Reptile & Amphibian Forums

I am very new to Mexicana and i am learning as much as possible. My wife thinks I have lost my mind. Anyway my question has to do with ranges and intergrades among Mexicana subspecies. Does it happen? Or is this something that has happened in the recent past with hybridizers? Any thoughts would be great.
Thanks,
William

Good question!

Short answer...no.

Long answer...there is zero evidence of recent gene exchange (i.e., intergradation) in the wild between mexicana-group kingsnakes (greeri, alterna, thayeri, mexicana, ruthveni--maybe the new species webbi belongs in here as well). Each of these occupies discrete areas in Mexico and their ranges do not come into contact with one another. Currently, ruthveni, alterna, and webbi (if webbi should be part of this) are regarded as distinct species, with L. mexicana comprised of three subspecies (mexicana, greeri, and thayeri--although thayeri is not universally regarded as distinct from mexicana mexicana). However, much of the current taxonomy of this group is old...dating from the 1960s, when samples from Mexico were few and far between, and concepts about species and subspecies were different than today. I won't say much more for now, other than to let you know there is work in progress that involves gathering of DNA samples from specimens throughout the collective range of the group, with a goal of determining how many species should be recognized in this group and identifying relationships among them.

Meanwhile, some breeders have for many years made inter-species crosses between mexicana-type snakes, as well as with things like pyromelana and zonata, and probably triangulum too. There are numerous examples of such "mutts" (hybrids, crosses, whatever one wishes to call them) both on this forum and in the Ksnake classifieds, often unrecognized as such by their owners. The experienced breeders can spot them. Sometimes, though, the distinctions are subtle, as when thayeri is crossed with ruthveni to bring an albino gene into thayeri; the hybrids are repeatedly backcrossed to the thayeri parent so that eventually one ends up with snakes sold as thayeri and that look remarkably like thayeri, but that are not thayeri. Or when thayeri is crossed with blair's phase alterna--the result is a thayeri-looking snake with unusually wide saddles--something one does not see in pure thayeri. The collector new to this group of snakes has no idea--how could he or she?--but if they stick around long enough they'll realize what they've got. All of this illustrates why most mexicana-group fanatics are very careful about where they acquire their animals, wanting to ensure that they're obtaining the "real thing". To other folks, it's not that big of a deal (but I am not among them).

Sorry for the long response! Here's a pic of a thayeri x pyromelana hybrid, showing the characteristic pyro white snout:

Cheers,

Bob

Bob,
Actually a long answer was the best, greatly needed and appreciated. I have read through a lot of past posts and seen discussions on hybrids, but nothing covering possible intergrades.
Thanks for the information and I look forward to any info that comes out of the DNA testing project. I feel projects such as that would go a long way to solving issues that are fought out regularly on other species as well.
Thanks,
William
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1.2 Thayeri Adults
0.2 Thayeri Sub-Adults
0.1 Thayeri Yearling
1.2 Thayeri LP '05
1.1 Anery. Hondos '05
1.0 Tang. Het Hypo Hondos '04
0.1 Tang. Hondo '04
1.0 Tang. Hypo Hondo '05
0.2 Tang. Het Pinbanded Hypo Hondos '05
1.1 Tricolor Het Albino Hondos '05
2.0 Jurrasic Kings '05
1.0 Alb. Striped Cal King '05
0.1 Banana Cal King Adult
1.1 Pueblan Adults
1.1 Sinaloan Adults
1.1 Alb & Normal Nelson Adults
0.1 Alb. Leopard Gecko

Nice reply. I still think its next to impossible to say with certainty that any of ou stock is 100% unadulterated thayeri. It should also be mentioned that geographic isolation of these forms is a current event. In the past their ranges likely overlapped and given climate change is a constant the ranges will likely overlap again in the future. Its a long view but a neat one.

