Genital coevolution between the male and female in Bittacidae (Insecta: Mecoptera).

The adults of Bittacidae assume a unique mating posture, by which the male twists his abdomen about 180° to contact the female genitalia in a belly-to-belly position. The males have an extremely elongated penisfilum, which enters the slender spermathecal duct to accomplish insemination during copulation. However, the interaction of the male and female genitalia remains largely unknown in hangingflies. Here, the interaction of genital structures between the males and females was investigated for three species of Bittacidae. In the context of what we know of other related groups, this is suggestive of antagonistic coevolution between the spines on the male epandrial lobes and the female subgenital plate. The length of the male penisfilum is significantly correlated with that of the female spermathecal duct. The coevolution of genitalia is briefly discussed based on morphological traits.