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Study catches 2 bird populations as they split into separate species (7/17/2009)

Tags:
speciation, birds
Populations of the Monarcha castaneiventris flycatcher vary in plumage color across the Solomon Islands, with a subspecies on Makira Island having chestnut bellies and blue-black upper parts (Monarcha castaneiventris megarhynchus) and a subspecies on neighboring satellite islands being entirely blue-black (melanic; Monarcha castaneiventris ugiensis)
Populations of the Monarcha castaneiventris flycatcher vary in plumage color across the Solomon Islands, with a subspecies on Makira Island having chestnut bellies and blue-black upper parts (Monarcha castaneiventris megarhynchus) and a subspecies on neighboring satellite islands being entirely blue-black (melanic; Monarcha castaneiventris ugiensis)

A new study finds that a change in a single gene has sent two closely related bird populations on their way to becoming two distinct species. The study, published in the August issue of the American Naturalist, is one of only a few to investigate the specific genetic changes that drive two populations toward speciation.

Speciation, the process by which different populations of the same species split into separate species, is central to evolution. But it's notoriously hard to observe in action. This study, led by biologist J. Albert Uy of Syracuse University, captures two populations of monarch flycatcher birds just as they arrive at that evolutionary crossroads.

Monarch flycatchers are small, insect-eating birds common in the Solomon Islands, east of Papua New Guinea. Uy and his team looked at two flycatcher populations: one found mostly on the large island of Makira, the other on smaller surrounding islands. Besides where they live, the only discernable difference between the two populations is the color of their feathers. The birds on Makira have all black feathers. Birds on the smaller islands have the same black feathers, but with a chestnut-colored belly.

The question of whether these two populations are on the road to speciation comes down to sex. When two populations stop exchanging genes-that is, stop mating with each other-then they can be considered distinct species. Uy and his team wanted to see if these flycatchers were heading in that direction.

It would be all but impossible to try to catalog every occasion on which an all-black flycatcher mated with a chestnut-bellied. So Uy and his team used another test.

Flycatcher males defend their mating territories. If a potential rival male enters another's territory, fights often ensue. If all-black males react less violently to chestnut-bellied males and vice versa, that's an indication that the two don't recognize each other as reproductive rivals. If they don't see each other as rivals, then one can assume that mating between members of the two populations is rare.

So Uy and his team made all-black and chestnut-bellied taxidermy models. They used the models to invade mating territories in each population. As expected, when all-black birds were presented with all-black models, they attacked. But when all-black birds encountered chestnut-bellied models, they were much less likely to go on the offensive. The same scenario held for the chestnut-bellied birds.

That males from the two populations no longer view the other as a reproductive threat is a good indication that not much mating is taking place between the two groups. Their evolutionary paths are diverging, Uy and his team found-all because of a change in plumage.

The researchers then went a step further. They looked into the birds' genomes to see what genes may have played a role in the different plumage pattern. They found only one: the melanocortin-1 receptor gene (MC1R). The MC1R gene regulates the production of melanin, which gives skin and feathers their color. The all-black and chestnut-bellied birds had different versions of the MC1R gene, which gave rise to the plumage change.

That change appears to have been enough to create a reproductive barrier for flycatchers. Not every species is so picky, so a color change doesn't always drive speciation. Nonetheless, these results suggest that it can take as little as one gene, in the right spot in the genome, to cause a fork in the evolutionary road.

Reference:

J. Albert C. Uy, Robert G. Moyle, Christopher E. Filardi, Zachary A. Cheviron, "Difference in Plumage Color Used in Species Recognition between Incipient Species Is Linked to a Single Amino Acid Substitution in the Melanocortin-1 Receptor." The American Naturalist August 2009.

Note: This story has been adapted from a news release issued by the University of Chicago Press Journals

Comments:

1. xznofile

7/17/2009 12:01:27 PM MST

this is just a shot in the dark: the colored flycatchers on the islands look like an inland bee eater (?) known to have poisonous plumage. it's possible that some kind of flying predator like a hawk or man-o-war bird migrates between the two regions and is familiar w/ the poison so they aren't predated. the different forest cover protects the inland flycatcher but expose the island version, so the red plumage gene is selected for reproduction by being the only one that isn't eaten, while the black versions are. beats me though why it doesn't migrate to inland paupaua, maybe the original poisonous feathered bird resents them.


2. John Mavity

7/17/2009 12:02:58 PM MST

Speciation refers to genetic capability, NOT social capability. (reference: "inter-racial" human couples may be socially taboo in some regions, but still be physically/genetically capable of producing offspring together, thus technically belonging to the same "species").
For this observation on animal "inter-racial" mating to be scientifically accurate, sample birds must be caught from EACH of the two groups, and artifically inseminated in a manner which is consistently successful within the groups separately;
if this artificial insemination repeatedly and consistently produces offspring when used between parents of the same group, and fails to produce offspring between parents of different groups, THEN it is valid to say the groups have LIKELY become different species.

As it is, two remote branches of the same family have different hair-color and discriminate accordingly. This is barely news, and certainly fails to demonstrate genetically-incompatible speciation.


