Meeting Abstract
The rapid evolution of male genitalia is a nearly ubiquitous pattern across sexually reproducing organisms, likely driven by the evolutionary pressures of male-male competition, male-female interactions, and perhaps pleiotropic effects of selection. The penis of many mammalian species contains a bone called a baculum that similarly displays astonishing rates of phenotypic divergence over time. The evolution of baculum size and shape does not consistently correlate with any aspects of mating system, hindering our understanding of the evolutionary processes affecting it. One potential explanation is that the baculum is not actually a homologous structure. Since approximately half of mammalian species have a baculum, it could have been independently derived, which would violate the assumption of homology inherent in comparative studies. Here, we specifically test this hypothesis by modeling the presence/absence of bacula of over 800 mammalian species across a well-established phylogeny. Our results reveal high support for 6 independent gains and 6 independent losses of the baculum across mammals. Indicating that the baculum should not be considered a homologous structure, which may help to explain why there is a lack of ecological correlates for bacular morphology.
