[Taxacom] Phylogenetic classification?

Wed Aug 5 17:01:45 CDT 2009

Dear Stephen,

Whatever the origin of a very small founder population (whether vicariance or dispersal), the founder effect in itself probably does not lead to speciation. This is the point made in population  genetics. In practice, a vicariance event (e.g. isolation or increasing isolation of a large island - small island - rock stack by erosion or subsidence) may lead to a small population but this is not as small as in a normal founder dispersal event, which may involve just one pregnant female.    

Michael

Wellington, New Zealand.

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

--- On Thu, 8/6/09, Stephen Thorpe <s.thorpe at auckland.ac.nz> wrote:

From: Stephen Thorpe <s.thorpe at auckland.ac.nz>
Subject: Re: [Taxacom] Phylogenetic classification?
To: taxacom at mailman.nhm.ku.edu
Date: Thursday, August 6, 2009, 9:07 AM

Dear Michael et al.,
There may be a small problem with jargon here. When I referred to  
"founder-effect" speciation, I was explicitly being neutral over  
dispersal/vicariance. In other words, by my understanding, what is  
important for speciation is a small isolated population - but how it  
got there seems irrelevant to me. Perhaps it is a small bit of a  
larger population that got isolated by vicariance, or perhaps the  
small population was started by dispersal from the larger population.  
Either way, it seems to me that novel mutations will be a drop in the  
ocean within a large and widespread population, but could well spread  
quickly and change the nature of a small population, thereby  
facilitating divergence and ultimately speciation...
Cheers,
Stephen

Quoting Michael Heads <michael.heads at yahoo.com>:

> Dear Geoff and colleagues,
>  
> I should clarify this. Nearly all phylogeographers follow  
> traditional biogeography and invoke 'dispersal', i.e. founder effect  
> speciation, all the time. But they are simply inferring it from the  
> distributions and a phylogeny. Population geneticists are a  
> different breed altogether and look in detail at mechanisms of  
> the speciation process per se, including lab experiments,  
> small-scale population sudies, etc. These are the ones I was  
> referring to (e.g. Coyne & Orr's book Speciation which summarises  
> this work).
>  
> I've just been reading M.C. Whitlock (a pop gen man) (2009) 'Founder  
> effects' in 'Encyclopedia of islands' (ed. R. Gillespie & D. Clague,  
> University of California Press).  He concludes: 'There have been  
> many attempts to mimic the conditions for founder effect speciation  
> in laboratory experiments. Although some experimental populations  
> develop a small level of reproductive isolation, the effect is rare  
> and of limited magnitude. The majority of evolutonary biologists  
> [pop gen people don't include biogeographers here!] believe that the  
> environmental differences between island populations and their  
> progenitors are more likely to be important in developing  
> reproductive isolation than are founder effects'.
>    Of course there is a founder effect, but it's not enough for  
> speciation. Mayr thought it was and proposed a 'genetic revolution'  
> in founders, but this is what the geneticists have become sceptical  
> about. As for 'ecological speciation' - that's another can of  
> worms!   
>
> Michael
>
> Wellington, New Zealand.
>
> My papers on biogeography are at: http://tiny.cc/RiUE0
>
> --- On Wed, 8/5/09, Geoff Read <gread at actrix.gen.nz> wrote:
>
>
> From: Geoff Read <gread at actrix.gen.nz>
> Subject: [Taxacom] Re: Phylogenetic classification?
> To: taxacom at mailman.nhm.ku.edu
> Date: Wednesday, August 5, 2009, 9:07 PM
>
>
>>>> On 2/08/2009 at 2:24 p.m., Michael Heads <michael.heads at yahoo.com> wrote:
>>>> Dear Steve et al.,
>>>>
>>>> This is what you'd expect based on Mayr's (1942) ideas that we were
>>>> all brought up with. But after looking very hard for many decades,
>>>> the geneticists now say there is little evidence for founder effect
>>>> speciation.
>
> A pity, it seemed so logical. But after seeing that comment about the
> undemonstrated founder effect made more than once by Michael Heads, I
> would like to add that on the other hand there are scientists happily
> reporting phylogenetic evidence for marine animal speciation via the
> broader process of _founder dispersal_, whilst also taking into account
> the vicariance speciation possibilities that Michael much prefers .
>
> D’Amato M, Harkins G, de Oliveira T, Teske P, Gibbons M 2008. Molecular
> dating and biogeography of the neritic krill Nyctiphanes. Marine Biology
> 155: 243-247.
>
> Teske PR, Hamilton H, Matthee CA, Barker NP 2007. Signatures of seaway
> closures and founder dispersal in the phylogeny of a circumglobally
> distributed seahorse lineage. BMC Evolutionary Biology 7: 1-19.
> (open access at:
> http://www.biomedcentral.com/content/pdf/1471-2148-7-138.pdf )
>
> Geoff
>
>
>
>
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