Meeting Abstract
Vertebrates have transitioned from egg-laying to live birth approximately 140 times across their evolution, 115 of which have occurred within lizards and snakes. In contrast, the mammalian lineage experienced this change one time with the evolution of the mammalian placenta followed by rapid diversification of structures and mechanisms to maintain fetuses. This transition is a major life history change requiring the coordinated evolution of mechanisms to retain the egg, lose the eggshell, and begin provisioning maternal resources to the fetus via a placenta. One major gene network implicated in development, growth, and function of the mammalian placenta is the insulin and insulin-like signaling (IIS) network. Although the IIS network is critical to the placenta in mammals, we currently have a poor understanding of the role of this molecular network in placental function in other clades. There is strong evidence that squamate reptiles have experienced significant positive selection in major regulators of the IIS network such as insulin growth factor 1, insulin, and their receptors, but this selection has not yet been investigated in the context of the repeated evolution of viviparity. Sceloporus is a genus of lizards that is ancestrally oviparous but has experienced three unique transitions to viviparity. I have isolated IIS network genes from shotgun genomes of 35 species in this genus. Using molecular evolution analyses, I am testing for unique patterns of selection in IIS network genes that may promote the lability of parity mode in this genus, given the network’s important role in mammalian placental function.
