Meeting Abstract
Insects show little genital variation within species, yet exhibit extraordinary diversity among species. One solution to this paradox suggests that even though intraspecific variation in relative size might be small and limit the effectiveness of selection, variation in shape alone might be sufficient to enable rapid divergence. This hypothesis predicts that intraspecific variation for genital shape should be higher when compared to genital size and that genital shape should evolve at a higher rate than genital size. We tested this hypothesis in male dung beetles by comparing intra- and interspecific variation in shape and size of genitalia and by calculating their evolutionary rates. For comparison we estimated the same parameters for the head and tibia. We found significant intraspecific variation in genital shape in all species examined, whereas only one species also exhibited significant size variation. Furthermore, genital shape evolved at higher rates than genital size. While shape also evolved relatively faster than size in head and tibia, genitalia had the highest rate of shape evolution of the three. We discuss the functional constraints that may bias the developmental evolution of size and shape of genitalia and other morphological traits.
