Ryan L. Earley

Modulation of aggressive behaviour by fighting experience: mechanisms and contest outcomes

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.

Eavesdropping on visual cues in green swordtail (Xiphophorus helleri) fights: a case for networking

Aggressive contests probably occur in networking environments where information about fighting ability is conveyed both to an opponent and to individuals peripheral to the fight itself, the bystanders. Our primary aim was to investigate the relative influences of eavesdropping and prior social experience on the dynamics of aggressive contests in Xiphophorus helleri. A bystanders 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 influences on bystander contest dynamics. Eavesdropping significantly reduced the bystanders 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.

Non-invasive measurement of steroids in fish-holding water: important considerations when applying the procedure to behaviour studies

Fish behaviourists are increasingly turning to non-invasive measurement of steroid hormones in holding water, as opposed to blood plasma. When some of us met at a workshop in Faro, Portugal, in September, 2007, we realised that there were still many issues concerning the application of this procedure that needed resolution, including: Why do we measure release rates rather than just concentrations of steroids in the water? How does one interpret steroid release rates when dealing with fish of different sizes? What are the merits of measuring conjugated as well as free steroids in water? In the ‘static’ sampling procedure, where fish are placed in a separate container for a short period of time, does this affect steroid release—and, if so, how can it be minimised? After exposing a fish to a behavioural stimulus, when is the optimal time to sample? What is the minimum amount of validation when applying the procedure to a new species? The purpose of this review is to attempt to answer these questions and, in doing so, to emphasize that application of the non-invasive procedure requires more planning and validation than conventional plasma sampling. However, we consider that the rewards justify the extra effort.

Social interactions tune aggression and stress responsiveness in a territorial cichlid fish (Archocentrus nigrofasciatus)

We examined the relative influences of pre-fight housing condition, contest intensity, and contest outcome in modulating post-fight stress hormone concentrations in territorial male convict cichlids (Archocentrus nigrofasciatus). Individuals were housed either in isolation or in semi-natural communal tanks. Pairs of male cichlids that differed considerably in body mass were selected from the same housing regime. Pre-fight water-borne cortisol levels were obtained before allowing the dyad to interact until contest resolution, after which time post-fight cortisol levels were obtained from the winner and loser. There were no outcome-related differences in post-fight cortisol concentrations following escalated or non-escalated contests, a result that held true for both housing regimes. Pre-fight cortisol levels were significantly higher than post-fight cortisol levels, suggesting that initial confinement in a beaker for the water-borne hormone samples was a stressor, but that the animals acclimated quickly to confinement. Fights involving previously isolated participants were significantly more intense than those involving group-housed animals, which we explain as being a function of established relationships between social isolation, heightened acute cortisol responsiveness, and the expression of excessive aggressive behavior. Only group-housed losers demonstrated the ability to modulate aggression or hypothalamic-pituitary-interrenal (HPI) activity in a graded fashion to acute increases in cortisol or changes in contest intensity, respectively. We discuss a variety of factors that could disrupt the ability of isolates to appropriately modulate interactions between social behavior and the HPI axis, and we examine a number of functional hypotheses underlying the sensitivity of group-housed losers to changes in contest dynamics.

An evolutionary framework for studying mechanisms of social behavior

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.

Elevated 11-ketotestosterone during paternal behavior in the Bluebanded goby (Lythrypnus dalli).

The relationship between androgens and paternal behavior is not straightforward, potentially because of the diversity of tasks a male must undertake to maximize reproductive success, notably alternating between courtship, aggression, and offspring care. In some species, these events are separated in time, but in others they are coincident. The endocrine profiles of species that simultaneously court, parent, and defend a nest, such as male bluebanded gobies (Lythrypnus dalli), are not well understood. We sampled a potent fish androgen, 11-ketotestosterone (KT), at different life history stages (experienced parenting males, experienced males not actively parenting, inexperienced males with their first clutch, and females), to examine this relationship. We found that experienced parenting L. dalli males have the highest KT levels of any group, while none of the other groups differed significantly. Males showed elevated KT levels when they had eggs compared to when they did not. Our data suggest that KT facilitates at least some aspects of parental care in L. dalli.

