Evolution of freshwater fish
I recently posted an article about the mystery of the natural occurrences of many isolated populations of the same freshwater species living in different lakes, rivers and streams that were apparently never connected to each other. I got several explanations, e.g., tornadoes that carry the wildlife from one body of water to another and sticky fish eggs that stick to migratory waterfowl. There is the interesting case of the golden trout, a subspecies of rainbow trout, that managed to remain isolated for a long time. Now I have run across a NY Times article about the evolution of freshwater fish. The article says,
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Though of course I found the article to be very interesting, it of course doesn't answer all of my questions.
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. . . take three-spine sticklebacks (Gasterosteus aculeatus). These little fish usually live in the ocean, but like salmon, they come into rivers to spawn. As the glaciers retreated at the end of the last ice age — a process that went on between ten and twenty thousand years ago — a series of lakes began to form in the northern hemisphere, and the sticklebacks moved into them. Initially, the lakes would have been linked to the oceans by streams and rivers, but as the glaciers retreated, the land rose up (ice is heavy), and the exits to the lakes closed, leaving the sticklebacks in each lake marooned and isolated. And so the animals stuck there began evolving to live exclusively in freshwater.
Which is a real-life version of the evolutionist’s dream: each lake is an evolutionary experiment, a natural laboratory. Because there are so many lakes, the experiment has been repeated many times; and because we know the ages of the lakes, we know roughly how long each experiment has been going on. And sure enough, fish in different lakes have evolved a variety of similar features, repeatedly and independently.
Marine sticklebacks, for example, boast body armor: from head to tail, they are covered in rows of bony plates. Many freshwater sticklebacks have lost these. In marine sticklebacks, the pelvis is a complicated affair that comes complete with a pair of long spines. In some freshwater populations, individuals have a much reduced, lopsided pelvic structure. In others, they have just a remnant, a small, lopsided bone: the ghost of pelvis past.
Mutations to a gene called Ectodysplasin have been implicated as the major culprit in loss of armor; another gene, Pitx1, has been fingered as the main agent of pelvis reduction. Yet the means by which the two genes have effected their changes are different.
Though of course I found the article to be very interesting, it of course doesn't answer all of my questions.
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posted by Larry Fafarman | 1/30/2008 09:30:00 PM
11 Comments:
Someone by the name of Charles R. Darwin reported on similar observations in the Galapagos Islands. Have you heard of him?
Three-and-a-half weeks, and Larry still hasn't been able to find even a single example of "natural occurences of many isolated populations of the same freshwater species living in different lakes, rivers and streams that were apparently never connected to each other."
The reason is simple. Larry is engaged in the fallacy known as "begging the question." He is asking the equivalent to the famous question "When did you stop beating your wife?" He assumes that there is a problem, without ever verifying that one actually exists.
Despite Larry's claims, the distribution of freshwater species very closely matches that expected by considering the geographical history of the waterways. Once you take the "apparent" back out of the question (remember, Larry had to add it after my first response to his alleged dilemma), there are very few true examples of what Larry is claiming.
So where's the mystery? Only in Larry's mind.
Anonymous driveled,
>>>>>> Someone by the name of Charles R. Darwin reported on similar observations in the Galapagos Islands. Have you heard of him? <<<<<<
Yes, idiot. Have you heard of Michael Behe? William Dembski? Jonathan Wells? Denyse O'Leary?
And I know all that crap about Darwin and Lincoln having the same official birthdays (we might not even know Lincoln's true birthday because he was born on the frontier, where people tend to lose track of dates).
As I remember, Darwin's work on the Galapagos Islands concerned the sizes of finch beaks and was a much less sophisticated study than what we have here. Darwin didn't know about genes.
Kevin Vicklund driveled,
>>>>> Three-and-a-half weeks, and Larry still hasn't been able to find even a single example of "natural occurences of many isolated populations of the same freshwater species <<<<<
You stupid dunghill, any book on freshwater fish biology, freshwater fishing, or freshwater botany is chock full of such examples.
>>>>>. . .there are very few true examples of what Larry is claiming. <<<<<
So even you admit that there are some examples. What an idiot.
" the same official birthdays "
Were birthdays relevant somehow?
Oh, yes, thanks for the card.
> And I know all that crap about Darwin and Lincoln having the same official birthdays <
And this has to do with...?
> You stupid dunghill, any book on freshwater fish biology, freshwater fishing, or freshwater botany is chock full of such examples. <
So Kevin is right. You can't cite any.
Dave Fafarman said...
> Oh, yes, thanks for the card. <
Larry, why would you be sending Fake Dave a birthday card? Perhaps because he is Real Dave and you are a clown.
Happy Birthday, Dave.
I received the following interesting email today. It appears that human evolution is subtler than we might have imagined.
* * * *
deCODE Discovers Gene Variants that May Help to Distribute the Work of Evolution between Men and Women
Reykjavik, ICELAND, January 31, 2008 –- Scientists from deCODE genetics (Nasdaq:DCGN) today report the discovery of two common, single-letter variants in the sequence of the human genome (SNPs) that regulate one of the principal motors of evolution. Versions of the two SNPs, located on chromosome 4p16, have a genome-wide impact on the rate of recombination -- the reshuffling of the genome that occurs in the formation of eggs and sperm. Recombination is largely responsible for generating human diversity, the novel configurations of the genome that enable the species to adapt and evolve in an ever-changing environment. Yet remarkably, the versions of the SNPs that increase recombination in men decrease it in women, and vice versa. This highly unusual characteristic may enable the variants to help to maintain a fundamental tension crucial for evolutionary success: promoting the generation of significant diversity within a portion of the population but keeping the pace of this change within certain bounds, maintaining it relatively constant overall and so supporting the stability of the genome and the cohesiveness of the species.
