Sex change in reptiles blamed on increased temperatures due to climate change

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Researchers at the University of Canberra have confirmed for the first time that sex change in reptiles can occur naturally due to exposure to increased temperatures resulting from climate change.

Published in the journal Nature, the study proves previous lab experiments that sex determination in reptiles isn’t just dependent on chromosomes, but also on temperature of their surroundings.

Lead author Dr Clare Holleley, a postdoctoral research fellow at the University of Canberra’s Institute for Applied Ecology, along with other researchers, who have long studied Australia’s bearded dragon lizards explains: “We had previously been able to demonstrate in the lab that when exposed to extreme temperatures, genetically male dragons turned into females.”

Researchers have also shown in their latest study that the reptiles which have undergone natural sex change are fertile.

Using field data from 131 adult lizards and controlled breeding experiments, Dr Holleley and colleagues conducted molecular analyses which showed that some warmer lizards had male chromosomes but were actually female.

“By breeding the sex reversed females with normal males, we could establish new breeding lines in which temperature alone determined sex. In doing so, we discovered that these lizards could trigger a rapid transition from a genetically-dependent system to a temperature-dependent system,” she said.

“We also found that sex-reversed mothers – females who are genetic males – laid more eggs than normal mothers,” Dr Holleley said. “So in a way, one could actually argue that dad lizards make better mums.”

Further, the researchers also reveal in the paper that controlled mating of normal males to sex-reversed females produces viable and fertile offspring whose phenotypic sex is determined solely by temperature (temperature-dependent sex determination).

The W sex chromosome is eliminated from this lineage in the first generation. The instantaneous creation of a lineage of ZZ temperature-sensitive animals reveals a novel, climate-induced pathway for the rapid transition between genetic and temperature-dependent sex determination, and adds to concern about adaptation to rapid global climate change.

University of Canberra Distinguished Professor Arthur Georges, senior author of the paper, also highlighted the importance that these discoveries have in the broader context of sex determination evolution.

“The mechanisms that determine sex have a profound impact on the evolution and persistence of all sexually reproducing species,” Professor Georges said.

“The more we learn about them, the better-equipped we’ll be to predict evolutionary responses to climate change and the impact this can have on biodiversity globally.”