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Author Topic:   Rapid Evolution in Lizards
molbiogirl
Member (Idle past 721 days)
Posts: 1909
From: MO
Joined: 06-06-2007


Message 1 of 57 (464226)
04-24-2008 4:14 AM


Last month, the PNAS published a remarkable study of evolution in action.

The abstract can be found here.

And a short summary can be found here or here.

The original paper is really quite brief (and under lock and key) but the summaries are very thorough, especially Pharyngula's, so you can get a pretty good idea of what the paper says.

A population of 10 lizards, Podarcis sicula, were released by scientists on an Adriatic island, Pod Mrcaru, back in 1971. The scientists weren't able to return to the island for 36 years, but when they did, they found that the lizard population had evolved an entirely new phenotypic feature: a cecal valve.

Have a look!

RAZD once said:

The purpose is to get a creationist definition of what "large scale change" is -- it is their criteria.

In only 30 generations, these lizards grew a new body part in response to environmental pressures. They were insectivores, but evolved into herbivores ... a cecal valve is necessary for digesting cellulose.

To quote Pharyngula:

Now here's something really cool, though: these lizards have evolved cecal valves. What those are are muscular ridges in the gut that allow the animal to close off sections of the tube to slow the progress of food through them, and to act as fermentation chambers where plant material can be broken down by commensal organisms like bacteria and nematodes — and the guts of Pod Mrcaru P. sicula are swarming with nematodes not found in the guts of their Pod Kopiste cousins.

Photographs illustrating the cecal valves in a male (A), a female (B), and a hatchling (C) P. sicula from Pod Mrcaru. Note the thick cecal wall and pronounced ridges. The arrow in C indicates the position of the cecal valve in a hatchling as seen from the outside.

This is more than a simple quantitative change, but is actually an observed qualitative change in a population, the appearance of a new morphological structure.

One of the authors of the paper commented:

Such physical transformation in just 30 lizard generations takes evolution to a whole new level, Irschick said.

"It would be akin to humans evolving and growing a new appendix in several hundred years."

"That's unparalleled. What's most important is how fast this is," he said.

It is easy to see how such changes, accumulating over millions of years, can lead to the evolution of entirely different species.

Body part + body part + ... = new critter.

I would love to hear what our resident "microevolution" v. "macroevolution" enthusiasts think.

Edited by molbiogirl, : No reason given.


Replies to this message:
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Admin
Director
Posts: 12580
From: EvC Forum
Joined: 06-14-2002
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Message 2 of 57 (464239)
04-24-2008 8:32 AM
Reply to: Message 1 by molbiogirl
04-24-2008 4:14 AM


Could you edit your proposal to explain the cecal valve just a little more? Just to help you see where some clarification might be helpful, I can't tell what I'm looking at in the diagram, but given that you say the cical valve is related to digestion, I'm guessing that I'm looking at a stomach or intestine. So if you could add a little text so that people wouldn't be left wondering about that then I'll take another look. Please post a note when you're done.


--Percy
EvC Forum Director

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molbiogirl
Member (Idle past 721 days)
Posts: 1909
From: MO
Joined: 06-06-2007


Message 3 of 57 (464259)
04-24-2008 1:06 PM
Reply to: Message 2 by Admin
04-24-2008 8:32 AM


All done.
Have a look and tell me what you think, Percy.
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Admin
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Message 4 of 57 (464264)
04-24-2008 1:19 PM


Thread moved here from the Proposed New Topics forum.
    
Blue Jay
Member (Idle past 778 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 5 of 57 (464297)
04-24-2008 5:07 PM
Reply to: Message 1 by molbiogirl
04-24-2008 4:14 AM


Good find, mgirl!

I bet this is what IDists will latch onto (from the NG summary you supplied):

quote:
"All of this might be evolution," Hendry said. "The logical next step would be to confirm the genetic basis for these changes."

They can hope it's just atavistic from an herbivorous ancestor. Maybe it's because of a gene that was just inactivated by the parent taxa, and only just reactivated on Pod Mrcaru. But, this argument will only hold up if this is found to be the case. Hendry's quote above suggests that he intends to test that right away.

---

Of course, I'm sure many IDists will argue that it's just a flap of muscle, not an organ. After all, it's still a far-cry from developing a new heart or eye, right?

Others will ask if the Pod Mrcaru population can still interbreed with the Pod Kopiste population, in which case no new species was formed, and it therefore does not count as macroevolution.

---

So, technically, there's still a lot of work to do before this makes it into evolutionary biology textbooks. But that's to be expected.

Again, good find!


I'm Thylacosmilus.

Darwin loves you.


This message is a reply to:
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ICANT
Member
Posts: 6187
From: SSC
Joined: 03-12-2007


Message 6 of 57 (464305)
04-24-2008 6:05 PM
Reply to: Message 1 by molbiogirl
04-24-2008 4:14 AM


Re-New Critter
Hi molbiogirl,

molbiogirl writes:

Body part + body part + ... = new critter.

