species/subspecies query

Mark Newton urodacus at LORDS.COM
Wed Nov 15 22:01:23 CST 2000


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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