Evolution in Action: Lizard Moving From Eggs to Live Birth | TigerDroppings.com
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JOJO Hammer
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Evolution in Action: Lizard Moving From Eggs to Live Birth

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Evolution has been caught in the act, according to scientists who are decoding how a species of Australian lizard is abandoning egg-laying in favor of live birth.

Along the warm coastal lowlands of New South Wales (map), 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.

Only two other modern reptiles—another skink species and a European lizard—use both types of reproduction. (Related: "Virgin Birth Expected at Christmas—By Komodo Dragon.")

Evolutionary records shows that nearly a hundred reptile lineages have independently made the transition from egg-laying to live birth in the past, and today about 20 percent of all living snakes and lizards give birth to live young only.

(See "Oldest Live-Birth Fossil Found; Fish Had Umbilical Cord.")

But modern reptiles that have live young provide only a single snapshot on a long evolutionary time line, said study co-author James Stewart, a biologist at East Tennessee State University. The dual behavior of the yellow-bellied three-toed skink therefore offers scientists a rare opportunity.

"By studying differences among populations that are in different stages of this process, you can begin to put together what looks like the transition from one [birth style] to the other."

Eggs-to-Baby Switch Creates Nutrient Problem

One of the mysteries of how reptiles switch from eggs to live babies is how the young get their nourishment before birth.

In mammals a highly specialized placenta 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. (See related pictures of "extreme" animals in the womb.)

In egg-laying species, 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. (Related: "Dinosaur Eggs Discovered Inside Mother—A First.")

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.

This adaptation presents a potential nourishment problem: A thinner shell has less calcium, which could cause deficiencies for the young reptiles.

Stewart and colleagues, who have studied skinks for years, decided to look for clues to the nutrient problem in the structure and chemistry of the yellow-bellied three-toed skink's uterus.

"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.

Evolutionary Transition Surprisingly Simple

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.

(Related: "Human Sperm Gene Traced to Dawn of Animal Evolution.")

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.

In general, the results suggest the move from egg-laying to live birth in reptiles is fairly common—at least in historic terms—because it's relatively easy to make the switch, Stewart said.

"We tend to think of this as a very complex transition," he said, "but it's looking like it might be much simpler in some cases than we thought."



Image: http://images.nationalgeographic.com/wpf/media-live/photos/000/254/cache/skink-evolves-live-birth-eggs_25436_600x450.jpg



Ba Ba Boooey
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
TL;DR

But very interesting


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Carson123987
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
cliffs? no way im reading that


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WikiTiger
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
here come the "it's adaptation, not evolution" arguments


Dr. 3
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
Thats Gawd testin' ya


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TK421
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
quote:

here come the "it's adaptation, not evolution" arguments



And as usual, it was started by an atheist.


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Quentin Compson
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
in


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7thWardTiger
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
That pic def needs a "come at me bro"


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HNTIGER1980
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Member since Oct 2011
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
So the chicken did come first.


Tigah in the ATL
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
But every time I open peanut butter there is no life I there; therefore, evolution is false.


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TheIndulger
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
TK421's got ya on that one wiki


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goldenbadger08
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
That damn monkey saying I has banana now get's me every time
This post was edited on 6/16 at 6:28 pm


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mach316
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Member since Jul 2012
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
Is there gonna be a test on this?


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Rickety Cricket
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
Sounds like a trap set by Lucifer. I don't buy it.


TK421
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
Another atheist bringing up religion.

Your lives would be utterly meaningless without religion.


HNTIGER1980
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
quote:


Your lives would be utterly meaningless without religion.


"Yes, without religion my life would be meaningless" -Said no Atheist ever.


TK421
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
quote:

"Yes, without religion my life would be meaningless" -Said no Atheist ever.


Of course they don't say it. But their hatred for religion is a major driving force in their lives. In a way, these guys love religion more than Jimmy Swaggart.


DrSteveBrule
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
quote:

Of course they don't say it. But their hatred for religion is a major driving force in their lives. In a way, these guys love religion more than Jimmy Swaggart.


Stop making general statements about a group. It makes you look stupid.


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blueboy
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
it's not the faith they hate. it's the faithful.

anchors aweigh, btw.


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JOJO Hammer
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Getting a barbed wire tribal tat
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re: Evolution in Action: Lizard Moving From Eggs to Live Birth
bump for day crew


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