[Taxacom] Evolution in hard times

[Ken Kinman]

Bob,
     I would agree with on Point 2.  When I say major extinctions wipe away 
the reticulations, I was referring to the big ones (end-Cambrian, 
end-Ordovician, end-Devonian, end-Permian, end-Triassic, end-Jurassic, 
end-Cretaceous, and end-Eocene).  Some extinctions in the Pleistocene were 
hard on the megafauna, but I don't regard them as major (widespread 
taxonomically) extinctions, severe enough to wipe away reticulations (as 
happened with the 8 big ones listed above).

      As for Point 1, I guess it depends on which taxa you are referring to. 
  Some small mammals for instance (like rats and mice) speciated during the 
Pleistocene.  I would expect larger animals that reproduce slowly to have 
much longer-lived species than rabbits or small rodents.  Rodents and other 
small mammals far outnumber the larger mammalian species, so I still think 
there was a lot of speciation going on in the Pleistocene for many mammals 
and other animals that reproduce at a fast clip.
   -----Ken
*********************************
>From: "Bob Mesibov" <mesibov at southcom.com.au>
>To: "TAXACOM" <taxacom at mailman.nhm.ku.edu>,<kinman at hotmail.com>
>Subject: Evolution in hard times
>Date: Wed, 27 Jun 2007 14:09:21 +1000
>
>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.
>---
>Dr Robert Mesibov

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