AMONG-FAMILY VARIATION FOR ENVIRONMENTAL SEX DETERMINATION IN REPTILES

Unlike birds and mammals, in many reptiles the temperature experienced by a developing embryo deter mines its gonadal sex. To understand how temperature-dependent sex determination (TSD) evolves, we must first determine the nature of genetic variation for sex ratio. Here, we anal yze among-family variation for sex ratio in three TSD species: the Ame rican alligator (Alligator mississipiensis), the common snapping turtl e (Chelydra serpentina), and the painted turtle (Chrysemys picta). Sig nificant family effects and significant temperature effects were detec ted in all three species. In addition, family-by-temperature interacti ons were evident in the alligator and the snapping turtle, but not in the painted turtle. Overall, the among-family variation detected in th is study indicates potential for sex-ratio evolution in at least three reptiles with TSD. Consequently, climate change scenarios that are po sited on the presumption that sex-ratio evolution in TSD reptiles is g enetically constrained may require reevaluation.