Garter Snake Question

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qaz
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Garter Snake Question

Post by qaz »

I was looking around flickr today and came across a picture of a garter snake that looked extremely similar to one I had seen in the past. I clicked on the image and it said the snake was a Maritime Garter Snake (T. s. pallidulus). I looked into the species a little and saw that its range in the U.S. is in the far northeast. The snake I was found in extreme upstate New York; apparently little out of range, but still not too far off.

Image

Image

So my question is: is it possible that this is a Maritime Garter? Or is it just a good-looking T. s. sirtalis?
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Dr. Dark
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Re: Garter Snake Question

Post by Dr. Dark »

T.s.s. all the way; they are SO incredibly variable.
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beemaster
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Re: Garter Snake Question

Post by beemaster »

Dr. Dark wrote:T.s.s. all the way; they are SO incredibly variable.
Yup. I catch T. s. sirtalis in SE Mass (far out of T. s. pallidulus range) that look just like the OP's snake all the time. I also catch many that look completely different. It's just a highly variable animal as far as pattern and coloration go.
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Andy Avram
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Re: Garter Snake Question

Post by Andy Avram »

A Maritime and Eastern Garter Snake are the same species, they are different subspecies (and seemingly pretty weakly defined at that) so it pretty much goes on range. Also, as Dave and B said, Easterns are a highly variable subspecies, nestled within a highly variable species so a variety of patterns can be found in any population. Yours is completely within normal variations of Easterns.
qaz
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Re: Garter Snake Question

Post by qaz »

Thanks for the feedback guys!
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Don Becker
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Re: Garter Snake Question

Post by Don Becker »

(far out of T. s. pallidulus range)
Or the range of T. s. pallidulus is poorly defined, and needs to be extended. I've been jokingly telling people for years that I find Chicago Garter Snakes (T. s. semifasciatus) in Iowa. Funny enough, there is a book, heck, a bible you might say, about to be published about Iowa's snakes, and from what I was told, it's going to include Chicago Garter Snakes.
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Jeff
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Re: Garter Snake Question

Post by Jeff »

Psyon is correct in the indefinite range of T. s. pallidulus -- it is, in fact, centered in a region, but snakes of its characteristic color pattern can be found in decreasing percentage away from the core range.

The type locality is Intervale, New Hampshire, and the characeristics (compared with T. s. sirtalis) were stated by its describer, Glover M. Allen, to be: dorsal stripe obscure, grayish, not yellow; ground color olive-brown, not blackish; chestnut color below the lateral stripe, as opposed to olive (in T. s. sirtalis); "lighter color of the belly".

Allen's decription was based on a "these here don't look like those there" philosophy, and his conclusions were not given serious consideration until Bleakney's 1959 study. Have a look at that, and you can come to a more credible solution (Bleakney 1959. Copeia 1959:52-56).

Subspecies boundaries are poorly fashioned, often based on old studies of few specimens.

Jeff
qaz
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Re: Garter Snake Question

Post by qaz »

So do you think their ranges could overlap in the area?
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Andy Avram
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Re: Garter Snake Question

Post by Andy Avram »

qaz wrote:
Post subject: Re: Garter Snake Question Reply with quote
So do you think their ranges could overlap in the area?
By the nature of how subspecies work - no, it can't happen. Since subspecies are geographic variants of a species, by definition you cannot have overlapping populations. In your case you either have pure Eastern subspecies, pure Maritime subspecies, or an intergrade. An intergrade is where two or more subspecies come into contact so you get a blending of characteristics that can run the gamut from pure looking subspecies to a complete mix.

Judging by Conant, upstate NY would be pure Eastern, but close to Maritime, but you could easily be in an intergrade zone.

And, again, Maritime seems weakly defined to me, and this is an extremely variable snake to begin with. I have caught many a specimen in Ohio that look exactly like the one you have pictred.
qaz
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Re: Garter Snake Question

Post by qaz »

Oh ok I see what your saying. In all my visits to the area, I've only seen individuals that exhibit characteristics of pallidulus, so is it possible that the range should be extended?

Or is this guy an integrate/just a funny looking sirtalis?
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Andy Avram
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Re: Garter Snake Question

Post by Andy Avram »

I am saying none and all. If if you open up the Peterson's Field Guide you will see a line drawn for the subspecies right at the state border in upstate New York. Since subspecies do not typically change abruptly, but rather intergrade over an area, the line should really be hatched to some degree to show the integration zone. Depending on where you are, you may be at the border, the Martimes may actually come into New York (in which case a researcher would have to do a study and write up a paper changing the subspecies boundary - but since subspecies are falling out of fashion not too many are likely to do that) or you are just seeing regular old Easterns.

