Names: Elaphe slowinski, Pantherophis and what is a turtle, tortoise and terrapin? The opinion of a Herpetopathologist

Background

I am a veterinary herpetopathologist. What exactly is that? Well it is someone that has spent too much time in school, first of all. I am a herpetologist, a veterinarian and a pathologist. The result? A veterinary herpetopathologist - someone with a bachelor's degree, a master's degree, a doctorate in veterinary medicine, and a PhD in veterinary pathology, specializing in the biology, physiology and diseases of reptiles. What is the sum total of all that education? Someone that no body understands, or cares much about. But that is what I am. A man obsessed with reptiles and amphibians and what makes them tick and what makes them croak (as in death, not vocalizing). I am a man obsessed with classification, both in terms of taxonomy and in terms of classifying disease into its myriad categories. As a man obsessed with classification, I decided to have as my first hub this little post. Here I address the two questions that have been asked of me the most in the past 6 years. What is the difference between a turtle, tortoise and terrapin? And that other question. What is the right taxonomy of ratsnakes, and what is Slowinski's corn snake?

For those interested in learning more about herpetology or reptile disease, or husbandry of reptiles and amphibians, check out my reading list.

http://astore.amazon.com/vetherppath-20

Turtles, Tortoises and Terrapins - What is correct?

One question that seems to be giving people some trouble is the difference among the terms turtle, tortoise and terrapin. Ok, no one group will be pleased with me taking this on, but at least some will agree with my definitions.


1) There is no set definitions. Its true.


Terrapin

  • Oxford's Compact Dictionary says: • noun a small freshwater turtle.

  • Not very specific is it? Also many herpetologists and some herp texts will say that terrapins live in brackish water.

Turtle?

  • Oxford says noun 1 a marine or freshwater reptile with a bony or leathery shell and flippers or webbed toes.

  • Other dictionaries (here the American Heritage Dictionary) give other definitions like:

  • Any of various aquatic or terrestrial reptiles of the order Testudines (or Chelonia), having horny toothless jaws and a bony or leathery shell into which the head, limbs, and tail can be withdrawn in most species.

Ok, one says they are aquatic one says they are either aquatic or terrestrial.


Tortoise?

  • The only one anyone seems to have any form of agreement on is tortoise.

  • : any of a family (Testudinidae) of terrestrial turtles; broadly : turtle

  • :noun a slow-moving land reptile with a scaly or leathery domed shell into which it can retract its head and legs.

Wait, that is not really specific. Well most agree that tortoises are terrestrial. The fact is that nothing is really settled and there are regional uses of the words.


To make things even more confusing, the scientifically accepted common name of the eastern box turtle is eastern box turtle and the scientific taxonomic name is Terapene carolina. So here is an example of an animal that is both a terrapin and a turtle! What is more is that it is terrestrial!


So what do you do? What can you say? Is there any recourse to untangle this mess?

YES! There is a way to save the day.


2) Take a definition and run with it. That is the best thing you can do. Most of the herpetologists I deal with use the following set of definitions, and I use this set too because it gives us a standard that we can use.

  1. Turtle: any testudine, a broad term roughly synonomous with Testudines and including aquatic and terrestrial species.

  2. Tortoise: any terrestrial testudine (turtle) that generally has elephantine appendages and a high domed shell (though the shell has its exceptions). The most commonly accepted genera for tortoise standards are Geochelone and Testudo.

  3. Terrapin: any turtle on the table or in the kitchen. The term terrapin came from the Algonquin Indian language and meant edible turtle. Thus, it is a culinary term not really a scientific term, and should remain so. Only when it is part of the accepted name should it be used, such as Diamondback Terrapin, but it should not be used to refer to a group of animals as a way of classification, unless you are a chef.

Also as an aside, there is still a large amount of use of the word Chelonia. While it is not wrong, the better word for the turtles as a group is Testudines. Testudine is the preferred word among herpetologists and it is really a more specific term. Check out Herpetology by Zug.


Pantherophis and Slowinski - a miserable mess

Ok, many people have been asking about the taxonomy of ratsnakes. Notice I use the word ratsnake not rat snake. That is personal preference, it really does not matter which you use, both are generally considered correct.


First lets deal with the Russian study that led to the internet confusion about the genus. It was this study (and if anyone has read it they can understand that it was a poorly done study) that led people to start using the genus Pantherophis. That is easily dispatched. Herpetological review in 2003 rejected this (Crother et al., 2003 Herp. Rev. 34: 196-203.) Further there has been no ruling by the International Committee for Zoological Nomenclature. Without a ruling from that body, any taxonomic change is a taxonomic suggestion only. Unfortunately, many people do not understand that.


You must remember that 85% of all things published are found to be wrong in scientific literature within a decade. Do not take taxonomic suggestions seriously. Do not jump on the bandwagon too quickly. Many papers get published because someone is trying to get their name in the literature and they get things through by selecting journals with less rigorous review.


The last farce was Burbrink's papers that used mitochondrial DNA to try to separate subspecies of Elaphe obsoleta that are known to interbreed and produce fertile offspring in the wild as different species and to name a color morph of Elaphe guttata after is dead friend Slowinski. The slowinski corn snake is nothing of the kind. Living in Louisiana, I have had the opportunity to go and examine numerous snakes of this morph and I have even seen animals freely interbreeding with Elaphe guttata when placed in cages with both morphs present. In fact the cage was about the size of a small room and had four of each kind in it. Interbreeding occurred freely as far as I and the owner could tell. I actually witnessed the act of breeding between the two morphs in the cage. Therefore I doubt the validity of the species. The resulting eggs were fertile and the offspring have gone on to breed with both morphs. Without a reason to separate the species, the morphs must be considered to be the same species. If they behave like a single species and there is gene flow, they must be the same species.


I could also go into the dangers of mitochondrial DNA, but that is a discussion for another time. Suffice it to say that mito DNA is bacterial in nature, more free to mutate than nuclear DNA and is a dangerous guide to deciding species. It is constructed like the DNA of a bacterium and even has bacterial type ribosomes that carry out the forming of protein from the instructions. It, like its bacterial ancestors (yes most cell biologists believe that mitochondria were bacteria at one time that became part of the eukaryotic cell) it lacks mutation correction machinery on the level of the eukaryotic nucleus and so it is more free to mutate. In nature, if the nuclear DNA is similar enough, the sperm and egg of mating individuals can form fertile offspring. Thus this is a natural species. It behaves in nature like a species. Thus, nuclear DNA is what is actually important in determining a species, not mito DNA. In theory, you can take the mitochondria from a frog and use them to replace the mitochondria in the egg of a dog. When the dog ovum is fertilized the frog mitochondria will remain, since sperm mitochondria are lost during fertilization and only maternal mitochondria are passed on. The result would, in theory because to my knowledge no one has actually done this, be a dog with frog mitochondria. So using a mito DNA test you would find that the lovely, red friend you had was not that pedigree Irish setter you paid so handsomely for, but was in fact a species of frog. But that "frog" would look like, act like and reproduce like an Irish setter.


Bottom line:

Mitochondrial DNA is not responsible for determining species status in nature, so why should it be used to determine species in human classifications?


The problem with all the taxonomy is that the natural species concept is ignored. Humans create delineations while nature works in a continuum. It really doesn't matter what percentage difference there is between the mitochondrial DNA of two morphs if their nuclear DNA allows them to behave like a single species in the wild.


Bottom Line:

I do not accept the Slowinski corn snake nor the genus Pantherophis as valid. There is simply no reason to.

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