An extraordinary feat achieved by a lizard could suggest the species is going through a rare evolutionary transition

Recently, a three-toed skink (Equalized Saiphos) achieved an extraordinary feat: he laid three eggs and gave birth to another baby by live birth in the same pregnancy. This suggests that the lizard species is in a rare form of transition between laying and living animals, according to published study Molecular ecology last month.

“We affectionately call the three-toed skink ‘the world’s strangest lizard” – but it can tell us a lot about the evolution of breeding strategies, “Camilla Whittington, one of the study’s lead authors and evolutionary biologist at the University of Sydney, wrote in an email to CNN.

The three-toed skinks, found in Australia, are already a fascinating species to evolutionary scientists, explains Whittington. One reason is that some populations reproduce by laying eggs, while others reproduce by live birth.

The mode of reproduction used by skinks generally corresponds to their environment. Sydney area skinks lay eggs, even though they have thin shells and almost fully developed embryos. In northern Australia, skinks give birth to live young.

But never before have scientists seen a species lay eggs and be born alive in a single pregnancy until it was observed in the Three-toed Skink last year, Whittington wrote. It was the first recording of a vertebrate doing so.

Why this could happen

There are a few explanations why the skink laid eggs and had a live baby in the same pregnancy, Whittingon said.

The first is that it was a form of “betting blanket,” meaning the ability to switch between spawning and live birth could provide the lizard with an advantage in unpredictable environments.

“For example, if it is cold or dry, it can be risky to lay eggs in an unprotected nest, and it is better for moms to carry babies until development is complete,” he said. -she writes. “If there are a lot of predators around and pregnant moms have a harder time escaping, carrying babies to term can be risky. Mothers who are able to act flexibly might therefore have an advantage in a unpredictable environment. “

Another explanation is that certain environmental characteristics could have caused the skink in question to lay part of its clutch abnormally early. Yet, said Whittington, two of the skink’s eggs hatched into healthy baby lizards, meaning if this phenomenon were to occur in the wild, the babies could still be viable.

Scientists don’t yet know what course evolution is taking

This finding could mean that the skink is only going through egg-laying or live birth. But scientists say it’s too early to say which way it’s headed.

In general, animals that give birth to live young evolved from ancestors who laid eggs and it would be rare for an animal to evolve the other way around, according to Whittington. And it’s worth pointing out that when this skink lays eggs, the embryos are almost fully developed and hatch much faster than other laying lizards.

Yet it is “impossible” to determine the course of natural selection in this species of skink, said Whittington. Their research shows that the uteri of “transitional” three-toed skinks and living three-toed skinks work similarly, which could allow the species to switch from live production to spawn, he said. she declared.

“At this time, we cannot rule out the possibility that transitional animals may be the descendants of living ancestors – which is why we continue to study these incredible lizards,” she wrote.

To complicate matters, if the environment changes, the direction of selection could change too! In some environments, natural selection could promote spawning. In others, it might be more beneficial to give birth to live young. . “

And this, said Whittington, is what makes evolution such a fascinating process.

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