Jean-Guy J. Godin

Context-dependent group size choice in fish

The costs and benefits of group membership vary with the size of groups, and individuals are expected to modify their choice of groups in response to ecological factors such as food availability and predation risk. We experimentally examined context-dependent group size choice in a shoaling fish, the banded killifish, Fundulus diaphanus, by using nondirectional odour cues to simulate a food source or a successful attack by a predator (food or alarm treatments) in the laboratory. Group sizes were significantly smaller in the food treatment and larger in the alarm treatment than in control trials. When presented with food and alarm cues together, fish formed groups that were larger than control groups but smaller than those seen with alarm cues alone. These results are consistent with theoretical predictions based on the known benefits and costs of grouping and with previous laboratory work examining the individual shoal choice behaviour of single fish. To examine possible mechanisms of group formation, we developed an individual-based model of shoaling behaviour in which simulated fish were allowed to modify the area over which they interacted with neighbouring individuals. Group size distributions produced by the model were a good approximation of our experimental data. We suggest that local behavioural interaction rules of this type are a potential mechanism by which fish may individually adjust grouping behaviour without requiring extensive information on the position and movement of all possible shoalmates.

Female mate choice under predation risk in the guppy

Abstract Sexual selection, and thus the evolution of both female mating preferences and preferred male traits, may be constrained by costs associated with mate choice. Recent theoretical models predict that female preference should decrease with increasing costs of mate choice such as predation risk. This general hypothesis was tested experimentally by presenting individual female guppies, Poecilia reticulata , originating from two Trinidadian populations with different predation regimes, with a choice of paired males (differing mainly in colour pattern) as potential mates in both the absence and presence of a cichlid fish predator that naturally co-occurs in one of these populations. Moreover, any reduction in female preference under risk was predicted to be positively correlated with the level of predation intensity occurring in their respective populations. In an experiment in which only the female could see the nearby predator, females from the high-predation population (Quare River) significantly reduced both their overall level of sexual activity and their preference for a particular male (most commonly the more colourful male) in the presence of the predator. In contrast, the sexual activity level and mating preference of females from the low-predation population (Paria River) were unaffected by the apparent threat of predation. Observed changes in female sexual activity level and mating preference could not have been mediated by any change in male behaviour when the predator was present, because the males could neither see or smell the predator nearby. In a corollary experiment in which both males and females from the risk-sensitive Quare River population could freely interact with one another and see the predator, females significantly reduced their preference for the more brightly coloured male in the presence of the predator, irrespective of predator-mediated changes in male courtship behaviour. These results are best explained by a reduction in female preference under increased apparent risk of predation, and are consistent with the general hypothesis that female mate choice in the guppy is potentially costly in terms of an increased risk of mortality due to predation and that females from different populations are differentially sensitive to this risk when assessing and choosing potential mates. Therefore, predators may exert direct selection on female mate choice in certain natural populations of the guppy.

Reversal of Female Mate Choice by Copying in the Guppy (Poecilia reticulata)

Ever since Fisher (1958) formalized models of sexual selection, female mate choice has been assumed to be a genetically determined trait. Females, however, may also use social cues to select mates. One such cue might be the mate choice of conspecifics. Here we report the first direct evidence that a female’s preference for a particular male can in fact be reversed by social cues. In our experiments using the Trinidadian guppy (Poecilia reticulata), this reversal was mediated by mate-copying opportunities, such that a female (the ‘focal’ female) is given the opportunity to choose between two males, followed by a period in which she observes a second female (the ‘model’ female) displaying a preference for the male she herself did not prefer initially. When allowed to choose between the same males a second time, compared with control tests, a significant proportion of focal females reversed their mate choice and copied the preference of the model female. These results provide strong evidence for the role of non-genetic factors in sexual selection and underlie the need for new models of sexual selection that explicitly incorporate both genetic and cultural aspects of mate choice.

