Chapters authored
Sequence of Germ Cells Differentiation During Spermiogenesis of the Amphibian Urodele Ambystoma dumerilii
The spermatogenesis, including the spermiogenesis, in Urodeles contains the meiotic process and the morphological differentiation of the spermatids developing the spermatozoa as in the rest of vertebrates. However, in Urodeles, there are essential differences in the structure of the testis, as a lobular structure; the distribution of the spermatogenic cells, in cephalocaudal progression in the testis; and the cystic condition of the developing spermatogenic cells in synchronous groups bounded by Sertoli cells. All the spermatogenic cells are situated in parallel position with the heads directed to the same side. The big size and elongated morphology of the spermatozoa also characterized this type of spermiogenesis. Spermiation occurs at the caudal portion of the testis to the efferent duct system, which includes the mesonephric nephrones.
Part of the book: Spermatozoa
Intraovarian Gestation in Viviparous Teleosts: Unique Type of Gestation among Vertebrates
The intraovarian gestation, occurring in teleosts, makes this type of reproduction a such complex and unique condition among vertebrates. This type of gestation of teleosts is expressed in special morphological and physiological characteristic where occurs the viviparity and it is an essential component in the analysis of the evolutionary process of viviparity in vertebrates. In viviparous teleosts, during embryogenesis, there are not development of Müllerian ducts, which form the oviducts in the rest of vertebrates, as a result, exclusively in teleosts, there are not oviducts and the caudal region of the ovary, the gonoduct, connects the ovary to the exterior. The lack of oviducts defines that the embryos develop into the ovary, as intraovarian gestation. The ovary forms the oocytes which may develop different type of oogenesis, according with the storage of diverse amount of yolk, variation observed corresponding to the species. The viviparous gestation is characterized by the possible intimate contact between maternal and embryonic tissues, process that permits their metabolic interchanges. So, the nutrients obtained by the embryos could be deposited in the oocyte before fertilization, contained in the yolk (lecithotrophy), and may be completed during gestation by additional provisioning from maternal tissues to the embryo (matrotrophy). Then, essential requirements for viviparity in poeciliids and goodeids are characterized by: a) the diversification of oogenesis, with the deposition of different amount of yolk in the oocyte; b) the insemination, by the transfer of sperm to the female gonoduct and their transportation from the gonoduct to the germinal region of the ovary where the follicles develop; c) the intrafollicular fertilization; d) the intraovarian gestation with the development of embryos in intrafollicular gestation (as in poeciliids), or intraluminal gestation (as in goodeids); and, e) the origin of embryonic nutrition may be by lecithotrophy and matrotrophy. The focus of this revision compares the general and specific structural characteristics of the viviparity occurring into the intraovarian gestation in teleosts, defining this reproductive strategy, illustrated in this review with histological material in a poeciliid, of the species Poecilia latipinna (Lesueur, 1821) (Poeciliidae), and in a goodeid, of the species Xenotoca eiseni (Rutter, 1896) (Goodeidae).
Part of the book: Animal Reproduction