Sex matters: sexually dimorphic fitness consequences of a behavioural syndrome

Abstract

There is growing evidence that correlated behavioural traits, or behavioural syndromes, influence behavioural evolution in some taxa. Few studies, however, investigate whether the effects of a syndrome are the same for both sexes. We test whether variation in social tendency, inferred from interindividual distance, is correlated with other aspects of behaviour in male comb-footed spiders, Anelosimus studiosus . We compared these results to those from previous studies on female social tendency to determine (1) whether both sexes share the same behavioural syndrome and (2) whether its effects on mating success are the same for both sexes. Trait types in the syndrome analysis include foraging behaviour, antipredator behaviour, exploratory behaviour and activity level. Our results suggest male A. studiosus , like females, can be categorized into two social classes: an aggregative (social) class and an intolerant (asocial) class. Social males (i.e. those with lower interindividual distance scores) were generally less aggressive towards prey and predators, and were less active. Furthermore, we provide evidence from a parent/offspring breeding study for an additive genetic component to male social tendency (heritability = 0.32). To determine the influence of the male syndrome on mating success, we performed staged male–male contests between social and asocial males for access to females. We found that male social tendency was the single best predictor of success in these trials, with asocial males outperforming social. This finding is opposite to the trend observed in female A. studiosus , where social females experience higher mating success. We propose that the diametrically opposed mating outcomes between the sexes could generate evolutionary conflict.