MORFOLOGÍA FUNCIONAL DE LOS MODOS REPRODUCTIVOS EN ELASMOBRANQUIOS DEL PACÍFICO MEXICANO

Abstract

ABSTRACT Cartilaginous fishes have several reproductive strategies, among which can be distinguished two reproductive modes: oviparity and viviparity, which can be divided into placental and aplacental. Among oviparous and viviparous species certain morphological adaptations in reproductive structures can be seen, principally in the ovaries, oviducal glands and uteri. The objective of the present study was to analyze and compare the external and internal morphology of reproductive structures in female sharks with different reproductive modes. Samples were obtained from the artisanal fisheries in different fishery camps in B.C.S. We analyzed the reproductive tract of pregnant females belonging to seven species of sharks and five species of rays. Ovaries presented differences among the reproductive modes; some species had paired ovaries while others had only one functional ovary. A highly differentiated oviducal gland was observed, especially among oviparous species. For the placental shark Sphyrna zygaena and the oviparous shark Cephaloscyllium ventriosum, we found sperm stored in the oviducal glands, this results are a first record for these species. Uteri presented morphological adaptations, principally among viviparous placental species, among which the formation of uterine compartments indicated adaptations that facilitate the transport of nutrients from the mother to the embryo. Histological changes were observed in the oviducal glands and uteri according to the different reproduction modes. There were structural differences in the uteri in the aplacental and placental sharks. In aplacental, the epithelia allowed the transport of substances to the embryo, where as in placental species the exchange is through the umbilical cord. The macroscopic and microscopic anatomy in the reproductive tract in elasmobranchs marks a trend towards adaptation that makes them unique among vertebrates.