Lizard can switch from female to male before birth, but not vice versa

By Christa Lest.

The first non-egg-laying animal known to switch sexes before birth is a lizard from Tasmania.

When the eggs are exposed to environments that are warm or cool, they will hatch with male sex organs and female chromosomes.

The spotted snow skink is a lizard that gives birth to live young and Peta Hill and her colleagues have found the same.

100 newly pregnant female spotted snow skinks were trapped and placed in individual terrariums by the researchers.

Two groups of 20 skinks had access to a heat lamp for 4 or 12 hours a day, which created temperature zones ranging from 20 to 37 degrees C and falling to 10 degrees C when the lamp was off. Three groups lived in controlled temperatures of 33, 29.5, and 26 degrees for eight hours a day and 10 degrees for the other 16 hours.

In the first month of life, the researchers examined the sex organs of newborn skinks. They assigned genetic sexes by taking the tails of the animals.

There were no male-to-female changes with the skinks with female sex organs. 7 per cent of the newborn skinks had male sex organs.

Read more: Turtle embryos may control their sex by moving inside their eggs

The skinks were mostly found in the cooler terrariums and were born to females from lower altitudes. 20 per cent of the offspring with male sex organs and XX chromosomes were born to females from low altitudes that only had four hours of heat lamp per day. Only 2 per cent of offspring born to females from low altitudes were kept in warmer conditions.

Benjamin Geffroy at the French Institute for the Exploitation of the Sea says that the findings are not only seen in a live-bearing reptile, but also because they are one-sided.

That might be explained by a generation effect. He says that skinks with male sex organs and XX chromosomes can grow up to be functional adult males. All the pair's offspring would be XX because they lack a Y chromosome.

I think it's interesting that we can explain the bias toward females in warm conditions if we consider that some males reproduce with other females, leading to more genetic females in the second generation. The theory could be supported by a longer study.

The Royal Society B's journal reference is the Proceedings of the Royal Society B.

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