POLIHRONAKIS, Maxi; University of Connecticut: Why are some genitalia asymmetrical?

The fraterna species complex (Coleoptera: Scarabaeidae: Phyllophaga) is currently comprised of approximately 30 taxa with distinct asymmetrical male genitalia as well as species-specific female genitalia. The most striking asymmetry arises between the two parameres located on the posterior portion of the male genitalic capsule. It is hypothesized that post-copulatory sexual selection is responsible for the observed genitalic diversity because external morphology among species appears evolutionarily static, and the mating system is polygamous. An intra- and interspecific analysis of character evolution has been initiated to test if selection is acting upon male and female genitalic morphologies. A quantitative analysis of intraspecific variation in the type species P. hirticula was carried out to determine the amount of variation available for selection to act on. I also mapped male and female genitalic characters onto a molecular phylogeny, produced using 1200 base pairs of sequence data from the mitochondrial gene cytochrome oxidase subunit I (COI), using parsimony and maximum likelihood methods. The data suggest higher degrees of asymmetry and complexity are derived relative to the plesiomorphic symmetrical condition. In addition, character analyses of genitalia among species outside this complex suggest that asymmetrical male genitalia have evolved more than once in this genus. These initial studies of the evolution of genitalia in this species complex provide evidence that selection is acting to produce diverse and asymmetric genitalia, as well as set the stage for tests of post-copulatory sexual selection.