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HalfMooner
Dingaling
Philippines
15831 Posts |
 Posted - 06/03/2006 : 14:56:46
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Creationists, we got yer "transitional fossil" right here, and it ain't even sleeping with da fishes: quote:
Electric Fish on Verge of Evolutionary Split
By Robert Roy Britt
LiveScience Managing Editor
posted: 02 June 2006
09:30 am ET
Electric fish emit weak signals from an organ in their tails that serves as a battery. Different emissions signal aggression, fear or courtship.
While the fish can apparently understand each others' warning signals, "They seem to only choose to mate with other fish having the same signature waveform as their own," explains neurobiologist Matt Arnegard of Cornell University.
But in the Ivindo River in Gabon, Arnegard and colleagues have found fish with the same DNA emitting distinctly different signals. The fish are likely on the verge of splitting into two species, the researchers announced today.
"We think we are seeing evolution in action," Arnegard said.
Electric animals
Because electricity is easily transmitted in water, many species of amphibians and fish have adapted to detect weak electric signals. Some, like sharks, use it to find prey. Others, like the electric eel, generate deadly voltages for defense or to kill prey. Others emit and detect electrical signals primarily as a means to communicate with their own kind.
Electric fish are called mormyrids. The roughly 20 distinct species that have been identified in the river, by their varying DNA, each emit distinct signals, which is the basis for Arnegard's new conclusion.
The process of splitting one species into two is called speciation. Scientists figure there are two ways it can happen. Groups can become geographically separated and take on new traits as their genes mutate. Or, animals can stay together but for some reason mate selectively to form distinct groups.
The latter method, called sympatric speciation, is seen to be less likely and somewhat controversial.
"Many scientists claim it's not feasible," Arnegard said. "But it could be a detection problem because speciation occurs over so many generations."
More work needed
Arnegard is a postdoctoral researcher in the laboratory of Carl Hopkins, a Cornell professor who has been recording electric fish in Gabon since the 1970s.
The latest finding is detailed in the June issue of the Journal of Experimental Biology.
Arnegard cautioned that it is possible the differing electrical signals might be like varying eye color and possibly won't result in speciation. . . .
Although these fish look alike and have the same DNA genetic makeup, they have very different electrical signals and will only mate with fish that produce the same signals. Researchers believe that these different electrical signals are the fishes' first step in diverging into separate species. Credit: John Sullivan via Cornell University
So, is youse gonna gimme some lip about dis, wise guy?
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“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
Edited by - HalfMooner on 06/03/2006 15:06:09
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Zebra
Skeptic Friend
USA
354 Posts |
Posted - 06/03/2006 : 23:46:49 [Permalink]
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Both that report and this one below say "the same DNA" - must be an oversimplification. I can't find the original article online.
This version from Science Daily has more comments about the DNA studies the researchers did (though still limited in details) & where there was overlap the same phrase was used:
quote:
[Cornell neurobiologists] know from their previous research that the various groups of local electric fish have different DNA, different communication patterns and won't mate with each other. However, they now have found a case where two types of electric signals come from fish that have the same DNA.
The researchers' conclusion: The fish appear to be on the verge of forming two separate species.
They can't literally have the same DNA, because they reproduce sexually (they aren't clones of each other). If the differences in the electric signals are genetically coded, which sounds like is the case from previous studies on different species of this fish, then there must be polymorphisms in the regions that code for the electric signals in the identical-except-for-electric-signal fish. But, keep reading - that's not what the researcher is said to have found.
And, if they do literally have "the same DNA" but different electric signals, then the electric signals are not coded genetically, and they are not about to diverge into different species.
quote:
The electric fish -- known as mormyrids -- emit weak electric fields from a batterylike organ in their tails to sense their surroundings and communicate with other fish.
The electric signal might be changed by nongenetic factors, like electrolytes available in the water or food, but sounds like the 2 populations of fish they studied were in the same waters so that's not likely an explanation for the differences seen...
quote:
Each species of mormyrid gives off a single characteristic electric impulse resulting in the flash of signals, indicating, for example, aggression, courtship and fear. While the fish may be able to understand other species' impulses, said Arnegard, "They seem to only choose to mate with other fish having the same signature waveform as their own."
Except for some, Arnegard has discovered.
When he joined Hopkins' lab, the team was about to publish descriptions of two separate species. But when Arnegard decided to take a genetic look at these particular fish, he couldn't find any differences in their DNA sequences.
"These fish have different signals and different appearances, so we were surprised to find no detectable variation in the genetic markers we studied," Arnegard said.
Because all of the 20 or so species of mormyrid have distinct electric signals, Arnegard believes the different impulses of the fish he studies might be their first step in diverging into different species.