Here's one way to frame this question/problem. Envision the range of thayeri, for example, as a narrow ellipse running north to south. At the northern end of the ellipse, alterna approaches, although there is not any known overlap in their distributions. At the southern end of the ellipse, there is a gap of, let's say, 60 km before one encounters mexicana populations. IF thayeri and alterna formerly shared a common gene pool, one could predict that northern range thayeri and southernmost alterna would each retain evidence of this historical contact--such evidence could be in the form of genetic similarity and might (or might not) be manifested in shared characters of color and pattern (e.g., do northern thayeri have the silver iris of alterna?). A similar test could be constructed for the presumed historical connection to the south, between thayeri and mexicana. These questions are straightforward on paper, a bit more problematic to actually resolve--you've got to get permits, funding, specimens from those critical in-between zones, and hope that sense can be made of the genetic data. Additionally, assuming (as most of us do), that mexicana-group snakes share a common ancestor, it might be possible using genetic distance data to establish broad timelines for when range separations (speciation events) took place.

Just food for thought.

cheers,

bob

I find this subject very interesting however; I do have some questions for the experts (of which I adamantly announce - I am not).

First, 60 km is nothing; now for one little snake 37 miles is daunting but to a population of little snakes; that is nothing. Their habitat is generally rough and inaccessible, how can anyone be sure where the population ends and the next begins? Unless there is a physical barrier, arid desert, large body of water, alpine mountain range etc that makes the range obvious, how do you know? With the limited ability for researchers to study the populations, how can the ranges be so well defined? When I visited with Richard Hoyer (Rubber Boa researcher) a few years ago, he told me of finding a Cal King over 100 miles (160 km) north of the reported northern most range. That one snake probably didn’t wander 160km, more likely, the population at the extreme of the range was so sparse that it went undetected, in 40 years he found one that far north.

There was also an MDNA study done on Rosy Boas (I’ll find the paper eventually) that showed an approximate eight percent difference in MDNA between the northern and Southern populations. Geology shows that these populations were separated approximately 11,000 years ago by a shallow sea and have more recently been reconnected. The populations are considered the same species, just different ssp, they freely interbreed and produce viable offspring. That would be like saying Humans, Gorillas, and Chimpanzees were all just ssp of the same species. My point is, what percentage of difference in MDNA is enough in Reptiles (colubrids specifically in this case) to warrant species status or even ssp status? The sample size was very small in this study.

It’s all very confusing to me, but interesting.

Rick:

Those are good questions. Hanging out with Hoyer can cause that! I made up the 60 km figure, as I'm not sure what it is (we just don't know). Frankly, though, distance is irrelevant. Stuff is where it is...and then we can try to figure out why by looking at climatic and geological history, and ecological factors. The key, though, is what I described above.

Here's another way to look at it. If "thayeri" turns out to be a cohesive genetic entity (the fancy term for that would reciprocally monophyletic)--meaning that all populational segments of thayeri are genetically more similar to one another than any of them is to alterna or mexicana. If that is the case, then game is over...there is no doubt that thayeri is a species distinct from the other guys. It does not matter whether these different forms meet or have physically distinct ranges--the critical issue is what happens at the edges, and this is definitely testable. Nor does it matter that all of these things are interfertile in captivity--the important question is whether these forms show evidence of recent or ongoing gene exchange.

As for your question about what level of genetic difference equates to distinct species...there is no pat answer, and my attempt to answer this here would be long and confusing. Maybe over a beer someday! Generally though, different groups of vertebrates show different patterns of genetic difference as it relates to species-level thresholds, probably a consequence of different generation times, dispersal abilities (birds fly, small salamanders move very short distances), and home range sizes.

In summary though, the next chapter on Mexican Lampropeltis will reflect whatever the evidence suggests, and not my speculation! Hope I did not confuse you any more.

Cheers,

Bob

Bob,
I hate to bring this up again, but I want to.....HAHAHA
What about the Lampropeltis found in Jalpan, Mexico by the Barkers? Should they be labelled as L. m. mexicana (San Luis Potosi) or L. ruthveni (Queretaro)? As you know better than I, Jalpan is actually in the state of Queretaro, the northern part.

