Dr Camilla Whittington holding a different species, the Cunningham's skink.



In a world first, researchers at the University of Sydney have observed a normally live-bearing Australian lizard lay three eggs and then weeks later, give birth to a live baby from the same pregnancy. This is the first time such an event has been documented in a single litter of vertebrate babies.

The three-toed skink (Saiphos equalis) is one of only a handful of rare "bimodally reproductive" species, in which some individuals lay eggs and others give birth to live babies. But up until now, no vertebrate has ever been observed to do both in one litter.

"It is a very unusual discovery," said Dr Camilla Whittington, from the School of Life and Environmental Sciences and Sydney School of Veterinary Science at the University of Sydney.

The three-toed skink is native to the east coast of Australia. In the northern highlands of New South Wales the animals normally give birth to live young, but those living in and around Sydney lay eggs.

"We were studying the genetics of these skinks when we noticed one of the live-bearing females lay three eggs," Dr Whittington said. "Several weeks later she gave birth to another baby. Seeing that baby was a very exciting moment!"

The observation was published in Biology Letters today, along with advanced microscopy of the egg-coverings.

There are at least 150 evolutionary transitions from egg-laying to live-bearing in vertebrates said Dr Whittington, who led the study alongside Dr Melanie Laird, a postdoctoral researcher at the University of Otago, and Emeritus Professor Mike Thompson.