Reproductive System of Brown-throated Sloth (Bradypus variegatus, Schinz 1825, Pilosa, Xenarthra): Anatomy and Histology

Female Genital Variation Far Exceeds that of Male Genitalia: A Review of Comparative Anatomy of Clitoris and the Female Lower Reproductive Tract in Theria

A review of the literature on the anatomy of the lower female genital tract in therian mammals reveals, contrary to the general perception, a large amount of inter-specific variation. Variation in female external genitalia is anatomically more radical than that in the male genitalia. It includes the absence of whole anatomical units, like the cervix in many Xenarthra, or the absence of the urogenital sinus (UGS), as well as the complete spatial separation of the external clitoral parts from the genital canal (either vagina or UGS). A preliminary phylogenetic analysis shows two patterns. Some morphs are unique to early branching clades, like the absence of the cervix, while others arose multiple times independently, like the flattening out or loss of the UGS, or the extreme elongation of the clitoris. Based on available information, the ancestral eutherian configuration of the external female genitalia included a cervix, a single vaginal segment, a tubular UGS, and an unperforated clitoris close to the entrance of the genital canal. The evidence for either bilobed or unitary glandes clitorides is ambivalent. Despite the wealth of information available, many gaps in knowledge remain and will require a community-wide effort to come to a more robust model of female genital evolutionary patterns.

Morphology of the genital organs of male and female giant anteaters (Myrmecophaga tridactyla)

BACKGROUND

The giant anteater belongs to the supraorder Xenarthra which occupies a systematically isolated position among placental mammals. The species is categorized as Vulnerable by the International Union for Conservation of Nature, and understanding its reproductive characteristics is critical for future conservation efforts.

METHODS

Gross and microscopic anatomy of the genital organs of 23 male and 21 female adult and young roadkill giant anteaters in Brazil were studied.

RESULTS

Male giant anteaters presented a short conical penis, intraabdominal testes, and prostate, vesicular and bulbourethral glands. A tubular remnant of the partially fused Müllerian ducts extended from the seminal colliculus through the prostate gland, continued cranially in the genital fold, bifurcated, and attached with one elongation each to the left and right epididymal corpus. The structure presented a total length of up to 10 cm and contained a yellowish liquid in its lumen. Histologically, the caudal section of this structure resembled the female vagina, the middle portion corresponded to the uterus, and the extensions showed characteristics of uterine tubes. In adult female giant anteaters, ovoid ovaries with occasional seminiferous cord-like structures were observed. The animals possessed a simple uterus, which was directly continuous with the vaginal canal. The caudal portion of the vagina had two lumina, separated by a longitudinal septum and opening into two apertures into the vaginal vestibule, cranial to the urethral opening. In the urethral and the lateral vestibular wall, glandular structures with characteristics of male prostate and bulbourethral glands, respectively, were found. The vestibule opened through a vertical vulvar cleft to the exterior. A pair of well-differentiated Wolffian ducts with a central lumen originated ventrally at the vaginal opening into the vestibule and passed in a cranial direction through the ventral vaginal and uterine wall. Each duct extended highly coiled along the ipsilateral uterine tube until the lateral pole of the ovaries where it merged with the rete ovarii.

DISCUSSION

The reproductive morphology of giant anteaters reveals characteristics shared with other Xenarthrans: intraabdominal testes, a simple uterus, and a double caudal vagina. The persistence of well-differentiated genital ducts of the opposite sex in both males and females, however, singles them out among other species. These structures are the results of an aberration during fetal sexual differentiation and possess secretory functions. The possibility of a pathological degeneration of these organs should be considered in reproductive medicine of the species.

CONCLUSION

Knowledge of the unique reproductive characteristics of the giant anteater is essential for future reproductive management of the species. Additionally, further research on the peculiarities of the persisting genital duct structures might help to understand sexual differentiation in placental mammals in general.

Morphology of the genital organs of the female red-rumped agouti (Dasyprocta leporina, Linnaeus, 1758) during estrous cycle phases and in advanced pregnancy

The study investigated the gross and microscopic anatomy of the genital organs of 20 agoutis at different stages of the estrous cycle and four in the final trimester of pregnancy. Specimens were euthanized and their reproductive organs were fixed in a 4% paraformaldehyde or 2.5% glutaraldehyde solution and submitted to routine histological techniques for light and scanning electron microscopy. In the ovary, during the proestrus phase, we observed developing follicles and corpus luteum (CL) in regression; during estrus, there were Graafian follicles; during metestrus, there was a hemorrhagic corpus, whereas in diestrus, there was a mature CL. The uterus was partially double because the cervix was cranially septate but caudally, the septum disappeared, forming a single ostium that opened into the vagina. Changes occurred along the estrous cycle in the uterine and vaginal epithelia, that is, an increase in the uterine epithelium height accompanied by an increase of thickness of the vaginal epithelium during the follicular phase and a decrease of thickness of both epithelia during the luteal phase. The endometrial lining was composed of a simple cuboidal epithelium to simple columnar epithelium with basal nuclei. The vaginal mucosa consisted of epithelium that varied from nonkeratinized stratified squamous (luteal phase) to keratinized stratified squamous (follicular phase). The clitoris was external to the vagina. It presented two protruding lateral keratinized spicules and a centralized urethra, with no common parts between the urinary and genital tracts. Anatomical and histological changes were observed mainly in the cervix, vagina and spicules of the clitoris during the EC.