Predation risk and alternative mating tactics in male Trinidadian guppies (Poecilia reticulata)

In the guppy (Poecilia reticulata), males have two alternative mating tactics. Individual males may either display to a receptive female prior to attempting to copulate with her or attempt to quickly sneakcopulate with a female without first displaying to her or without a prior receptive response from her. In this study, I experimentally investigated the effects of simulated local increases in the risk of predation (in the form of a cichlid fish predator model in situ) on the mating tactics used by free-ranging male guppies in two typical macrohabitats (riffle and pool) of a Trinidadian river. Focal male guppies displayed to females significantly less often on average, and conversely attempted sneak copulations more often, in the presence of the predator model than in its absence; this pattern was similar for both habitats. These fish therefore performed a lower proportion of sigmoid displays and increased their sneaky mating attempts when the apparent risk of predation had increased locally. This predator-mediated response is consistent with a trade-off between mating success and risk of mortality due to predation. The results are the first to confirm risk-sensitive mating behaviour in free-ranging male guppies within a population, and demonstrate the potential importance of predators in influencing the relative use of alternative mating tactics in this species on a microgeographical scale in the wild.

Who Dares, Benefits: Predator Approach Behaviour in the Guppy (Poecilia reticulata) Deters Predator Pursuit

Animals commonly approach (or inspect) potential predators at a distance, a practice which is inherently risky and apparently paradoxical. Individuals which dare inspect predators, and who are therefore willing to accept the associated costs, must gain additional fitness benefits from doing so which non-inspectors do not. Here, we report a direct fitness benefit for predator inspection behaviour in the form of a reduced risk of predation on inspectors compared with non-inspectors. Using guppies (Poecilia reticulata) and blue acara cichlid fish (Aequidens pulcher) as a model prey-predator system, we demonstrate experimentally that the predators were significantly less attentative to, and less likely to attack and kill, guppies which inspected them than those which did not. They were thus more likely to abort an initial approach towards an inspecting guppy than a non-inspecting one, and as a consequence, inspectors incurred a significantly lower risk of attack and death than non-inspectors when approached by the predator. Our results constitute strong evidence for a predator pursuit-deterrence function of predator inspection behaviour in the guppy, and also have implications for the conditions necessary for the evolution of predator approach behaviour as a cooperative strategy in prey.

Foraging under the risk of predation in juvenile Atlantic salmon (Salmo salar L.) : effects of social status and hunger

SummaryFollowing exposure to a predator, socially dominant individuals may reduce their risk of predation by waiting until subordinates have resumed foraging before doing so themselves. Although such status-related ordering in the resumption of foraging activity has been observed in several bird species, the underlying mechanism(s) facilitating such a delay remains unknown. Social status per se and status-related foraging benefits prior to a threat of predation (i.e., individual hunger level) have both been suggested as possible mechanisms. We tested between these two alternative suggestions using pairs of stream-dwelling juvenile Atlantic salmon, for which the dominant-subordinate relationship was known. Fish were tested at equal and unequal hunger levels. Fish were presented with drifting prey, followed by a predation threat in the form of an aerial predator model. Which fish (i.e., dominant or subordinate) initially resumed foraging activity after exposure to the predator model was recorded. When both fish were at an equal hunger level, the dominant fish was more likely to resume foraging first. When the dominant and subordinate fish differed in their hunger level, the hungrier fish was the first to resume foraging regardless of social status. These results support the conclusion that hunger level, rather than social status per se, determines the order in which juvenile Atlantic salmon resume foraging after exposure to a predator.

Social influences on female mate choice in the guppy, Poecilia reticulata: generalized and repeatable trait-copying behaviour

In vertebrates, the mating preferences of individual females can be flexible and the probability of a female mating with a particular male can be significantly increased by her having previously observed another conspecific female affiliate and mate with that same male. In theory, such mate-choice-copying behaviour has potentially important consequences for both the genetic and social (‘cultural’) transmission of female mating preferences. For copying to result in the ‘cultural inheritance’ of mating preferences, individual females must not only copy the mate choice decisions of other females but they also should tend to repeat this type of behaviour (i.e. make similar mating decisions) subsequently and to generalize their socially induced preference for a particular male to other males that share his distinctive characteristics. Here, we show experimentally that individual female guppies, Poecilia reticulata, not only copy the observed mating preferences of other females for particular males, but that the preference now assumed via copying is subsequently repeated and generalized to other males of a similar colour phenotype. These results provide empirical evidence for social enhancement of female preference for particular phenotypic traits of chosen males rather than for the particular males possessing those traits, and thus have important implications for our understanding of the role of social learning in the evolution of female mating preferences and of male epigamic traits.

