Re: things to keep in mind....

[ Follow Ups ] [ Post Followup ] [ The Rat Snake Forum ]

Posted by Terry Cox on October 12, 2002 at 09:20:35:

In Reply to: things to keep in mind.... posted by vvvddd on October 11, 2002 at 23:41:20:

: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.

Of course, there are many different possible scenarios of how it all got started. Obviously, all colubrines are related somehow, and they occupy almost every continent. Colubrines evolved originally from some type of proto-stock from tropical climes, and that proto-stock probably leaned towards being venomous, i.e., rear-fanged and/or possessing Duvernoy's glands. At one time Europe was connected to North America, also. I believe Europe, Asia, and N. A. (Laurasia) shared many different genera at one time, or, at least ancestral stock to modern genera. Our modern genera in N. A. may have evolved separately from Old World genera, but from ancestral stock that was related. I don't think it could have been just one species.

Another thing I'd like to put into the mix is the fact that we have several other subfamilies besides the colubrines. The one that I'm thinking about right now is the Xenodontine subfamily of colubrids. From what I know, American genera have been questioned as far as what subfamily even they belong to. For instance, the Lampropeltines may be considered "colubrines" by most, if not all workers, at this point, but at one time they may have been considered to have evolved from Xenondontine stock, an ancestor such as Clelia. I remember a time I had to argue Lampropeltis was even a colubrine, let alone closely related to Elaphe. See why this is difficult for some of us old timers.

I don't believe all the species/genera in the clade we're referring to (N.A. E, L, and P) came from a single, primitive, ancestral species. I believe there were many species/genera that filled all the ancestral niches that existed when the continents were connected somehow, and that modern genera have evolved from all of these. They weren't necessarily closely related. That has to be determined.

At any rate, the question is how closely related our N.A. Elaphe, Lampropeltis, and Pituophis (and maybe other genera) are. Are they close enough that when we revise N.A. Elaphe, that we can lump them all in one genus? I agree that the New World Elaphe should be placed in separate genera from Old World ratsnakes, but also believe that some degree of relatedness should be maintained. I guess that's always going to be a topic for argument and discussion.

: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. Yes.

: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.

Maybe, depending on the ancestors of Lampropeltis and Pituophis (and it's beginning to look like they are closely related at this time:)

The two groups may only be linked at all by a single ancestral species that obviously lived several million years ago.

As per discussion above, I seriously doubt that there was only one species involved. I believe the continents shared many species.

: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.

Then we'd have to come up with another theory of where the American colubrines came from and how they are related enough to Old World colubrines to be in the same subfamily.

: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).

Yes, but how closely related were their ancient ancestors? Did they need to be closely related to produce species/genera that are so much alike? I think so.

: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.

Interesting point. I always thought some Asian Elaphe showed some similarities to Boiga, i.e., carinata and related species. I think there's some connection with Boiga (even though it's a separate subfamily, Boigines), but that it's very distant. I think there's characters other than Duvernoy's glands that also link them.

Duvernoy's may be a fairly primitive character, and shared by many ancient genera, not unusual to be in primitive Elaphe. It may help show how modern N.A. genera are and maybe some Eurasians. We also need to look at fossil specimens to help see the age of species/genera.

: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

I've always been interested in the evolutionary relationships, Van. I'm no professional, but am interested in phylogenetics. I don't need to ever get published or anything, but do think there's a place for amateurs to offer their contribution and maybe influence the general thinking.

Thanks for your input and keeping this thread alive. I'd love to know how much expertise there really is in this area of ratsnake biology. Too bad more professional type people don't jump in on discussions when something is needed, like the correct terminology or links to literature, etc. I appreciate all who do contribute and also those who tolerate or ramblings, etc. I know this stuff is definately not for everybody, and I hope they don't think we're just wasting space..haha. Later.

Follow Ups: