Rapid Evolution in Lizards

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

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.

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.

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

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.

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).

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.

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.

Well, it isn't an elephant from a bacterium, so it doesn't count.Plus, where are the intermediates?

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.

But what good is HALF a cecal valve?

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.

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.

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.

They were still genetically the same as the ones they had left in 1971.

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.

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.

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.

So the lizard was genetically the same as his ancestor but his diet had caused some changes in his physical makeup. (Evolution)

It had not caused any changes in his being a lizard.

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).

If you have found different evidence I would appreciate being able to read it.

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.

Until you give the reference for your information you are the one making the bare assertion.

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."

What does the picture of the two lizards you have to do with the two lizard populations under discussion have? Please explain.

Quote from Here says there is no firsthand accounts.

Creos look at macroevolution as transmutation or when one critter becomes a totaly different critter.

Macroevolution generally refers to evolution above the species level.

No cecal valves have ever been observed before in this species or genus.

BTW you can give what you think the ToE version is.

Macroevolution generally refers to evolution above the species level.

Is there somewhere I can read the paper?

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Two mitochondrial DNA fragments (12S rDNA and 16S rDNA) were amplified by PCR by using the primer pairs...

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.

To leap to the conclusion that there was new genetic data added at this early stage is unfounded and unreasonable.

You asserted earlier in the discussion that genetic testing was necessary to prove genetic change.

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).

If the intestinal separation is still there then shout evolution.

Sounds like a testable hypothesis to me!

... humans evolving and growing a new appendix in several hundred years.