3. foo bar

7/17/2009 12:18:44 PM MST

John, the article isn't suggesting that the two birds are currently different species.

It is suggesting that one tiny change in one gene which effects plumage, is acting as a sexual barrier which will one day lead to genetically-incompatible species.

It is the seed of change that we are talking about, not the change itself.


4. schmon schmavity

7/17/2009 12:58:31 PM MST

Yes. The point is that the gene has created a reproductive barrier which has serious potential to drive the two populations apart genetically. While they may not constitute two separate species today, as time progresses new mutations in either group will be extremely unlikely to cross this barrier. Therefor, speciation is a highly probable eventual outcome, assuming the trend continues. It demonstrates something very interesting about what sorts of things can have the potential to cause one species to split into two.


5. Fo Ible

7/17/2009 2:27:43 PM MST

Unfortunately for the racists, this does not work amongst humans!


6. amphiox

7/17/2009 2:48:51 PM MST

John Mavity, your definition of species is actually wrong.

There are quite a number of closely related species that can produce viable and fertile hybrids in artificial settings, like zoos, or through artificial insemination.

These species are still classified as separate species.

The barrier to gene exchange needs only to operate in the natural setting, and it does not matter if it is behavioral (ie mate selection) or genetic (ie chromosome mismatch) or physical (ie size differences preventing successful mating) or whatever. Whether the barrier can be overcome by unnatural interventions is irrelevant to the definition.

The barrier does not even have to be absolute. There are quite a number of well documented fertile hybrid populations that have arisen completely naturally in the wild. (Some examples are Brown/Grizzly and Polar Bear, Wolves and Coyotes, Domestic Dogs and Wolves, and a whole bunch of plants) The parent species are still considered to be separate species even though the hybrids exist.

Nature is a continuum, and there are rarely any absolute boundaries, no matter how inconvenient it is for us humans and or love of classifying things. All definitions are a little arbitrary and fuzzy at their edges.


7. MB

7/19/2009 3:29:48 AM MST

Title: "Study catches 2 bird populations as they split into separate species"

First thoughts: Wow! Finally... a break through... sounds interesting, let's bother to read this.

Reality: Study observes two extremely similar birds that have different colours to not be inter mating as frequently as intra mating. Upon looking for a difference in the biochemistry of the birds they find that (shock horror!) the only difference is in the bit that determines colour.

Conclusion: Birds are still birds, dogs are still dogs.

This is not to do with species, this is to do with the colour of the feathers of two otherwise very similar birds.

The birds in this study have not "split into separate species", they are still birds, they just interbreed less frequently. They can still breed. Even if they could not, they are still birds.

Evolution! Oh how I want to believe in you! Oh how easy my life would be if you were true, if I could nod and agree... but where is the evidence? Where is the science? Everywhere we search it seems there is nothing but hysteria and grants for nodders.



8. ad

7/19/2009 3:49:31 AM MST

MB
you want evidence of evolution? there is not a lack of it you could start out with reading "the origin of the species..." and the many many other books and studies that have come after this???


9. Bob

7/19/2009 5:31:50 AM MST

MB--

So penguins, kiwi, and ostriches are all the same species? After all, they are still birds. Good to know.

I guess that also means that we are apes since we are all primates.

And I better make sure that my house cat doesn't get a tiger pregnant since they are both cats.

What a maroon, what an ignoramouse.


10. Mike

7/19/2009 6:22:53 AM MST

I agree that this doesn't sound like a big deal. What always puzzles me about definitions of species is that all domestic dogs are considered one species, despite a ridiculously broad range of phsyical traits (and surely, one could argue, on the basis of "natural" mating habits there are definite boundaries as well). Yet the slightest physical differences in a butterfly--never mind the genetics--and you've got yourself a new species. My only guess to why this is, is that the practice of dog breeding is much older than species classification, plus scientists are always wanting to be the "discoverer" of new species.


11. Shawn

7/19/2009 9:24:15 AM MST

These just brings up more questions:

1. When the mutation first occurred, why did a female choose such a funny-coloured mate?

2. When the population was still small, how did the males attract outside females to prevent intense inbreeding?


12. blood_test_Bob

7/19/2009 10:00:00 AM MST

I 2nd the comments about the actual definition of species. If evolution is not just a theory so be it, but manipulating science for the advancement of an agenda is perverse. Therefore, testing the genome only proves a pigment mutation which was already known.yippy.


13. jiggly_jim

7/19/2009 10:34:31 AM MST

Are people intentionally not getting the point of this article?

This is not about two different species. It is about two different populations of a single species that are no longer interbreeding. The difference in the two populations, in this case, has been neatly isolated to a single mutation that impacts coloration.

This is significant because, although these birds are still the same species, they don't interbreed. They are therefore more likely to split into increasingly divergent genotypes - eventually possibly becoming distinct species.

As the article clearly states in several places, this research is about observing the *beginnings* of speciation, that is to say, they are answering the question: "What happens in a single species before it fully differentiates into two species?"

