A new study has found a species of Tasmanian lizard can change sex before birth when it is exposed to cool temperatures in utero.
Researchers from the University of Tasmania have discovered the Tasmanian spotted snow skink can switch from female to male, but not the reverse, as part of an evolutionary response to the surrounding climate.
Ecologist Dr Peta Hill said that while sex reversal had previously been observed in fish, amphibians and egg-laying reptiles, this was the first time it had been seen in reptiles that produce live offspring.
“Our research shows that male Tasmanian spotted snow skinks tend to do better in cool temperatures, while females favour a warmer climate. The lizards have evolved a mechanism to change sex in the womb when they are exposed to low temperatures,” Dr Hill explained.
“Now we know that these mechanisms are not limited to egg laying species, it raises the question of whether it has potentially occurred more broadly across evolution.
“Our work also adds an important further direction for climate change research as we and others ask how common such effects are and how they may change into the future.”
The study involved 100 newly pregnant lizards captured from field sites in the Central Plateau and Orford, Tasmania. The researchers placed the skinks in individual terrariums in the laboratory, using heat lamps and incubators to expose them to different temperatures throughout gestation.
At birth, the offspring were sexed by examining their sex organs and assigned a genetic sex by sequencing DNA from the end of their tails. This enabled any genetic mismatches to be identified.
The experiment yielded 423 newborn skinks, 7 per cent of which were found to have male sex organs and XX chromosomes, indicating a sex reversal of female-to-male before birth.
All of the lizards born with female sex organs also had XX chromosomes, which signals there were no male-to-female sex reversals.
The 31 babies who had changed sex from female to male were mainly found in the cooler terrariums with limited exposure to the heat lamp or lower incubator temperatures.
Pregnant females were given access to heat lamps for either four hours per day or 10 hours per day, or held in incubators at either 26°C, 29.5°or 33°C for eight hours per day.
“We know from previous studies on this and other reptiles that temperature also influences birthdate and cooler temperatures are associated with delayed birth,” Dr Hill said.
“The majority of the XX male babies in this study were born in the four hour and 26°C treatments and had later birthdates, confirming the links between climate, birthdate and sex. This is key to understanding how sex determination systems have evolved but also important for understanding species’ response to future climates.”
Behavioural ecologist Professor Erik Wapstra said that improving our understanding of how sex is determined would have wide-ranging benefit and be of substantial interest to scientists around the world.
“Australia is a world leader in research on evolutionary and ecological drivers of sex determination, especially using reptiles as model systems,” Professor Wapstra said.
“The long-term population data we have collected on the Tasmanian spotted snow skink is one of the most comprehensive collections on a wild animal in the southern hemisphere.”
The paper “Sex reversal explains some, but not all, climate-mediated sex ratio variation within a viviparous reptile” was published in the journal Proceedings of the Royal Society B.
https://royalsocietypublishing.org/doi/10.1098/rspb.2022.0689