“Rapid Evolution” Method Found in Eyeless Fish

I'm active in debates about evolution vs creation in forums in my own language, and while most of creationist arguments there are pretty much standard, there was an intriguing one recently.We were presented with this picture of small fish A. Mexicanus tetra, which is able to switch from normal appearance to cave-adapted in few generations.It is argued by creationists that such cases prove that evolution is not able to make big changes and adaptations, and all information is already included in genome; the phenotype just switches as required. Source here: http://www.biosciencetechnology.com/...od-found-eyeless-fishSo, what to think of it? It's just some regulatory genes switching on and off so that endangered species might change forms? We would expect that over many generations natural selection favors pale fishes with smaller eyes, but this is not the case.Evo-devo might give some explanations; it is known that some changes in body forms (from leg to fin for example) are not beacuse genes mutated randomly; infact genes stay the same; it's gene expression that changes. This is why human babies might be born with tail and horses with more digits; genes are still in us, it's just genes for tail that are supressed.So, is it possible that this fish gradually evolved to cave-like fenotype while still retaining all genes for "normal" version? Basically it evolved the machanism to switch back and forth? It would be very benefitial for those who are living in borderline zone between light and dark.
This sounds a bit like ad-hoc explanation, so I'd like to hear other opinions, possibly from experts.This could go in biological evolution.Edited by Bojan, : some typos

Thread copied here from the Rapid Evolution Method Found in Eyeless Fish thread in the Proposed New Topics forum.

Well, first of all I'd like to see some kind of evidence for this switching mechanism, rather than it being caused by mutation and selection. If the switching mechanism existed, wouldn't it happen after one generation, after the first generation of fish spent a lifetime in the dark? Or indeed within one generation, like tanning? Instead, you say "a few" generations. How few?In the second place, even if this mechanism exists, there's a huge logic fail there from the word "prove" onward. It's like saying: "John often walks to the shop on the corner and back, it takes him 10 minutes. Such cases prove that all journeys are short, and that no-one takes long transatlantic flights on so-called "planes" as you guys claim". But the existence of one mechanism to move short distances does not prove that there is not another mechanism to move long distances.

Hello,The Stickleback fish is another example of such retention of "switching" genes.Stickleback genomes reveal path of evolution | Nature

Lots of fish do it. Clownfish change from male to female and selectively; there is only one female in a colony and all the rest are males. When the female dies the most dominate male changes into a female. Wrasses move in the opposite direction. In neither case does it take even a generation.

Nitpick: Evolution doesn't "know" whether a species is endangered or not. It can't anticipate that the environment will change back and forth. All it can do is react to changes after they happen. If a switching mechanism does exist, it must have evolved in the "conventional" way.

Well that is phenotypic plasticity, like me tanning. But in the case of the OP, where it takes "a few generations" we have something different on our hands.

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Well, first of all I'd like to see some kind of evidence for this switching mechanism, rather than it being caused by mutation and selection. If the switching mechanism existed, wouldn't it happen after one generation, after the first generation of fish spent a lifetime in the dark? Or indeed within one generation, like tanning? Instead, you say "a few" generations. How few?

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Well, the article doesn't say, but it seems like it's within few generations, or less. The general mechanism is by blocking protein HSP90 (whatever that is) artificialy by cemichals, or naturaly because of decreased light and cold (basicaly cave conditions).

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In the second place, even if this mechanism exists, there's a huge logic fail there from the word "prove" onward. It's like saying: "John often walks to the shop on the corner and back, it takes him 10 minutes. Such cases prove that all journeys are short, and that no-one takes long transatlantic flights on so-called "planes" as you guys claim". But the existence of one mechanism to move short distances does not prove that there is not another mechanism to move long distances.

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Of course, and we all know that creationists approach all "problems" by trying to discredit one example and then, somehow, all evolution is disproved. They do it by mentionig Nebrasca man, so all fossils are fake, they mention 1 case of stalagmite growing fast, so all of them probably grew within 6000 years, and so on.This is why I'm interesting in this particular case, I'm curious about most likely evolutionary mechanism which explains how such ability (to switch between forms) evolved.