There is no "manipulating science" going on, no matter what evo-deniers would like to believe.


14. Danny

7/19/2009 11:52:22 AM MST

@Shawn:

Good science is supposed to bring up more questions. Those are excellent follow-up questions to this observation. Maybe this example will be able to provide some of the answers. Maybe the researchers will have to look for other examples to answer your questions.

A good place to start would be to try to identify how attraction in any bird species is governed, and whether variations in that attraction are due to genetic changes or learned behavior, or something else.

Here, researchers have identified two populations which might be able to answer some of those questions. That's what makes this report exciting!


15. Danny

7/19/2009 11:55:35 AM MST

@bloodtestBob:

The point of the genetic analysis is not to demonstrate that a pigment change ocurred--that is clearly obvious from visual examination, of course.

The point of the genetic analysis is to see how many genetic differences lie between the two populations. That only a single change, in pigmentation, is observed is exciting. From this, the scientists can conclude that speciation can (potentially) arise from a little as one single gene mutation.


16. Bob Villa

7/19/2009 12:03:09 PM MST

What I think the real outcome of the study is, once you go black, you never go back.


17. Beni

7/19/2009 12:39:16 PM MST

Personally I fail to see the novelty of this article. There is evidence by the population genetic analysis that there is contemporary gene flow between the species, and as far as I see there is absolutely no evidence that gene flow is decreasing over time (what would be required if speciation is ongoing).

In other words: Sure these populations are different (what is to be expected by separated population), and there is assortative mating going on, but this says nothing about what happened in the past, or what is going to happen in the future.

You may take humans as an analogy. You'll also find a skin color polymorphism which has pretty simple underlying mechanisms, and you'll probably also find assortiative mating based on skin color. Yet this does not mean at all that humans are on the verge of speciation.

There are several known examples of species that could potentially interbred but do not in nature, Cichlid fishes being probably the most prominent( read: most extensivly studied) example.

On the other hand, I think these guys got an interesting study system (at least something else than boring cichlids :-) ) and a proper genetic analysis might indeed provide much more conclusive results (But then again, I'm obviously quite biased as a population geneticist).

Danny: You're second statement seems fairly far-fetched. They only investigated a single gene, and found one point mutation there, but this does not mean at all that the remaining billions of basepairs of this species do not have an impact.


18. Danny

7/19/2009 12:58:45 PM MST

@Beni:

I agree, that I had it wrong about the single gene. I went back and read the abstract and realized that of course there are other genetic changes. I suppose what's exciting then is that the researchers were able to pinpoint a single change that discriminates the two populations, at least phenotypically. There is still room for other mutations to assort between the two groups, but undetected by the analysis. Perhaps one of them carries the instructions for mate selection by color?


19. MB

7/21/2009 2:58:00 AM MST

@bob

The definition of "species" is a bit fuzzy, depending on the needs of the evolutionist argument in any particular case.

The fact is that these two populations are not different species. Are you contending that they are? They are just birds with different coloured feathers. Would you argue the same about different coloured people preferentially mating with similar colours? Are whites and blacks different species?

"What a maroon, what an ignoramouse."

Ad hominem attack.

@ad
Yes, I would like evidence please. Sorry about that ... it is called science. If you read the origin of species properly, then you would understand that Darwin himself gave the acid test of his own theory ... that test has still not been passed.

I suggest that you go and study your religion.. I mean your science, of evolution before engaging in these high level debates.


20. Monteray Jack

7/21/2009 7:21:59 PM MST

http://plover.net/~bonds/adhominem.html

You don't know what an ad hominem is, do you, MB? Abusing you after disproving your logic isn't "ad hominem."


21. MB

7/22/2009 3:32:57 AM MST

@Monteray Jack

But he did not disprove my logic. He simply repeated the ill logic of you evolutionary buffoons. Hence, it was indeed such an attack.

You fool.


22. Monterey Jack

7/22/2009 9:43:53 AM MST

"So penguins, kiwi, and ostriches are all the same species? After all, they are still birds. Good to know.

I guess that also means that we are apes since we are all primates.

And I better make sure that my house cat doesn't get a tiger pregnant since they are both cats.

What a maroon, what an ignoramouse."

He used your logic, and look! It falls flat. Apparently, we are all apes. (which is not what you want to hear)

Doesn't matter if he attacked you, that's not how he tried to undermine your argument (& succeeded). What you pulled, however, is an ad hominem because you didn't address his points before dismissing them for calling you a buffoon.

Now for calling me a buffoon I'm claiming ad hominem for the win!


23. sha sha

3/7/2010 2:08:24 AM MST

Different species are defined by animals that can no longer breed viable offspring that can live to breed another successful generation. That's all.

This article is finding out why a bird species diverged into two distinct differences in an observable life time and how this is one example of the beginning of divergence, which is just before they change enough in which they can no longer breed viable offspring.

At this point, they have no interest in breeding with each other.

Yes, birds are still birds, but a Panguin cannot breed with a FINCH, because they are two different species. How they got that way is being explained through evolution.


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