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

Abstract

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.

Background and common lesions in the female reproductive organs of giant anteaters (Myrmecophaga tridactyla)

“…We consider our results to be similar to the structural findings in female giant anteaters made in a previous study ( 13 ). Furthermore, the background and common reproductive lesions visualized have previously been described in humans and in domestic and wildlife species ( 14 – 16 ).…”

“…Six female giant anteaters were included after being received at our institutional wildlife center within a maximum interval of 12-h after death due to blunt trauma force ( Table 1 ). Their ages were determined based on their body weights according to the existing literature ( 13 ). Representative sections of both the ovaries and uterus were systematically collected and fixed in neutral-buffered 10% formalin during necropsy.…”

“…Ovarian and uterine morphological analyses were performed according to the methods established by Rossi et al ( 17 ) and Fromme et al ( 13 ). The evaluation was performed in a double-blind fashion: one at São Paulo State University (N.S.R.)…”

“…A recent study has identified the structural and ultrastructural morphology of the prostate gland in giant anteaters and revealed its histological and immunohistochemical features ( 12 ). Another study has described the morphology and histology of the reproductive tracts ( 13 ).…”

Case report: Persistent Müllerian duct syndrome and enlarged prostatic utricle in a male dog

“…There are other reports of this syndrome in cats ( 3 ), goats ( 4 , 5 ), bison ( 6 ), and beavers ( 7 ). The persistence of Müllerian ducts as a remnant uterus, dorsal to the prostate, bifurcating and extending cranial to the epididymis, is a normal finding in male giant anteaters ( 8 ). All reported clinical cases of PMDS are due to mutations in genes encoding Anti-Müllerian Hormone (AMH) and/or AMH receptors (AMHR) ( 2 , 9 – 14 ).…”