Rat snake Taxonomy confusion

[M.Dwight]

I lost track of rat snake taxonomic changes after they renamed the black rat for a third time in a decade But now it’s time for me to catch up (again!) Well, I’ve read the latest Latin for the black rat (Eastern rat?) is Pantherophis alleghaniensis. But, I’ve also noticed on many sites they are also calling the yellow rat snake P. alleghaniensis. What?
Ok, catch me up here folks..what is current accepted scientific names for the black and yellow rats. And please don’t tell me they’ve lumped them both into “Eastern rat snakes.”

 

[jander]

Everything east of the Apalachicola River and the Appalachian Mountains is considered Pantherophis alleghaniensis. The fact is, a "black rat snake" from New Jersey is more closely related to a "yellow rat snake" from Florida than it is to another black rat snake from Ohio. There are multiple species concepts (and that is an entirely different topic in itself) but most widely used and accepted concepts today deal with evolutionary history and independently evolving lineages. The three species (obsoletus west of the Mississippi River, spiloides between the Mississippi River and Apalachicola River/Appalachian Mountains, and alleghaniensis east of the Apalachicola River and Appalachian Mountains) form three distinctly diverging lineages. What this means is that these three populations are evolving in separate directions. There can still be gene flow, but if the rate of divergence overtakes the rate of gene flow, the lineages will (and are) continue to evolve independently.

As for the "black rat snakes," one possible solution is that each population contains the alleles for black pigmentation, and in the northern parts of their range this is specifically selected for. As past glaciers retreated northwards, the rat snakes expanded their range northward. If the black pigmentation was advantageous (say, for aiding in thermoregulation in cooler climates) it would be selected for. Basically, there can be many different genetic variations that are coding for the same color (which is why basing subspecies on color alone is a bad idea). As I said before, a rat snake from New Jersey is actually genetically more similar to a rat snake from eastern Florida.

The old Pantherophis obsoletus subspecies (black, texas, yellow, everglades, etc.) was just based off of color patterns, and it in no way reflected the evolutionary history of the rat snakes. Whether or not you accept the new species, I hope I was able to shed light on where they came from. There's a lot more to it, but did that help in any way?

 

[M.Dwight]

Thank you!

Thank you for responding John. That’s just the info I was looking for. As a non-professional hobbyist my opinions on modern taxonomic methodology and conclusions is inconsequential. I just like to know what the biologist are up to.
However, as a long time hobbyist I would like say one thing. I can’t argue with the mitochondrial findings. I understand this process and am a believer in its importance. BUT, as a hobbyist I can’t overlook the morphology differences between the Florida form and the northern black form of alleghaniensis. I’m not talking about color/pattern difference here but physical morphology. I won’t go into extreme detail but it is quite obvious to my eye that my yellow forms (wild caught from the Ft. Myers, Fl. local) are very different from my northern black forms. My yellows have a more laterally compressed body, longer & thinner head shapes, different orbital size/placement, both male and female yellows have longer tails for the same overall body length. And my yellows have a more arboreal feel in the hand than my blacks. You could blind fold me, hand me an adult black and a adult (S.Florida) yellow and I bet I could tell them apart. Beyond the color/pattern of these two forms it seems clear to me they’re evolving in different directions.
Thank you again for the up-to-date information.

 

[Ron Allen]

I was under the impression that The ICZN had rejected the renaming, and thus Elaphe and obsoleta remained.
Could be old info though.