Advantages of living in the dark: The multiple evolution events of 'blind' cavefish
This is the blind Mexican cavefish (Astyanax mexicanus) along with its sighted cousin the Mexican tetra. Credit: Professor Richard Borowsky
The blind Mexican cavefish (Astyanax mexicanus) have not only lost their sight but have adapted to perpetual darkness by also losing their pigment (albinism) and having altered sleep patterns. New research published in BioMed Central's open access journal BMC Evolutionary Biology shows that the cavefish are an example of convergent evolution, with several populations repeatedly, and independently, losing their sight and pigmentation.
The blind cavefish and the surface dwelling Mexican tetra, despite appearances, are the same species and can interbreed. The cavefish are simply a variant of the Mexican tetra, albeit one adapted to living in complete darkness. A team of researchers from Portugal, America, and Mexico studied the DNA from 11 populations of cavefish (from three geographic regions) and 10 populations of their surface dwelling cousins to help understand the evolutionary origin of the physical differences between them.
While results from the genotyping showed that the surface populations were genetically very similar, the story for the cave populations was very different. The cave forms had a much lower genetic diversity, probably as a result of limited space and food. Not surprisingly the cave populations with the most influx from the surface had the highest diversity. In fact there seemed to be a great deal of migration in both directions.
It has been thought that historically at least two groups of fish lived in the rivers of Sierra de El Abra, Mexico. One group originally colonized the caves, but became extinct on the surface. A different population then restocked the rivers and also invaded the caves.
Prof Richard Borowsky, from the Cave Biology Group at New York University explained, "We were fortunate in being able to use A. mexicanus as a kind of 'natural' experiment where nature has already provided the crosses and isolation events between populations for us. Our genotyping results have provided evidence that the cave variant had at least five separate evolutionary origins from these two ancestral stocks."
Dr Martina Bradic who lead the research continued, "Despite interbreeding and gene flow from the surface populations the eyeless 'cave phenotype' has been maintained in the caves. This indicates that there must be strong selection pressure against eyes in the cave environment. Whatever the advantage of the eyeless condition, it may explain why different populations of A. mexicanus cave fish have independently evolved the same eyeless condition, a striking example of convergent evolution."
More information: Gene flow and population structure in the Mexican blind cavefish complex (Astyanax mexicanus) Martina Bradic, Peter Beerli, Francisco García-de León, Sarai Esquivel-Bobadilla and Richard Borowsky BMC Evolutionary Biology (in press).
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BioMed Central
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It doesn't matter, the tiniest statistical advantage over billions or trillions of generations produces a trend toward that advantage.
Eyes are useless in complete darkness, and not only do they save energy but also if the eye can become diseased or infected and cause death it is definitively advantageous to not have them. You don't seem to understand that in the wild most organisms are on the verge of starvation ALL THE TIME. Any way to make the little bit of energy you are able to acquire last longer and go further is important.
Jan 23, 2012
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And a cheetah that can reach 60 miles per hour, or a springbok jumping higher than a man, is not an easy way to "argue" that asnimals are all just shy of starving.
It's amazing how little those devoted to "evolution" actually are aware of its rules.
Jan 23, 2012
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And notice something else. Defenders of "evolution" say that losing color and eyes bestows a small but significant extra energy that made them compete successfully to survive. Then how could each successive influx of fish survive? The later fish will be sighted and colored, competing with the supposedly more energetic blind and colorless fish! How did these later fish survive to evolve?
Jan 24, 2012
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Jan 24, 2012
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It's not infinitesimally small...
It didn't necessarily take that long...
You defined it as an advantage... a small one but an advantage none the less, so yes an advantage would produce an advantage...
That advantage can remain an advantage across unrelated changes to the environment.
False, not having eyes is not having eyes. From the fishes point of view having eyes in complete blackness all the time is equivalent to not having eyes, no extra instinct is required.
cont
Jan 24, 2012
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You can't see mates in the dark, and for fish and many other animals sight is not the primary sense to navigate their environment.
