A fundamental problem in biology is understanding the ecology, genetics, and evolution of diverse sex-determining mechanisms. To address these questions, we have focused on reptiles as model organisms because they exhibit a tremendous diversity in modes of sex determination, including temperature-dependent sex determination (TSD) (Janzen and Paukstis, 1991, Quart. Rev. Biol.; Valenzuela et al., 2003, Am. Nat.; Janzen and Krenz, 2004). In the past we have studied the adaptive significance of TSD (Janzen and Paukstis, 1991, Evolution; Janzen, 1995, Evolution; Valenzuela and Janzen, 2001, Evol. Ecol. Res.; Janzen and Morjan, 2002, J. Herpetol.; Morjan and Janzen, 2003, Copeia; Janzen and Phillips, 2006, J. Evol.