Taxonomic discussion

[mtolypetsupply]

I agree with Gertie, awesome brain candy! But I don't get 80% like Pratty does, I'm down more around the 50% mark, maybe. I request some photoshopping of pics with arrows and highlighting and such so that us newbies can really drink in the depth of this!

Thanks!

[Stefan-A]

I managed to dig up this:.

http://apt.allenpress.com/perlserv/?request=get-abstract&doi=10.1643%2F0045-8511(2001)001[0508%3ACBPDNM]2.3.CO%3B2&ct=1

Cytochrome b Phylogeny Does Not Match Subspecific Classification in the Western Terrestrial Garter Snake, Thamnophis elegans

We sequenced a 307-bp fragment of the mitochondrial cytochrome b gene from 42 individuals representing 14 populations of the western terrestrial garter snake, Thamnophis elegans. Current taxonomy recognizes either five or six subspecies of T. elegans based on color and scale morphology, but all agree on three major geographic races (T. e. elegans, terrestris, and vagrans). Although the cytochrome b phylogeny did not match subspecific classification of the populations, it did yield geographically proximate groups. Populations from the Sierra Nevada range and Monterey, California, formed one monophyletic group of T. e. elegans and T. e. terrestris. This Sierran/Monterey group was included in a larger group with eastern populations from the Great Basin (T. e. vagrans). The other well-supported group was comprised of populations from the western Great Basin (T. e. vagrans). One population from the northern California coast (T. e. terrestris) was basal to both groups of populations. Thus, neither T. e. vagrans nor T. e. terrestris formed monophyletic groups. Average percent sequence divergence between the outgroup (T. sirtalis) and T. elegans was 7.9–12%. Within T. elegans, divergence among populations ranged from 0.3–7.7%.

http://www.eeob.iastate.edu/faculty/...arn2001cop.pdf

[Garter_Gertie]

Steph, what a GREAT idea! That would be so helpful!

[Zephyr]

I like it here in MI... Where it's either T. sirtalis sirtalis, T. sauritus sauritus, or T. butleri butleri.

[ssssnakeluvr]

I managed to dig up this:.

http://www.eeob.iastate.edu/faculty/...arn2001cop.pdf

interesting article.....some of the terminology lost me...but I get the idea...needs more genetic research..good reading!

[Steven@HumboldtHerps]

I managed to dig up this:.

http://www.eeob.iastate.edu/faculty/...arn2001cop.pdf

Thank you so much for this article Stefan. You don't know how much enthusiasm it has injected into my bloodstream. I am virtually foaming at the mouth! Although I am many classes away from understanding the genetic details (basically, how these tests are performed), I do understand cladistics, and the results are clear to me that ONCE AGAIN we are reminded of just how much more testing needs to be done. The results of this article do however tell me that the terrestris nomenclature is not necessarily dead yet! So far, it only implies that the Monterrey terrestris specimens need reassignment to the Mountain Garter (T. e. elegans) clade. The vagrans groups are of course also in need of revision.

So what do I mean when I say I don't think the terrestris group is "dead" yet? I am referring to the Coast garters here in Humboldt. The article says this population is basal to the other clades, meaning there are fewer derived characteristics in Humboldt Coasts than in all T. e. elegans and vagrans elswhere. Thus, one could technically keep the nomenclature for this particular group. The next question is where do the known regions of all previously known Coast Garters diverge; somewhere between Monterrey and Humboldt? Is there an obvious geographical barrier somewhere? Is there intergradation between subspecies? The fact that Humboldt Coasts have been singled out is especially fascinating to me because of all of the crazy Coast morphs I come across here in Humboldt County.

I would like to illustrate or explain some simple cladistic terminology in my next reply to this thread, but I have to run a few scans of the paper Stefan referred to me. I feel this is necessary - good for a garter forum, especially for all of you who aren't science majors, but would like to learn more about species relationships.

[Steven@HumboldtHerps]

Hello again! So we're discussing (We are?!):

"Cytochrome b Phylogeny Does Not Match Subspecific Classification in the Western Terrestrial Garter Snake, Thamnophis elegans"

by Anne M. Bronikowski and Stevan J. Arnold (Copeia, 2001 (2), pp. 508-513)

I scanned the charts and map (Hope I don't get in trouble) and outlined what I think the results mean to me. Please do your own research, and respond accordingly, for I am one who loves it when I have to stand corrected. All good research aims to disprove as as well as prove a theory! Short primer first.

