Rapid loss of behavioural plasticity and immunocompetence under intense sexual selection

Phenotypic plasticity allows animals to maximise fitness by conditionally expressing the phenotype best adapted to their environment. While evidence for such adjustment in reproductive tactics is common, little is known about how phenotypic plasticity evolves in response to sexual selection. We examined the effect of sexual selection intensity on phenotypic plasticity in mating behaviour using the beetle Callosobruchus maculatus. Male genital spines harm females during mating and females exhibit copulatory kicking, an apparent resistance trait aimed to dislodge mating males. After exposing individuals from male- and female-biased experimental evolution lines to male- and female-biased sociosexual environments, we examined behavioural plasticity in matings with standard partners. While females from female-biased lines kicked sooner after exposure to male-biased sociosexual contexts, in male-biased lines this plasticity was lost. Ejaculate size did not diverge in response to selection his...