Fox Lab Behavioral and Evolutionary Ecology / Herpetology

Two modes of sex determination occur in squamates: genotypic sex determination (GSD) and environmental sex determination (ESD). An example of ESD is temperature sex determination (TSD), in which the sex of the hatchling is determined by the incubation temperature of the egg. Collared lizards, Crotaphytus collaris, are oviparous diurnal crotaphytids distributed in the southwestern United States and northern Mexico. The species has been understudied with respect to sex determination, and to date it is not l known with certainty if sex is controlled by TSD or GSD. No sex chromosomes have been identified for the species, but regardless, GSD is considered the mechanism by which sex is determined in C. collaris. We are conducting trials in which eggs are incubated at different temperatures (21°, 27°, 28°, 30°, 32°, 33.5°, and 35°C). So far we see that temperature influences sex of the hatchling, and within the window of ecologically relevant temperatures, fewer females are produced at cooler temperatures and more females at higher ones. We conclude that C. collaris has TSD. We are also observing that size and body dimensions of hatchlings also are influenced by incubation temperatures.