Wednesday, 12 September 2018

New Structure Evolved in Just 36 Years!

Italian Wall Lizard, Podarcis sicula
Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource | PNAS

It's another one of those 'non-existent' things that creationists must dread being shown.

No. This time it's not yet another of those 'missing' transitional fossils or intermediate forms. This time it's yet another example of something else 'impossible' and 'never observed'. It's yet another example of observed rapid evolution, including the evolution of new structures.

It's a paper from 2008 that utterly destroys a key creationist claim, yet they are still making it. Thanks to @GrrlScientist for promoting this research today.

To begin at the beginning.

In 1971 a bunch of scientists, intending to observe how a population of the Italian wall lizard, Podarcis sicula, adapted to a new environment, transferred just five males and five females from the small Croatian island of Pod Kopiste in the southern Adriatic Sea, to the nearby island of Pod Mrcaru. And there they stayed while Yugoslavia fragmented and descended into warring factions.

Thirty-six years later another group of scientists visited the island, where they discovered that not only had the teeming descendants of the relocated lizards replaced and apparently exterminated the former resident species, Podarcis melisellensis, on Pod Mrcaru, but that they had also diverged considerably from the original population on Pod Kopiste. That they were indeed the descendants of the original founder population was confirmed by analysis of their mitochondrial DNA, which was identical to those on Pod Kopiste.

Their findings were published in 2008 in PNAS.

The major significant changes were:
  • A change of diet. The Pod Mrcaru lizards now eat mostly plant material, not the insects their ancestors ate.
  • To cope with this different diet, the Pod Mrcaru lizards have a measurably larger head which allows for more powerful jaw muscles and a more powerful bite, needed to bite the plant matter into small chunks for swallowing and digestion.
  • The Pod Mrcaru lizards are less territorial and less aggressive than their ancestors because they no longer need to defend a territory to ensure enough insects. This has enabled a much higher population density. They are also less active.
  • To digest the vegetarian diet, the Pod Mrcaru lizards have developed caecal valves in their intestines. These slow down the flow of food through the digestive system and act to turn sections into fermentation vats to break down the plant cell walls.

This latter is the most dramatic morphological change since only 1% of lizard species have caecal valves. It amounts to a new structure in this species, evolved in just 36 years.

Here then we have a measurable morphological, behavioural and ecological changes in a population in just 36 years and the evolution of new structures in the gut, all brought about by a change in the environment.

Unfortunately for creationists, the usual response to this sort of evidence of observed evolution is to fall back on an artificial distinction between what they call 'macro-evolution' and normal evolution and proclaim it to be 'still lizard kind' as though under this definition of 'kind', all lizards are the same 'kind'. However, when pressed to explain what 'macro-evolution' is, they will normally include different structures.

So what they need to explain in this example is why evolving a new structure is not a change in kind. Any creationists prepared to try for a new definition of evolution which includes the evolution of a new structure while still being the same 'kind'?

Herrel, A., Huyghe, K., Vanhooydonck, B., Backeljau, T., Breugelmans, K., Grbac, I., Van Damme, R., Irschick, D.J. (2008).
Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource.
Proceedings of the National Academy of Sciences
, 105(12), 4792–4795. DOI: 10.1073/pnas.0711998105

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  1. I had to tweet this. I remember reading it before but lost track of it. Thanks for blogging this important information. I also now follow @GrrlScientist -thanks to you!


    1. This is an excerpt from the paper you cited : “Although the presence of cecal valves and large heads in hatchlings and juveniles suggests a genetic basis for these differences, further studies investigating the potential role of phenotypic plasticity and/or maternal effects in the divergence between populations are needed.” (Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource., Proceedings of the National Academy of Sciences 105.12 (2008): 4792-4795.)
      The authors are admitting that although the changes might be genetically based ( random mutation in the genes) further studies are needed to rule out phenotypic plasticity and/or maternal effects.
      The following paper confirmed changes due to plasticity:
      Excerpt from abstract: “The plasticity experiment suggests that at least some of the changes associated with a dietary shift toward a higher proportion of plant material may be plastic.”
      Excerpt from body of paper: , we also performed a preliminary analysis of the plasticity of some of these modifications. By examining individuals from Pod Mrcˇaru after they had been fed an exclusively arthropod diet, we sought to test whether the changes in gut morphology are reversible (and HENCE PLASTIC).
      Excerpt from RESULTS section: Our results suggest that in P. sicula, at least some of the changes associated with a dietary shift toward a higher proportion of plant material may be PLASTIC. Specimens from the Pod Mrcaru population, which in nature eat substantial amounts of plant material, exhibited a reduction in diges-tive tract length and a TOTAL LOSS OF CECAL VALVES AFTER HAVING BEEN FED AN EXCLUSIVELY ARTHROPOD DIET FOR 15 WEEKS. Although parts of their gastroinstestinal systems were still better developed than those of specimens feeding mainly on arthropods in the wild, it seems likely that a prolonged exposure to an ani-mal-based diet would have erased even those differences. These observations call for a more flexible view of the digestive system in lizards. PLASTICITY of gastrointestinal morphology and function has long been de-scribed in birds and mammals In reptiles, there is evidence that digestive function may change in response to dietary demands on ontogenetic, seasonal, and instantaneous timescales. All of these observations suggest that many lineages of vertebrates, including lizards, exhibit considerable phenotypic plasticity in the mor-phology and physiology of their digestive system. In these lineages, dietary shifts from carnivory to omnivory (as observed in many lizard families; Cooper and Vitt 2002) may constitute less of an evolutionary challenge than previously thought. Now we'll see who is honest and who is not. If you're honest you will either incorporate these findings into your article or you will remove this obsolete article. You also made numerous errors and misstatements and falsehoods on the C14 dating. This blog is pure propaganda.

    2. Here's the citation:
      Vervust, Bart, et al. "Anatomical and physiological changes associated with a recent dietary shift in the lizard Podarcis sicula." Physiological and Biochemical Zoology 83.4 (2010): 632-642.

    3. Strangely, you seem to have forgotten to include the previous sentence in your selective quote, Celeste (I note you chose to remain anonymous):

      "The relatively large fraction of leaves included into the diet of lizards in the introduced population of Pod Mrčaru has apparently also resulted in the evolution of cecal valves, a structure previously unreported for this species and rare in this family and scleroglossan lizards in general (13, 14, 18)."

      I'm sure that was just an oversite and you had no intention of deliberately misleading readers of this blog. That would be dishonest.

  2. Nothing to do with 'a new structure'. Cecal valve arose due to changed diet from insects to plants. All necessary information was already present in lizard's genome and epigenetic information profiles just switched them on. Evolution didn't happen.

    1. New structures are not new structures, eh?


      Nothing better to offer Tomi?

    2. Tomi’s comment is supported by this paper:

    3. What a shame you didn't read that paper. It says nothing about cecal valves. Nice try at misleading people though.


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