Insights into adaptive behavioural plasticity from the guppy model system

Behavioural plasticity allows organisms to respond to environmental challenges on short time scales. But what are the ecological and evolutionary processes that underlie behavioural plasticity? The answer to this question is complex and requires experimental dissection of the physiological, neural and molecular mechanisms contributing to behavioural plasticity as well as an understanding of the ecological and evolutionary contexts under which behavioural plasticity is adaptive. Here, we discuss key insights that research with Trinidadian guppies has provided on the underpinnings of adaptive behavioural plasticity. First, we present evidence that guppies exhibit contextual, developmental and transgenerational behavioural plasticity. Next, we review work on behavioural plasticity in guppies spanning three ecological contexts (predation, parasitism and turbidity) and three underlying mechanisms (endocrinological, neurobiological and genetic). Finally, we provide three outstanding questions that could leverage guppies further as a study system and give suggestions for how this research could be done. Research on behavioural plasticity in guppies has provided, and will continue to provide, a valuable opportunity to improve understanding of the ecological and evolutionary causes and consequences of behavioural plasticity.

Parental breeding decisions and genetic quality predict social structure of independent offspring

Across the animal kingdom, newly independent juveniles form social associations that influence later fitness, mate choice and gene flow, but little is known about the ontogeny of social environments, particularly in wild populations. Here we test whether associations among young animals form randomly or are influenced by environmental or genetic conditions established by parents. Parents' decisions determine natal birth sites, which could affect who independent young initially encounter; secondly, mate choice determines genetic condition (e.g. inbreeding) of young and the parental care they receive, which can affect sociability. However, genetic and environmental factors are confounded unless related offspring experience different natal environments. Therefore, we used a long-term genetic pedigree, breeding records and social network data from three cohorts of a songbird with high extra-pair paternity (hihi, Notiomystis cincta) to disentangle (1) how nest location and relatedness contribute to association structure once juveniles disperse away from birth sites, and (2) if juvenile and/or parental inbreeding predicts individual sociability. We detected positive spatial autocorrelation: hihi that fledged closer by were more likely to associate even after dispersing, irrespective of genetic relatedness. Juvenile inbreeding did not predict sociability, but those raised by more inbred fathers formed more, stronger, associations, which did not depend on whether that male was the genetic parent or not. These results suggest that the natal environment created by parents, rather than focal genetic condition, establishes the foundation for social associations. Overall, we highlight how social inheritance may play an important role in population dynamics and evolutionary potential in wild animals.

Juvenile Experience with Male Cues Triggers Cryptic Choice Mechanisms in Adult Female Redback Spiders

Simple Summary

Females of many species vary in their receptivity to male mating attempts. When many males are present in the habitat, the theory predicts that females should be choosy and discriminate among potential mates. When few males are available, females should mate readily with the first male who courts, and thus avoid the risk of remaining unmated. We predicted that cues perceived as juveniles that indicate male availability would affect the mating behaviour of adult females. In our first experiment, juvenile females were exposed to airborne chemicals produced by males at high or low densities. In our second experiment, we mimicked a natural situation where males or other juveniles live on the webs of females shortly before they become sexually mature, and compared this to females developing in isolation. As was consistent with our predictions, we found that the adult females changed their behaviour after exposure to cues of high male availability during development. When the females perceived many males nearby (high density airborne cues or living with males) they more often interrupted copulation, or cannibalized the males before the mating was complete as adults. In comparison, when the cues indicated low male availability, the adult females were more likely to allow the males to complete mating, and cannibalism was less common.

Abstract

Female choice may be linked to population density if the expected encounter rates with potential mates affects choosiness (the energy and risk engaged to express mate preferences). Choosiness should covary with male availability, which could be assessed using the social cues available during development. We tested whether the exposure of juvenile females to cues of male density affected the mechanisms of choosiness of adult Latrodectus hasselti spiders in two experiments simulating natural contexts. The juvenile females were exposed to (1) volatile chemicals from two densities of adult males (airborne cues), and (2) tactile, vibrational and chemical cues from adult males or other females (cohabitation cues). As adults, the females mated readily, regardless of the treatment, but there was strong evidence for post-copulatory mechanisms of choosiness in females exposed to cues of high male availability. These included abbreviated matings (in both experiments), cannibalism of the males before the mating was complete (cohabitation), and, remarkably, a reduction in the successful placement of internal sperm plugs (cohabitation). These shifts decrease the likelihood that the first mate would monopolize paternity if the female chose to mate again. We conclude that female choosiness may impose a strong selection on males despite the high mating rates, and these effects can hinge on the cues of male availability detected by juveniles.

