Egg retention and intrauterine embryonic development in Sceloporus aeneus (Reptilia: Phrynosomatidae): implications for the evolution of viviparity

Egg retention (ER) and intrauterine embryonic development (IED) have been considered intermediate stepsin the evolution from oviparity to viviparity. Sceloporus aeneus is an oviparous lizard that is closely related to theviviparous species (Sceloporus bicanthalis). The present study addresses the following 2 questions: 1) Are intermediatestages of egg retention (ER and IED) present in populations of Sceloporus aeneus? and 2) Are ER and/or IED explainedby elevation, precipitation or phylogenetic effects? Results indicate that in S. aeneus, ER differs among populations. ERwas negatively related to altitude and pluvial precipitation, whereas average environmental temperature had no effecton ER or IER. In contrast to previous observations of oviparous species related to viviparous species, populations of S.aeneus with advanced IED are associated with environmental factors such as low elevation and aridity instead of highelevation and cold climate, whereas the comparative analysis shows that there are no significative evolutionary changesthroughout the phylogeny, which means that the altitude has no effect on the transition to the evolution of viviparity inS. aeneus-S bicanthalis.