[Taxacom] Panbiogeography

[Michael Heads]

Hi Jason,

I'd be interested to know the area that you work in - I'm always keen to
learn about different areas.

Sympatric speciation: the different races of *Rhagoletis pomonella
*(Tephritidae)
on hawthorn and apple trees are often cited as evidence for sympatric
speciation. Sequence data instead suggested allopatric differentiation
followed by overlap (Feder et al. 2003).

Sympatric speciation would lead to two species with more or less the same
distribution but different ecology. In the proposed cases I've seen, the
distributions are actually quite different - they just show some overlap.

I didn't mean to imply that all groups show high levels of geographic
structure. But marine biology and  microbiology have both undergone
'paradigm shifts' (their words) over the last decade as the sequencing
studies show such high levels of structure. These were completely
unexpected in the old dispersal model and reading the accounts you can
sense the excvitement and bewilderment at the new findings. The old idea of
'everything is everywhere' (and the environment selects) has been rejected.

Michael


On Tue, Apr 8, 2014 at 12:51 PM, JF Mate <aphodiinaemate at gmail.com> wrote:

> I think that Richard hit the proverbial nail on the head with his
> questions, to which I would readily answer "yes" to the first two. In
> my mind the argument is not if the relative contribution of dispersal
> or vicariance is 50:50 or 1:99; or on the specifics of chameleon
> biogeography in Soqotra. These, in themselves, are not vey interesting
> to me or most others since they fall outside my/our study group or
> area. My only interest is simply making it clear that panbiogeography
> fails to consider a mechanism that, albeit possibly minor globally in
> comparison to vicariance, is nevertheless real. The examples of
> dispersal are there, plain to the eye to see. So even though
> vicariance does carve out whole biotas (a mechanism that few since the
> 1950?s has denied) once in a while chance messes things a bit by
> giving a lucky few the opportunity to colonize areas that are out of
> reach to others.
>
> As to the relative importance of one mechanism over the other, this
> question will answer itself after we have accumulated a sufficient
> number of well supported, taxonomically complete and widely agreed
> upon phylogenies covering all groups of organisms, a task that nobody
> currently reading this blog will see achieved in their lifetimes.
>
> Richard has, however, provided more food for thought with his other
> questions:
>
> Q4, Sympatric speciation: the case that always surfaces is Rhagoletis
> pomonella hawthron vs apple races. It believe that this and other
> "trophic" races are the closest examples we have of sympatry outside
> of parasite induced (i.e. Wolbachia) assortative/disassortative
> mating. I am not sure if "ring species" would count although they are
> quite relevant when you consider that gene flow, even when unimpeded,
> has limits.
>
> Q5, Michael provided two examples of small, easily transported species
> showing highly sructure phylogeographic patterns. I can provide two
> different examples. In Daphnia pulex there is little structure
> throughout the N. hemisphere
> (
> http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0046620
> ).
> Similarly several Aphodius (Scarabaeidae) species show Palearctic
> distributions with little structure (J.F.Mat? unpub).
>
> Q6, I?m afraid I have no experience in marine environments but a
> similar scenario can be seen in Europe. N and C European plains allow
> for easy migration of species E-W. However the glacial periods have
> resulted in periodic extinction and recolonization events that have
> left a clear imprint in the genetic make-up of populations. The
> constrast between N and C Europe and S. Europe in this Triops paper
> (http://www.naturkunde-chemnitz.de/dateien/Thorid.Zierold.pdf) is
> pretty much text book and found in countless other examples. Multiple
> S European refugia (high genetic diversity) and little or no genetic
> diversity in N and C Europe. Often one or two species have colonized
> these areas whereas the refugia may contain several species that stay
> put (from personal experience, Aphodius (Liothorax) complex but pretty
> much any invert lineage shows this pattern).
>
> Best
>
> Jason
>
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-- 
Dunedin, New Zealand.

My recent books:

*Molecular panbiogeography of the tropics.* 2012. University of California
Press, Berkeley. www.ucpress.edu/book.php?isbn—80520271968

*Biogeography of Australasia:  A molecular analysis*. 2014. Cambridge
University Press, Cambridge. www.cambridge.org/9781107041028