Hi, This paper answers the question:
Warner, D. A., and R. Shine. 2008. The adaptive significance of temperature-dependent sex determination in a reptile. Nature 451, 566-568. Luis J. Villanueva-Rivera [EMAIL PROTECTED] http://research.CoquiPR.com http://www.AvesPR.org Doctoral Graduate Student and Researcher Human-Environment Modeling & Analysis Facility Department of Forestry and Natural Resources Purdue University West Lafayette IN 47907 On Tue, Oct 28, 2008 at 12:19 AM, Wirt Atmar <[EMAIL PROTECTED]> wrote: > Thilina asks: > >> I have a question on the temperature dependant sex determination of >> reptiles. What is the evolutionary or ecological advantage of such a >> phenomena, especially in reptiles when the females are produced under both >> low and high temperature extremities? > > The simple answer is that no one knows. > > You could speculate that a species population that moves too far out of its > temperature preferendum would begin to drop in fecundity. You could also > speculate that such a population might depend on being "rescued" by female > parthenogenesis, a process that is being reported in increasingly more > reptilian > species each year, but all of this is just speculation. > > What you can say is that temperature-determined sex determination is ancient > and > an odd system to have persisted so long. Mammals are universally > chromosomally-determined, so their system must have evolved sometime after the > split of the mammal-like reptiles from the main amniote branch (~325 Ma). > > Similarly, birds are also universally chromosomally-determined, but > gender-reversed, and they too are reptile descended, arising sometime in the > mid-Mesozoic (~190 Ma) from the theropod ("beast-footed") dinosaurs, strongly > suggesting that dinosaurs were similarly chromosomally determined. > > Crocodiles and their relatives are the only remaining living animals of the > Crurotarsi, one of the two subclades of the archosaurs; the other clade is the > Ornithodira (dinosaurs, pterosaurs, and birds). One clade (Ornithodira) is > chromosomally determined, the other (Crurotarsi) temperature-determined. > > Both of these clades lie within the Sauropsida, a sister clade to the > Therapsida, the "mammal-like reptiles," the group from which true mammals > descended. This split in clades is believed to have occurred in the > Carboniferous (~340 Ma), making chromosomal sex determination older in the > mammal-like reptiles than in the dinosaurs, but making both forms of sex > determination quite old. > > Wirt Atmar >
