Abstract
Wild populations of an Australian lizard have sex chromosomes and also exhibit temperature-controlled sexual development, providing insight into how these two sex-determining mechanisms may evolve back and forth. See Letter p.79 There have been repeated evolutionary transitions in reptiles between genetic and temperature-dependent sex determination, the regulatory process that initiates differentiation of the gonads in the early embryo to form either testes or ovaries. Various mechanisms have been proposed to explain the transition, including a role for sex reversal. Clare Holleley et al. present the first report of reptile sex reversal in the wild, associated with rapid transition between genetic and environmental sex determination. In a study of the Australian bearded dragon (Pogona vitticeps), they observe sex reversal at the warmer end of the animals geographic range. When sex-reversed females mate with normal males, the chromosomal sex determination system is lost and temperature-dependent sex determination is established. It is not known whether climate-induced changes in sex determination are advantageous or detrimental to the process of evolutionary adaptation.
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