Are they Ruthveni found far north of their range or are they Mexmex found far south of their range? Or maybe a bigger question......Are they an isolated species of Lampropeltis that will be named at a later date?
My own personal belief is that they are intergrades between the "modern day" (I will explain the term in a bit) Ruthveni and Mexmex, thus the 'milksnake' look to them?

The reason I think this is along the same lines of Rick's thinking......Snakes DO NOT read maps.......LOL

Seriously.........What is between Valle De Las Fantasmas and Queretaro?????? Jalpan is........What geographical, environmental, topagraphical or ecological barricade is in place to stop these two species from intergrading?
I think these isolated populations did, in fact, occur due to environmental influences, but once they adapted to them they (creating the 'modern day' species) became able to expand and breed with other isolated populations that had gone through the same evolutionary process as themselves........
Wow that was deep for me........LOL
But that is merely my hypothesis.....I wish I had the means of proving this to be true or false........
John Lassiter

John:

Okay...well, the Barkers never found anything in or near Jalpan (Dave confirmed this just a few days ago). Some years ago, there were three snakes collected in the mountains west-northwest of Jalpan (which sits at lower elevation in the Jalpan Valley). These snakes eventually ended up with Steve Hammack, and at least for a period were bred and sold as L. triangulum smithi--nobody really knew what they were, and apparently there was some variation within the original group, such that some folks thought they were ruthveni, mexicana, or triangulum. What a mess! There is more to this story, but you're getting the short version.

A tissue sample was obtained from one of those original snakes, and when Rob Bryson did his initial mt DNA study of mexicana group snakes, that one Jalpan snake came out as the same thing as the sample from Amealco, Queretaro...which of course is ruthveni. So, what we know FOR SURE is that at least ONE of the snakes taken in the mountains near Jalpan was a ruthveni. Is it possible that another species (mexicana) occurs there as well and was collected as part of that original group? Maybe.

So, we can speculate until the beer runs out, but at the end of the day we come back to the evidence. The evidence says...that ruthveni occurs in the mountains near Jalpan, and of course we know that L. t. dixoni occurs in the lower elevations around Jalpan proper. We agree that further exploration is needed in those areas. When new evidence is obtained, either via the collection of new material or when the next round of genetic work is completed, we'll see where it leads.

Cheers,

Bob

Okay.......I guess I will have to take your word on it all.......LOL

I guess that is the reason things are questioned.......One person says to himself, "well....how do I know that is true. I guess need to go figure it out for myself......" I wish!

BTW Bob,
I appreciate all your insight and the fact that you are willing to share some of it here on the forum for us to experience....

John Lassiter

John:

Well, I really DON’T want you to take my word for any of this (and I know you’re kidding). This really isn’t about what any one of us believes, thinks, hopes, etc., but rather having an objective means of examining evidence. Obviously, not everyone is in a position to personally conduct fieldwork in remote areas of Mexico, or to have access to molecular labs for genetic analysis, or to have the training necessary to do data analysis. But, we can all try to get a handle on how such problems/questions are approached by scientists—in effect, they become our surrogates by doing the research and publishing the results in peer-reviewed outlets.

And, you are quite welcome. Happy to share my meager thoughts on the subject!

Cheers,

Bob

"that all populational segments of thayeri are genetically more similar to one another than any of them is to alterna or mexicana. If that is the case, then game is over...there is no doubt that thayeri is a species distinct from the other guys"

Can't quite swollow that. Look at the boa example, when (not if) ecological factors change such that the populations are rejoined is the time we'll know if speciation has occured. Of course this opinion as it relates to thayeri is based on my understanding that populations of mexicana are geographically isolated. That may or may not be the actual case.

Tony:

I'm simply paraphrasing what would be considered standard operating procedures for scientists who practice phylogenetic systematics. Whether or not two "things" will interbreed in nature is not considered a useful indicator of species-level differences.

