> Dear Porcine avionic supporters;-
>     Here's something to think about. Lumpers and Splitters: Is the
> designation of species determined solely by our perception of it? Is
> there a standard established to tell us when shell characteristics
> (or how many variants) warrent the designation of "new species".
> Beauty may be in the eye of the beholder, but I would think "species"
> would have a more scientific backing. It does seem that the eye of
> the beholder determines speciation. If no such standard exists, can
> we establish one? Will such a standard vary from family to family?
>               Art
 
my two cents...  The biological species concept dictates that species are
interbreeding units. In some cases, this is a difficult test (eg, in
geographically separated populations that do not interbreed simply due to
distance). So say we have 2 different morphs -- some people lump these and
call them 2 morphs of one species, while others split them into two
species. How can we determine who is right? We can interbreed the two
morphs and check if the offspring are fertile and contain character of the
parents. We can also look at this in a more indirect method. If the two
morphs do interbreed naturally (or had a recent history of interbreeding),
they will be exchanging DNA such that they maintain a common gene pool. We
can therefore look at a particular gene in individuals of the different
morphs -- if they are true species and thus no gene flow from one morph to
another, we would find unique DNA sequences to each morph; if they are
morphs of the same species though, we would find a mix of sequences across
the two morphs.
 
Example: during my work with Conus, I have touched on a similar issue.
Conus sponsalis nanus and Conus sponsalis sponsalis have been thought to
represent two morphotypes of C. sponsalis. I have looked at the DNA from
these types from around the Pacific. C. spon. spon. consistently have a
sequence unique to them while C. spon. nanus have a sequence unique to
them (although the Hawaiian C. spons. nanus appear to have a unique
sequence in comparison to PNG and Palau C. spons. nanus, but this is
another issue). This is true even for sequences obtained from the
different morphs from the same geographic region (PNG and Palau). These
results imply that the two morphs do not interbreed and therefore
represent two (possibly three) species. Note: C. nux, which is sometimes
thrown in with the C. sponsalis complex as well, also has unique sequences
to it.
 
Certainly this test is not foolproof. Two recently diverged species may
contain similar DNA sequences just because they only recently speciated.
Also, populations that are geographically separated may contain unique
sequences because of differential selection in the two regions or lack of
exchange of individuals (and thus low gene flow) between the two sites.
The two populations may be diverging from each other, but still be
capable of interbreeding if the opportunity arose.
 
my two cents...
Tom
 
T.F. Duda, Jr.
Biological Laboratories, Box #48
16 Divinity Avenue
Cambridge, MA 02138
617 496-8667  -- BL Rm 367