So what would that way be?If we look some examples in nature, it's obvious that changes in phenotype don't happen in a way that previous versions are "erased" in genome. Humans sometimes are born with tails, dolphins get back legs and so on. Atavisms are evidence that the general "blueprint" for a limb, for example, is preserved, and change in form is because of different gene expression / regulation.
There was an article recently about a mutant chick embryo which got a reptile snout after researchers tampered with gene regulation.So, is this the evolutionary mechanism? Animal slowly evolves different form through changes in gene regulation, while also retaining the ability to switch back quickly through epigenetics? Epigenetics is the study of changes in gene expression caused by certain base pairs in DNA, or RNA, being "turned off" or "turned on" again, through chemical reactions.

Do read the article and follow the link to Science. It is really interesting and not really helpful to creationists.To summarise:HSP90 canalises development - when it is suppressed, the fish are more sensitive to genetic variations.When the variations are expressed, they become available to selection.Eventually the fish reach a state where the new form is stable even when HSP90 is working. But it is evolution that gets them there.Oh, creationists can try to use it in their excuses, but all it is is a new way in which evolution can work. It doesn't actually demonstrate anything which would help them.

There are two main ways that gene expression changes: change in stimuli and mutations. A mutation in a regulatory sequence can change the expression of the genes it regulates. External stimulus can also trigger gene expression cascades that are already present, such as skin damage from UV rays can increase melanin production (i.e. tanning).It is important to understand the impact that these two types of changes in gene expression have on the process of evolution, and it is best not to confuse them.

I think that the OP title "Rapid Evolution" is possibly
a misnomer insofar as what constitutes rapid in evolutionary time spans. The genetic templates are already in place and have probably been so for many thousands of years. It is the resultant environmental stressors or pressures that seemingly cause the morphological and physiological changes within the "few" generations. In other words the dominoes have been already put into place. At least from how I understand it. If one wishes to study rapid evolution they would be better off with bacteria or fruit flys.

And chemicals like thalidomide can suppress fetal development of different parts (arms, etc) and several organism show an evolutionary history of interrupted development becoming 'normal' -- such as:Axolotl (Ambystoma mexicanum) – Our Wild World

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Although ‘water monster’ is pretty harsh, axolotls are funny looking creatures. This is because axolotls are not fully developed salamanders. Much like frogs, salamanders are born in the water and then must undergo metamorphosis to start their adult lives on land. But this doesn’t happen in the axolotl; instead they spend their entire lives in water, and never grow up (much like Peter Pan, but in a less endearing way).

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Axolotls retain the characteristics of youthful salamanders, including external gills and a fin on its back. This sort of arrested development is known as neoteny. Neoteny is often seen in domesticated animals, most obviously dogs (shorter snouts, floppy ears and playful attitudes are all characteristics of puppies). For the axolotl, staying in this immature state makes sense, since the waters in which they live have very little food. Metamorphosis in salamanders is triggered by thyroid stimulating hormone, which is derived from iodine. Iodine in particular is lacking in the axolotl’s habitat, causing neoteny. But this might also help the salamanders survive; neotenous animals are smaller and require much less food, and in an uncertain environment like that of the axolotl, this might be the best way to live.

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If organisms reach sexual maturity before some parts are fully developed then neoteny can be propagated.Note that humans exhibit neotony as well ... that is one of the reasons humans appear hairless compared to apes, the vellus hair (short, light\blond) is retained (especially in women) rather than being replaced by mature hair (longer, darker), and also why the human skull is 'frozen' in a juvenile form compared to other apes.Certainly eyes are part of the development in a mature fish, but are not fully formed in early fetal development.EnjoyEdited by RAZD, : punctuation

It's still a fish...... ;-)

Looking at "some" examples seems to be the problem here. If some species can switch back to an earlier phenotype (or switch back and forth), we still can't conclude that all evolution works that way. It isn't enough evidence to suggest that the general blueprint is preserved in perpetuity.