[Taxacom] Dytiscoid evolution (was Examples of Eurasian-Australian distribution)

Kenneth Kinman kennethkinman at webtv.net
Fri Jul 23 22:09:09 CDT 2010

 Dear All, 
      I was looking at a paper by Balke et al., 2005, which
seems to indicate that Hygrobiidae and Dytiscidae are perhaps not sister
families after all.  Instead, they have Hygrobiidae splitting off first,
then Dytiscidae, and then a clade containing Aspidytidae and
Amphizoidae.  This might make more sense, since the latter two live in
rivers, not ponds.       
      In any case, Aspidytidae and Amphizoidae are either extremely
poorly known and sampled, or extremely relictual.  Aspidytidae in
particular, having been only been recognized since 2002, may be found in
far more localities in Africa and Asia in the future, so their seemingly
"curious" distribution may not appear so curious in the future.         
     I'm not sure whether or not all of this will affect my hypothesis
that Dytiscidae has outcompeted Hygrobiidae (or other families in the
superfamily), thus forcing them into relictual (and relatively
specialized) distributions and life-styles.  The even bigger question is
perhaps whether the common ancestor of these four families lived in
rivers or ponds.  In any case, that common ancestor most likely lived in
Eurasia, which would suggest that Hygrobia evolved there and then
invaded Australia, not vice versa.  Either way, one can't help but
wonder if Hygrobiids may still exist in places like New Guinea, waiting
to be discovered.   

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