"This might be a snapshot of evolution," Arnegard said.
Whoa Nelly, the science writers should have had their skeptic antennas up here. Something's not right. Couple of possibilities:
(1) the variations are in regions of DNA they didn't study, & saying the DNA was the same was a broader statement than warranted;
(2) variations are minor polymorphisms but they were looking for previously identified alleles w/ more marked differences in DNA;
(3) DNA study was done incorrectly (e.g., samples thought to be from different fish were actually from the same fish);
(4) Researcher is using overly simplified phrasing when discussing DNA findings with science reporters (or, science reporters simplified the stories - but if so, 2 sites used same term "the same DNA")
(5) Electrical differences can occur for reasons besides genetic differences (variations in local water, diet...?)
In either case, the hopeful conclusion that these two groups of fish are about to diverge into distinct species sounds unwarranted from the information provided, though of course that could just reflect the limits of conveying the complexities in a science news story - still, I would have hoped that the science writers would have caught this, or commented on it... |
I think, you know, freedom means freedom for everyone* -Dick Cheney
*some restrictions may apply |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 06/04/2006 : 00:18:46 [Permalink]
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I would assume, though without real knowledge, that an Electric Fish Genome Project has never been completed. I'm guessing the researchers compared a relatively few nuclear genes, and found no differences. Duh.
The genes affecting the differences in electrical signal, it seems to me, might even be non-nuclear, mitochondrial genes. The mitochondria might well be the powerhouses creating the electricity, and the genetic differences between the various non-interbreeding subspecies of the fish might be entirely mitochondrial.
That the sub-species won't interbreed is itself a strong indication of speciation, regardless of where any genetic differences are located.
Wouldn't it be interesting if speciation could happen with mitochondrial genetic differences alone?
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“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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Zebra
Skeptic Friend
USA
354 Posts |
Posted - 06/04/2006 : 09:39:32 [Permalink]
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If the researchers are studying "the DNA", or more likely (as you say) a particular portion of the fishes' genome, one would HOPE they know where the code for the electric signals is - at least, where it is in species of this fish they have studied so far. Duh.
Then, if they are seeing differences between identical-looking fish with the same known genes for battery-organ/electrical signals, then the FIRST question from the researchers and the science reporters should be: what is the basis for this difference?
Is it: (1) genetic, but not where we're looking in the chromosomal DNA? (2) genetic, but not where we're looking because it's in the mitochondrial DNA? (3) genetic, but we didn't find it because we made a damn fool mistake in the process of testing? (4) nongenetic, something environmental, which we hope it's not because then we're not seeing a genetic difference emerge which is really what we hope we're seeing, and we're forgetting the important point that looking for what you hope to see & ignoring other possibilities can seriously mislead even the best scientist with the hottest new research techniques?
If it's genetic but not in the region of code that had been previously identified as associated w/ electric signal, that's interesting - previously unrecognized gene, whether it's new or newly showing polymorphisms with phenotypic differences. Or, interesting if it's mitochondrial, but then the changes should be passed as matrilinear (or whichever gender of this animal supplies the mitochondria from parent to child). |
I think, you know, freedom means freedom for everyone* -Dick Cheney
*some restrictions may apply |
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dv82matt
SFN Regular
760 Posts |
Posted - 06/04/2006 : 10:02:54 [Permalink]
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quote:
Originally posted by Zebra
Both that report and this one below say "the same DNA" - must be an oversimplification.
I think you hit the nail on the head right there. Probably just meant that they didn't find the differences they'd expect to find if they were different species. |
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Zebra
Skeptic Friend
USA
354 Posts |
Posted - 06/04/2006 : 10:35:36 [Permalink]
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Right. So then, where's the emphasis on how unusual that finding is, and how that has to be probed further? And how it might not mean these fish are, to as the title of the first article trumpeted, "Electric Fish on Verge of Evolutionary Split." Maybe just shoddy science reporting.
Here's the same news as reported in Cornell News Chronicle Online, includes more comments by the researcher & seems more level-headed & informative: quote:
Evolution in action? African fish could be providing rare example of forming two separate species, Cornell scientists speculate
by Sara Ball
...So Arnegard suspects that the different shapes of the electric impulses from these mormyrids might be a first step in sympatric speciation.
One the other hand, the fish could be a single species. "This could be just a polymorphism, like eye color in humans, that violates the fishes' general evolutionary pattern but doesn't give rise to separate species," said Arnegard, who will return to Gabon in June to conduct further tests, funded by the National Geographic Society.
Right. That's a definite possibility, though still interesting that fish would express mating "preference" in a minor trait that could be analogous to eye color in humans.