When making decisions about whether any particular group of snakes, lizards, rats, etc. has reached a species-level threshold, we rely on present evidence (which takes into account the history of those various lineages)--it is impossible to try to predict the future and so we don't bother. For example, Lizard Species A occurs only on a small island off the coast of the mainland, where Lizard Species B is widespread. Studies indicate that A and B shared a common ancestor XX thousand yrs ago, but that now there are fixed genetic differences between them, and they differ in other characters as well, and so are considered separate species. The sea level separating the small island from the mainland is quite shallow, and geologists predict that during the next ice age sea levels will lower and there will once again be a positive land connection between island and mainland. A and B will be in contact (assuming that the cooling climate doesn't simply wipe them out!). Possible outcomes of this reconnection are: 1) No interbreeding...each species maintains its genetic integrity; 2) there is limited hybridization, such that F1 hybrids are occasionally found but there is no evidence of backcrossing. Both A and B would still be regarded as distinct species that hybridize rarely. 3) A and B freely interbreed, produce fertile offspring, and over time B is genetically "swamped" by A. Depending on what results, you'd be left only with Species A, or perhaps something that is a bit different (reflecting the genetic contributions of B) and thus scientists name Species C to reflect this. It could be fun to speculate about what might happen in another million years, but it's not part of the current approach to sorting things out.

Cheers,

Bob

Agreed, just pointing out that our little system is often inadiquate to the task. Too often have to pound square pegs into round holes. I know the big guys entertain threshold levels of differences to make "their" determination of species status but the hall mark of a species remains reproductive isolation and I don't believe that is messesarily fixed at the species level.

Bob, thanks for responding in “semi-dumbed down” terms that I could mostly understand. I also appreciate not being “flamed” for being ignorant in the scientific realm as I commonly see on other KS forums (I think it discourages people like me who want to know more but are nothing close to experts in the field).

Yes, it was a thought provoking morning spent with Mr. Hoyer. He did not know me from a hill of beans but still took the time to drive/hike all over Western Oregon taking me to, what should be, secret study sights (my lips are sealed). It fulfilled a 30 year goal to see a Rubber Boa in the wild (saw two). I also learned that shorts are inappropriate wear for hiking through the brush (poison oak & berry vines) of Oregon.

Where do I get the “next chapter on Mexican Lampropeltis”?

I guess I still have a problem with your statement (and believe me it’s not personal)

“If "thayeri" turns out to be a cohesive genetic entity (the fancy term for that would reciprocally monophyletic)--meaning that all populational segments of thayeri are genetically more similar to one another than any of them is to alterna or mexicana. If that is the case, then game is over...there is no doubt that thayeri is a species distinct from the other guys.”

Because, (hope you can stay with my layman’s thinking) even if the thayeri population is a cohesive genetic entity; if the MDNA variance with the next closest cohesive genetic entity is not outside of normal deviation then how can it still be considered a distinct species? It sounds like “an acceptable, normal deviation” is not known. With the Rosy Boa example, an eight percent difference in MDNA between populations could certainly warrant two separate species of Lichanura, at the vary least form a hypothesis to be researched further. However, the difference between North West and North East populations of Lichanura are 2 to 3 percent, which MAY not warrant distinct species recognition. What is the acceptable difference between cohesive genetic groups?

Are we supposed to be having a beer now?

I hope I have framed my question coherently.

When you are through “figuring out” mexicana, can you decipher the Central American Milks, one wide-ranging ssp. or the mess we have now?

without a doubt. I think I'll go back to just posting fuzzy pictures of thayeri. I like this girl from last year.

Rick:

Don't worry, you're doing fine; I would say I'm trying to describe the questions/problems in straightforward terms, rather than "dumbing down". This can be pretty arcane stuff for people not formally trained in evolutionary biology, and it's only gotten more so since I was in grad school (over 20 yrs ago)--harder than ever to keep up. But, you are right...we're now at the adult beverage stage...we need a chalkboard and John Madden to go any farther. Honestly, this would be easier to explain with some diagrams and a map of Mexico (and some Corona or Modelo Negro)--not that it will reveal answers, but at least it will be easier to understand the nature of the problem and how evidence is evaluated.

All for now!

