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Posted by vvvddd on October 11, 2002 at 23:41:20:
In Reply to: Re: Hey, DT, I'm back.... posted by Terry Cox on October 11, 2002 at 18:53:39:
What TC is describing is more akin to gene flow (migration of genes between sympatric populations) than genetic drift (drift of a population from heterozygosity to homozygosity).
Other things to keep in mind:
1) IF the American Elaphe/Pit/Lamp clade was begun by an ancestor that crossed the land bridge, then that ancestor has had enough time to evolve into nearly (if not more) a hundred species and populations (more species if Triangulum is ever separated ;). If, of course, most of the evolution occurred after the land bridge disappeared.
2) From above, you have to assume that the populations of the Asian ancestor that stayed IN ASIA must have had the same amount of time to evolve into their many forms.
You must conclude from the above two points (if they are true) that American Elaphe, Pituophis, and Lampropeltis (not to mention whatever other genera are part of this clade) are more closely related to each other than they are to the Asian relatives. The two groups may only be linked at all by a single ancestral species that obviously lived several million years ago.
Of course, Asian clades may have evolved from an ancestral species that did NOT cross the land bridge (or did not have closely related species cross). Then they are even less related.
Rat snakes almost definitely represent convergent evolution. It is obvious that way way back they shared an ancestor (so does all life), but they both fill the same relative niches in their respective ecosystems. Once the niche becomes available, one or more species will eventually evolve to fill that niche. Ratsnakes fill a niche which is generally semi-arboreal to semi-fossorial. They are usually generalists in terms of habitat, though some species are more specialized (Gonyosoma for example).
Some Asian Elaphe are starting to show some relation to Boiga also, since they have Duvernoy's Glands (basically the precursor to venom gland). American elaphe lack any trace of a duvernoy's gland.
It all depends on which method of classification is more popular:
1) Phenetics- classification by phenotypic characters regardless of evolutionary relationship
2) Phylogenetics- classification by evolutionary relationships through the use of morphological, behavioral, and (perhaps most importantly) molecular studies.
Van