HalfMooner, you opened this as a challenge to creationists, but imo if this is a skeptics site not a pro-evolution site then we should be skeptics, dammit. |
I think, you know, freedom means freedom for everyone* -Dick Cheney
*some restrictions may apply |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 06/04/2006 : 11:59:06 [Permalink]
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quote:
Originally posted by Zebra
HalfMooner, you opened this as a challenge to creationists, but imo if this is a skeptics site not a pro-evolution site then we should be skeptics, dammit.
As the cheating wrestler said, "This choke's on me." Thank you both for your feedback, dv82Matt and Zebra. Though this is going in a different direction than I might have expected, this is also a much better discussion and more interesting than I might have expected.
One thing you touched upon, Zebra: The possibility that there really are no genetic differences, nuclear or mitochondrial, between the non-interbreeding supposed subspecies. What if subtle differences in water temperature or chemistry, or the amount of sunlight falling upon the water when they were spawned caused a different expression of the same electrical-control genes? Or, what if the electrical signaling of these fish is partially-learned behavior, like birdsong?
I could imagine something like speciation happening with no genetic differences behind it. The groups could become genetically isolated because of their preferences for the "right" mating signal ("I like Doris, but she's into Rock and I'm into Classical"). Then, only after such a de facto separation, genetic drift might set in.
By biological definition, I wonder: Must genetic differences exist to count as speciation?
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“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
| Edited by - HalfMooner on 06/04/2006 13:29:12 |
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dv82matt
SFN Regular
760 Posts |
Posted - 06/04/2006 : 17:51:34 [Permalink]
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quote:
Originally posted by Zebra
Right. So then, where's the emphasis on how unusual that finding is, and how that has to be probed further? And how it might not mean these fish are, to as the title of the first article trumpeted, "Electric Fish on Verge of Evolutionary Split." Maybe just shoddy science reporting.
Well, to be fair, the article (the one HalfMooner posted) does include a blurb about how more work is needed, but yeah I agree that the title was overly zealous.
As you pointed out even if speciation is not occurring something interesting is still happening. It may be that the pattern of the electrical signals is not linked to DNA at all (kind of like fingerprints in humans) or something similar.
HalfI hadn't thought of learned behaviour (ie arbitrary behaviour not specifically linked to any DNA) as being a driver of speciation before. It's a facinating idea. I'm getting ahead of the science here but if true might it mean that the gene is not always the fundamental unit of selection? After all in this scenario the specific genes carried would be irrelevant to the selection proccess. |
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 06/04/2006 : 19:12:38 [Permalink]
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quote:
Originally posted by dv82matt
HalfI hadn't thought of learned behaviour (ie arbitrary behaviour not specifically linked to any DNA) as being a driver of speciation before. It's a facinating idea.
Indeed. Imagine a plague that strikes down all of humankind except (for example) the Hatfields and the McCoys. Sure, there might be the odd hybridization event here and there, but for the most part they'd become reproductively isolated even when neighbors.quote:
I'm getting ahead of the science here but if true might it mean that the gene is not always the fundamental unit of selection?
Nah. An organism's learned behaviour is just another part of the selective environment, as far as genes are concerned. Some genes, after all, have something to do with the capability to learn in the first place. With the fish, if one did not learn any particular signal at all, it'd be doomed. A fish which learned more than one signal might be more likely to reproduce, but then again... Look at mockingbirds and mynas: they mimic other species' sexual signals, yet breed exclusively with mockingbirds and mynas (respectively). |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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dv82matt
SFN Regular
760 Posts |
Posted - 06/04/2006 : 21:01:59 [Permalink]
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quote:
Originally posted by Dave W.
Imagine a plague that strikes down all of humankind except (for example) the Hatfields and the McCoys. Sure, there might be the odd hybridization event here and there, but for the most part they'd become reproductively isolated even when neighbors.
In practice would this actually happen though. I mean cultural phenomona like feuds between families occur on a much shorter timescale than evolutionary events like speciation.
quote:
An organism's learned behaviour is just another part of the selective environment, as far as genes are concerned. Some genes, after all, have something to do with the capability to learn in the first place. With the fish, if one did not learn any particular signal at all, it'd be doomed. A fish which learned more than one signal might be more likely to reproduce, but then again... Look at mockingbirds and mynas: they mimic other species' sexual signals, yet breed exclusively with mockingbirds and mynas (respectively).
It's true that from the genes point of view learned behaviour is just another environmental factor. What is interesting to me is the idea that there could be an additional selection metric independent of genes at work.
In the case of humans I can't help wondering if it would be at all accurate to say that we are on the verge of a fundamental shift from genes as the fundamental unit of selection to memes becoming the fundamental unit. |
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 06/05/2006 : 18:08:48 [Permalink]
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quote:
Originally posted by dv82matt
In the case of humans I can't help wondering if it would be at all accurate to say that we are on the verge of a fundamental shift from genes as the fundamental unit of selection to memes becoming the fundamental unit.
