"The important implication of this is that there is probably a whole continuum of reptiles with varying degrees of interaction between sex genes and temperature," Quinn said in an email.
Until now animals were assumed to use one mechanism or the other, with reptiles such as crocodiles, turtles, and tortoises relying on temperature, and mammals, birds, and most amphibians depending on genes.
"Theory in Tatters'
A dual system for determining sex has also been suggested for another Australian lizard, the three-lined skink, by a team led by Rick Shine, professor of evolutionary biology at the University of Sydney.
Shine said that the new findings "verify a remarkable phenomenon."
"The evidence that nest temperatures can override sex chromosomes is absolutely clear-cut," he commented.
"The work is exciting because it suggests that a long-held dogma in this research field—that in any given population, sex is determined by a single process—is now in tatters.
"The factors that determine an animal's sex are truly basic to its biology, and it's becoming increasingly clear that we don't really understand what those factors are, at least in some major groups of animals.
"I suspect that future studies will show that many kinds of animals have far more complex sex-determining systems than we currently imagine," he added.
Quinn, the lead researcher of the new study, said a better understanding of such systems may benefit humans, leading to the discovery of sex-development genes that lie behind genetic disorders.
Reptiles like the central bearded dragon might be able to switch between genes and temperature as sex determiners in order to adapt to changing environmental conditions, he suggested.
(Read related story: "Virgin Birth Expected at Christmas—By Komodo Dragon" [December 22, 2006].)
But there are fears that global warming may heavily skew sex ratios in some reptiles, causing population crashes that could potentially lead to extinctions.
(Read related story: "Warming May Drive Gender-Bending Reptiles Extinct, Scientists Say " [November 10, 2006].)
"The concern now is that the current rate of climate warming could be too rapid for these species to adapt," Quinn said.
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