Flag for Taxon: Gray Ratsnake (Pantherophis spiloides)
| Flagger | Content Author | Content | Reason | Flag Created | Resolved by | Resolution |
|---|---|---|---|---|---|---|
| loarie | Gray Ratsnake (Pantherophis spiloides) |
controversy about species delimination |
Nov. 29, 2018 17:52:08 +0000 | loarie |
see comments |
Comments
@bobbyfingers if you look at both the mtDNA AND morphological analyses in Burbrink's paper, you will see that the Gulf Hammocks population consistently comes out with the S. Florida populations of alleghaniensis - so not just mtDNA. Even the otherwise poorly resolved morphological analyses support this.
@wolfgang_wuster I understand your point about mtDNA. Of course I know that mtDNA is passed down only through the maternal line. (Heck, I teach about it in four classes every year.) I guess I got confused in the process of trying to play it out over several generations.
@bobbyfingers If iNaturalist ultimately decides to call these snakes P. spiloides, then I'll happily go along with that. In the meantime, I will continue to identify members of this complex east of the Appalachian crest and Apalachicola River as P. alleghaniensis because right now iNaturalist's taxonomy is based on Burbrink. Either way, my primary concern is for the quality of the data. There's no reason for you (or me or anyone else) to make this personal. Once egos get involved, good science goes down the drain real fast.
Moving on...
I've made two points that I would still like to see someone address:
The Gibbs study that showed extensive interbreeding between P. alleghaniensis and P. spiloides in Ontario and suggested that perhaps the two species should be lumped: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.454.6494&rep=rep1&type=pdf
Why is external morphology so important in the first place? I know it makes life easier for hobbyists who want to be able to ID snakes quickly in the field, but from the perspective of speciation, it shouldn't matter. Snakes don't choose their mates based on external coloration, so why are we trying to force them into "species" based on external coloration?
The Gibbs study strongly supports lumping them, but it would be useful if a similar study were repeated further south - after all there are things like ring species where things act like good species in one place and merge like single species in another.
Morphology matters because, due to the limitations of mtDNA and the lack of nuclear data in most of the range of this group (i.e., excepting the Gibbs paper), morphology is the nearest proxy we have to overall genetic affinities. Basically, where mtDNA and morphology tell the same story, then morphology supports the mtDNA arrangement. Where they do not, then I would be reluctant to accept the mtDNA evidence on its own for the purposes of systematics.
Well I too believe that mtDNA is the weakest excuse to make a species, and I can say that that was 100% opinion. My question is if mtDNA is the strongest factor, because I have researched and researched the physical differences between the two and it is infinitesimal if at all, and my biggest question is if we go to a population of "Black" or "Gulf Hammock" Ratsnakes and discover that some are Eastern and some are Gray (by value of mtDNA) are these snake in a range overlap and refuse to breed (like a typical species) or are these snakes a hybrid population? If mtDNA is the way to tell the two apart, you cannot tell. I think we are looking at two "pre" species that were separated for thousands of years and are reintergrating.
So, I guess I agree with Gibbs and that is what I am trying to do. I want to look at P. alleghaniensis, spiloides, and obsoleted (for it is disputed along streches of the Mississippi River which is which) to build a stronger range map, locate areas of overlap, try to determine key physical traits, and sun further test on the DNA to see of there is another way to tell if there is any hybrids. And true, snakes do not chose a mate by color, but maybe there is different pharamones in the animals that other species do not like. It was just recently found that humans use scent to pick a mate, maybe there is something similar. I would assume that if these snakes were separated for thousands of years, they would have evolved some different characteristics. The "Gulf Hammock" snakes I believe are a lineage of hybrids that mtDNA unpredictably (in a way that there may have been an imbalance of males to females, and since temp. is a factor in sexing snakes, maybe a cold snap produced mostly females and the Gray species adapted better) the Gray mtDNA dominated. I don't know, these may be answers to questions that we do not have yet. But I think samples need to be taken from, not a hundred or a couple hundred animals, but thousands of animals across the US. If we are going to use mtDNA, lets build a solid map. To my knowledge, zero snakes have been tested in VA, and the Department of Game and Inland Fisheries refuse to recognize the Gray as a VA species. But I want to scrutinize all aspects of DNA, physical features, and behavior.
Sorry if I was ranting. I understand I do not have a paper to validate my views, but that is my best interpretation of these studies and my personal "logic".
@wolfgang_wuster The idea of a ring species is an intriguing hypothesis in this case, given that Burbrink didn't do any sampling in the northeast. I know it's still a bit far-fetched given the data we have available now, but it's possible that the Apalachicola River area is where the two "ends" of the ring meet and there's no hybridization.
@loarie Regarding iNaturalist's position, the fundamental issue here (after you wade through all the nerdy details) is that the external coloration of these snakes shows very little correlation with the genetic data that we have available. For better or worse, amateur field herpers (who make up the vast majority of the iNat herp community) tend to err on the side of morphological data. The professional herp research community, on the other hand, tends to err on the side of the genetic data - partly because external coloration probably plays very little role in snake speciation, and partly (and maybe even more importantly) because genetic data is what's been published recently.
For all of its limitations, Burbrink's second study (the one that's been addressed in this thread) is the only one that has attempted to reconcile the genetic and morphological data, so it's essentially the best we have at the moment. But obviously there is a lot more work that needs to be done.
I agree that it seems a lot of people are calling this a snake because of appearance, and iNat, is all visual appearances. The apearance of the animals and location decides the identification that anyone can make. We cannot see the DNA in a photo. The issue is that I understand this snake may be slightly out of range for P. spiloides, but keep in mind that I have seen Ratsnakes get stuck in hollows in trees on logging trucks, and carried in haybales on trailers. Once, I had a coeworker that had one in her car, under the hood, for five days. This means, like treefrogs, they can be unknowingly transported by people. I believe this is what happened with the Pennsylvania Yellow Ratsnake. The odds are grater that this is a moved snake "Gulf Hammocks" Ratsnake than an extremely odd "Yellow" Ratsnake. I agree that there is a possibly of odd genes, but if that was the case than we would likely see a "Black" in the everglades, a "Yellow" in VA, or even a "Gray" (color not species) in DC.
Now what I mean by all of this is that it "looks" Like a "Gulf Hammocks" and most herpetoligist call that a P. spiloides. There is no concrete evidence that this is P. alleghaniensis. This argument is based on the map, but a map is only as good as its maker and I think we can ALL agree that that map made is shaky at best, and maps change. When the first Burmese Python was found in the everglades, no one said, "That cannot be a Burmese Python, the map shows Asia. I want a DNA test." Now I get that that is an extreme example, but what I am saying is we have to look at the animal, and use maps for certain "probability" calls (like "Black" Ratsnakes). I think we have to call it how it looks, because we have nothing else to go on.
A paper examining the phylogeny of Pantherophis (and other Lampropeltini) in a multi-gene context was just published: https://www.sciencedirect.com/science/article/pii/S1055790317306863. I'm not a herpetologist, but it may be useful in informing y'alls treatment of these taxa.
@cypseloides That's a cool paper, thanks for the link. However, it does not really illuminate species limits and distributions in Pantherophis.
@tysmith: Burbrink had sampling of Gulf Hammocks rat snakes in both of his papers, and both morphology and mtDNA grouped it as an eastern rat snake. I really can't see any basis for saying it's a spiloides.
@wolfgand_wuster Fig 1 does show that P. alleghensis and P. spiloides are paraphyletic, so should probably be lumped.
see https://www.inaturalist.org/observations/11388345
there's controversy about where exactly Pantherophis spiloides stops and Pantherophis alleghaniensis starts.
If folks are advocating we deviate from the Reptile Database delineation of these species, then we should add details to the taxonomy details and atlas pages for Pantherophis spiloides:
https://www.inaturalist.org/taxa/67642/taxonomy_details
https://www.inaturalist.org/atlases/695
and Pantherophis alleghaniensis:
https://www.inaturalist.org/taxa/59644/taxonomy_details
https://www.inaturalist.org/atlases/646