Landmark Study Reveals Snow Skinks Can Change Sex Before Birth


You may have seen them before, small spotted skinks that scatter from the rocks beneath your feet as you enjoy a hike on a hot day on the east coast of Tasmania.

These are the snowy spotted skink or Carinascincus ocellatus and they are only found in Tasmania.

After years of speculation, scientists were finally able to confirm that they could perform an interesting trick before they were born.

A study from the University of Tasmania found that skinks can change sex during gestation, depending on the temperature felt by the mother during pregnancy.

“When temperatures are cooler in this species, the female genotype will develop as a male,” said molecular ecologist Dr Peta Hill.

Dr. Hill obtained his skink samples by catching them on a cotton “fishing” line.(Provided: Peta Hill )

But so far, scientists have only been able to prove that the reversal goes one way – from female to male in cooler temperatures.

“In individuals at warmer temperatures there was no sex reversal, or very minimal sex reversal, so sex-reversed offspring the majority were found in cooler temperatures,” she said.

It is the first living reptile to display sexual inversion. There are a handful of egg-laying reptiles that can do this, including the bearded dragon.

The discovery came after some interesting fieldwork – Dr. Hill traveled to Ben Lomond National Park and had to “fish” for pregnant lizards.

She put mealworms on the end of a cotton line as bait – the lizards bit the bait and were pulled into a bucket.

“We brought in females from the wild, just after they came out of hibernation, so they were just pregnant, and we incubated them at certain temperatures throughout their pregnancy,” Dr Hill said.

A spotted snow skink on a rock.
In cooler temperatures, females will develop into males, but whether the reverse is true remains to be determined.(Provided: Peta Hill)

Why are they doing this?

The oddity has everything to do with the temperature that will be favored by the unborn skink – male skinks tend to cope better with cold and female skinks with heat.

But the discovery raises some interesting questions when it comes to climate change.

“Climate change is not just about global warming, it’s about the climate becoming more variable and so that’s going to affect the distribution of this species across Tasmania,” Dr Hill said.

Colder winters could mean more male offspring, while warmer temperatures could mean more female offspring.

“As the climate becomes more unpredictable, and also warmer, that’s going to affect the distribution of species, and the sex ratio could play a pretty big role.”

The study only saw female-to-male sex reversals in cooler temperatures, but while sex reversals in the opposite direction did not occur during the study, that doesn’t mean it does not happen.

“We know that in warm years we get an overproduction of daughters, female offspring. So we haven’t fully explained that yet,” said Dr Hill’s supervisor, conservationist Dr Erik Wapstra.

“Females are more important for population growth – we are not convinced that a warming climate is therefore negative for the species, it could even increase the population size in the short term.”

A baby snow skink spotted on a human hand.
The Tasmanian spotted snow skink can change sex in utero depending on the temperature felt by the mother.(Provided: Peta Hill)

But, he said, that could mean people are struggling in the long run.

“If climate causes a population to be skewed, there will invariably be a negative impact on populations at some point because you need a male and a female to produce offspring. So, simply put, you usually have equal sex ratios in adults,” Dr. Wapstra said.

“Climate change could absolutely affect that and there’s a lot of work on things like crocodiles and turtles to suggest that’s a big and major impact of climate change now and in the future.”

Dr Hill agreed – adding that scientists don’t know exactly how many animals exhibit the phenomenon.

“I think it’s much more widespread than we currently think…there are other species that have been inferred to play a role.

“It’s definitely a concern for reptiles,” she said.

“When the sex ratios of populations are systematically skewed towards one sex, this can limit the health of their population, most certainly.”


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