Did the critter cease to be a lizard?

I was under the impression it was still a lizard.

God Bless,


"John 5:39 (KJS) Search the scriptures; for in them ye think ye have eternal life: and they are they which testify of me."
This message is a reply to:
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molbiogirl
Member (Idle past 721 days)
Posts: 1909
From: MO
Joined: 06-06-2007


Message 7 of 57 (464309)
04-24-2008 6:22 PM
Reply to: Message 6 by ICANT
04-24-2008 6:05 PM


Yes, it is still a lizard.

Are you suggesting that there is only one lizard kind?


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molbiogirl
Member (Idle past 721 days)
Posts: 1909
From: MO
Joined: 06-06-2007


Message 8 of 57 (464312)
04-24-2008 6:40 PM
Reply to: Message 5 by Blue Jay
04-24-2008 5:07 PM


Maybe it's because of a gene that was just inactivated by the parent taxa, and only just reactivated on Pod Mrcaru.

I've been browsing other sites that discuss this paper and found this.

Comment #41.

The authors state that cecal valves are a rarity in scleroglossid reptiles. A morphological comparison between these valves and those of other lizards that possess them may indicate whether this is a truly novel feature or a reactivation of a dormant or pseudo-gene. The question will be difficult to resolve because of the possibility of convergent evolution.

ABE:

Comment #49.

This hasn't anything to do with your comment, Bluejay.

Just a pre-emptive strike on the creo camp:

The cecal valves don't sound like the kind of thing that could be due to phenotypic plasticity. Phenotypic plasticity refers to where the growth of morphological features is under environmental control. An example is the barnacle penis: barnacles in higher turbulent flow regimes have shorter and thicker penises than those in more sheltered conditions - these differences are not under genetic control and are determined by the environment in which the individual develops. This is phenotypic plasticity (I wrote a blog post on barnacle penises a while back, hence my use of this example).

ABE:

Wow. The commenters over at Pharyngula are having a field day.

Comment #52.

I'm assuming this is a predominance of one possible phenotype, not a change in the genetic structure of the lizards, and that the genes for this phenotype were already present in these lizards.

Correct--you're assuming. If your assumption is correct, then this study could be ascribed to phenotypic plasiticity. There is no evidence, however, that your assumption is correct.

No cecal valves have ever been observed before in this species or genus, and are in fact very rare in the entire family Lacertidae (only known in the specialized herbivore Galliota*).

Other issues raised above:

1. This is not a case of hybridization or interbreeding. (Mitochondrial) genetic analyses show that the introduced population is indistinguishable from the source population (for the markers observed, which would have revealed melisellensis genes if present).

2. Podarcis melisellensis is insectivorous, not omnivorous, anyway.

3. Podarcis melisellensis was locally extirpated on this tiny island, but the species is alive and well elsewhere in the Adriatic area. Their local extinction seems a clear case of competitive exclusion (the subject of the original experimental introduction).

4. No indication of reproductive barriers or speciation, though I doubt the breeding experiments have been done. This is a very short time period.

An interesting comparison: this lizard species, Podarcis sicula, was introduced to Long Island, NY about 1967 and is thriving in many local areas. They still look and act just like the source population (known from genetic studies to be Rome). No herbivory to speak of.**

*Herrel A, Vanhooydonck B, VanDammeR (2004) Omnivory in lacertid lizards: Adaptive evolution or constraint? J Evol Biol 17:974-984.

**Burke, R.L. and Mercurio, R. 2002. Food habits of a New York population of Italian wall lizards, Podarcis sicula (Reptilia, Lacertidae). American Midland Naturalist 147:368-375.

Edited by molbiogirl, : No reason given.

Edited by molbiogirl, : No reason given.


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NosyNed
Member
Posts: 8839
From: Canada
Joined: 04-04-2003
Member Rating: 2.7


Message 9 of 57 (464313)
04-24-2008 6:42 PM
Reply to: Message 6 by ICANT
04-24-2008 6:05 PM


Still a ...
I was under the impression it was still a lizard.

Yes, just as you are still a vertebrate. Because that is the name given to the sort of worm-like guy that was the only vertebrate around once upon a time. The rules for naming clades (as I understand them) mean that you have to be one and stay one.

Likewise you are also a primate.

I´m not clear why you aren´t also a fish; perhaps there is a cladist who can explain that.


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molbiogirl
Member (Idle past 721 days)
Posts: 1909
From: MO
Joined: 06-06-2007


Message 10 of 57 (464316)
04-24-2008 6:55 PM
Reply to: Message 1 by molbiogirl
04-24-2008 4:14 AM


UD
Oh. Dear. God.

Uncommon Descent is arguing it's LaMarckian.