Cheers,

Bob

for all the information, I appreciate it and look forward to hearing/reading about your research in more detail (don’t wait too long). Although realistically, as a hobby breeder, what I have is less important than what I believe I have as long as I like them. The natural history and taxonomy is extremely interesting to me though, not sure why. Maybe I should have been a Biologist instead of flying around in helicopters (I don’t even get to do that now, they say I’m too old and falling apart).

Are you ready to tackle the Central American Milks yet? I loose sleep at night thinking about how messed up their taxonomy is (I’m kidding).

Rick:

You’re more than welcome. We all have different levels of interest in this, but for many (I think) it is helpful to try to make some sense of the natural history of our animals. For example, I suspect that people who keep gray-banded kingsnakes derive even greater enjoyment from them after having spent time in the field searching for them. They then have at least some idea of where and how the snakes live, and perhaps an enhanced appreciation for them. Knowing something about the evolutionary history of the group is part of this.

I don’t have any clues on tropical milksnakes (well, maybe a few, but they're just informed hunches), but I think there is at least one group of researchers actively involved in gathering tissue samples—hopefully for all of “triangulum” (which we all suspect is really a hodge-podge of several species). However, I can’t offer any information about their progress or a timeline for publication of results. Obviously, when that work is completed, it will be of great interest to many folks.

Cheers,

Bob

Like the boa example. In that case seperation was not sufficient in duration to allow complete specieation. IMHO the same would happen with Mexicana should there populations ever find themselves in contact again.

As for the percentage of dna difference that is required to complete speciation I think thats the wrong way to look at it. The dig issue is how the change effects the population's biology. In theory even a small difference could could result in reproductive isolation while at the same time large differences may not.

I'm not an expert either but I do like to look at populations as being very dynamic. Its just much more interesting to me that way and is the main reason I sometimes rile against the locality concept. Seems to me that some of the more vocal locality proponents are locked into the here and now and miss the wider view even as they assert that their way reflects appriciation of natural history.

>However, much of the current taxonomy of this group is >old...dating from the 1960s,

I thought Gartska's 1982 study was the current taxonomy of this group? I also thought he did away with all the subs in mexicana?
I know his study isn't widely accepted, but I still thought this is where current taxonomy stood on them?
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Ace

Ace:

You are correct in that we are mostly using Garstka’s 1982 taxonomy, although there were some other players preceding him that have influenced our thinking. For example, Gehlbach & Baker (1962) reduced greeri to a ssp. of mexicana a mere one year after Webb described greeri as a new species. A few years later they (Gehlbach & McCoy, 1965) went one step farther and claimed that the type specimen of greeri was actually an intergrade between alterna and mexicana mexicana (and thereby zapped greeri from the taxonomic landscape). The two most recent publications involving this group, by Hilken & Schlepper (1998, a semi-popular article in German), and Bryson et al. (2005; species description of L. webbi) regard greeri, mexicana, and thayeri as taxonomic categories at some level, although this is not formalized.

One must also bear in mind that those older (circa 1960s) taxonomic works most definitely reflected the thinking of their time. For example, if we were starting from scratch today and trying to sort out the various mexicana-type snakes, we’d undoubtedly set them up as stand-alone species (subspecies have pretty well vanished from modern herpetological systematics) pending evidence to the contrary. 40-50 years ago, however, it was common to regard things like getula, triangulum, Pituophis, tiger salamanders, etc. as being single species with an enormous range and consisting of numerous subspecies. As each of these wide-ranging ‘species’ is analyzed using modern systematic tools and with additional evidence (esp. molecular) at hand, one by one these single “species” turn out to be groups of related species. This should not be dismissed as the old “lumpers vs. splitters” dichotomy, but rather the inevitable development of more rigorous and more objective analytical tools, as well as a better understanding of the nature of species.

Cheers,

Bob

Thank you for the history lesson, I was going to get a few books/journals from Herplit as a Christmas present to myself, looks like I have some new studies to look for! I can't wait to see what comes of the DNA study!
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Ace