Indirect genetic effects: a key component of the genetic architecture of behaviour

Behavioural ecology research increasingly focuses on why genetic behavioural variation can persist despite selection. Evolutionary theory predicts that directional selection leads to evolutionary change while depleting standing genetic variation. Nevertheless, evolutionary stasis may occur for traits involved in social interactions. This requires tight negative genetic correlations between direct genetic effects (DGEs) of an individual's genes on its own phenotype and the indirect genetic effects (IGEs) it has on conspecifics, as this could diminish the amount of genetic variation available to selection to act upon. We tested this prediction using a pedigreed laboratory population of Mediterranean field crickets (Gryllus bimaculatus), in which both exploratory tendency and aggression are heritable. We found that genotypes predisposed to be aggressive (due to DGEs) strongly decreased aggressiveness in opponents (due to IGEs). As a consequence, the variance in total breeding values was reduced to almost zero, implying that IGEs indeed greatly contribute to the occurrence of evolutionary stasis. IGEs were further associated with genetic variation in a non-social behaviour: explorative genotypes elicited most aggression in opponents. These key findings imply that IGEs indeed represent an important overlooked mechanism that can impact evolutionary dynamics of traits under selection

Data from 'Testing the direct and genetic benefit hypotheses of polyandry in the wood tiger moth’ Santostefano F, Galarza JA, Mappes J, BEAS 2018

Data from 'Testing the direct and genetic benefit hypotheses of polyandry in the wood tiger moth’ Santostefano F, Galarza JA, Mappes J, BEAS 2018<br>Contains two xlsx datasets and associated readme file<br

Do social partners affect same-sex sexual behaviour in male water striders?

Same-sex sexual behaviour (SSB) represents an emergent trait of two interacting same-sex individuals. Although empirical studies have investigated how social environments can influence SSB, little is known about the effect of the interacting partner and its associated phenotype on SSB. In species where females are larger than males or males express male-specific behaviour, a male's morphology or behaviour can serve as a way for other males to recognize its sex and express SSBs. Here we used both a trait-based and variance-partitioning approach to test for the effect of the interacting male's identity and his multivariate phenotype on SSB, using water striders, Gerris lacustris, as a model. We repeatedly subjected males to dyadic interactions with the same and different partners and measured their SSBs. We used the variance-partitioning approach to estimate the partner's identity effect, and the trait-based approach to assess which trait of the partner explains changes in SSB. We found that the partner's SSB reduced the tendency of males to show SSB. SSB was affected by their interacting partner's identity, but the partner effect was not due to the repeatable components ('personality') of the partner's SSB. Males also did not differ in their responses to variation in the partner's SSB at different levels (between-partner, or partner 'personality', and within-partner levels, or partner 'plasticity'). Taken together, these findings provide the first empirical evidence that SSB can be plastically expressed in response to traits in social partners. We also highlight the usefulness of combining the trait-based and variance-partitioning approach to test whether partners represent a component of the social environment affecting the expression of labile traits. (C) 2016 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved

dataset Santostefano et al. RSPB-2017-1567

dataset Santostefano et al. RSPB-2017-156

Among‐individual behavioural variation in the ornamental red cherry shrimp, Neocaridina heteropoda

Abstract Personality variation, defined as among‐individual differences in behaviour that are repeatable across time and context, is widely reported across animal taxa. From an evolutionary perspective, characterising the amount and structure of this variation is useful since differences among individuals are the raw material for adaptive behavioural evolution. However, behavioural variation among individuals also has implications for more applied areas of evolution and ecology—from invasion biology to ecotoxicology and selective breeding in captive systems. Here, we investigate the structure of personality variation in the red cherry shrimp, Neocaridina heteropoda, a popular ornamental species that is readily kept and bred under laboratory conditions and is emerging as a decapod crustacean model across these fields, but for which basic biological, ecological and behavioural data are limited. Using two assays and a repeated measures approach, we quantify behaviours putatively indicative of shy–bold variation and test for sexual dimorphism and/or size‐dependent behaviours (as predicted by some state‐dependent models of personality). We find moderate‐to‐high behavioural repeatabilities in most traits. Although strong individual‐level correlations across behaviours are consistent with a major personality axis underlying these observed traits, the multivariate structure of personality variation does not fully match a priori expectations of a shy–bold axis. This may reflect our ecological naivety with respect to what really constitutes bolder, more risk‐prone, behaviour in this species. We find no evidence for sexual dimorphism and only weak support for size‐dependent behaviour. Our study contributes to the growing literature describing behavioural variation in aquatic invertebrates. Furthermore, it lays a foundation for further studies harnessing the potential of this emerging model system. In particular, this existing behavioural variation could be functionally linked to life‐history traits and invasive success and serve as a target of artificial selection or bioassays. It thus holds significant promise in applied research across ecotoxicology, aquaculture and invasion biology

Ecological conditions drive pace-of-life syndromes by shaping relationships between life history, physiology and behaviour in two populations of Eastern mosquitofish

The pace-of-life syndrome (POLS) hypothesis predicts variation in behaviour and physiology among individuals to be associated with variation in life history. Thus, individuals on the “fast” end of POLS continuum grow faster, exhibit higher metabolism, are more risk prone, but die earlier than ones on the “slow” end. Empirical support is nevertheless mixed and modelling studies suggested POLS to vary along selection gradients. Therefore, including ecological variation when testing POLS is vastly needed to determine whether POLS is a fixed construct or the result of specific selection processes. Here, we tested POLS predictions between and within two fish populations originating from different ecological conditions. We observed opposing life histories between populations, characterized by differential investments into growth, fecundity, and functional morphology under identical laboratory conditions. A slower life history was, on average, associated with boldness (latency to emergence from a refuge), high activity (short freezing time and long distance travelled), and increased standard metabolism. Correlation structures among POLS traits were not consistent between populations, with the expression of POLS observed in the slow-growing but not in the fast-growing population. Our results suggest that POLS traits can evolve independently from one another and that their coevolution depends upon specific ecological processes

Effects of chronic and acute predation risk on sexual ornamentation and mating preferences

Phenotypic plasticity is wide-spread in animals, but how plastic responses to predation threat affect traits under sexual selection and influence mating preferences is not well understood. Here, we examined how chronic predation risk during development and acute predation risk during mate choice affect the expression of male secondary sexual traits and female mating preference in the three-spined stickleback, Gasterosteus aculeatus. Males reared under chronic predation risk developed less intense red breeding colouration but showed higher courtship activity than males that grew up in a predator-free environment. Acute predation risk during mate choice did not influence male behaviour or ornamentation. Predation risk experienced during development did not affect female mating preferences, while acute predator presence induced a switch in preferences for male courtship activity. Male body size and eye colouration influenced the intensity of female mating preferences, while the trait changing most in response to predation risk during development (red colouration) had no significant impact. The observed interplay between developmental plasticity in male ornamental traits and environment-dependent female mating preferences may lead to dynamic processes altering the strength and direction of sexual selection depending on both the chronic and acute risk of predation. These processes may contribute to the maintenance of within- and among-population variation in secondary sexual traits, and may, ultimately, facilitate speciation