What we seem to be seeing isn’t exactly Lamarckism, but a kind of form of it: i.e., the environment produces changes in the phenotype of the lizards which is inheritable, but is doing so via genetic regulatory mechanisms; IOW, epigenetics.

http://www.uncommondescent.com/intelligent-design/rapid-evolution-is-it-ns-or-the-environment-that-matters/


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Blue Jay
Member (Idle past 778 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 11 of 57 (464317)
04-24-2008 7:10 PM
Reply to: Message 10 by molbiogirl
04-24-2008 6:55 PM


Re: UD
This is the alternative they have proposed instead of natural selection:

Uncommon Descent writes:

...the environment, specifically the proteins/enzymes/chemicals of the plant life on the new Adriatic island has interacted with the genome to quickly bring about these changes.

Obviously, it's a distinct possibility that environmental chemistry could act in a method similar to hormones, as is witnessed by cellular responses to environmental stimuli. But, in the case of these lizards, isn't Dembski (or whoever)'s epigenetics explanation just phenotypic plasticity, anyway? Isn't this still just natural selection?

It wouldn't be hard at all to test this: when the genetics studies on these lizards come up, they'll find whether epigenetics or phenotypic plasticity is involved.


I'm Thylacosmilus.

Darwin loves you.


This message is a reply to:
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ICANT
Member
Posts: 6187
From: SSC
Joined: 03-12-2007


Message 12 of 57 (464318)
04-24-2008 7:11 PM
Reply to: Message 7 by molbiogirl
04-24-2008 6:22 PM


Re-Lizard
Hi molbiogirl,

molbiogirl writes:

Are you suggesting that there is only one lizard kind?

I was not suggesting anything. I was just pointing out that although the lizard had changed quite a bit he was still a lizard.

God Bless,


"John 5:39 (KJS) Search the scriptures; for in them ye think ye have eternal life: and they are they which testify of me."
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molbiogirl
Member (Idle past 721 days)
Posts: 1909
From: MO
Joined: 06-06-2007


Message 13 of 57 (464320)
04-24-2008 7:22 PM
Reply to: Message 12 by ICANT
04-24-2008 7:11 PM


Re: Re-Lizard
ICANT. If you would like to contribute something to the discussion, then please do so.

In the future, should you feel the need to pop in and point out the obvious -- "It's a lizard." -- please exercise a little restraint.

More Pharyngula shots across the creo bow:

Comment #103

Well, it isn't an elephant from a bacterium, so it doesn't count.

Plus, where are the intermediates?

Comment #104

Brilliant. Of course there will be several "but the lizard is STILL a lizard, not a dog." type of accusations. When will the IDers learn that lizard to dog equals magic, NOT science? Evolution is NOT alchemy.

Comment #105

But what good is HALF a cecal valve?

Edited by molbiogirl, : No reason given.


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Blue Jay
Member (Idle past 778 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 14 of 57 (464321)
04-24-2008 7:23 PM
Reply to: Message 12 by ICANT
04-24-2008 7:11 PM


Re: Re-Lizard
ICANT writes:

...although the lizard had changed quite a bit he was still a lizard.

The lizards changed a lot, ICANT: they developed an entirely new biological feature that didn't exist in their ancestral population, which ID has claimed is not possible. If the genetics confirm it, it will be definitive proof of macroevolution, and ID will once again have to revise their "theory" to include yet another concept of evolutionary biology that has been proven, or, at the least, have to redefine yet another term so they don't have to change their core tenets.

Read this summary, which molbiogirl provided in the OP: it's title is "Still just a lizard," and it addresses your very concern. It's pretty much written just for you.

Edited by Bluejay, : Grammar


I'm Thylacosmilus.

Darwin loves you.


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molbiogirl
Member (Idle past 721 days)
Posts: 1909
From: MO
Joined: 06-06-2007


(1)
Message 15 of 57 (464322)
04-24-2008 7:35 PM
Reply to: Message 11 by Blue Jay
04-24-2008 7:10 PM


It wouldn't be hard at all to test this: when the genetics studies on these lizards come up, they'll find whether epigenetics or phenotypic plasticity is involved.

There doesn't seem to be a consensus over at Pharyngula re: phenotypic plasticity.

And right around Comment #174, they start going at it tooth and nail.

Commenter #98 has a bit to say re: epigenetics:

Very often valves are not muscular in their makeup but rather they are mesenchymal cells that are secreting lots of extracellular matrix proteins to make the valves more resistant to stress/strain/force so that muscular contraction- an energy dependent event- isn't required for dividing the regions separated by the valves. If this were the case it would take a tremendous amount of changes in gene expression within the muscle but a more simple event to make more mesenchymal cells and valves.

As does Commenter #72.

Obviously genetics will be important in resolving what's going on, but I don't think it will be any easier to pin down through genetics whether this is a newly-evolved feature or not. The most definitive result (pseudogene present in originating population is activated in Mrcaru lizards) is the one we are least likely to observe. More likely are subtle changes in promoters that alter the concentration or developmental expression profile of growth factors (or their receptors), in which case we are left with much the same question as with morphological studies.

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