Structure of the testis and spermatogenesis of the viviparous teleost Poecilia mexicana (Poeciliidae) from an active sulfur spring cave in Southern Mexico

Abstract

We describe the histological characteristics of the testis and spermatogenesis of the cave molly Poecilia mexicana, a viviparous teleost inhabiting a sulfur spring cave, Cueva del Azufre, in Tabasco, Southern Mexico. P. mexicana has elongate spermatogonial restricted testes with spermatogonia arranged in the testicular periphery. Germ cell development occurs within spermatocysts. As spermatogenesis proceeds, the spermatocysts move longitudinally from the periphery of the testis to the efferent duct system, where mature spermatozoa are released. The efferent duct system consists of short efferent duct branches connected to a main efferent duct, opened into the genital pore. Spermatogenesis consisted of the following stages: spermatogonia (A and B), spermatocytes (primary and secondary), spermatids, and spermatozoa. The spermatozoa are situated within spermatocysts, with their heads oriented toward the periphery and flagella toward the center. Once in the efferent duct system, mature spermatozoa are packaged as unencapsulated sperm bundles, that is, spermatozeugmata. We suggest that the histological characteristics of the testis and spermatogenesis of P. mexicana from the Cueva del Azufre, and the viviparous condition where the spermatozoa enter in the female without been in the water, have allowed them to invade sulfurous and/or subterranean environments in Southern Mexico, without requiring complex morphofunctional changes in the testis or the spermatogenetic process.

Testicular structure and development of the male germinal epithelium in the freshwater drum Aplodinotus grunniens (Perciformes: Sciaenidae) from the Usumacinta River, Southern Mexico

“…This is considered to be a primitive condition present in more basal taxonomic groups such as Cypriniformes, Characiformes and Salmoniformes (Parenti & Grier, 2004). Only derived Atherinomorph fish from the orders Atheriniformes, Beloniformes and Cyprinodontiformes show testicular restricted type where spermatogonia are confined to the blind portion of the seminiferous lobules at the periphery of testis (Grier & Uribe, 2009; Parenti & Grier, 2004; Torres‐Martínez et al., 2019; Uribe et al., 2009; Uribe et al., 2014). Although A. grunniens spermatogonia were randomly distributed throughout the length of the seminiferous lobules, they appeared more frequently located next to the tunica albuginea, where they formed germinal nests integrated by spermatogonia and Sertoli cells.…”

Gonad Ontogeny and Sex Differentiation in a Poeciliid, Gambusia holbrooki: Transition from a Bi- to a Mono-Lobed Organ

“…However, in some other poeciliids, the lobes are not completely fused, even in adulthood. For example, in P. Mexicana, the testes remain as paired lobes in adults, although the lobes are in the closest vicinity to an incomplete fusion [81]. Regardless, this morphological fusion of gonad lobes appears to have evolved for supporting viviparity in poeciliids, i.e., integrating two lobes to form an anterior ovarian section to produce gametes and a dorsal and posteriorly extending uterus-like cavity for gestation.…”

“…It must be noted that the morphological details of gonad formation are not completely conserved among poeciliids. Instead, they show varying degrees of gonad fusion [81], implying their comparative utility in deciphering the evolutionary links that lead to the more specialised ovary and uterus of higher vertebrates.…”

Analysis of clasp2 Transcription Pattern in Male Germ Cells during Spermatogenesis: A Comparative Study in Zebrafish (Danio rerio) and Guppy (Poecilia reticulata)

“…In the present studies, we aim to analyze clasp2 gene transcription levels during fish germ line cell formation. We decided to use two excellent fish models, zebrafish and guppy (Poecilia reticulata) teleost fishes, in which oogenesis and spermatogenesis processes are best described [33][34][35][36]. In detail, by quantitative PCR, we measured total clasp2 transcription levels in different zebrafish and guppy tissues, observing a higher transcription in the testis, similarly in the two models.…”