The Evolution of Live Birth and the Insulin and Insulin-like Signaling Network in Sceloporus Lizards

Abstract

Transitions to live birth have occurred in approximately 150 different vertebrate lineages, with 115 of these alone within the clade encompassing snakes and lizards. Many questions remain about how this transition occurs and how molecular networks are evolving associated with the new character state, including the insulin and insulin-like signaling (IIS) network, which fills major roles in structuring and maintain the mammalian placenta. The genus Sceloporus is made up of over 100 species and includes three major groups of live bearing lizards. The recent publication of genomic data for 33 of these species makes them an ideal model to begin investigating the evolution of the IIS network, focusing on two major features: differences in substitution rate in these genes between viviparous and oviparous species, and positive selection within viviparous groups. We provide evidence for widespread increases in substitution rates across genes in this network in viviparous lineages and more limited evidence of positive selection in genes which have major functions related to angiogenesis, tissue proliferation, and oncogenesis.