Genital interactions in southern sea otters (enhydra lutris nerei)

Studies of copulatory fit, the interaction of the genitalia during intromission, provide insights on the biome- chanics of mating. Past studies on copulatory fit have primarily used insects as model species, although a recent approach has been developed to understand how genitalia interact during copulation in larger taxa. In this study, the copulatory fit of sexually mature post-mortem southern sea otters (Enhydra lutris nerei) was examined. Frozen-thawed excised penises were inflated with melted Vaseline to simulate erection. Silicone endocasts were made of the vaginal lumen of frozen-thawed female reproductive tracts. Each penis (n = 3) and vaginal endocast (n = 3) was 3D scanned to create digital models. Each digitized penis was positioned on each digitized vaginal endocast in simulated copulation and rotated 90, 180, and 270 degrees to determine the angle of best fit. The most surface contact and optimal fit occurred in a dorsal-ventral position. If sea otters mate in a non-dorsal-ventral position, it is hypothesized that pre-copulatory sexual conflict will ensue.