Sex-shifting dragons hatch a ‘third sex’

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Male or female …. or both? Sex isn’t straightforward for central bearded dragons (Pagona vitticeps).
Credit: Don Farrall / Getty Images

In most animals, sex is determined by chromosomes or environmental variables. But not sex-shifting super-dragons.

A new study on the central bearded dragon (Pogona vitticeps), a desert-dwelling Australian lizard that grows up to 60 centimetres long, found they can morph into a “third sex” that is partially male and female.

When the eggs of these bearded dragons are incubated in a hot nest – that is, temperatures above 32 ºC – embryos that are genetically coded as male will develop into female-bodied dragons.

Astoundingly, the findings suggest this transformation, called sex-reversal, results in a stronger, bolder female, with more gusto and fertility than the other lizards – in a sense, a kind of super-dragon that is female in body with a mix of male and female in other traits.

The paper, published in Proceedings of the Royal Society, says the animals represent a “third sex”, in addition to males and females of the species that are known as concordant – that is, their genetic sex matches their phenotypic sex.

“These animals develop into functional females, whose annual output of eggs exceeds that of ‘normal’ (genetically concordant) females,” the paper written by researchers in Australia and China reads.

In an interesting twist, because sex-reversed dragons do not have a standard female chromosome, the sex of their young is always determined by nest temperature, rather than genetics.

This change in how a dragon’s sex is determined can happen within one generation. Given the heightened strength of these super-dragons, the species may be rapidly evolving towards this method of sex-determination.

The team wanted to study the traits of these genetic novelties.

They examined the behaviour of a group of more than 100 young lizards, including 20 sex-reversed females, and tested each lizard’s willingness to explore a new environment, as well as levels of sociability and activity.

Across the board, sex-reversed females tested as more bold, active and sociable than concordant females, aligning them more closely with their genetically male counterparts.

“Although functionally female (i.e. capable of producing viable eggs), the only phenotypic trait in which sex-reversed females resembled normal females was in body condition,” the paper reads.

According to the findings, sex-reversed females were also closer to males in body temperature, and in some tests, the lizards even outperformed the concordant males in the group.

“Sex reversal (by egg incubation at high temperatures) changes not only a lizard’s gonadal sex, but also some of its behavioural and morphological traits,” the paper explains.

The researchers say more work is needed to determine whether these characteristics are maintained all the way through the lizards’ adult life.

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