[Taxacom] Panbiogeography

[JF Mate]

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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