Evidence for speciation via mutation?

[Biochemist]

Continuing a portion of the discussion from the punctuated equilibrium thread:

 

The direct evidence for speciation by mutation is thin. There is a lot of indirect evidence, such as:

 

1) Mutations that cause damage certainly occur, and can be caused in the laboratory.

2) Some mutations exist that happen to be "beneficial" occur, but none have been demonstrated to increase the quality or quantity of information in a gene; they merely show that damage to a gene may cause a slight shift in function that might be useful. (e.g., the mutation of the gene that digests ribulose). But serial damage would be unlikely to create further incremental benefit.

3) Many mechanisms for modification to the genome are known (e.g., chromosome duplication, transposons, increased genomic alteration in the pericentromeric region of the chromosome, etc), but to my knowledge, no one has demonstrated that these are actually mutative mechanisms, versus a life-supporting genomic mechanism.

 

Can anyone surface direct evidence of mutation driving speciation, or even mutation increasing information content in a gene?

[bumab]

Can anyone surface direct evidence of mutation driving speciation...

 

I'm not sure you'd take the evidence! TM posted some good examples in the PE thread. Mutations can create reproductive barriers which drive speciation through both natural selection and genetic drift. If a mutation causes a deterioration in a gene that creates a new species, then, speciation occured through mutation.

 

You are hoping to find a mechanism for intentional speciation. How would you seperate this from random mutation speciation? Seems they'd be indistinguishable from the fossil record- or at least both sides could claim both. And a new mechanism has the burden of proof. ;)

 

...or even mutation increasing information content in a gene?

 

Chromosomal duplication increases the information load.

[Biochemist]

I'm not sure you'd take the evidence! TM posted some good examples in the PE thread.

It is true that I did not regard the ribulose enzyme example as particularly strong . Did you mean something else?

Mutations can create reproductive barriers which drive speciation through both natural selection and genetic drift. If a mutation causes a deterioration in a gene that creates a new species, then, speciation occured through mutation.

I think this is the defintion. I am just looking for evidence to support this model.

You are hoping to find a mechanism for intentional speciation. How would you seperate this from random mutation speciation? Seems they'd be indistinguishable from the fossil record- or at least both sides could claim both.

Actually, I am looking for the reverse. I want to see the evidence of speciation through mutation, because I really can't find much.

 

One would expect to see a series of morphologically similar species in series. One would expect to be able to find at least some of ther current descendents, and study/sequence their DNA for evidence of gradual, serial improvement. I don't think either is the case. All of the examples I have seen where we investigated apparently-serial species, their genetics to not support serial speciation (that is, their genes are closer so some other morpholocially distinct species than the proffered parent species).

 

So, I am not looking for support of a new theory. I want to see direct support for the old one.

Chromosomal duplication increases the information load.

I suspect this is true. Do we have any evidence that chromosome duplication can be a result of mutation?

[TeleMad]

The concpet of a ring species might be useful here.

 

Picture a species expanding southward but running into some barrier, like a mountain range. The advancing species splits into two arms and continues by wrapping around the barrier, moving south along the left and right borders of the mountain range. Eventually, at the end of the barrier, the two arms come back together. A ring is formed.

 

The farther any given population is from the origin of the two-arm split at the north, the less gene flow there is between it and those at the northern split. And the reduction in gene flow is much more pronounced between that arm population and it's mirror image population on the opposite arm because the distance is double that between it and the populations at the split. Every population can interbreed with its nearest neighboring populations, but the populations at the two extremes of the two arms, where they finally overlap in the south, are different enough from one another that they cannot successfully interbreed. According to the biological species concept, the two overlapping populations that cannot interbreed are two different species.

 

Here we have a continuum of populations, all able to interbreed along the chain, but with the two endpoint-populations forming separate species because of their inability to interbreed.

[Biochemist]

...Here we have a continuum of populations, all able to interbreed along the chain, but with the two endpoint-populations forming separate species because of their inability to interbreed.

Interesting example TM. Has anyone documented any serial/geographic fossil records to demonstrate such a behavior?

[Eclogite]

There is this classic example with seagulls:

"Also a possible explanation for the Larus ring species complex: genus Larus (seagulls) fragmented in Siberia during the Pleistocene. Diverged populations of Larus argentatus (herring gull) colonized eastern Siberia, across the Bering straits, across North America, Iceland and back to Northern Europe becoming increasingly diverged at each step. Hybrid zones exist between successive populations but the ends of the ring are reproductively isolated implying that speciation has gone to completion (an example of geographic speciation)"

Source: http://biomed.brown.edu/Courses/BIO48/23.Cases.HTML

[Biochemist]

There is this classic example with seagulls: "Also a possible explanation for the Larus ring species complex: genus Larus (seagulls) fragmented in Siberia during the Pleistocene....

