Description of the penile histology of Eumops patagonicus: A bat from northeastern Argentina

Abstract

The order Chiroptera is one of the most numerous in terms of species among mammals. This order exhibits great diversity in the morphology of their reproductive systems and gonads. In females, a wide variety of uterine morphologies is observed, as well as variations in ovarian morphology and functionality. On the other hand, in males, the testicles exhibit typical mammalian morphology,but the penile structure shows particularities unique to each species. In mammals, the penis is an organ that facilitates fertilization. It has a cylindrical shape with a body through which the urethra runs, and an erectile tissue called the corpus cavernosum, along with a distal portion, the glans, where the urethra continues and ends externally, surrounded by a second erectile tissue, the corpus spongiosum. In some species of bats, the presence of accessory erectile tissues and a penile bone or baculum, also found in other mammals, has been observed. The histological description of this organ is important at the phylogenetic level within this order due to the variation betweenspecies. Therefore, the objective of this study is to describe the penile morphology of Eumops patagonicus at the histological level, belonging to the family Molossidae, a species abundant in urban areas of northeastern Argentina. Samples of E. patagonicus penises were collected (n=8), processed for conventional histology, and stained with hematoxylin-eosin and Gomori´s trichrome. The samples were photographed, differentiating three sections: base, middle, and tip sections. The base section corresponds to the body, while the middle and tip sections correspond to the glans. It was observed that the base of the penis is formed by the urethra, which is surroundedby the corpus cavernosum enclosed by its tunica albuginea of dense connective tissue, which emits an incomplete septum dividing it into two regions. Two peripheral nerves are observed on the sides. In the glans region, the urethra is surrounded by the corpus spongiosum, which is delimited by its tunica albuginea, and in the central region, the presence of a baculum is noted. Externally, the penis is covered by thin skin with a large number of hair follicles, which are absent in the glans that is covered whit skin. Compared to other previously described Eumops species, E. patagonicus has corpus spongiosum in the glans region accompanying the urethra. Moreover, this study reveals the presence of an incomplete septum in the corpus cavernosum, which is not observed in other Chiroptera species. This description of the penis of a member of the Eumops genus lays the foundation for future comparative studies between species of the same genus and family, as it has been of great importance in other taxa such as Rodentia, carnivorous Mustelids, and primates, especially the description of the presence of a baculum.