[Taxacom] Panbiogeography

[JF Mate]

Apologies to Taxacomers for this ongoing thread.

Dear Michael, out of curiosity I have checked the book (or what was
available to me) and I will point out the following quotes:
p248-249:  "To summarise, in spite of the unsatisfactory knowledge of
their taxonomy, Gastrotricha do exhibit specific
patterns of diversity and distribution. Notwithstanding possible
problems and biases in the interpretations of
gastrotrich distribution, some blueprints emerge: the percentage of
widespread taxa is high, especially among the highly
speciose chaetonotids; some species have a more restricted geographic
range, but even these species are relatively
widespread within one biogeographic region."
p252: " Notwithstanding possible problems and biases in the
interpretations of rotifer distribution, one pattern is
clear: the percentage of widespread taxa is high; some species are
more restricted geographically, but even the species
with more restricted distributions are relatively widespread within
one biogeographic region. Moreover, almost all genera
and higher taxa are really cosmopolitan, one feature that is
completely different from macroscopic organisms, even if
the defi nition of taxa higher than species in diff erent groups may
not be directly comparable."
p254: "The confusion over group-complexes and potential errors in
published taxonomic records would imply that the phylum
Tardigrada was not a good subject for biogeographic studies. However,
there seems to be a general understanding that
while there are cosmopolitan genera, most of these exhibiting
parthenogenesis and capable of cryptobiosis (Pilato, 1 979),
not all genera are cosmopolitan and many of these have a lower
capacity for cryptobiosis and/ or reproduce sexually (Kristensen,
1987 )

Some things stay put, many are very widespread. Still, the number of
"widespread" microbial species is north of 20-30% which is
unheard of in pretty much any other group that I can think of. As to
the "strawman", if you read carefully other publications by the
editor you can see that the "paradigm" he is challenging is really
this, a paper by Finlay, B.J. (2002: Global dispersal of free-living
microbial eukaryote species. Science 296, 1061-1063). It is behind a
paywall so I can?t acess it right now. But from the
abstract (plus other later papers Finalya and collaorators) I can
conclude that in their research they find Protozoa to be "widespread"
and that they are essentially different to bigger organisms. So out
comes the "forgotten phyla brigade" to say, not so fast.
Everybody needs a target to stick their own research but this
paragraph from a separate paper (Fontaneto, D. & Hortal, J. (2012).
Microbial biogeography: is everything small
everywhere? In Microbial Ecological Theory: from Individuals to
Ecosystems (ed. by L.A. Ogilvie and P.R. Hirsch)) puts everything in
perspective: "Only recently, microbial biogeography has gained renewed
vigour because of the resurgence of the
?Everything-is-Everywhere? hypothesis (Finlay, 2002; Fenchel & Finlay
2003; Finlay  & Esteban, 2007; see O?Malley, 2008 and Williams, 2011
for historical reviews of
this idea). We will not deal with the discussion on whether it is a
true hypothesis in strict terms, as ?regardless of detail or
explanation, the phrase ?everything is
everywhere? is clearly false, and in any case, one would need to know
in what sense the words ?everything? and ?everywhere? are intended. As
soon as something is not
found everywhere then everything (obviously) is not everywhere. This
much could be easily agreed upon? (quotation from Williams, 2011)."
So Fontanto et al agree that the statement is at best a catchy
sound-bite, so why use it at all I wonder? Hardly a paradigm shift. So
how does this throw a spanner into dispersal exactly?

As for sympatric speciation:

"On Rhagoletis, Feder et al. (2003) wrote: ?we infer that an
ancestral, hawthorn-infesting R. pomonella population
became geographically subdivided into Mexican and North American
isolates ?1.57 million years ago. Episodes of gene
flow from Mexico subsequently infused the North American population'.
Michel et al. (2007 Mol Ecol) suggested that
?volcanic activity in the eastern EVTM [Eje Volcanico Trans Mexicano]
may have been responsible for the initial
geographical isolation of the Mexican and northern hawthorn-fly
populations'. This is a common pattern, with allopatric
differentiation, followed by subsequent overlap and local ecological sorting."

Feder et al are clear that it is introgression and not lineage
sorting. Further, they provide a mtDNA tree so you can see that it is
not
Mexican flies moving into apples (i.e. there is only one
metapopulation in the US and not two cryptic, sympatric populations)
but Northern
flies which had some genes from a different population.
But once infused into the Northern population it was sorted and
selected along a latitudinal cline and they were an exaption (probably
amongst
others, as the authors concede) that allowed R. pomonella to exploit
apples when introduced much later.
The actual speciation only started afterwards as a consequence of the
different fruiting times, assortative mating, etc. All sympatric
processes.

In regards to the range overlap of sister species, sympatric
speciation doesn?t have to result in broad sympatry. In fact it
probably will lead to the opposite
result due to local adaptation. Focusing on the R. pomonella complex,
host races? ranges will be contained within that of their host and not
of the original R. pomonella population.
Furthermore, chromosomal inversions, although they do not preclude
mating they can facilitate local adaptation (reduced recombination)
and in
the process kickstart speciation (genetic isolation). For a recent
example check Lowry D. B, Willis J. H (2010) A widespread chromosomal
inversion polymorphism contributes to a major
life-history transition, local adaptation, and reproductive isolation.

Best

Jason