Lizard That Lays Eggs and Gives Live Birth Might Be Undergoing a Major Evolutionary Transition
Ya think?
ScienceX.com / April 3, 2020
Charles Foster and Camilla WhittingtonThere are two main reproductive strategies in vertebrates.
Animals that lay eggs are called “oviparous.” For instance, many fish species spawn eggs that are fertilized externally. In other oviparous species, including birds and some lizards and snakes, eggs are fertilized inside the mother, an eggshell is added, and then eggs are laid.
Depending on the species, much or all of the nutrition needed to grow a healthy baby is supplied in the egg yolk.
In contrast, “viviparous” animals carry embryos internally until they are fully developed. The embryos can rely entirely on yolk for nutrition, or the parents can provide supplementary nutrition, sometimes via a placenta (as in humans).
I’m with you so far… Learned that in Miss Busty’s biology class.
Despite the vast differences between egg-laying and live birth, some species can do both. This phenomenon called “bimodal reproduction” is exceptionally rare. There are more than 6500 species of lizards worldwide, but only three exhibit bimodal reproduction.
We’re lucky enough to have two of these in Australia. Our research group at the University of Sydney studies the bimodally reproductive three-toed skink, in the hope of understanding how live birth evolved.
I just wanted the excuse to use the word “skink” in a post. “Three-toed” is a bonus.
The three-toed skink displays geographic variation in reproductive mode. It has four very tiny legs, and only three toes per foot.
In northern NSW, the three-toed skink gives birth to live young, but near Sydney, they lay eggs. Even though they reproduce differently, previous research has shown these lizards are a single species.
Even the egg-laying members of the species are odd, as the eggs are retained within the mother for a relatively long time. After being laid, ordinary skink eggs are incubated for at least 35 days before they hatch, but some three-toed skink eggs hatch in as few as five days after being laid.
One female even laid eggs and gave birth to a live baby in the same litter.
She’s a rebel.
Australia probably just breeding something else that will kill you.
Without my looking them up on the internets, are these large skinks or the little ones? When I was younger we’d look for skinks in the piney woods in the summer time. They were small and brown or black and I mistook them for small snakes the first time I caught one. There legs were very small as you mentioned.
If that question is a non-starter I’d like to discuss Miss Busty.
Not without some photographic evidence my good man!
Unless miss Busty lays eggs I don’t see how she comes into tonight’s discussion.