Species III

Michael Gochfeld gochfeld at eohsi.rutgers.edu
Sat Sep 8 09:48:35 EDT 2001

Ron's examples are great and reassuring to us skeptics.  I like to know about
how genetic distances are being used, and both of Ron's examples were new to
me. At first the principle hinged, as I recall, on the work of Crow and Kimura
who postulated neutral mutations (unseen by selection).  That generated a lot
of discussion about whether there was (or even could be in theory) such a
thing.  That set off a search for parts of the genome that were in places that
couldn't be seen by selection.

Mike Gochfeld

Ron Gatrelle wrote:

> Michael Gochfeld wrote:
> Like Norbert I remain to be convinced that genetic distance (represented as
> percent) means the same thing in different taxa (or for that matter in
> diffrerent fragments of the same two taxa).
> Norbert Kondla wrote:
> Another is what I call the chemical species concept. Looking at the
> chemistry of selected gene segments is growing increasingly fashionable.
> Certainly gene chemistry, like genitalia, can provide some potentially
> useful data but there is always room for interpretation. The chemical
> species concept might argue that two butterflies with, for example, less
> than 3% difference in gene chemistry are the same species. Extending this
> logic to mammals would result in chimpanzies and humans being declared the
> same species. I have some difficulty accepting that there is some magic
> level of similarity in gene chemistry that defines what is or is not a
> species.
> ___________
>     Pterourus rutulus and P. eurymedon have the same mtDNA sequence. Yet
> they
> are obviously sympatric (co-occurring) species. This tells me that mtDNA
> analysis is just about worthless relative to these two species.  It has
> recently been determined that Phyciodes batesii batesii and P. b.
> maconensis are "very different" in their mtDNA. Yet this does not yet
> release one to say that batesii batesii and maconensis are in fact two
> species.  How many variables are there just like and in-between these
> extremes that _have_ been put forth to us as the Holy Grail final word on
> if X is a species or subspecies?  Quite a bit I bet.
>     What is going to happen when someone accidentally puts two chemically
> identical (or almost so) critters that live a long way from each other -
> and by chemical analysis have been "proven" to be the "same" species -
> together and finds they will not mate and if they are coerced to do not
> produce viable offspring?   And what will be the explanation when the two
> very genetically different "species" that live a long way apart are for
> some reason put together and it is found that they mate and produce
> offspring like Gypsy moths?
>     Genetics is not the all and all answer all at the specific and
> subspecific level.
>     We already know that genitalia are not the magic bullet either. In some
> genera all the genitalia are basically the same. In some they vary with the
> subspecific morphology.
>     There are likely differing reasons that Kondla, Gochfeld and Gatrelle
> all have a lack of total faith in what Norbert called the "chemical species
> concept."  Perhaps others need to not just automatically swallow the whole
> hook, line and sinker of those who so elevate this area/means of analysis
> as the arrival point of taxonomic detecting and systematic discernment.
> With this area of argument I say there is lots of subjectivity.
> Ron Gatrelle
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