Caution, scientific comment ahead
Now, now, I'm one of those "they," and Natrix as a New World genus fell almost 30 years ago so it's very old news. All anyone in the systematics business is trying to do is to figure out relationships and lineages so that we can gain a better understanding of how evolution works at various scales and how/where lineages moved around the planet in the really old days. In the much more recent old days we counted scales, studied color patterns, looked at tooth arrangements, determined tail length proportions, delved deeply into internal anatomy, and so on down the morphological turnpike, with little regard at the species level as to whether the characters themselves gave much of a clue about ancestry versus progeny except for the most egregiously primitive characters (e.g, snakes with legs). Now we still use morphology and we also use gene sequence data (molecular biology) but we look at the data differently--what species pair shares a derived (not primitive) character (aka apomorphy, when shared, called a synapomorphy), and can they be arranged into a lineage that makes sense when multiple characters are considered, relative to a distantly related form (outgroup)? This is simple enough, but it also makes us want to assemble neat lineage trees (cladograms, phenograms) that make deeper sense in that any given branch of the tree that has a name includes all of the family tree in the lineage and in the name we give the lineage--a part of the branch that is broken out and placed in another branch for no reason other than tradition is unacceptable. These days systematists are just revolted by that thought (aka a paraphyletic group) because it complicates trees and makes us use place keepers when it would just be simpler to arrange them in the relationship that the synapomorphies indicate--it's a lot of work to build a realistic tree, a job that has generated many PhD's. Well and good, but until everyone goes along we're stuck with entire traditional classifications that are widely accepted (e.g., "Reptilia") but are paraphyletic--they were developed when knowledge of relationships was much less robust, and there is also a sentimental issue--we all grew up with Natrix and it slides off the tongue easier than Nerodia. That's why a lot of herpetology classes in universities now include birds in the study plan, which most systematists agree rightly belong as part of "Reptilia" but which birders and even some ornithologists fight tooth and nail to keep as a distinct group (when I teach herpetology I acknowledge the place of Aves in Reptilia but I don't cover them because life is already too short). In a nutshell, these days when a systematist determines that a previously recognized group or genus is actually more than one distinct lineage, that's automatic paraphyly and we need to separate them and we also need two names, not just one. Thus, when Doug Rossman figured out that the Old World Natrix (grass snakes) are on an evolutionary trajectory that is different from the New World water snakes (called Natrix at the time), he demonstrated the difference and also had to come up with a new name for the New World snakes. The rules of nomenclature come in here, and because of that he had to select the earliest available name which was Nerodia, first proposed in about 1852.
To my knowledge no one has lately suggested a rearrangement for Desmognathus that would change its genus, but new species of Desmognathus are coming to light all the time thanks to far better sampling and better analytical techniques than were in place back when Nerodia was Natrix.
Bottom line--unless you're a specialist or are trying to publish in the technical literature, you can call it pretty much whatever you want. If you say Natrix sipedon everyone will know what animal you mean and systematists won't care about the usage. Prim and proper sorts might though, so say "Nerodia" when in their company. And by the way, Pseudacris for the former Hylas is still controversial, so both names are acceptable if not strictly correct.
Sean Barry
University of California, Davis
Former denizen of Haddonfield, with lifelong memories of the Pine Barrens where I first learned to say "Natrix" in 1960 and "Nerodia" much later.
uuglypher said:
Crap! I 'spose they changed ol' Natrix sipedon as well...
(yeah, yeah ... I heard about "Nerodia"... have they screwed around with Desmognathus sp. yet?)
Well anyway; lemme tellya'bout back in th'day...
Dave
