A more simpler transition than first thought.

topic of the day 028

Evolution:

Lizard moving from Eggs to Live Birth

from National Geographic

A yellow-bellied three-toed skink carrying embryos, visible as light orbs inside its body.

Where?

Along the warm coastal lowlands of New South Wales.

Who? What?

The yellow-bellied three-toed skink lays eggs to reproduce. But individuals of the same species living in the state's higher, colder mountains are almost all giving birth to live young.

Why?

Evolutionary records shows that nearly a hundred reptile lineages have independently made the transition from egg-laying to live birth in the past and by studying differences among populations that are in different stages of this process, we can begin to put together what looks like the transition from one [birth style] to the other.

How?

In mammals, the young get their nourishment before birth with a highly specialized placenta that connects the fetus to the uterus wall, allowing the baby to take up oxygen and nutrients from the mother's blood and pass back waste.

In egg-laying species on the other hand, the embryo gets nourishment from the yolk, but calcium absorbed from the porous shell is also an important nutrient source.

Some fish and reptiles, meanwhile, use a mix of both birthing styles. The mother forms eggs, but then retains them inside her body until the very last stages of embryonic development. The shells of these eggs thin dramatically so that the embryos can breathe, until live babies are born covered with only thin membranes—all that remains of the shells.

"Now we can see that the uterus secretes calcium that becomes incorporated into the embryo—it's basically the early stages of the evolution of a placenta in reptiles," Stewart explained. Both birthing styles come with evolutionary tradeoffs: Eggs are more vulnerable to external threats, such as extreme weather and predators, but internal fetuses can be more taxing for the mother.

For the skinks, moms in balmier climates may opt to conserve their own bodies' resources by depositing eggs on the ground for the final week or so of development. Moms in harsh mountain climates, by contrast, might find that it's more efficient to protect their young by keeping them longer inside their bodies.

Then? So?

This is an interesting topic since we could see how evolution could affect certain organisms to adapt to their surroundings at the same time. We do adapt to our surroundings ... just look as skin colour, body hair and more prominently: the eyes!

- post is sourced from the aforementioned article written by Brian Handwerk -

Lesson Learned:

Any living organism would evolve to cater to its environment, it's just rare to see the difference between before and after at the same time.