Contributions to the study of oviparity-viviparity transition: placentary structures of Liolaemus elongatus (Squamata: Liolaemidae)

CROCCO, M. C., IBARGUENGOYTIA N. R. Y CUSSAC V.

JOURNAL OF MORPHOLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Año: 2008 vol. 269 p. 865 - 874

0362-2525

Abstract In order to study the structural and functional diversity of placentas and the oviparity-viviparity transition in Amniota, we collected basic observational data and made measurements regarding the placenta of the reptile Liolaemus elongatus (Liolaemidae). It is a viviparous, mainly lecithotrophic species with placental structures specialized for uptake of oxygen and inorganic nutrients transport. During the early embryo stages (25 to 28) we observed the allantoplacenta and the omphaloplacenta, and a moderate distension of the uterine wall and major glandular activity in the uterine mucosa and submucosa respect of the non pregnated female. The uterine epithelium increases in height, first as a growth in the height of some dispersed cells localized in all regions of the placenta, and later as groups of cells localized in the periembryonic and central-abembryonic regions. At embryo stage 39, the allantoplacenta reaches its maximum extension around the yolk sac. The omphaloplacenta is restricted to the abembryonic zone and to the yolk mesodermal cleft, which limits the newly formed isolated yolk mass. At more advanced embryo stages (39 to 42) the blood supply of the periembryonic zone of the egg increases, matching the profuse allantoic vascularization. The omphaloplacenta is still present at stage 39, and becomes part of the omphalallantoic placenta at stage 42. At embryo stage 42 the omphalallantoic placenta is formed by maternal vessels and the allantois that enters the yolk cleft through the intravitelline mesoderm. In L. elongatus most nutritional resources seem to be provided by the yolk that remains attached to the newborn for two or three days as an external supply. The embryo's wet weight increases twice the weight of the decrease observed in the vitelline mass but the dry wet diminishes, probably due to water uptake and inorganic maternal provision.