"This is the latest in a series of landmark papers from deCODE in which we have utilized our unique capabilities in human genetics to elucidate some of the key mechanisms driving human evolution," said Kari Stefansson, CEO of deCODE. "We are also excited that we can now immediately enable individuals to see if they carry such variants, by folding the findings announced today –- and others we expect to publish in the near future – into our deCODEme™ personal genome analysis service."
The deCODE team identified the SNPs through a genome-wide analysis of more than 300,000 SNPs in approximately 20,000 participants in the company's gene discovery programs. The SNPs, referred to as rs3796619 and rs1670533, are within the RNF212 gene, and are estimated to account for approximately 22% of paternal variability in recombination and 6.5% of maternal variability. Little is known about RNF212, though it is a mammalian homolog of a gene called ZHP-3 known to be crucial for the success of recombination in other organisms. The paper, entitled 'Sequence Variants in the RNF212 Gene Associate with Genomewide Recombination Rate', is published today in the online edition of Science, at www.sciencemag.org/sciencexpress.
deCODE has made a number of breakthrough discoveries in the understanding of recombination, fertility and human evolution. In 2002, deCODE published the most detailed recombination map to date of the genome, demonstrating that there are hotspots and coldspots for recombination in all chromosomes, and that these are very different in women and men. This map provided a template for completing the final assembly of the sequence of the human genome. deCODE scientists then showed that recombination rate varies between families and between women; that recombination rate increases with the age of the mother; and that higher recombination rate correlates with fertility, indicating that evolution appears to place a premium on the generation of human diversity. In 2005, deCODE identified a genetic variant that correlates with higher recombination rate, the first genetic variant ever demonstrated to be under positive evolutionary selection in human populations in real time. References for these and all deCODE's major discoveries can be found at www.decode.com.
>>>You stupid dunghill, any book on freshwater fish biology, freshwater fishing, or freshwater botany is chock full of such examples.<<<
Seeing as you haven't read any of those books, how would you know? The ones I have read, however, are chock full of examples like those in the NY Times article or the golden trout - the distribution of obligate freshwater species* closely follows the boundaries of watersheds, modulo historical changes in hydrology and specific habitat requirements**. One such book is The Practioner's Guide to Freshwater Biodiversity Conservation. Of particular interest is the end of Chapter 2, starting on page 29, a section titled "Distibution Patterns of Freshwater Biodiversity." Here is an extended passage from the book:
Biodiversity in freshwater ecosystems is distributed in a fundamentally different pattern than that of marine or terrestrial systems. Species adjust their ranges to some degree as climate or ecological conditions change. However, freshwate habitats are relatively discontinuous, and many freshwater species do not disperse easily across land barriers (watershed boundaries) that separate river drainages into discrete units. Therefore, the spatial extent of strictly freshwater species tends to correspond to presently or formerly contiguous river basins or lakes. Watershed boundaries and, for most freshwater species, the intolerable conditions of the ocen into which most rivers flow are the principal barriers to the dispersal of freshwater species between systems. Species can extend or become restricted in their ranges within a river basin relatively easily, but usually can do so between river basins only as a result of geologic changes that affect the locations of watershed boundaries. For example, large-scale glaciation brought formerly neighboring river basins into contact with each other along the margins of the ice. This glaciation also created debris dams that separated formerly connected basins from each other. One river can also capture another by eroding into a neighboring valley, and large-scale geologic movements can allow species formerly restricted to one system to move into another. Species can also extend their range accidentally, for example, through the accidental transport of eggs by waterbirds, or by flooding, and in even some documented accounts by tornadoes or water spouts!
*species that require freshwater at all times for survival. Obviously, species that can survive out of freshwater for long periods of time are more able to bypass barriers
**for example, a fish that can only survive in swift-flowing streams may find a wetland to be an impassible barrier
>>>>>Biodiversity in freshwater ecosystems is distributed in a fundamentally different pattern than that of marine or terrestrial systems . . . .
Species can also extend their range accidentally, for example, through the accidental transport of eggs by waterbirds, or by flooding, and in even some documented accounts by tornadoes or water spouts! <<<<<<
Yes, some of these odd means of dispersal -- e.g., tornadoes and the attachment of sticky eggs to waterfowl -- arose in our discussions!
Still, though, I can't help but feel that the natural ranges of many freshwater species are larger than what one would expect to result from natural causes. Anyway, it is food for thought.
<< I can't help but feel that the natural ranges of many freshwater species are larger than what one would expect to result from natural causes. >>
If you "feel" it, perhaps it is not due to the activities of Little Green Men?
<< Anyway, it is food for thought. >>
Urrp! Have some Pepto Bismol (TM).
<< One such book is The Practitioner's Guide to Freshwater Biodiversity Conservation. >>
Kevin, I note that this is an $80 book from Amazon with no discounts. (Also has zero customer reviews.) Just curious -- did you find it in a college library, or do you own it?
Thanks for posting this. It raises a question that has puzzled me for some time now: How fresh water fish of the same species can be found in lakes and streams hundreds of miles apart. The "tornadoes and glaciers" explanations (as usual, rife with the typical naturalist qualifiers like "may", "may be", "could be", "quite possibly", and the like) just don't cut it.
How often do tornadoes (which typically appear in Kansas, Oklahoma, and parts of Texas - far away from any oceans) scoop up fish from the ocean and deposit them into lakes? Just doesn't make sense.
Another question: Can all salt water fish survive in fresh water?
I would appreciate some civil answers to these questions - that is, without the name-calling.
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