[Taxacom] Dispersal... again

[Michael Heads]

Hi Jason,
?
My comments are below.

Michael

Wellington, New Zealand.


My papers on biogeography are at: http://tiny.cc/RiUE0


________________________________

From: Jason Mate <jfmate at hotmail.com>
To: Taxacom <taxacom at mailman.nhm.ku.edu>
Sent: Friday, 28 October 2011 10:27 AM
Subject: Re: [Taxacom] Dispersal... again



OK, back to work. Please find my points below.
Michael, are we talking about continental drift or genetic drift? The literature you offered as ?New Modern Synthesis? is just population genetics in evolutionary biology, which is a continuation of the work of Haldane and Dobzhansky. 

MH: No, it's completely different. The new model is opposed to the modern synthesis model and in many?ways is derived more directly from the geneticists, i.e. the original geneticists such as?T.H. Morgan (Nobel prize for genetics?but ridiculed in the modern synthesis for not understanding genetics).?The earlier workers saw the direction of evolution as due to mutation, in the modern synthesis it is due to selection and adaptation.?The new model has very different?interpretations of?these key concepts, as well as 'gene pool',?and all the others.??Michael Lynch has an interesting 2007 book: 'The origins of genome architecture'. These broad genomic changes can be happening?throughout a population (e.g. broad shifts in CG composition), not because of random mutation in an individual followed by gene flow, adaptation and selection.?

In any case you are not explaining how the application of random genetic forces applies to your version of vicariance and neither do Lynch nor Stoltzfus. 

MH: The genetic forces are not random - that's the point.

In fact they point fingers at the non-mathematically inclined biologists that place too much stress on selection (i.e. most of us in TAXACOM). 

MH: There are non-random forces that are not selection.

Still I find their work to be similar to Wright?s shifting balance theorem, although I admit not goint over their papers carefully. Nevertheless, they stress not the organisms but the genes. 

MH: Well, they are geneticists. Actually their arguments stress?genomic evolution.

In this point they differ from Mayr, 

MH: who was not a geneticist.

for whom the genes were interdepent so the unit of selection was the genome, which was as well shielded from the outside by the phenotype. Notwithstanding this, he recognised the role that random genetic forces (drift, mutations, recombination) had in the evolution of populations and species.

MH: Yes, he thought everything was random.

You keep bringing THE quote from 1965 as it somehow defines his ideas, but his body of work speaks otherwise. 

MH: I think it?defines his ideas in a?clear and succinct way.?I've read most of what Mayr wrote, including dozens of?his early papers. 

Maybe he did not make it sufficiently clear that continental drift was yet another interruption in gene flow but his ideas do not contradict it so most people are OK with them. In fact if I look at your statement:
?...a widespread ancestor 'breaks down' into subordinate groups by repeated, non-random mutation.?
and Mayr?s 1976 quote: "Not all population discontinuities in nature originate by the colonization of islands. Sometimes they arise by the contraction of a species range and the separation of a previously continuous area into separate ranges." (Mayr 1976)?
It is obvious that the second part of the statement is perfectly compatible with vicariance of any sort. So I am not sure why you take issue with it. 

MH: I don't take issue with it. The point is he did not apply this principle in practice, to his analyses of actual groups. This was written in 1976, a couple of years after critique of his work had begun to appear in journals such as Syst. Zool.? 

Furthermore your own quote is parapatric speciation paraphrased.
Mayr, in the historical context and with the data of the 40?s, 50?s and 60?s was correct. You are judging him in hindsight, enjoying the benefits of the huge advances in population genetics and phylogenetics. 

MH: I'm?interested in Mayr only as the?source, the type specimen,?of the current?ideas - most people accept the modern synthesis as basically correct, give or take sympatric speciation, founder effect speciation?etc.?

Did Mayr make mistkaes? Yes, he did, from our present context. Not accepting recognising speciation was a mistake

MH: you seem to have missed out something here - 'sympatric'?? I think he was correct to dismiss sympatric speciation. Most supposedly sympatric groups?actually show high levels of allopatry and the area of sympatry probably represents secondary overlap. The limnetic and benthic forms of three-spined sticklebacks in the British Columbia lakes turned out not to form monophyletic pairs in lakes. Instead, they are?related to limnetic and benthic forms, respectively, in other lakes. The two forms?didn't evolve by sympatric speciation within?a lake but diverged before?their secondary overlap (e.g. caused by marine flooding).??

, but the tools to work out this have only been commonly available for the last 30 years. Not recognising your version of vicariance (I am still trying to figure out what it is) is at best an oversight.

MH: Yes, it was an oversight. Relying on chance to explain spatial patterns in evolution?meant that large parts of the?modern synthesis were flawed at the outset. (It's not just 'my version' of vicariance - it goes back to Hooker and Huxley and?is now?used in many publications).??

So, going back to dispersal, I have some questions to ask. How does a species achieve a ?wide range? if not by spreading out from somewhere? Doesn?t this entail an initially smaller range? 

MH: If?a mirror is?struck by a hammer (vicariance), the individual, broken?shards do not move to their current position?- they 'evolve' in situ, by the fracturing of a larger entity.??

At what level does speciation occur in your scenarios? I am of the opinion that it is at the level of (panmictic) populations but maybe you have other ideas? 

MH: I'd say speciation?occurs after the  groups are subspecies and before they are subgenera.?? 

What is the distinction between ?dispersalist?ideas and yours? 

MH: I accept dispersal but not 'chance dispersal'. They accept both and?think of them as the same process.?

What distance covered counts as dispersal?

MH: Any distance.?Any change in position can be regarded as dispersal in the broadest sense (Frederic Clements), but?a change in position can?be caused by evolution, as well as physical movement.



Best
Jason 
P.D. I am not familiar with any Mayr 1980?s in The Auk other than that on subspecies. Is it the same one? ?


MH: No, see his 'Review of 'Vicariance biogeography''. The Auk 99:618-620. 1982.
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