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ABSTRACT Despite the remarkable morphological diversity found in vertebrate genitalia, it has historically been difficult to quantify shape variation of soft tissue structures due to limitations of 3D landmarking methods. New techniques such as automatic landmarking now allow us to examine such structures in detail, and with these methods we quantify the intraspecific variation in the genitalia of Burmese pythons (Python bivittatus). Despite previous assertions that a vaginal pouch is not present in pythons, we find thatP. bivittatushave well developed vaginal pouches, that are morphologically diverse, and change shape over ontogeny. Vaginal pouches and hemipenes are isometric. Hemipenes also vary in shape ontogenetically, but we find no evidence of directional asymmetry in shape or size between adult right and left hemipenes suggesting a lack of laterality. We identify a potentially intersex neonate with hemipenes, testes, and a vaginal pouch. We discuss our results in the context of snake genital evolution and suggest other mechanisms for selection beyond the standard “lock and key” hypothesis. Future work examining genital shape variation of other snake families will provide more insight into the coevolutionary patterns shaping the genitalia diversity across snakes and vertebrates more broadly. 

Alpacas (Vicugna pacos) are reported to be the rare mammal in which the penis enters the uterus in mating. To date, however, only circumstantial evidence supports this assertion. Using female alpacas culled for meat, we determined that the alpaca penis penetrates to the very tips of the uterine horns, abrading the tract and breaking fine blood vessels. All female alpacas sacrificed one hour or 24 hours after mating showed conspicuous bleeding in the epithelium of some region of their reproductive tract, including the hymen, cervix and the tips of each uterine horn, but typically not in the vagina. Unmated females showed no evidence of conspicuous bleeding. Histological examination of mated females revealed widespread abrasion of the cervical and endometrial epithelium, injuries absent in unmated females. Within one hour of mating, sperm were already present in the oviduct. The male alpaca’s cartilaginous penis tip with a hardened urethral process is likely responsible for the copulatory abrasion. The entire female reproductive tract interacts with the penis, functioning like a vagina. Alpacas are induced ovulators, and wounding may hasten delivery of the seminal ovulation-inducing factor beta-NGF into the female’s blood stream. There is no evidence of sexual conflict in copulation in alpaca, and thus wounding may also be one of a variety of mechanisms devised by mammals to induce a beneficial, short-term inflammatory response that stimulates blastocyst implantation, the uterine remodeling associated with placental development, and thus the success of early pregnancy.