How does temperature determine sex?

May 24th, 2018

In a recent issue of Science magazine, Clare Holleley (FSP Project Leader) and colleague Arthur Georges (University of Canberra) share exciting new science shedding light on the mechanisms of temperature-dependent sex determination (TSD) in reptiles.

A turtle with a bright red stripe on the side of its head, sitting on a rock

Adding an image of the red-eared slider turtle as it is the reptile discussed in the journal publication.

Scientists have identified a gene as a master switch in temperature dependent sex determination in the red-eared slider turtle. Credit: Greg Hume

Sex determination in reptiles is a complex affair because in many species incubation temperature and genes interact to regulate sexual development and decide sexual fate, male or female. The genetic pathways that determine sex are understood in many organisms, but exactly how temperature can influence sex determination has remained a mystery for over 50 years. This problem has been intractable, despite keen interest in the area, because temperature could exert a sex-determining effect on any of the many autosomal genes involved in sexual differentiation.

Georges and Holleley summarise the exciting findings of Ge et al. who have reported the first functional evidence implicating the chromatin modifier gene, Kdm6b, as a master switch in temperature dependent sex determination in the red-eared slider turtle (Trachemys scripta elegans). Kdm6b controls the outcome of turtle sex determination because it controls the epigenetic state and thus expression of a “master” sex determining gene, Dmrt1.

This study reveals links between the environment, epigenetic state and sex determination, it also may help us explain why reptiles today display such an astonishing diversity of sex determination systems. Conserved thermosensitive epigenetic processes may have allowed the independent recruitment of novel sex determining genes throughout reptile evolution.

Read Arthur Georges and Clare Holleley’s report here, or Ge et al. publication here.

Graphic prepared by N.Desai/Science.

Image credit: RedEaredSLider05 by Greg Hume under a Creative Commons Attribution 3.0. Full terms available at