Are fast explorers slow reactors? Linking personality type and anti-predator behaviour

Response delays to predator attack may be adaptive, suggesting that latency to respond does not always reflect predator detection time, but can be a decision based on starvation–predation risk trade-offs. In birds, some anti-predator behaviours have been shown to be correlated with personality traits such as activity level and exploration. Here, we tested for a correlation between exploration behaviour and response latency time to a simulated fish predator attack in a fish species, juvenile convict cichlids (Amatitlania nigrofasciata). Individual focal fish were subjected to a standardized attack by a robotic fish predator while foraging, and separately given two repeated trials of exploration of a novel environment. We found a strong positive correlation between exploration and time taken to respond to the predator model. Fish that were fast to explore the novel environment were slower to respond to the predator. Our study therefore provides some of the first experimental evidence for a link between exploration behaviour and predator-escape behaviour. We suggest that different behavioural types may differ in how they partition their attention between foraging and anti-predator vigilance.

Geographic variation in multiple paternity within natural populations of the guppy (Poecilia reticulata).

Mating can increase an individuals risk of mortality by predation. In response to predation hazards, males in some species court females less often, but alternatively engage in coerced copulations more frequently and females become less selective. Such predator‐mediated shifts in mating tactics may result in higher levels of multiple inseminations in females and, thus, in greater frequencies of females with broods of mixed paternity. We tested this hypothesis using two polymorphic microsatellite loci to estimate conservatively multiple paternity in broods of female guppies (Poecilia reticulata) originating from ten natural populations that have evolved under different fish predation regimes in Trinidad. The frequency of broods that were multiply sired was significantly greater on average in populations experiencing high predation pressure compared to populations experiencing a relatively low predation risk. These results suggest that the intensity of male sperm competition covaries geographically with predation pressure in this species and that the local risk of predation mediates the opportunity for sexual selection within populations.

Who dares, learns: chemical inspection behaviour and acquired predator recognition in a characin fish.

Individuals that dare approach predators (predator inspection behaviour) may benefit by acquiring information regarding the potential threat of predation. Although information acquisition based on visual cues has been demonstrated for fish, it is unknown whether fish will inspect predators on the basis of chemical cues or whether such inspection behaviour results in information acquisition. Here, we first ascertained whether predator inspection behaviour can be mediated by chemical cues from predators by exposing groups of predator-naive glowlight tetras (Hemigrammus erythrozonus) to the chemical cues of a potential fish predator (convict cichlid Cichlasoma nigrofasciatum) that had been fed either tetras (which possess an alarm pheromone) or swordtails (Xiphophorus helleri, which lack Ostariophysan alarm pheromones). Tetras showed a significant increase in antipredator behaviour when exposed to the tetra-diet cue, but not when exposed to the swordtail-diet cue. Chemically mediated predator inspection behaviour was also affected. Both the latency to inspect and the minimum approach distance to the predator significantly increased, and the mean number of inspectors per predator inspection visit significantly decreased when tetras were exposed to the tetra-diet versus the swordtail-diet chemical cues. We then examined a potential benefit associated with chemically mediated predator inspection behaviour. Only tetras that were initially exposed to the tetra-diet cue and that had inspected the predator acquired the visual recognition of a convict cichlid as a predation threat. Our results thus demonstrate that (1) predator inspection behaviour in the glowlight tetra can be initiated by chemical cues, (2) chemically mediated inspection behaviour is affected by the presence of alarm pheromone, and (3) inspectors benefit by acquiring the recognition of novel predators. Copyright 1999 The Association for the Study of Animal Behaviour.