Socially cued anticipatory plasticity predicts male primary mating tactic but not mating behaviour rates

Compared to many types of phenotypic plasticity, developmental plasticity of mating behaviour in response to the social environment has received less attention. Understanding this type of plasticity is a challenge because when individuals adjust their trait expression in response to the trait distributions of other individuals, they change the social cue that those trait distributions represent. This feedback may limit when behavioural plasticity in response to social cues will prove adaptive. We used a livebearing fish (sailfin molly, Poecilia latipinna) to test two models for social plasticity: (1) socially cued anticipatory plasticity, which hypothesizes that developing juveniles use social environment directly to predict their optimum phenotype, and (2) condition dependence, which hypothesizes that developing juveniles use social environment indirectly to assess their competitive standing relative to other members of the social environment. Using a full-sibling split-brood design, we reared juvenile fish from birth until maturity in one of four social treatments: (1) three unrelated juveniles, (2) three females, (3) one small male and two females or (4) one large male and two females. Assessing mating behaviours at maturity and 1 month postmaturity, we found that a male's primary reproductive tactic (odds of using a courtship display over sneaking behaviour) was directly affected by the social environment during development as predicted by socially cued anticipatory plasticity (males were more likely to court when reared only with females and more likely to sneak when reared only with juveniles). However, rates of each type of mating behaviour (courtship or sneaking) were affected by interactions between social environment and heritable factors (sire size class and male body size), contrary to predictions from either socially cued anticipatory plasticity or condition dependence. These results suggest that socially cued anticipatory plasticity may be an important driver in the evolution of alternative mating behaviours and more likely to affect behavioural repertoires than current models of developmental plasticity suggest.(c) 2022 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.