Of course it is, for the cheetah it is the primary means of acquiring food and for the springbok it is the primary means of not becoming food.
You have no idea what you are talking about, I studied evolutionary biology formally at CMU, I have written practical genetic algorithms to solve optimization problems. Your statements make you appear foolish, or at least ignorant of evolutionary theory.
Jan 24, 2012
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Because you have no idea what you are talking about. The same mutations occur constantly, in all species. The same mutations occur in humans over and over and over again and have for hundreds of years. Of course most mutations are detrimental, as would be the lack of eyes EXCEPT when the fish were living in the cave. It makes complete sense that this mutation would be selected for in the cave and selected against outside of it.
Again, you don't know what you are talking about.
Jan 24, 2012
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More importantly, look up Dunning-Kruger syndrome and consider that if you speak authoritatively about a technical topic with no formal education pertaining to that topic this syndrome just might apply to you.
Jan 24, 2012
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This all the evidence anyone needs to realize that this penrod clown doesn't know anything about evolutionary theory.
The same mutations occur over and over again... ever heard of genetic diseases in humans? Here is a list of hundreds of them that occur repeatedly in humans:
http://en.wikiped...isorders
...and yes, these are detrimental mutations, but whether a mutation is beneficial or detrimental depends on the environment. Under the right conditions a mutation could be either, and that is what is happening with these fish. Outside of the cave where there is light this lack of eyes is a detrimental mutation, inside the cave where it is pitch black it is an advantageous mutation... selection takes over accordingly.
Jan 24, 2012
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Jan 25, 2012
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While DC is right in saying the same mutations could occur, that's not even what this article is saying.
The scientists are talking about the same effects. That is, the mutations led to the same phenotype (non-functional eyes, albinism), but it is precisely because the mutations are different that we can tell there were 5 separate events. So, in one population a G could have changed to a C and removed carotenoid processing form the fish (which would also remove pigmentation btw), while in another retinal development is dsiturbed. Same phenotypes, different mutations.
Jan 25, 2012
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Interesting, I should have read the article more closely.
Regardless, it doesn't change my criticism of Penrods statements.
Jan 25, 2012
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And, if you accept Darwin, then the mutations are infinitesimally small, accumulating over centuries. Remember, too, the mutations must also breed true, they can't be like albinism, they supposedly must be so small they don't interfere with the breeding process the way massive changes often if not always do.
Jan 25, 2012
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Really? I didn't say they were always starving.. Is this the best you can do?
I'd like to know what Darwin has to do with this... Darwin is credited with the initial idea, but what we know now goes FAR beyond what he knew... with all due respect.
Also, this statement is false, single mutations can create significant changes.
Jan 25, 2012
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Jan 25, 2012
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Pulling shit out of your ass... they are mutations like any other. Point mutations, insertions, deletions, etc.
Completely false, there is no reason to assume that any particular mutation will cause a noticeable effect. The mutations on that list are the particularly nasty ones, because they naturally receive the most attention. Most will have little if any obvious effect.
Jan 25, 2012
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And Darwin does have a place in this, since the rule being promoted is that of random mutation changes creating manifestations that build up over time. As with so many who have no legitimate gripe, Deathclock just finds fault with everything I do.
And, since the discussion here is about Darwinian "evolution" supposedly producing workable new features, only changes that produce viable manifestations, that don't represent fatal conditions for the creature, are under consideration. Yes, mutations can cause significant changes, but they are supposedly not coordinated to occur in areas where an entire feature will be altered in a usable manner. There is no record anywhere of a single mutation, in one generation, producing a feasible improvement in the creature's make-up.
Jan 25, 2012
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I'm not going to argue semantics with you
My point is MODERN evolutionary theory is a far cry from Darwin's original understanding. It always seems like most people arguing against evolution are under the false assumption that our knowledge ended with Darwin's original theory, which is obviously not the case.
Jan 25, 2012
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Jan 25, 2012
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The telomere-telomere fusion of two ancestral chromosomes into human chromosome number 2 is a pretty damn good example.
