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sir_toejam



Posts: 846
Joined: April 2005

(Permalink) Posted: Feb. 24 2006,19:44   

here's an interesting bit for discussion...

Quote
New evidence that natural selection is a general driving force behind the origin of species


http://www.physorg.com/news11181.html

Quote
“Darwin’s famous book was called ‘On the Origin of Species,’ but it was really about natural selection on traits rather than species formation. Since our study suggests that natural selection is a general cause of species formation, it seems that Darwin chose an appropriate title after all.”


...yet another "gap" bites the dust.

  
Alan Fox



Posts: 1373
Joined: Aug. 2005

(Permalink) Posted: Feb. 24 2006,22:03   

The original paper is available on line. Here is the abstract.

Certainly seems to shoot JAD's "the environment never had anything to do with it" out of the water.

  
jeannot



Posts: 1200
Joined: Jan. 2006

(Permalink) Posted: Feb. 25 2006,00:02   

There are also two cases of sympatric speciation reported in Nature, 10 days ago: one in cichlid fishes, one in palms.
Sympatric speciation involves disruptive selection, this is an adaptive mode of speciation.
Speciation without isolation (except hybridation) has always been controversial, but the last discoveries provide some indisputable evidence of its existence.

I am working on a example of adaptive ecological (and maybe sympatric) speciation in an aphid.

  
sir_toejam



Posts: 846
Joined: April 2005

(Permalink) Posted: Feb. 25 2006,08:35   

thanks Alan.

good luck, Jean; keep us posted!

  
jeannot



Posts: 1200
Joined: Jan. 2006

(Permalink) Posted: Feb. 25 2006,10:02   

Yes, thank you both for the links.

Quote
“Darwin’s famous book was called ‘On the Origin of Species,’ but it was really about natural selection on traits rather than species formation. Since our study suggests that natural selection is a general cause of species formation, it seems that Darwin chose an appropriate title after all.”


They have to be careful with such a claim. What is “a general cause of species formation”… > 50 % of species formation, > 5% …?
Their published results show an association between ecological divergence and reproductive isolation in all the tested taxa, at the same level of genetic distance (= time of evolution in generations). From this, we can suppose that ecological divergence (= adaptation) accelerate reproductive isolation, hence speciation. This is an important result but it doesn't demonstrate that natural selection is involved in most speciation events.
Example: in angiosperms, they show a high positive correlation between species' habitat and post-mating isolation (r=0.43). Ok, in this phylum, ecological divergence seems to accelerate speciation. However, we can still imagine the possibility that most species pairs (90 %) developed reproductive isolation very slowly through allopatry and genetic drift, and that only a small percentage of angiosperm species diverged rapidly through their adaptation to different habitats. This would produce a highly significant correlation as well.
Nevertheless, their huge dataset should easily provide an answer to my interrogation. Maybe a more complete paper is on its way. :)

EDIT: the best evidence of sympatric speciation so far, Sympatric speciation in Nicaraguan crater lake cichlid fish

  
sir_toejam



Posts: 846
Joined: April 2005

(Permalink) Posted: Feb. 25 2006,10:56   

Quote
Nevertheless, their huge dataset should easily provide an answer to my interrogation. Maybe a more complete paper is on its way.


that's why i thought this to be an interesting paper to discuss.

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They have to be careful with such a claim.


i read it as more of an abstract "sound bite".  

I have time to finish reading it tonight, and will jump in again tommorrow.

oh, btw, one of the co-authors on that cichlid paper (Axel Meyer) and i were both grad students in the same lab at the same time at Berzerkely.  I'm happy to see he's done well.

cheers

  
George



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Joined: Feb. 2006

(Permalink) Posted: Feb. 25 2006,13:04   

"Nothing in evolution makes sense except in the light of ecology."

I'm glad to see that plants were a focus of the study.  They seem to me to be neglected in most discussions of evolution in favour of charismatic megafauna.

  
jeannot



Posts: 1200
Joined: Jan. 2006

(Permalink) Posted: Feb. 25 2006,23:46   

Quote (jeannot @ Feb. 25 2006,16:02)
However, we can still imagine the possibility that most species pairs (90 %) developed reproductive isolation very slowly through allopatry and genetic drift, and that only a small percentage of angiosperm species diverged rapidly through their adaptation to different habitats. This would produce a highly significant correlation as well.
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I'd like to comment my own imprecision.
Actually, estimating the role of ecology in the speciation process is not so trivial. When two allopatric sibling species occupy two very close niches (i.e. small ecological divergence), what exactly is the impact of natural selection in their reproductive isolation (in the case of a secondary contact between both species)?
I don't think one can give a precise answer.

  
Alan Fox



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(Permalink) Posted: Feb. 26 2006,04:42   

Maybe a dumb question,

But a single cichlid species gets dropped in (via eggs on birds feet or some other improbable but not impossible scenario, presumably) to  virgin territory of a new isolated lake. If in the population there was sufficient variation, such that some individuals were better able to exploit bottom feeding and others top feeding, and two species developed accordingly, would this be sympatry or allopatry. It seems to me that the line dividing environments may be a bit fuzzy.

  
jeannot



Posts: 1200
Joined: Jan. 2006

(Permalink) Posted: Feb. 26 2006,05:36   

Alan,
I know it's not very legal, but I feel free to post a paragraph from their paper.
Quote
Taken together, we present astrong case where only sympatric speciation can account for the origin of a new species from a more widespread one in Lake Apoyoin, 10,000yr (Supplementary Table2). The Lake Apoyo population of the Midas cichlid and the  Arrow cichlid form a monophyletic assemblage (Fig. 2andSupplementaryFig. 3); they are reproductively completely isolated as shown by mate-choice experiments and the analyses of three sets of molecular markers (Table1) ; they are sympatrically distributed, no genetic structuring was detectedin A. citrinellus and A. zaliosus, and even individuals from opposite sides of the crater lake show no sign of differentiation (SupplementaryTable4, SupplementaryFig. 4). The recent volcanic origin of Lake Apoyo, its small size, its degree of isolation, the homogeneous habitat and the sympatric occurrence of both species throughout the lake, as well as the absence of genetic structure in each of the two species rule out the possibility of micro-allopatric or parapatric differentiation.

  
Alan Fox



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Joined: Aug. 2005

(Permalink) Posted: Feb. 26 2006,05:39   

Thanks Jeannot

  
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