|
Register | Sign In |
|
QuickSearch
Thread ▼ Details |
|
Thread Info
|
|
|
Author | Topic: Rapid Evolution in Lizards | |||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
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.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
Have a look and tell me what you think, Percy.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
Yes, it is still a lizard.
Are you suggesting that there is only one lizard kind?
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
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.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
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. Rapid Evolution: Is it NS or the Environment that matters? – Uncommon Descent
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
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.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined:
|
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.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
They were still genetically the same as the ones they had left in 1971. First. A mitochondrial analysis was identical. Mitochondrial. Nothing has been said yet re: nuclear mutations. That is yet to come. Second. Are you under the impression that evolution can occur ONLY thru mutations? You didn't read those comments too closely then. ABE:
PZ's comment, # 193.
No one claimed it was the result of a novel mutation -- I'd actually be very surprised if it were (although new mutations may well have contributed to the phenoytpe). I expect this is the result of selection for novel combinations of alleles in the founder population, plus developmental plasticity. So what? THAT'S EVOLUTION, TOO. Edited by molbiogirl, : No reason given.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
I put forth evidence presented by a scientist that DNA had been tested on the lizards on both islands 6 times in three years and that they were both genetically the same. No. You didn't. You made a bare assertion. This is evidence:
Genetic mitochondrial DNA analyses indicate that the lizards currently on Pod Mrcaru are indeed P. sicula and are genetically indistinguishable from lizards from the source population. Fig. 5. Neighbor-Joining tree of Jukes-Cantor distances derived from a concatenated alignment of partial mitochondrial 12S rDNA and 16S rDNA sequences, showing phylogenetic relationships among a selected number of populations of P. sicula and P. melisellensis including individuals from the two populations studied here. The tree includes previously published data (13, 14) retrieved from genbank. Lizards cluster according to species and the populations from Pod Kopi[icirc]ste and Pod Mr[icirc]caru are identical and P. sicula. This suggests that the original species inhabiting Pod Mr[icirc]caru (P. melisellensis) has gone extinct on this island. Newly sequenced P. melisellensis specimens were from Pasadur on Lastovo Island. Only bootstrap values [mt]70% are shown. Populations sampled in this study are indicated in bold. Mitochondrial DNA is completely different than nuclear DNA.Mitochondrial DNA is completely separate from nuclear DNA. Do you understand the difference between mitochondrial and nuclear DNA?Do you understand why it makes a difference whether they tested the mitochondrial v. the nuclear DNA? Do you understand that the only creatures on this planet that have identical genomes are twins/clones? So the lizard was genetically the same as his ancestor but his diet had caused some changes in his physical makeup. (Evolution) We know nothing of the nuclear genome of this population. Therefore, we cannot say that the lizards are "genetically the same". Because we don't know that and we won't know that until their nuclear genomes are sequenced.
It had not caused any changes in his being a lizard. Let's take this one step at a time. Here are two lizards.
Do you agree that speciation is "macroevolution"? Do you agree that, although they are both lizards, they are two species? Do you agree that these two species have significant differences in their NUCLEAR genomes? Do you agree that these two species have many obvious morphological differences? Do you agree that these many obvious morphological differences are "body parts"? Do you agree that these two species have evolved these differing body parts? Do you agree that these two species evolved these different body parts gradually, over a very long time? Do you agree that these two species evolved one new body part at a time? Do you agree that a cecal valve is a new body part?
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). This population of lizards evolved a new body part. This population of lizards evolved a new body part that no other lizard in its genus or family has. This population, given enough time, will accumulate more and more specialized body parts that no other member of its genus or family has. It's like you believe in inches, but not in miles.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
In Message 23 (your response to Bluejay) you wrote:
If you have found different evidence I would appreciate being able to read it. I provided not one but two quotes from the paper itself that shows it was mitochondrial DNA that was sequenced.
Genetic mitochondrial DNA analyses indicate that the lizards currently on Pod Mrcaru are indeed P. sicula and are genetically indistinguishable from lizards from the source population. Fig. 5. Neighbor-Joining tree of Jukes-Cantor distances derived from a concatenated alignment of partial mitochondrial 12S rDNA and 16S rDNA sequences, showing phylogenetic relationships among a selected number of populations of P. sicula and P. melisellensis including individuals from the two populations studied here. The tree includes previously published data (13, 14) retrieved from genbank. Lizards cluster according to species and the populations from Pod Kopi[icirc]ste and Pod Mr[icirc]caru are identical and P. sicula. This suggests that the original species inhabiting Pod Mr[icirc]caru (P. melisellensis) has gone extinct on this island. Newly sequenced P. melisellensis specimens were from Pasadur on Lastovo Island. Only bootstrap values [mt]70% are shown. Populations sampled in this study are indicated in bold. In fact, this is the third time I have mentioned it.
Message 8.
Message 16. Message 24. In the future, please take the time to carefully read the thread before responding.
