[Taxacom] Panbiogeography

[John Grehan]

Jason,


“ What I can say is that panbiogeography, through its outright rejection of
dispersal”

Just saying so does not make it true. I think this is a bit naughty.

“has less explanatory power than other approaches.”

In some ways I think this might be the crux of the matter. For many
dispersalist approaches the explanatory power generates acknowledged
mysteries, puzzles, anomalies etc. This is greater explanatory power?
Heads' has shown in his book that for such cases there are alternatives that
are quite straightforward with regard to existing knowledge about
tectonic structures that are spatially correlated with distributions that
would support a vicariance origin. I am not sure I can figure out the
advantage of approaches that produce mysteries, puzzles, anomalies etc.

“On sympatric speciation…By definition it will be rare”


There seems to be agreement here.


“using mtDNA have found very little variation, suggesting a very recent
origin for these races.”


Or they are old races that have not differentiated much.


John Grehan


On Thu, May 1, 2014 at 2:44 AM, JF Mate <aphodiinaemate at gmail.com> wrote:

> Dear Michael
>
> I´m surprised that you, of all people, use the numbers game to bolster your
> position. Nevertheless, and in spite of the 412 papers quoting "Everything
> is everywhere", smaller organisms, or at least their genes, appear to be
> better at dispersing (30%+ very widespread according to your own sources),
> than bigger organisms, a not unexpected result. I have even provided the
> example of an arthropod (D. pullex) that is so widespread throughout the
> globe it barely has genetic structure throughout the N. hemisphere. So what
> are you arguing exactly? That vicariance is more important? I can´t argue
> with that. What I can say is that panbiogeography, through its outright
> rejection of dispersal, has less explanatory power than other approaches.
>
> The reference by Rossberg etal (2013) is just to prove a simple point, that
> we don´t know what exactly we are dealing with when we talk about
> "microorganisms". We may have reticulation to such a degree that the idea
> of "species" may be meaningless (for example of E. coli strains).
>
> On sympatric speciation. Allopatry´s effects are community-wide, whereas
> sympatry will occur in particular lineages when conditions conducive to
> speciation (whatever they may be) are met . By definition it will be rare,
> so this in itself is not evidence against it´s existence. We may assume
> that most lineages will speciate no-sympatrically and only rarely will a
> species-pair speciate via sympatry. Barraclough and Vogler´s method doesn´t
> (can´t) account for this. So mapping is not going to help you very much.
> Furthermore, as shown in the R. pomonella complex, if the genes involved in
> speciation form a gradient (i.e. they are an exaption that determines their
> geographical distribution) then the expectation of range overlap cannot be
> met.
>
> Bolnick and Fitzpatrick´s (2007) review of sympatry provides a large number
> of examples with varying support for sympatry. There are certainly gaps in
> the knowledge so some may prove to be nonsympatric speciation, and Howea
> may be such a case (however see reply to Tuessy (2006) by Savolainen et al
> (2006) which answers your concerns). That still leaves a lot of other
> cases, including R. pomonella, which strongly indicate sympatric
> speciation.
>
> Finally, regarding your comments on Peccoud et al. They are not making any
> phylogeographic claims. Instead they are looking at the genetic structure
> of a single species, the pea aphid, in a small area (40Km). They identify
> 11 clades which correspond to host races, with hybridisation ranging from
> 0% in 3 lineages to 9% in two others. The low hybridisation is due to
> assortative mating (mating happens on the host plant, like in R. pomonella)
> and lower fitness of hybrids or of races switching hosts.
>
> Other studies looking at phylogeography in this species using mtDNA have
> found very little variation, suggesting a very recent origin for these
> races. A later paper by Peccoud et al (2009 PNAS) suggests a radiation
> burst 9,5-3,000 years ago for the sampled host races (sequencing the
> symbiont Buchnera sp). All this suggests that the initial diversification
> and the ongoing reinforcement has happened in sympatry.
>
> Best
>
>
> Jason
>
> >
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