WEISS, S.L.; JENNINGS, D.H.; PAINTER, D.L.; MOORE, M.C.; Arizona State Univ, Tempe; Arizona State Univ, Tempe; Arizona State Univ, Tempe; Arizona State Univ, Tempe: Endocrine capacity of oviductal tissues of oviparous (Urosaurus ornatus, Sceloporus virgatus) and viviparous (S. Jarrovi) lizards

Studies of the evolution of viviparity largely focus on specific mechanisms that allow for viviparous reproduction. However, it is necessary to discriminate features that originated after the evolution of viviparity from those that were present prior to its evolution. In viviparous reptiles, the placenta metabolizes steroids and regulates steroid exchange between maternal and embryonic circulation. We investigated whether this capability for steroid metabolism also exists in oviparous lizards. Since the reptilian placenta evolved from the wall of the oviduct, we used in vitro incubation to compare steroid metabolism in oviducts from two oviparous lizards (Sceloporus virgatus and Urosaurus ornatus) to that in non-placental oviductal tissue from viviparous lizards (S. jarrovi). Results suggest that oviductal tissues in both oviparous and viviparous lizards are capable of steroid metabolism in vivo. The taxa differ in their capacity for in vitro conversion of pregnenolone to progesterone, but not in their capacity for in vitro progesterone or corticosterone metabolism. Since oviductal tissues from the two species of Sceloporus metabolize progesterone faster than oviducts from U. ornatus, we conclude that the metabolic capacity of oviductal tissue is not necessarily related to reproductive mode and instead may differ phylogenetically. This raises the intriguing possibility that differences in steroid metabolic capacity of oviductal tissues in oviparous species may influence the likelihood of evolving viviparity. The ability of the oviducts of oviparous species to metabolize steroids may have evolved as a way of regulating exposure of eggs to maternal steroids while the albumin and shell are formed.