Thermal adaptation of maternal and embryonic phenotypes in a geographically widespread ectotherm

Current theories predict the thermal adaptation of both maternal and embryonic phenotypes such that the fitness of the entire life cycle is maximized. Our studies of the eastern fence lizard (Sceloporus undulatus) have generated evidence that maternal and embryonic phenotypes are designed to promote growth and development in cold environments. Females in colder environments allocate more energy per egg enabling offspring to grow faster and reach a larger size at hatching. Females in cold environments also nest exclusively in warm, open sites that maximize rates of embryonic growth and development, although this behavior involves risky migrations. Likewise, thermal adaptation of embryonic physiology also promotes growth and development in cold environments. When incubated in the laboratory under shared environmental conditions, embryos from colder environments developed faster and grew more efficiently than embryos from warmer environments, which is a pattern called counter-gradient variation. Because thermal adaptation can produce geographic variation in a suite of maternal and embryonic phenotypes, biologists should develop theories of coadaptation that consider costs and benefits of behavioral and physiological strategies at both stages of the life cycle.