Given books like "How to Pick Up Women" and women who say that the most attractive thing they find in men is a sense of humor, I would be wondering if that shift hasn't already happened. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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Dude
SFN Die Hard
USA
6891 Posts |
Posted - 06/06/2006 : 18:46:02 [Permalink]
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Reproductive isolation, regardless of how it is achieved, is indicitave of a speciation event.
The apparent reproductive isolation occuring among these fish was, I though, the main point of that article.
You always have to take "scientific journalism" with a grain of salt. There is little choice but to oversimplify if you expect to hold the interest of a general audience when speaking about technical and complex concepts.
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Ignorance is preferable to error; and he is less remote from the truth who believes nothing, than he who believes what is wrong.
-- Thomas Jefferson
"god :: the last refuge of a man with no answers and no argument." - G. Carlin
Hope, n.
The handmaiden of desperation; the opiate of despair; the illegible signpost on the road to perdition. ~~ da filth |
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trogdor
Skeptic Friend
198 Posts |
Posted - 06/07/2006 : 20:50:21 [Permalink]
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quote:
Originally posted by Zebra
Both that report and this one below say "the same DNA" - must be an oversimplification. I can't find the original article online.
This version from Science Daily has more comments about the DNA studies the researchers did (though still limited in details) & where there was overlap the same phrase was used:
quote:
[Cornell neurobiologists] know from their previous research that the various groups of local electric fish have different DNA, different communication patterns and won't mate with each other. However, they now have found a case where two types of electric signals come from fish that have the same DNA.
The researchers' conclusion: The fish appear to be on the verge of forming two separate species.
They can't literally have the same DNA, because they reproduce sexually (they aren't clones of each other). If the differences in the electric signals are genetically coded, which sounds like is the case from previous studies on different species of this fish, then there must be polymorphisms in the regions that code for the electric signals in the identical-except-for-electric-signal fish. But, keep reading - that's not what the researcher is said to have found.
And, if they do literally have "the same DNA" but different electric signals, then the electric signals are not coded genetically, and they are not about to diverge into different species.
quote:
The electric fish -- known as mormyrids -- emit weak electric fields from a batterylike organ in their tails to sense their surroundings and communicate with other fish.
The electric signal might be changed by nongenetic factors, like electrolytes available in the water or food, but sounds like the 2 populations of fish they studied were in the same waters so that's not likely an explanation for the differences seen...
quote:
Each species of mormyrid gives off a single characteristic electric impulse resulting in the flash of signals, indicating, for example, aggression, courtship and fear. While the fish may be able to understand other species' impulses, said Arnegard, "They seem to only choose to mate with other fish having the same signature waveform as their own."
Except for some, Arnegard has discovered.
When he joined Hopkins' lab, the team was about to publish descriptions of two separate species. But when Arnegard decided to take a genetic look at these particular fish, he couldn't find any differences in their DNA sequences.
"These fish have different signals and different appearances, so we were surprised to find no detectable variation in the genetic markers we studied," Arnegard said.
Because all of the 20 or so species of mormyrid have distinct electric signals, Arnegard believes the different impulses of the fish he studies might be their first step in diverging into different species.
"This might be a snapshot of evolution," Arnegard said.
Whoa Nelly, the science writers should have had their skeptic antennas up here. Something's not right. Couple of possibilities:
(1) the variations are in regions of DNA they didn't study, & saying the DNA was the same was a broader statement than warranted;
(2) variations are minor polymorphisms but they were looking for previously identified alleles w/ more marked differences in DNA;
(3) DNA study was done incorrectly (e.g., samples thought to be from different fish were actually from the same fish);
(4) Researcher is using overly simplified phrasing when discussing DNA findings with science reporters (or, science reporters simplified the stories - but if so, 2 sites used same term "the same DNA")
(5) Electrical differences can occur for reasons besides genetic differences (variations in local water, diet...?)
In either case, the hopeful conclusion that these two groups of fish are about to diverge into distinct species sounds unwarranted from the information provided, though of course that could just reflect the limits of conveying the complexities in a science news story - still, I would have hoped that the science writers would have caught this, or commented on it...
I read parts of the article and I believe I figured out what they meant by “the same DNA.” The researchers found no genetic difference that would indicate that these fish had been two separate species for a significant period of time. But the fact remains that the fish were primarily mating with fish that were sending the same electrical frequencies. These two facts would seem to indicate that the some fish had recently begun using a different signal, a signal that isolated them from the general mating population, 5thus creating a new species. From the list above this is most similar to option 1 and 4 but slightly different from both.
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