[Taxacom] Taxonomic challenges at species level

Richard Zander Richard.Zander at mobot.org
Tue Jan 27 09:03:38 CST 2009


I think rapid speciation with survival of the parent species is common.
In paraphyly, doubtless one of the species in the paraphyletic taxon is
an ancestor of the (let's call it) autophyletic taxon. Why postulate an
additional ancestor species different from an extant one? It's not
parsimonious to do so.

Also, there are cases of a single taxon appearing in distant spots on a
molecular cladogram. Isn't this evidence that an ancestor of the same
taxa gave rise to these populations (which differ only molecularly) and
all other taxa intermediate on the cladogram are descendents. Probably
rapidly evolved, too, as this seems attendant on quantum or peripheral
evolution according to the literature I've read (perused, skimmed).

*****************************
Richard H. Zander 
Voice: 314-577-0276
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166-0299 USA
richard.zander at mobot.org
Web sites: http://www.mobot.org/plantscience/resbot/
and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
*****************************

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kenneth Kinman
Sent: Monday, January 26, 2009 10:17 PM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] Taxonomic challenges at species level

Hi Richard,
      I think we certainly agree that speciation is rarely abrupt, and
thus where to draw the line along the fuzzy boundaries can be
problematic.   However, I guess we can be thankful that nature has
spared us that problem in the vast majority of cases.  Extinction of
most of those "fuzzy" intermediate populations over time generally has
left us with large numbers of clearcut species.                
      The less clearcut cases also thankfully give us something
challenging to work on, however frustrating they might sometimes be when
we don't have enough information to solve them as quickly as we might
like.  Otherwise, taxonomy would be about as exciting as shelving books
at a library.  :-)                      
       I also would agree that it would be a rare case of an individual
becoming a separate species from its parents.  HOWEVER, there are
probably a fairly large number of cases where an individual (or pair of
individuals) is actually the founder of a new species (the founder
effect).  It's only in retrospect that the "uninterrupted" isolation of
such an individual (or pair) and its descendants can be viewed as a
speciation event.  In cases where that isolation has been interrupted,
gene flow resumes.  But occasionally it is not interrupted and allows
enough divergence for genetic isolation (speciation).

      This contingency of what might or might not occur in currently
isolated populations is a major contention between splitters and
lumpers.  Just how likely is isolation to continue long enough (and we
have no natural contact zones to test their interfertility).  By
contrast, the
problems of Rassenkreis (circles of subspecies) seems less problematic,
and simply depends on more study to find various areas where gene flow
still occurs.  I think Charles Darwin would be both amazed and delighted
at our modern technological abilities to pursue these problems.

     But then again, I truly think he would also be horrified that
nomenclature could be so destabilized due to an irrational rejection of
paraphyly (by strict cladists) as always being somehow unnatural and
undesirable.  I suspect that he would criticize PhyloCode as being too
radical, as much as many PhyloCodists criticize Darwin as being
old-fashioned.  Given the limitations of his times, he was still "before
his time" and still has lessons to teach us.  Not surprising that he is
still so often quoted.
           --------Cheers,
                           Ken Kinman

************************************************        

Richard Pyle wrote:
If we define a speciation event as the shift from high "propensity to
reproduce" to low "propensity to reproduce", then cases where this shift
is abrupt (proportional to the time between such shifts along the
evolutionary path) are much easier to visualize as demarcations between
species.  And in such cases, it is very useful and practical to think of
species as "real" units of nature, that exist in nature of human
definitions, and are marked by these abrupt shifts. In cases where the
shift is not so abrupt, and perhaps even continues long enough for
another shift to begin (i.e., the tranisiton periods overlap), then
species boundaries become much less clear, and it is much less useful to
think of species as "real" entities in nature. 
My contention is, and has been, that almost none of these shifts are
instantaneous (i.e., there are likely to be very few cases where an
individual organism would be regarded as being a different species from
its parents), and as such, there will always be some fuzziness in the
boundaries. 


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