Utilization of computated tomography to view genital interactions in orcas (Orcinus orca) during intromission

Computed tomography (CT) has been an essential tool for imaging anatomy in a clinical setting. CT scans can provide insights on genital interactions between the sexes during intromission and is a valuable tool for species with internal fertilization as copulatory biomechanics can be discerned during penile penetration. We use CT scans of orcas (Orcinus orca) in simulated copulation to increase understanding of genital co- evolution and copulatory fit between the sexes. The penis of a postmortem sexually mature orca was inflated with pressurized saline to simulate erection and inserted in a ventral-ventral positioning into the vagina of a postmortem sexually mature female orca. The specimens were CT scanned in simulated copulation and resulting image slices were segmented by tissue type to create a 3D visualization of the genitalia interacting and determine significant landmarks in contact between the sexes. The ventral-ventral positioning produced a tight fit between the genitalia. One major vaginal fold was located cranially in the vagina. The integument of the penis maintaining contact throughout the vagina until tapering at the cervix, maintaining contact with the right distal wall of the vaginal tissue. Understanding of contact points between the sexes yields insights into possible stimulatory functions of genital contact in cetaceans (whales, dolphins, and porpoises) and sexual selection forces driving reproductive morphological co-evolution.