Jan 25, 2012
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Yes, mutations can have both significant and insignificant effects on the phenotype... is this news to you?
Nope, a mutation occurs in a single generation, I was talking about a specific change to the phenotype.
I guess one giant ad hominem is preferable?
Also, you seem to be under the impression that mutations can take more than one generation... they cannot.
Jan 25, 2012
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All mutations occur in a single generation... you clearly don't even know the BASICS of what you are talking about.
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Like, in the end, someone who says, "Aww...penrod doesn't want to play anymore..." can necessarily be trusted to be sincere and not just treating the issue like a game. By their own words Deathclock indicates they weren't serious, they toss out disclaimers just to try to derail legitimate discussion.
Jan 25, 2012
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Wow... go ahead and ask the website administrators about it if you're so paranoid.
Jan 25, 2012
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You don't even know what I was referring to, do you? That fusion represents the significant difference between the modern great apes and humans. That fusion caused a weakening of a jaw muscle. The weaker jaw muscle, attached to a skull plate, allowed that plate to expand further in adolescence before fusing with the other skull plates, making room for a larger brain. It explains humans weaker bite force and larger skulls and our intelligence.
You are clueless.
...and are you going to admit that you know nothing about evolution since you somehow thought a single mutation does or can occur over multiple generations? I mean, this shows you don't even know what a mutation is... you've lost, give it up.
Jan 25, 2012
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And, note davhaywood's malignant thinking. davhaywood portrays it as a fault my stopping arguing when purportedly I lose. But, itsn't it a fault to continue to argue when you've been disproved? By their own words, dayhaywood says it is wrong not to continue arguing when you've been proved wrong! Which explains Deathclock and davhaywood's actions!
Jan 25, 2012
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unless of course you want to admit that you know nothing about evolution since you didn't even know what a mutation is (as evident by the fact that you thought a mutation could somehow occur over multiple generations)
Jan 26, 2012
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On another note, stop feeding the trolls. They grow big and hairy.
Jan 26, 2012
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Jan 26, 2012
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Problem is that penrod believes the earth is flat!
Jan 29, 2012
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Your point doesn't make sense, Julian. In your previous statement you said, "The later fish will be sighted and colored, competing with the supposedly more energetic blind and colorless fish! How did these later fish survive to evolve?" I was simply explaining how genetic information from the surface fish could be present.
Jan 29, 2012
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By the way, my point about you ceasing to talk once you lose, but never ADMITTING DEFEAT OR CHANGING YOUR POSITION was what was remarkable. You may discontinue a one specific conversation where you have clearly been outpaced, but you will happily pick up right where you left off in another article, having blissfully expunged any pertinant information from preceeding conversations. Good day, sir. And please stop trolling legitimate scientific discussions, stick to your prayer groups.
Feb 23, 2012
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1. Darwin NEVER talked about mutations in the way we understand them today. Just mentioning that itself shows you know jackshit about biology or its history. Darwin only talked about variation and natural selection. Today we know that evolutionary mechanisms include random variation, biased mutations, genetic drift, genetic hitchhiking and gene flow. Some mutations have more of a probability of occurring simply based on the genetic code. Genetic drift can cause neutral mutations to become 'fixed', so to say and give rise to phenotypes. Oh by the way, ever heard of the Baldwin Effect? We also include neo-lamarckism in modern evolutionary theory.
Feb 23, 2012
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3. The adaptation of the fishes to no light and the invasion by surface fish is a complex matter for you to understand. How do you not get the fact that if eye-bearing surface fish do go down, their eyes don't matter because its just too dark there?
Feb 23, 2012
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Feb 23, 2012
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5. The problem is, you don't get what evolution is. Evolution is not a monkey becoming a man. Or a mouse becoming a horse. Evolution is just a change in allele frequency over generations. Nothing more, nothing less. So you will not see major changes during your lifetime. Speciation has been observed which was probably set into motion millennia ago. We can see that. Bacteria are more helpful that way. They evolve very quickly. And viruses.
You are the missing link. Please evolve.
Feb 26, 2012
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