Rock dragons are medium-sized agamid lizards restricted to arid or semiarid rocky habitats in southern Australia. When eggs from two species (Ctenophorus decresii and Ctenophorus ornatus) were incubated at constant temperatures in the laboratory, temperature affected incubation period, hatchling tail length, and sex determination. At the lowest incubation temperature (25 C), all hatchlings were female; the proportion of males increased at higher incubation temperatures. Rock dragons are fast growing and short-lived lizards; in the field they reproduce for only one or two seasons. Females lay multiple clutches of eggs from spring through to late summer which, in the climatically temperate part of Australia where these species occur, suggests that the date of hatching may be a good predictor of hatchling sex. Any sex differences in hatching date would, in turn, translate into sex differences in body size at the beginning of the next reproductive season. If the relationship between body size and reproductive success differs between the sexes in adult rock dragons, this would provide a plausible basis for the evolution of temperature-dependent sex determination in these species.
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Vol. 2000 • No. 4