Until you give the reference for your information you are the one making the bare assertion. I provided 3 links in the OP. I provided 2 quotes from the paper. Here are the last 2 lines from the first link:
There's no dispute that major changes to the lizards' digestive tract occurred. "That kind of change is really dramatic," he added. "All of this might be evolution," Hendry said. "The logical next step would be to confirm the genetic basis for these changes." Please take the time to answer the questions I posed re: mitochondrial v. nuclear DNA.
What does the picture of the two lizards you have to do with the two lizard populations under discussion have? Please explain. Please take the time to answer each of the questions I posted re: species and body parts, not just the last one. Then we can move on to a discussion of what speciation means.
Quote from Here says there is no firsthand accounts. This study was published two weeks ago.This website is no longer current. Creos look at macroevolution as transmutation or when one critter becomes a totaly different critter. It makes no difference whatsoever what creos think.What matters is the scientific consensus. And the scientific consensus is: Macroevolution generally refers to evolution above the species level. To repeat:
No cecal valves have ever been observed before in this species or genus.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
BTW you can give what you think the ToE version is. The first LINE of the Berkeley website you linked in Message 27!
Macroevolution generally refers to evolution above the species level. For the umpteenth time, read the relevant links/thread before you post.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
Is there somewhere I can read the paper? I provided the link in the OP. If you pay the $10 fee, yes, you can read it.
Purchase Short-Term Access
Purchase this Article - You may access this article (from the computer you are currently using) for 2 days for US$10.00.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
Thank you, Bluejay.
This ...
Two mitochondrial DNA fragments (12S rDNA and 16S rDNA) were amplified by PCR by using the primer pairs... ... is identical to the quote I provided this morning:
Fig. 5. Neighbor-Joining tree of Jukes-Cantor distances derived from a concatenated alignment of partial mitochondrial 12S rDNA and 16S rDNA sequences, showing phylogenetic relationships among a selected number of populations of P. sicula and P. melisellensis including individuals from the two populations studied here. The tree includes previously published data (13, 14) retrieved from genbank. Lizards cluster according to species and the populations from Pod Kopi[icirc]ste and Pod Mr[icirc]caru are identical and P. sicula. This suggests that the original species inhabiting Pod Mr[icirc]caru (P. melisellensis) has gone extinct on this island. Newly sequenced P. melisellensis specimens were from Pasadur on Lastovo Island. Only bootstrap values [mt]70% are shown. Populations sampled in this study are indicated in bold. It seems ICANT only listens to you, however.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
To leap to the conclusion that there was new genetic data added at this early stage is unfounded and unreasonable. Would you like to support that bare assertion? Remember. This is a feature not found in any other members of this lizard's genus. Your argument seems to be based on personal incredulity.
|
|||||||||||||||||||||||||||||||||||||||||||
molbiogirl Member (Idle past 2669 days) Posts: 1909 From: MO Joined: |
You asserted earlier in the discussion that genetic testing was necessary to prove genetic change. I wasn't the one insisting that evolution required nuclear genomic change. ICANT was. Evolution does not require genomic change. It can, and does, happen that way -- but it is not required.
Inherant (sic) in that assertion is that an unfounded or at least premature assumption has been made. Re the species not showing the colonic separation ever before it was stated that this species was almost entirely on an insect diet therefore there would not be the environmental stimulous (sic) for a phenotype change. the change in the skull structure is likely the result of the increased muscular strength of the muscles of mastication(wolf's law muscular stress on bone causes bone to hypertrophy). Have you ever heard of LaMarck? Your ideas are LaMarckian. LaMarckism was discarded over 130 years ago.
If the intestinal separation is still there then shout evolution. You are under the mistaken impression that this is "a tiny little change". Growing an entirely new digestive organ is not such a little thing, dear sir.
Sounds like a testable hypothesis to me! Believe me. A discovery of this magnitude is going to be examined from every possible angle. Interbreeding with the original population, backbreeding on the original diet, genomic sequencing, ad nauseum. The fact remains, however, that this lizard grew a whole new body part. This is not something one can simply brush off as an "adaptation". No other member of this lizard's GENUS has a cecal valve. Are you aware of the significance of this statement? Homo sapiens. Genus = Homo. Species = sapiens. Members of the genus Homo: Homo habilis (Handy Man)Homo rudolfensis (Rudolf Man) Homo ergaster (Working Man) Homo erectus (Upright Man) Homo floresiensis (Flores Man) Homo antecessor (Predecessor Man) Homo heidelbergensis (Heidelberg Man) Homo neanderthalensis (Neanderthal Man) Homo rhodesiensis (Rhodesia Man) Homo cepranensis (Ceprano Man) Homo georgicus (Georgia Man) Homo sapiens (us) For this lizard to have developed an entirely new body part is the equivalent of (to quote one of the paper's authors):
... humans evolving and growing a new appendix in several hundred years. Do you think that growing an appendix is "an adaptive change" that can be reversed with a different diet? Edited by molbiogirl, : sp
|
|
|
Do Nothing Button
Copyright 2001-2023 by EvC Forum, All Rights Reserved
Version 4.2
Innovative software from Qwixotic © 2024