The evolution of chirally dimorphic insect genitalia

Abstract

Many insect species have asymmetric (male) genitalia. A recent review of the literature (Huber et al., 2007) shows that this can be explained by structural and mechanical advantages, sometimes in association with a lateral mating position. Although asymmetry could in principle lead to antisymmetry (the occurrence of two mirror-image morphs of the same chiral shape within a species), Huber et al. report that this condition is very rare, due to yet unrevealed causes. This makes the small collection of cases where antisymmetry does occur particularly interesting from an evolutionary viewpoint. Here, I review these cases and, based on studies of antisymmetry in other organisms, I propose testable hypotheses for explaining the maintenance of antisymmetry in insect genitalia.