Out of curiosity what makes you think the snake pictured is out of the realm of possibility for an Eastern? This coming season I can catch gobs of them in Ohio that look identical to yours.
qaz
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Re: Garter Snake Question

Post by qaz »

I don't think its NOT an eastern, I've just never seen any definite easterns like it. Plus since it was found so close to the border I thought there was a possibility of it being a maritime.

Thanks for the help!
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Don Becker
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Re: Garter Snake Question

Post by Don Becker »

Andy Avram wrote:By the nature of how subspecies work - no, it can't happen. Since subspecies are geographic variants of a species, by definition you cannot have overlapping populations.
I don't think I agree with that. Intergrade zones are exactly where they overlap. If you have an intergrade area of T. s. pallidulus, and T. s. sirtalis, the snakes in the area have to be some sort of subspecies. They either match the characteristics defining them as T. s. pallidulus, or it would default back to the nominal subspecies of T. s. sirtalis. It would become a bit more complicated where the intergrade area is between two subspecies of which neither is the nominal one. Once you split a species into subspecies though, every animal has to be counted as one of the subspecies.

Also, just because the Peterson guide draw a line, it doesn't mean the line is in the right place. That even applies to species as a whole. The lines were drawn based with the information that was available at the time of publication.
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Andy Avram
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Re: Garter Snake Question

Post by Andy Avram »

psyon wrote: I don't think I agree with that. Intergrade zones are exactly where they overlap. If you have an intergrade area of T. s. pallidulus, and T. s. sirtalis, the snakes in the area have to be some sort of subspecies. They either match the characteristics defining them as T. s. pallidulus, or it would default back to the nominal subspecies of T. s. sirtalis. It would become a bit more complicated where the intergrade area is between two subspecies of which neither is the nominal one. Once you split a species into subspecies though, every animal has to be counted as one of the subspecies.
Don,
Not quite, but I do agree with, “Intergrade zones are exactly where they overlap.” It is easier to think about things as populations as opposed to individuals. Each subspecies is a sub-population with a set of characteristics that define it on a geographic basis within the species whole. Where two of these sub-populations (subspecies) meet their characteristics blend with a host of blending from characteristics exactly like a pure subspecies to a complete and thorough mix. This is best looked at as a mixed population – the intergrade zone. Within this zone, no matter what the individual animal looks like, it is best to define them as an intergrade. I will say in the past they have been looked at on an individual basis (the way you described) but eventually it switched to a population basis.

Which gets us to your next point. Nothing would default back to the nominal subspecies, and it is no more complicated with two or more subspecies that do not include the nominal form. The nominal subspecies is not the “core”, “main”, “default” or “oldest” subspecies within the species whole but rather the first one named. So the type specimen of a species is described, and if subsequently, additional subspecies are described then whatever subspecies belongs to the type specimen becomes the nominal. It has nothing to do with evolutionary history and everything to do with taxonomic precedent.

Lastly, while I prefer to think of subspecies and integrade zones as populations within populations, and define them as such - so in this case, if the above snake was an intergrade, and if it was unclear which subspecies make it up, it would be called an Eastern x Martime Garter Snake (Thamnophis sirtalis sirtalis x. pallidulus) or if the subspecies were implied just Common Garter Snake intergrade (T.s. sirtalis x pallidulus), or some combination thereof. Now to circle back to your “default” comment. As has been done in the past, you can define the snakes in the intergrade zone as either one subspecies or the other, but if there is a blending of characteristics it would be called an intergrade. So in the above case, in the intergrade zone, you could define individual snakes as “Eastern Garter Snake”, “Martime Garter Snake” or “Common Garter Snake intergrade”. But this style as largely fallen out of fashion. (I realize you make computer programs to log data on herps and it may be a pain to add intergrade populations so I can see where defining them as either or works better for you.)
psyon wrote:Also, just because the Peterson guide draw a line, it doesn't mean the line is in the right place. That even applies to species as a whole. The lines were drawn based with the information that was available at the time of publication.
I couldn’t agree more with this!

Andy
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Andy Avram
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Re: Garter Snake Question

Post by Andy Avram »

And just because I wanted to fool around in Paint, and I think it might help some other people with the subspecies concept in a very simplified picture:
Image

Here is a picture of a species of snake.

