Long-term effect of social interactions on behavioral plasticity and lifetime mating success.

Behavioral traits often change over an individual's lifetime. Experience, physiological senescence, and age-dependent differences in optimal behavior can, in theory, all cause longitudinal behavioral changes. Yet most studies of behavioral plasticity and selection on behavior focus on short-term population-level responses to social factors such as conspecific density or sex ratio. Longer-term effects of social interactions on individual behavior have rarely been tested. Here we tested these effects by exposing male water striders (Hemiptera: Gerridae) to two different social conditions throughout their lifetime; we call these the nonsocial and social treatments. We then measured each male's lifetime mating success and individual behavioral plasticity by observing four different behaviors (exploring a novel environment, dispersal ability, sex-recognition sensitivity, and tendency to remount a resistant female after being dislodged) every 2 weeks. The social environment influenced individual variation in behavioral plasticity as well as population-level behavioral plasticity. Moreover, when we calculated linear selection gradients of individual behavioral traits and their plasticities on lifetime mating success, male remounting tendency and individual plasticity in exploration ability were likely to be the most important factors explaining variation in male lifetime mating success. In conclusion, the variation in social interactions throughout an individual's lifetime contributes to the individual variation in behavioral plasticity, which can significantly affect a male's lifetime fitness.