Within-population variation in female mating preference affects the opportunity for sexual selection and the evolution of male traits, but things are not as simple as expected

Females from the same population usually have phenotypic variation in their mating preferences. However, the effects of this within-population variation on the sexual selection acting on males are still unclear. We used individual-based models to explore how within-population variation in female preference (i.e. which male trait value is preferred) and preference strength (i.e. how strong the preference is) affects the opportunity for sexual selection (I_s ) and the evolution of a sexually selected male trait. We found the highest I_s values when females had high variation in preference and an open-ended preference function. The lowest I_s occurred when the magnitude of variation in female preference and male trait value were the same and preference function was closed. Male trait exaggeration was higher when there was high within-population variation in preference and females had an open-ended preference function. Also, higher male trait variation was maintained by high variation in preference, but only for a closed preference function. Thus, we found that only within-population variation in female preference, not in preference strength, influences the opportunity for sexual selection and the evolution of sexually selected male traits. Moreover, we found that the shape of the preference function (i.e. open-ended or closed) and the magnitude of within-population variation in female preference compared to male trait variation also influences the I_s and consequently the evolution of male traits.

The impact of social structure on breeding strategies in an island bird

The social environment is a key factor determining fitness by influencing multiple stages of reproduction, including pair formation, mating behavior and parenting. However, the influence of social structure across different aspects of breeding is rarely examined simultaneously in wild populations. We therefore lack a consolidation of the mechanisms by which sociality impacts reproduction. Here we investigate the implications of the social environment before and during breeding on multiple stages of reproduction in an island population of the ground nesting shorebird, the Kentish plover (Charadrius alexandrinus). We utilise information on mating decisions, nest locations and nesting success across multiple years in combination with social network analysis. Sociality before breeding was connected with patterns of pair formation. In addition, site fidelity and personal breeding experience was associated with the spatial organisation of breeding pairs. Our results provide evidence that, while differential social interactions at localised scales influence patterns of reproductive pairing, site fidelity and personal breeding experience influence the structure of populations at the landscape scale. Our results underline the tight link between the social structure of populations and patterns of mating, while revealing that the relative influence of sociality, breeding experience and local ecology are dynamic across different facets of reproduction.

Role of sexual imprinting in assortative mating and premating isolation in Darwin's finches

Global biodiversity is being degraded at an unprecedented rate, so it is important to preserve the potential for future speciation. Providing for the future requires understanding speciation as a contemporary ecological process. Phylogenetically young adaptive radiations are a good choice for detailed study because diversification is ongoing. A key question is how incipient species become reproductively isolated from each other. Barriers to gene exchange have been investigated experimentally in the laboratory and in the field, but little information exists from the quantitative study of mating patterns in nature. Although the degree to which genetic variation underlying mate-preference learning is unknown, we provide evidence that two species of Darwin's finches imprint on morphological cues of their parents and mate assortatively. Statistical evidence of presumed imprinting is stronger for sons than for daughters and is stronger for imprinting on fathers than on mothers. In combination, morphology and species-specific song learned from the father constitute a barrier to interbreeding. The barrier becomes stronger the more the species diverge morphologically and ecologically. It occasionally breaks down, and the species hybridize. Hybridization is most likely to happen when species are similar to each other in adaptive morphological traits, e.g., body size and beak size and shape. Hybridization can lead to the formation of a new species reproductively isolated from the parental species as a result of sexual imprinting. Conservation of sufficiently diverse natural habitat is needed to sustain a large sample of extant biota and preserve the potential for future speciation.

Change in male coloration associated with artificial selection on foraging colour preference

Sensory drive proposes that natural selection on nonmating behaviours (e.g. foraging preferences) alters sensory system properties and results in a correlated effect on mating preferences and subsequently sexual traits. In colour-based systems, we can test this by selecting on nonmating colour preferences and testing for responses in colour-based female preferences and male sexual coloration. In guppies (Poecilia reticulata), individual functional links of sensory drive have been demonstrated providing an opportunity to test the process over more than one link. We measured male coloration and female preferences in populations previously artificially selected for colour-based foraging behaviour towards two colours, red and blue. We found associated changes in male coloration in the expected direction as well as weak changes in female preferences. Our results can be explained by a correlated response in female preferences due to artificial selection on foraging preferences that are mediated by a shared sensory system or by other mechanisms such as colour avoidance, pleiotropy or social experiences. This is the first experimental evidence that selection on a nonmating behaviour can affect male coloration and, more weakly, female preferences.