Red snake on gray - Subspecies A
Blue snake on gray - Subspecies B
(In theory the gray ranges would be much larger than the green)
Any colored snake on green - Intergrade (this can be donated as "Snake A x B intergrade")

So regardless of the amount of mixing, if any, as long as the snake is within the green background it is an intergrade, but it should show well mixed individuals in the core gradually looking more like a "pure" subspecies for individuals on the end.

Now, where the intergrade boundary on a real set of subspecies is drawn is certainly up for debate.
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Don Becker
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Re: Garter Snake Question

Post by Don Becker »

Nothing would default back to the nominal subspecies
It has to default to something. Once you define one subspecies, there has to be a second. If you have D. beckeri with a type specimen from Iowa, and then discover a dwarf subspecies that exists in Ohio, you might describe the dwarf race as D. beckeri avrami, and define it's range as the borders of Ohio (just to simplify things). You are saying that that the animals within that defined boundary are D. b. avrami, and everything else would be D. b. beckeri unless other subspecies are defined. When you have areas of intergradation, animals in an area would either meet the criteria to be considered D. b. avrami, and if they don't meet that criteria, they would just simply be D. b. beckeri.

I treat every animal individually, and I label them based on the subspecies they match the description for. I think that is important to do so. The whole idea of a subspecies, is that the animals in a geographic region are different in some reason. If we ever only look at the populations as a whole, and go by defined lines, we will never progress the knowledge we have of the species. By evaluating each individual animal, and labeling them based on the subspecies they key out to, we can show that the currently defined boundaries need to be changed, or maybe that the subspecies as a whole is bunk, because there isn't really a well defined area where what ever characteristics exist. The ringneck snakes at Snake Rd are a good example of this. Three or four different subspecies overlap there. There are animals that have the ventral patterns of Prairie Ringneck Snakes, some are clearly Northern Ringneck Snakes, some are clearly Mississippi Ringneck Snakes. By simply labeling them all as Ringneck snakes, we lose the knowledge of what trains those individuals held. It may be that 100 years ago, none of those snakes would have keyed out to Northern Ringneck Snakes, and now the genes from the north east populations are becoming more prominent in the region, and 100 years in the future it may be the dominant form and forced out all others.

Here is another issue, by simply dismissing the animals as intergrades, and not analyzing them further. If you have your Peterson guide handy, open it to page 328. You will see the range map for Heterodon nasicus. You will notice the small patch in NW Illinois is marked as an intergrade area of H. n. nasicus and H. n. gloydi. But now the subspecies of H. nasicus are all elevated to species status. So what are those snakes in NW Illinois? Are they H. nasicus, or H. gloydi? What about if T. s. pallidulus was suddenly elevated to species status? What would the original snake in question be then?
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Andy Avram
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Re: Garter Snake Question

Post by Andy Avram »

Your reasons for trying to key out individuals within a zone of integration is a good and valid one. If the boundary of the subspecies was drawn wrong, or has migrated over time, then this would be the only way or recording it. Actually based on that alone, I can totally see the merit of figuring out things within the zone - I am a believer, but...

I would agree with what you are saying up to the point of "when you have areas of intergration..." in the first paragraph. It would actually give you less data by saying it either is the new subspecies or defaults to the nominal (or another) is incorrect. An individual would either key out to either subspecies or show a blending of characteristics which would most accurately be labeled as the intergrade between the two subspecies. This is actually how it used to be done pre-1950's. This would actually give you much more information and data if you are trying to assess the boundary, without trying to force something into a subspecies category, and help confirm the accuracy of the subspecies boundary (and reinforce they are the same species and not different species with allopatric ranges). Here in Ohio we have Blue and Northern Black Racers. I live in the intergrade zone and all the racers I have ever caught here are easily keyed out to an intergrade with obvious influences from both subspecies. It would be less informative for me to try and force them into Northern Black or Blue category. I mean if two subspecies are coming together they are going to have complete gene flow between the populations and there are going to be intermediates at that zone. One way or another it is important to recognize them. Even if you say "Northern Black Racer showing Blue Racer influence."
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Don Becker
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Re: Garter Snake Question

Post by Don Becker »

Andy Avram wrote:I live in the intergrade zone and all the racers I have ever caught here are easily keyed out to an intergrade with obvious influences from both subspecies.
Do they look about like these?
Image
Image
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