[Taxacom] Evolution in hard times

[Bob Mesibov]

Ken, your word-picture of speciation patterns is very valuable as a 
framework, and I would have agreed with it wholeheartedly until recent 
years. However, two developments suggest that the story is (surprise!) not 
as simple as it seems.

(1) "Just think how much isolation and speciation must have occurred during 
various Ice Ages in North America and Eurasia." My browsing of the 
phylogeography literature repeatedly turns up papers which suggest that - 
for terrestrial taxa, at any rate - speciation nodes tend to *precede* the 
late Pliocene/Pleistocene glaciations by several million years. A 
substantial proportion of some contemporary taxa appear to have originated 
no later than the end of the Miocene, and are linked in time, at any rate, 
with a global cooling and drying event.

(2) There is now biogeographical evidence from plants (cpDNA haplotype 
distributions) that when different lineages are stuck together in glacial 
refuges for thousands of years, they hybridise *more* than they do when 
spread out in interglacial times. Far from stripping clades of messy 
reticulations, hard times may *encourage* reticulation.

I can send/point you to some relevant papers off-list.
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Dr Robert Mesibov
Honorary Research Associate, Queen Victoria Museum and Art Gallery
and School of Zoology, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
(03) 64371195; 61 3 64371195

Australian Millipedes Checklist
http://www.qvmag.tas.gov.au/zoology/millipedes/index.html
Tasmanian Multipedes
http://www.qvmag.tas.gov.au/zoology/multipedes/mulintro.html
Spatial data basics for Tasmania
http://www.utas.edu.au/spatial/locations/index.html
Biodiversity salvage blog
http://biodiversitysalvage.blogspot.com/
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