SURVEY OF THE OVIDUCT OF SALAMANDRIDS WITH SPECIAL REFERENCE TO THE VIVIPAROUS SPECIES

Urodeles include oviparous and a few obligately viviparous species tha t belong to one family, the Salamandridae. Oviducts of both groups hav e basically the same design, but some modifications became necessary a s viviparous species evolved. The entire oviduct of urodeles is lined by a monolayered epithelium, which is regionally differentiated into l arge glands and smaller secretory cells rich in glycoproteins. Secreto ry products important for fertilization form the egg jelly, which also is present in viviparous species. In the latter species, however, the re appear to be fewer oviductal convolutions and subdivisions of the g landular part of the organ, as well as fewer gland cells. Viscous, aci dic secretory products predominate in viviparous species, whereas resi stant neutral mucins predominate in oviparous species. In viviparous s pecies, the caudal portion of the oviduct became altered to retain the developing offspring. This ''uterus'' lacks glands, but epithelial ce lls produce carbohydrate-rich material. Offspring remain in the uterus anywhere from several months to five years, depending on the species and climatic conditions. The Na+-K+-ATPase system, common in vertebrat e epithelia, is used to regulate the intrauterine milieu. Subepithelia l vessels mediate gas exchange and the removal of waste products, main ly urea. Secretions of the uterine epithelium may contribute to the fl uid surrounding the young, but do not seem to support nutrition. Sourc es of nutrition for the young vary from one (sub)species to the next. Some feed on yolk reserves (Salamandra salamandra and certain of its s ubspecies), others on unfertilized eggs and siblings (other S. salaman dra subspecies and Mertensiella luschani with subspecies), and yet oth ers on degrading embryotrophic eggs as well as on cells derived from a specialized uterine trophic zone (S. atra and subspecies). Certain ba sic alterations in the uterine epithelium during pregnancy are most li kely under endocrine control. Others, such as the flattening of cells, the discharge of secretory products, and the development of the troph ic zone, may be induced by interactions with the offspring. J. Exp. Zo ol. 282:507-525, 1998. (C) 1998 Wiley-Liss, Inc.