Meeting Abstract
Genitals often comprise the most morphologically diverse and fastest evolving structures within a group. New studies have provided compelling evidence that sexual selection is driving this divergence in genital morphology, and directly link genital shape to reproductive success. Within mammals, the Carnivora are renowned for males possessing a mineralized element (the baculum) within the glans of the penis, which is extremely diverse in shape. Baculum size has previously been found to be under direct sexual selection. However, the extent to which baculum shape is driven by sexual selection in Carnivora is unknown, in part due to methodological difficulties associated with quantifying shape change in such diverse structures. We use a new method (α-shapes) for quantifying shape complexity in the carnivoran baculum, outside the traditional paradigm of geometric morphometrics. We hypothesise that baculum α-shape complexity will correlate positively with relative testes mass, a proxy for post-copulatory sexual selection. Using microCT data of 77 species, spanning 11 Carnivoran families, we calculate whole-baculum α-shape complexity, in addition to α-shape complexity at the tip, midshaft and base. Across Carnivora, α-shape complexity of the baculum was positively correlated with relative testes mass, suggesting a role for post-copulatory sexual selection in driving baculum shape. Furthermore, whilst absolute α-shape complexity was greatest in the tip, the rate of evolution in α was fastest at midshaft. This surprising results suggests more attention should be paid to the baculum midshaft, particularly the urethral groove and its potential role in protecting the urethra and ensuring sperm delivery during copula.