Great link, Eclo. The link describes a good set of examples of speciation, allopatric and otherwise. The question I have is still whether anyone demonstrated a mutative mechanism. It would probably have been easiest to demonstrate in the Hawaiian Drosophila. Since they have a speciation trail from older islands to younger ones, has anyone looked at the genetic code to serialize (for example) a) unexpressed genes, ;) protogenes in the unexpressed code, or c) genes that express nonfunctional proteins in earlier species that later became expressed and functional after an apparent mutation?

[C1ay]

Interesting example TM. Has anyone documented any serial/geographic fossil records to demonstrate such a behavior?

http://www.google.com/search?q=ring%20species brings up quite a few results that look interesting.

[Biochemist]

http://www.google.com/search?q=ring%20species brings up quite a few results that look interesting.

These are interesting C1. They are good straightforward examples of apparent gradualism, but I am still trying to find out if anyone has done genetic work to implicate a mutative mechanism. It seems to me that serial species would be easy (relatively) to study in this regard.

[TeleMad]

Interesting example TM. Has anyone documented any serial/geographic fossil records to demonstrate such a behavior?

 

Here are a couple:

 

”The various Ensatina salamanders of the Pacific coast all descended from a common ancestral population. As the species spread southward from Oregon and Washington, subpopulations adapted to their local environments on either side of the San Joaquin Valley. From one population to the next, in a circular pattern, these salamanders are still able to interbreed successfully. However, where the circle closes -- in the black zone on the map in Southern California -- the salamanders no longer interbreed successfully. The variation within a single species has produced differences as large as those between two separate species.”

(http://www.pbs.org/wgbh/evolution/library/05/2/l_052_05.html)

 

Here’s a page that indicates DNA analysis confirms the above hypothesis, and also gives another example of a ring species: greenish warblers. http://www.actionbioscience.org/evolution/irwin.html

 

 

 

 

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PS: The herring gull example provided by someone else may no longer be a good example: it may be that they are not a true ring species.

 

"Proc Biol Sci. 2004 May 7;271(1542):893-901. Related Articles, Links

 

The herring gull complex is not a ring species.

 

Liebers D, de Knijff P, Helbig AJ.

Institute of Zoology, University of Greifswald, Vogelwarte Hiddensee, 18565 Kloster, Germany.

 

Under what circumstances speciation in sexually reproducing animals can occur without geographical disjunction is still controversial. According to the ring-species model, a reproductive barrier may arise through 'isolation by distance' when peripheral populations of a species meet after expanding around some uninhabitable barrier. The classical example of this kind of speciation is the herring gull (Larus argentatus) complex, with a circumpolar distribution in the Northern Hemisphere. Based on mitochondrial DNA variation among 21 gull taxa, we show that members of this complex differentiated largely in allopatry following multiple vicariance and long-distance-colonization events, not primarily through isolation by distance. Reproductive isolation evolved more rapidly between some lineages than between others, irrespective of their genetic distance. Extant taxa are the result of divergent as well as reticulate evolution between two ancestral lineages originally separated in a North Atlantic refugium and a continental Eurasian refugium, respectively. Continental birds expanded along the entire north Eurasian coast and via Beringia into North America. Contrary to the ring-species model, we find no genetic evidence for a closure of the circumpolar ring through colonization of Europe by North American herring gulls. However, closure of the ring in the opposite direction may be imminent, with lesser black-backed gulls about to colonize North America.

(http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15255043&dopt=Abstract)

[bumab]

For what it's worth, the ring needs to be broken to truely create two distinct, genetically isolated species, however, since gene flow is still possible around the long way of the ring.

 

The biological species concept is difficult to define- interbreeding is convenient, but doesn't cover all the bases.

[Biochemist]

Here’s a page that indicates DNA analysis confirms the above hypothesis, and also gives another example of a ring species: greenish warblers. http://www.actionbioscience.org/evolution/irwin.html

This is a great link, TM. It does not detail the genetics of the situation, but it does reference the journal article in Evolution that dug into it.

[Biochemist]

I pulled this link out of one of the trails off of TeleMad's link above.

 

http://www.pnas.org/cgi/content/full/94/15/7761#SEC3

 

These ensatina salamanders are really ineteresting, in that their home turf is surprisingly small (as small as 5 meters) and it looks like it seldom exceeds 60 meters for a entire individual's life. These guys are the new poster children for the couch potatos of the animal kingdom.

 

It certainly explains why the big salamander in my backyard was there for years. He was certainly a pleasant critter.

 

This makes allopatric speciation significantly more likely, since a short walk is the functional equivalent of a population boundary. The same is apparently true of the Ensatina in Costa Rica as in California, altough there is no ring-oriented geography in Cost Rica.

 

I think this is a really good example of allopatric speciaiton, but I still can't find any credible evidence of a mutative mechanism. This appears to be a cleaner example of speciation through genetic drift (i.e.,allele fixation and loss).