evolution and maintenance of mechanisms governing variation in sociality.The study of social behavior in the 21st century All animals interact with conspecifics at some point in their lives. Members of the same species tend to be each other's fiercest competitors and strongest allies, as evidenced by the intense cooperation and conflict that characterize many intraspecific interactions [1]. These interactions are the products of genetic, epigenetic, endocrine, and neural mechanisms that -in conjunction with environmental conditions -affect Darwinian fitness and evolve via natural selection. Building upon Aristotle's four questions, Tinbergen [2] posited that understanding behavior requires the integration of studies of mechanism and function. Only by asking questions both from a proximate perspective (i.e., focusing on causation and development) and an ultimate perspective (i.e., focusing on adaptive value and evolutionary descent) can behavior be fully understood. Social behavior in particular lends itself to such an integrative approach not only because it commands the attention of many disciplines [3] but also because even many behaviors commonly considered nonsocial often occur in a social context (e.g., mating, fighting, parental care). Social behavior is also special because the selective agents are other members of the same species, and this results in intriguing evolutionary dynamics. Nevertheless, in the intervening decades since Tinbergen's

We use extensive geographical sampling and surveys of nuclear microsatellite and mitochondrial DNA loci to investigate the phylogeographic structure of the only recognized self-fertilizing vertebrates, the mangrove killifishes, currently thought to comprise two cryptic species, Kryptolebias marmoratus and Kryptolebias hermaphroditus. All genetic markers revealed three concordant main clades. The Northern clade includes populations from Florida, northern Cuba, Bahamas, Belize and Honduras and corresponds to K. marmoratus. The Southern clade encompasses populations from Brazil and corresponds to K. hermaphroditus. This species was considered endemic to southeastern Brazil, but molecular data corroborate its occurrence in northeastern Brazil. The Central clade, not previously resolved with genetic data, includes populations from Panama and Antilles. Despite the geographic proximity of the Northern and Central clades, the latter is genetically closer to the Southern clade. The discovery of the Central clade raises some taxonomic issues -it can either be considered a distinct species or united with the Southern clade into a single species with two subspecies. Another possible taxonomic solution is a single selfing species, K. marmoratus, with three subspecies. We show that the Central and Southern clades are highly selfing (97-100%), whereas selfing rates of the Northern clade populations vary geographically (39-99%). Genetic patterns indicate that populations in SE Brazil are recent, contrary to expectations based on the known distributions of related species.

Aggressive contests probably occur in networking environments where information about ® ghting ability is conveyed both to an opponent and to individuals peripheral to the ® ght itself, the bystanders. Our primary aim was to investigate the relative in¯uences of eavesdropping and prior social experience on the dynamics of aggressive contests in Xiphophorus helleri. A bystander' s ability to witness an encounter was manipulated using clear, one-way mirror, and opaque partitions. After watching (or not watching) the initial contest, the bystander encountered either the winner or loser of the bout. Treatment comparisons of bystander± winner or bystander± loser contest dynamics indicated the presence or absence of winner, loser, or eavesdropping effects. Winner and loser effects had negligible in¯uences on bystander contest dynamics. Eavesdropping signi® cantly reduced the bystander's propensity to initiate aggression, escalate, and win against seen winners regardless of whether the watched bout had escalated or not. Though eavesdropping had relatively little effect on bystander± loser contest dynamics, bystanders were less prone to initiate aggression and win against losers that had escalated in the witnessed bout. Thus, bystanders appear to preferentially retain and utilize information gained about potentially dangerous opponents (winners or persistent losers). Our data lend clear support for the importance of eavesdropping in visually based aggressive signalling systems.

Summary1. Natural selection can generate correlated suites of phenotypic traits by acting independently on physiological and behavioural characters or on mechanisms that exert pleiotropic actions. 2. Current theory, supported by artificial selection studies, suggests that physiological and behavioural stress responses are at least partially under genetic control and covary in a predictable manner. Indeed, physiological mechanisms such as hormonal stress responsiveness may underlie variation in behaviour, including consistent behaviours described as temperament or personality, with bolder, more exploratory and active individuals being less hormonally responsive to stressors. 3. This relationship, however, has yet to be demonstrated in natural populations. We investigated the relationship between hormonal and behavioural stress responsiveness in multiple natural populations of a tropical freshwater poeciliid fish, Brachyrhaphis episcopi, that experience different levels of predation pressure and hence encounter different rates of stressful events. Predation can impose a strong selection pressure, and living with a high risk of predation is known to select for specific behavioural traits. 4. We quantified variation in stress responsiveness via cortisol release rates (exp. 1) and behaviour in an open field test followed by cortisol release rates (exp. 2). Populations exposed to high levels of predation were consistently more exploratory and active and had lower release rates of cortisol in response to a stressor than conspecifics sampled at sites with few predators. 5. However, this difference in stress responsiveness was only apparent after fish had experienced the mild stress of behaviour testing (in exp. 2), which resulted in elevation of cortisol levels. The relationship between hormone release and behaviour was also not apparent within populations once independent factors were controlled for, highlighting the importance of factors such as size and sex on individual variability. 6. This study demonstrates that the relationship between hormonal and behavioural stress responsiveness can result from natural selection pressures, such as that imposed by predation.