Boy Bill, do you ask the hard questions. As far as I have been able to find
out, only one study has been published on the genetics of African polecats,
comparing them to Steppe and European varieties. It was done in Russia,
which means it is not well known (I can e-mail the reference or send a copy
of the article--it's in Russian with an English abstract). The conclusions
from that study indicate the European polecat is the more likely ancestor.
I might point out that this study dates to the 70s, when biologists were far
more dogmatic in their conclusions, and genetic studies were not nearly as
accurate as today's tests.
Biologists have struggled for the last century to try and explain
interspecies/intrafamilial relationships, and have yet to really succeed.
One way is to visualize relationships as branches of a tree; one branch
being European polecats, another as Steppe polecats, etc. But branches
don't generally merge, and two species, closely related, can. So a more
accurate example might be the interconnecting meanderings seen in slow and
shallow creeks. Darwin thought of species in this way. But it is also
flawed. There have probably been as many examples as writers, and none have
been all that accurate. Still, we need something to explain the
relationships between groups of animals if we ever hope to make any
reasonable explaination of how nature works.
When we look at a species, we often see it as the individual example set
before us. An albino ferret, or a sable European polecat. But a species is
actually all ferrets or all polecats considered as a whole. If you plotted
all the characteristics of a species population 3-D, it would form a ball,
with the most "typical" or "average" individuals nearest the center. The
sphere that represents ferrets would have contained within it part of the
sphere that represents polecats. Add the representitive spheres of all
extant and extinct polecats, and parts of each sphere would also be
contained within that of the ferret, some more so than others. There are
points of overlapping where it is very difficult to assign species
identifications to individual animals. You simply say it is more
ferret-like than polecat-like. You can add the spheres of all other
weasels, even all other mustelids, and find that ALL have some overlap
within the ferret sphere, and in fact, the combined groups even form a
sphere withich contains all mustelids. You can do this for carnivores, for
mammals, for vertebrates, even for all life, and the 3-D plots will always
form a basic spheroid shape, with the most typical nearest the center.
Back to mustelids. Mentally erase the outer "wall" of the mustelid sphere,
and look within, and you would see regions where there are apparent points
of density that "stand out." These areas of density represent different
species, and their distance and position from the center (or common
ancestor) can represent the degree of relatedness between them. The
assumption is often made that the closer the points of density, the more
related the groups, which is unfortunate, because the degree of change is
not correlated to time nor space. One point of density may migrate towards
another point, so that two species NOT closely related will take on the
appearance of close relatedness.
If you looked only at the overlapping of polecat spheres (including the
ferret), you would see that they are mostly contained within each other;
something that looked like a bumpy ball. ALL polecats are very closely
related. I know of no study that would support this, but I would expect all
polecats to share at least 98% of their genetic code with each other, and
possibly more like 99%. (For example, humans and chimps share 96-98%.) This
way, it is easy to understand why the typical European polecat may be sable,
but there are some that look marbled, or striped, or even ferretish. In
fact, within EACH species of polecats, there are individuals that appear to
be more like other species than themselves.
I think the Steppe polecat is closer to the common ancestor than European
polecats, mainly because they are so closely related to the black-footed
ferret--they can successfully interbreed, etc, and are found in a larger
geographic area. Also, the European polecat has an extra pair of
chromosomes when compared to the Steppe polecat, and it is not hard to
imagine a speciation event taking place where the result was the splitting
of one chromosome into two, resulting in an extra pair. These mistakes
happen all the time, usually resulting in the death of the offspring, but
not always, otherwise WE wouldn't be here. This is simplier and more common
than the reduction of chromosomes.
IMHO, I think a common ancestor of all polecats bred several lines, one
becoming the ancestor of the African polecats, the other resulting in the
Steppe polecats (including the BFF). The Steppe line had a random muatation
resulting in the European line. The ferret may have been from the Steppe
line, and had the same sort of mutation as the European polecats, or more
probably, it came from the European polecats or from a close lineage which
is now extinct. Complicated, isn't it? Remember this one most important
rule: Morphology does not prove relationships. Just ask an African and an
Australian (non-European extract, that is).
Bob and the 13 Spheriod Mustelids.
[Posted in FML issue 1476]
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