species/subspecies query

Ken Kinman kinman at HOTMAIL.COM
Wed Nov 15 16:07:02 CST 2000


Mark,
     Unless indirect biological tests (which Don discussed) show otherwise,
I would agree with your view that they should be regarded as a single
species, which may or may not split into two or three separate species in
the future.  As long as there is the potential for genetic exchange between
populations A & C by way of the intermediate population B, it seems
preferable to regard it as one species which is in the process of
speciation.
      If population B becomes extinct for some reason, then A and C should
probably be regarded as separate species, assuming the potential for genetic
exchange would plummet to near zero.  It is contingent on future events, and
I believe we too often jump the gun in splitting such species.  The splitter
and lumpers could argue endlessly about exactly how much potential remains
for genetic exchange between the populations given various scenarios, but I
tend to be a lumper and assume full speciation has not taken place unless
there is considerable evidence that it has.  Not that there are no instances
of overlumping, but my experience is that oversplitting is more of a problem
than overlumping (especially at species level).
    But of course each case is different and needs to be evaluated in the
context of related groups.  I don't know much about incompatibility systems
in plants, but even among metazoan groups there is a tremendous variety in
the way incompatibility arises and evolves.  Given this and the
philosophical differences between lumpers and splitters, it is no surprise
that the issue of subspecies vs. species status comes up over and over
again.  It comes with the territory, and there are no simple answers
(annoying as that may be).
     But in the example you cited, I would say your approach is definitely
not "out of line", and is in my view the preferable approach.  Some
splitters would disagree with us, but that is all part of the checks and
balances that make for a healthy "give and take" in science.
                        --------Ken Kinman
*********************************************************
>From: Mark Newton <urodacus at LORDS.COM>
>Reply-To: Mark Newton <urodacus at LORDS.COM>
>To: TAXACOM at USOBI.ORG
>Subject: Re: species/subspecies query
>Date: Wed, 15 Nov 2000 22:01:23 +1030
>
>Tony said:
><<Dear Mark, I would call it incipient species. They remain different
>species,
>in natural condition, i.e. if there is no messing up by human hands. I have
>two examples in Indonesia (not three, as in your case) : freshwater fish
>Tilapia mossambica originally from southern East Africa and Tilapia
>nilotica
>from the Nile; they have been spread widely all over the world now.
>However,
>in Indonesia these two species will be kept separated as two distinct
>species (each with respective permanent - I wont call it stable -
>characters) in separate habitats. But, if they are mixed together, they
>regenerate into one single species, namely mossambica. So, I think nilotica
>is an incipient species. In your case, the number of species is different,
>but the process of speciation may be the same. I hope this little account
>explains. I am an entomologist, specializing in taxonomy of the robberfly
>(Asilidae - Diptera). My name is Soenartono (Tony) Adisoemarto.>>
>
>Hi Tony, thanks for that and everyone else too who has given me help
>understanding this species definition confusion.
>I understand exactly what you are saying about the fish in your example
>above.
>I see numerous ways now of interpreting such situations and this I find
>annoying in that different taxonomists can basically choose their own
>reasoning and species definitions when describing species. To me this is
>inconsistant, and not good science, although I do see that different
>situations drive different ways of thinking.
>To my way of thinking, the example above would be better expressed if the
>two fish were treated as one species, simply because they seem more like
>two
>separate populations of the one fish. If they were expressed as subspecies
>of each other it would be more obvious to anyone unfamiliar with them that
>they are so closely related that in fact they are really the same except
>for
>the geographic isolation and hence some gene frequency and allele
>differences, and at some time were a single population. The different
>species names does not indicate this.  I realise that the two fish are
>independent gene pools and dont mix, but if they are in fact derived from
>the one fish and still produce viable offspring then surely they are
>geographic variants rather than species.
>Can anyone explain if my interpretation is way out of line with respect to
>this.
>
>Cheers
>Mark
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