[Taxacom] Scale insects and Nothofagus

[Kenneth Kinman]

Hi Michael,
      There seem to be two main reasons (perhaps there are others) that
have been put forward by those who do not think Nothofagus distribution
is totally vicariant.  One is the early date at which New Zealand broke
off of Antarctica (at least 80 million years ago), not all that long
after Nothofagus itself originated.  If vicariant, it's Nothofagus fauna
should be sister group to the rest of Nothofagus (instead the South
American fauna shows that pattern, even though South America and
Australia were still connected to Antarctica well after New Zealand
broke away).  Arguing against this with "main massings" will probably
cause most non-panbiogeographers to simply roll their eyes.      
      The second problem is that a totally vicariant Nothofagus rests
upon the argument that all four extant subgenera of Nothofagus
originated in the Cretaceous.  This caused problems for the totally
vicariant view when evidence was found that these four subgenera are
perhaps much younger, and that the Cretaceous subgenera were simply
convergent with extant subgenera.     
     Anyway, the results of Hardy et al., 2008, now convince me that the
longer-range trans-ocean dispersal of Nothofagus between Chile and New
Zealand is indeed an unlikely (and unnecessary) event (which should make
a lot of people happy).  However, the shorter trans-ocean dispersal
between Australia and New Zealand is much more likely, and a number of
researchers believe at least one or two such dispersals are necessary to
explain Nothofagus distributions.  Congruence with the distribution of
their felt scale insects bolstered that view (Hardy, et al., 2008).            
             ---------Ken Kinman                       
-------------------------------------------------------
Michael Heads wrote:
Dear Ken, 
   Why does the congruent distribution/phylogeny of the scale
insects and Nothofagus indicate dispersal and not vicariance?   
Michael Heads 
Wellington, New Zealand. 
My papers on biogeography are at: http://tiny.cc/RiUE0 

--- On Sat, 31/7/10, Kenneth Kinman <kennethkinman at webtv.net> wrote: 
From: Kenneth Kinman <kennethkinman at webtv.net> 
Subject: [Taxacom] Scale insects and Nothofagus (dispersed together) To:
taxacom at mailman.nhm.ku.edu 
Received: Saturday, 31 July, 2010, 4:33 AM 
Hi John and others, 
      Well, the first insect pest (on Nothofagus) that I looked at
this morning actually indicates that felt scale insects and Nothofagus
not only evolved together, but that both groups show the same pattern of
trans-ocean dispersal between Australia and New Zealand.   The
study by Hardy et al., 2008 (see weblink below) studied the phylogeny of
these felt scale insects with both morphology AND molecular sequences,
and it was congruent with earlier studies on Nothofagus alone,
indicating trans-ocean dispersal (NOT vicariance).  Not hard to
imagine lots of these insects hitching a ride on floating Nothofagus
trees between Australia and New Zealand.    
       Whether these or other insect pests can limit the
dispersal ability of Nothofagus is another question, but an interesting
one.  If such insects can decrease plant vigor in mature trees, just
think what kind of damage they could do to young trees trying to
disperse to new territory.  Trans-ocean dispersal between Australia
and New Zealand may have taken many raftings before Nothofagus was
successful in becoming established.  Over millions of years, there
could have been thousands of such raftings, but the vast majority failed
for any number of different reasons.  But looks like it succeeded at
least once, and I am not the only one who thinks so.  
        ---------Ken                  
http://espace.library.uq.edu.au/view/UQ:171696