Viviparity has an intriguing interface with reptilian thermal biology. Reptiles behaviorally regulate their body temperature. Thus, developing embryos of oviparous species are subject to the same body temperature as their mother only until oviposition, while developing embryos of viviparous species are subject to mother's body temperature throughout development. Because thermal requirements of females and embryos are not identical, interests of mothers and offspring may be in conflict. The resolution of this conflict is an important component in the evolution of viviparity and of present day interactions between mothers of viviparous species and their developing embryos. The proposed research is directed towards two major questions. Has the evolution of viviparity been constrained by conservative thermal tolerances of embryos? Viviparity has evolved from oviparity in almost 100 lineages of snakes and lizards, and it is favored in cool climates where increased egg retention requires more favorable thermal environment for embryonic development than nests. However, an evolutionary shift from oviparity to viviparity is possible only if embryonic development is not compromised by the environment imposed by the pregnant female. The investigator will evaluate temperature tolerances of embryos of oviparous lizards from linages where it has not. The hypothesis to be tested is that viviparity is more likely to evolve in lineages where thermal requirements of females and thermal tolerances of their embryos are similar than in lineages where they differ. Is the thermoregulation by pregnant females of viviparous species constrained by thermal tolerances of embryos? Temperatures selected by pregnant females of viviparous lizards differ from those selected by non.pregnant females. Are shifts in body temperatures associated with pregnancy related to adult body temperatures per se? This research will evaluate diel temperature profiles of viviparous lizards when pregnant and not pregnant. The hypothesis to be tested is that species that exhibit relatively high body temperatures when active alter their thermal behavior more when pregnant than closely related species that exhibit relatively low body temperatures. Rejection of this hypothesis for all or some lineages would suggest thermal tolerances of embryos are more labile than laboratory studies predict or that thermal tolerances of embryos evolve rapidly.