Back in the ol' days (not too long ago!) taxonomical divisions (the Linnaeus system - which was brilliant for its time - until molecular biology came to town...) was primarily based on morphological (anatomical) features, similarities and differences. A lot of the species' organizations were right on! Genetic research has changed some of that. The new system is known as cladistics, it uses many of the traditional classification terminologies such as Kingdom, Phylum, Class, Order, Family, Genus, species / subspecies (epithet), but the classification is based on groups that have shared derived characteristics that stemmed from one common ancestor. Thamnophis is a pain when it comes to comparing morphology; they are so variable in their expression. For those of you who are familiar with the taxonomy you know a lot of the genetic research done so far may only be scraping the surface of what may still be revealed. Branches on a cladogram (cladistic tree) may represent either a monophyletic group, a paraphyletic group, or a polyphyletic group. Taxonomists always want to end up with a monophyletic group; this group is composed a of a single common ancestor and all its descendants. A group that includes the common ancestor and only some of the descendants is paraphyletic. A polyphletic group shows descendants, but not the common ancestor (this one doesn't help at all).

Here is the T. elegans cladogram. You'll notice it includes the outgroup used to test elegans: sirtalis. T. sirtalis and T. elegans share ancestry, but are quite distinct from one another. Call it a control group... I honestly recommend reading the paper; I personally had to gloss over a good part of the "Materials and Methods".

The colors used should be self-explanatory when compared to the map, but basically: RED is the entire group of those T. elegans tested (incl. elegans, terrestrus, and vagrans); ORANGE is the sirtalis outgroup; AQUA is the Sierra/Shasta Mountain Garter and Monterrey Coast Garter grouping (clade) which has close lineages (YELLOW, LAVENDER, & PINK) with Wandering Garters in the eastern Great Basin (BLUE) - This group mentioned so far comprises the LIGHT GREEN. Wanderings in the western Great Basin (BROWN) are a sister group to LIGHT GREEN; likewise our lonely Humboldt Coast Garter seems to create a 3rd group. This new cladistic interpretation shows 3 different groups of elegans (PURPLE or RED) that have one common ancestor. I understand how sister taxons can be separated over time as in the case of western Great Basin species being different from their western and eastern "cousins' (Just look at Sand Boas and Rosy Boas!), but what's the deal with the Humboldt terrestris (if that's what we're still going to call it...). Is it an ancestral line? Does it look like other groups simply because of convergent evolution (when 2 species with no immediate common ancestor and often from different latitudes around the world look similar because of adaptations to the similar environment they both live in...Compare Central American Eyelash Vipers to Tanzanian Bush Vipers!). Or even if we could go back in time and see the common ancestor of these 3 groups, would we be able to tell the difference even then?

Ah, the questions I have! I need to find these scientists and volunteer to find samples for them or something.

Thanks for your patience.

Steve

[aSnakeLovinBabe]

I am glad that I am actually able to understand this stuff


I do not however... take the time to study too much of it past which snake are which species... primarily because we are humans applying strict and exact labels to things that are constantly changing and evolving around the groups we put them into. Our labels can only be so exact... and who gets to decide who is right and who is wrong? When is that exact moment that an isolated population of a species has changed enough to be its own species? When in reality... it is still what it originally was... just slightly modified! And will continue to change... forever! Who are we to make up names and stick them on everything? In the eyes of the animals... it is totally irrelevant. A snake is a snake no matter what his lineage, and unfortunately we will never be able to truely label a snake that is on the fence like the ones in the pictures without knowing his exact ancestry. We could speculate until the end of time.. but it will never reach a definite no matter how many agree. And even when you have a captive bred specimen... you can never actually be 100% sure that a parent of a snake does not have some tiny amount of another species or subspecies in it. You can be 99, but you can't be 100. So it's all very confusing and there are never true definites other than the assumed ones. That is the only reason I really don't bother joining in on stuff like this.

personally.... I am positive that the san francisco garter is doomed, as it stands now. Even if they did somehow make a comeback... which is doubtful considering the vast majority of the world does not give two sh*ts about snakes and will not move over or stop to avoid smushing one with their car... (hell some will even aim for the snake) And simply not enough land or snakes remains for them to make a sufficient comeback. Inhabitable land even in protected zones will get smaller every year due to the usual pollution and drying up of ponds and creek beds. If the species does somehow make a comeback... They will have expierienced such a tight genetic bottleneck that they may eventually phase out anyway... they will basically be genetic clones of one another... much like the way cheetahs went through. Yes, it is sad, yes it is awful, and no one wants to see the beautiful snake dissapear... but I simply do not see much hope for them unless a taxonomic change is made to group san frans and cali red sideds closer together. When I look at a San fran... I see a striped cali red sided... but that's just me and I have never had the opportunity to study any of it in detail.

[Stefan-A]

When is that exact moment that an isolated population of a species has changed enough to be its own species?

The linnean system wasn't designed to take evolution into account. Had the guy lived 150 years later, we might have ended up with a much more accurate method of naming and classifying organisms.

[Garter_Gertie]

And that's why we're changing the process, Stefan, because we know more now than 150 years ago.

Just think what scientests will be able to do 150 years from now.

But always, I think, we're getting closer and closer to either grouping better or realizing it's fruitless.

Fascinating.