OUFIERO, C.E.*; ANGILLETTA, M.J.; Univ. of California, Riverside; Indiana State University: Parallel evolution of embryonic growth and development in the eastern fence lizard (Sceloporus undulatus)

Geographically widespread ectotherms encounter thermal gradients that generate variation in behavior, physiology and life-history. Because rates of physiological processes are very sensitive to temperature, cold environments are thought to favor genotypes that have high capacities for growth despite environmental constraints. Two different adaptive responses can enhance the growth of juveniles: embryos in colder environments can (1) develop faster, or (2) make more efficient use of available resources. In this study, we examined embryonic adaptation of growth and development in the eastern fence lizard (Sceloporus undulatus) through a common garden experiment. Eggs from five populations were incubated under shared environmental conditions, and growth efficiency and incubation period were measured. The populations comprised two separate clades, one west of Appalachia (IN & FL), and one east of Appalachia (NJ, VA & SC). We determined if individuals from cold environments (IN, NJ & VA) grew more efficiently and hatched earlier than individuals from warm environments (FL & SC). Incubation period was measured as the time taken for each embryo to hatch. Growth efficiency was measured as the proportion of yolk allocated to growth throughout development. In both clades, embryos from colder environments exhibited faster growth and development. Our results indicate that strong selection on body size in cold environments has led to the parallel evolution of counter-gradient variation in rates of growth and development.