The diversity of male mating organs in rats has been regarded as an important trait in taxonomy because it is closely related to reproductive isolation leading to speciation.So far, many studies have described the baculum as a symptomatic trait of species classification, but there are few studies on the functional morphology of male copulators.In addition, research on male copulators of Japanese rats has hardly been studied since it was investigated around 1940.Therefore, the research group focused on the diversity of male copulator morphology in Japanese rats.

　This time, as a result of anatomical comparison of 6 species of Murinae from Japan and 5 species of Cricetidae, all 11 species have a baculum inside the penis, which is a male copulator. It was present, and a trigeminal structure consisting of a regular papillary process and two lateral papillary processes was found in the distal part.It was revealed that the degree of development of each species varies greatly depending on the species, resulting in a variety of male copulatory morphology.Histological analysis also suggested that the lateral papillae move outward during mating, contributing to the swelling of the distal penis.Since no muscle tissue is found around the tissue, it is thought that only the blood flow, not the muscle, is involved in the movement of the lateral papilla process.

　The results of this study show for the first time that the morphology of the distal part of the penis, which has not been noticed so far, varies from species to species and has functional significance in the swelling mode of the penis of mice.New insights into the role of male copulators in breeding strategies
It is expected to lead to seeing.

Paper information:[Mammal Study] Comparative morphology of the male genitalia of Japanese Muroidea species