Intersexual correlation for same-sex sexual behaviour in an insect

Same-sex sexual behaviour is widespread across taxa and is particularly common in insects, in which up to 50% of copulation attempts by males are directed towards other males in some species. Research effort has focused on male–male same-sex behaviour and the prevailing theory is that benefits of high mating rate combined with poor sex discrimination explain the high incidence of male–male mounting. However, the evolution of female–female mounting is more enigmatic, since females typically do not mount males in order to mate. Using a full-sib design, we found an intersexual correlation for same-sex mounting in the beetle Callosobruchus maculatus. Variation in male–male mounting across families explained over 20% of variation in female–female mounting. Moreover, we found no evidence that same-sex behaviour was related to general activity level in either sex or carried a fitness cost to females. Taken together, our results suggest that female–female mounting is a relatively low-cost behaviour that may be maintained in the population via selection on males.