Reciprocity between endocrine state and contest behavior in the killifish, Kryptolebias marmoratus

Given the dramatic behavioral effects of winning and losing contests, and pronounced changes in stress and sex steroid hormones post-fight, it is reasonable to suppose that these hormones also dictate future behavior. We sampled water-borne cortisol, testosterone (T), and 11-ketotestosterone (KT) before and after contests in the mangrove killifish, Kryptolebias marmoratus, to determine how endogenous steroid hormone levels might predict and respond to contest dynamics or success. Pre-fight cortisol related negatively, and pre-fight T related positively to contest initiation and winning, particularly in the smaller opponent. In the pairs where a larger fish won the contest, winners with higher pre-fight T and lower pre-fight cortisol delivered more attacks to the losers. Contest duration and escalation influenced post-fight hormone concentrations primarily in losers. Escalation significantly increased post-fight cortisol, T, and KT for losers but not for winners. However, winners that attacked losers at higher rates had higher levels of post-fight cortisol. Losers also demonstrate the most consistent post-fight hormone responses, particularly to contest escalation and duration. Despite the bidirectional relationship between hormones and contest behavior, we found no overall mean differences in pre- or post-fight cortisol, T, or KT between eventual winners and losers. Thus, it is evident that the categorical states of winner and loser cannot alone reveal the complex, reciprocal associations between endocrine systems and social behavior.

Individual recognition, dominance hierarchies and winner and loser effects

Winner and loser effects are defined as an increased probability of winning an aggressive interaction at time T, based on victories at time T − 1, T − 2, etc., and an increased probability of losing at time T, based on losses at time T − 1, T − 2, etc., respectively. Prior theoretical work on dominance hierarchy formation has demonstrated that when players are not capable of individual recognition, loser effects always produce a clear top–ranked (alpha) individual, but all other ranks in a group remain unclear; whereas winner effects always produce strict linear hierarchies in which the rank of each individual is clear. Paradoxically, however, when individual recognition—a phenomenon long thought to stabilize hierarchies—is possible, winner and loser effects have no impact on the probability of forming strict linear hierarchies.

Social eavesdropping and the evolution of conditional cooperation and cheating strategies

The response of bystanders to information available in their social environment can have a potent influence on the evolution of cooperation and signalling systems. In the presence of bystanders, individuals might be able to increase their payoff by exaggerating signals beyond their means (cheating) or investing to help others despite considerable costs. In doing so, animals can accrue immediate benefits by manipulating (or helping) individuals with whom they are currently interacting and delayed benefits by convincing bystanders that they are more fit or cooperative than perhaps is warranted. In this paper, I provide some illustrative examples of how bystanders could apply added positive selection pressure on both cooperative behaviour and dishonest signalling during courtship or conflict. I also discuss how the presence of bystanders might select for greater flexibility in behavioural strategies (e.g. conditional or condition dependence), which could maintain dishonesty at evolutionarily stable frequencies under some ecological conditions. By recognizing bystanders as a significant selection pressure, we might gain a more realistic approximation of what drives signalling and/or interaction dynamics in social animals.

Measuring water-borne cortisol in convict cichlids (Amatitlania nigrofasciata): is the procedure a stressor?

[Cortisol is an important indicator of health and behavioral state in fishes, and is produced in response to stressors including confinement, handling and social conflict. An inherent difficulty in measuring circulating cortisol is the implementation of invasive procedures that can be potent stressors. Recent studies show that cortisol can be reliably quantified from fish holding water by placing individuals in a small beaker for a predetermined collection period. We investigated whether convict cichlid fish ( Amatitlania nigrofasciata ) mount a significant stress response to beaker confinement and whether they habituate to the collection method. We also determined the relationship between plasma and water-borne cortisol, and changes in cortisol release rates following handling and cortisol administration. Initial beaker exposure induced high cortisol release rates but cichlids quickly habituated after 3–4 exposures. We revealed significant positive correlations between plasma and water-borne cortisol, and marked increases in water-borne cortisol release rates after cortisol injection that persisted for between 4 and 24 h, depending on the dosage. In conclusion, we provide convincing evidence for the utility and validity of the water-borne collection method to measure cortisol release rates in convict cichlids., Cortisol is an important indicator of health and behavioral state in fishes, and is produced in response to stressors including confinement, handling and social conflict. An inherent difficulty in measuring circulating cortisol is the implementation of invasive procedures that can be potent stressors. Recent studies show that cortisol can be reliably quantified from fish holding water by placing individuals in a small beaker for a predetermined collection period. We investigated whether convict cichlid fish ( Amatitlania nigrofasciata ) mount a significant stress response to beaker confinement and whether they habituate to the collection method. We also determined the relationship between plasma and water-borne cortisol, and changes in cortisol release rates following handling and cortisol administration. Initial beaker exposure induced high cortisol release rates but cichlids quickly habituated after 3–4 exposures. We revealed significant positive correlations between plasma and water-borne cortisol, and marked increases in water-borne cortisol release rates after cortisol injection that persisted for between 4 and 24 h, depending on the dosage. In conclusion, we provide convincing evidence for the utility and validity of the water-borne collection method to measure cortisol release rates in convict cichlids.]