[Taxacom] Centropyge (was barcode of life)

Stephen Thorpe stephen_thorpe at yahoo.co.nz
Sun Jul 4 23:44:34 CDT 2010


Ken,
Well, it is up to you to evaluate the evidence how you like, the important thing is that you do evaluate evidence, rather than just claim that it is a matter of arbitrary/subjective choice. That is the real issue here. The only problem for me in your conclusion is that if you were to apply it consistently, any two forms which demonstrated the slightest propensity to hybridise would have to be the same species, as your argument seems to be 'if they can interbreed, then we don't know how far they could go, so we should be "conservative" and assume it could go to completion ...'
Stephen




________________________________
From: Kenneth Kinman <kennethkinman at webtv.net>
To: taxacom at mailman.nhm.ku.edu
Sent: Mon, 5 July, 2010 2:58:39 PM
Subject: [Taxacom] Centropyge (was barcode of life)


Hi Stephen, 
         Even if we collected 10 or 100 times more
information about these two Centropyge "populations" and it showed a
stable and narrow border zone, that doesn't mean it is going to remain
that way hundreds or thousands of years from now. Even on the very short
scale of decades, humans could cause massive dead zones off the western
coasts of the Americas and eastern coasts of Australasia. No telling how
this alone could affect even such a widespread Pacific species (or pair
of semi-species according to your view). And we don't know if the
"hybrid zone" was as narrow hundreds or thousands of years in the past.    
        Give such a lack of information (presently, even
more so in the past, and certainly in the future), it seems preferable
(more conservative) to assume that gene flow could easily have been even
more significant in the past (or will be so in the future). And as I
said in my previous post, the coloration morphology may not truly
reflect how much gene flow there actually is anyway.  On the other hand,
we DEFINITELY know that they are interbreeding. That is a known, while
too much of the rest is still full of unknowns. I wouldn't be at all
surprised if Centropyge individuals from opposite side of their ranges
(far from the intergradation zone) readily interbred and produced
so-called "hybrids". President Obama's parents were of very, very
different colorations, but I would regard him as an intergrade, not a
hybrid. 
      And Mayr's definition of a biological species includes both
actually AND potentially interbreeding populations.  Therefore I think
he was also taking into account the vagaries and uncertainties of the
past, present, and future interbreeding and gene flow levels.  So when
there is clearly "swarming" interbreeding in any zone (however narrow),
it is probably wiser to take the uncertainties very seriously and to
conservatively assume more gene flow than we suspect (even at just the
present time).
        ---------Ken

---------------------------------------------- 
Stephen Thorpe 
          On my view (a, or the, BSC), your opinion
of them as subspecies is merely a fallible alternative to calling them
distinct species. One or other of these two options is right and the
other wrong. Your assessment of the evidence leads you to one
conclusion, but my assessment of the same evidence might lead me to the
other (and let's say it does, for argument's sake). You think the butler
did it, I think it was the gardener! But if it turned out that gene flow
really was limited to the narrow border zone, and that this was stable,
then on my view I would be obliged to call them distinct species,
whereas on your view you could still choose to call them subspecies
because of the greater informativeness and alphabetic contiguity of
doing so. 


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