Reptile & Amphibian Forums

Desert flats stretching east to the Sierra Madre Oriental, north of Doctor Arroyo, Nuevo Leon, Mexico. Many thayeri have been found in this vicinity.

Dan
www.serpentsonline.com

Another beautiful shot, and thayeri country no less! High resolution copies of these would make fantastic dessktop wallpaper. You do take some very nice landscape shots.

Mike

That looks quite different than mountainous the habitat near Iturbide. Do you know the elevation?

Very good observation Aaron. This area is indeed different than Iturbide.....no steep canyons or rock cuts, just desert scrub. Iturbide is more sub-tropical. Off hand I do not know the elevation, but I'll try and get that info and post it. Perhaps Bob knows, he had a very good map on our trip.

DV

That stretch runs about 5600–6500 ft (1700-2000 m) elevation, but it's on the western side of the Sierra Madre Oriental, and thus in a rainshadow.

BH

Dan, Bob, Jason, and others lucky enough to see L. m. thayeri in the field,

Are the two different phases, Milksnake phase and Leonis, more or less prevalent than the other phase in certain types of environments? I know MSP is dominant over Leonis, so I would expect more of them but certain areas may have more Leonis phase than other areas.

I can use Cal Kings as a good example; the banded form is dominant but in grassy coastal areas in Southern California, approximately 1/3 of the Calkings found are striped. However, if you go to the desert or mountain areas, a striped individual is rarely encountered.

I am just curious; my first thought would be Leonis were more common in the lower elevation flood plains (like the arroyo you pictured) or grassy areas.

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Rick
Never Enough
Reptiles

Rick:

Your question about association of pattern type with habitat is a good one. Presently, there are probably too few specimens with locality data to make sense of things. The temptation for us as biologists is to assume, justifiably, that color and pattern matter in the context of natural selection, and that these are traits that typically undergo strong local selection pressure for reasons of survival. Maybe MSP snakes occur in more verdant settings closer to the range of venomous coral snakes, and thus the MSP thayeri can be conveniently explained as a traditional mimicry system. I do believe that all of the most eastern specimens--those coming from "greener" environments--have been tri-colored, but these also turn up in other parts of the range. Melanistic ones have been found at both the northern and southern ends of the range. So, at this point we just don't know, but it sure is interesting to speculate as to what is going on. After all, how many species of snakes on a worldwide basis exhibit such incredible diversity of pattern and color? An explanation for that remains elusive...but that's part of the allure of field work!

Cheers,

Bob

Bob,
Thanks for fueling my speculation further. I suspected the number of specimens would be low but hoped that a pattern of leonis phase distribution had surfaced. Unfortunately, I’m not a field biologist (I missed my calling). I’m just someone that has 90 minutes to think too much while driving home everyday.

Using my Calking example, that I think works pretty well as a comparison. All phases, banded (MSP), striped (Leonis phase), and melanistic can and do occur across the entire range. Banded (MSP) is the dominant form and therefore constitutes the majority of individuals. However, certain environments allow the other forms to flourish more than they would in a different environment. I guess what I am trying to say (purely a hypothesis) is that it is not natural selection for a certain trait that makes it more prevalent in a given area but a “lack of selection” against a trait that allows it to occur in higher numbers.

Striped Calkings would seem to have no advantage over banded in a grassy environment, but likewise, in that environment, there is no disadvantage to being striped either so they survive to reproduce in higher numbers than they would somewhere else.

Hope I make since, even though none of this matters at all to a hobbyist like me, that is only breeding domesticated livestock. It still interests me though.
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Rick
Never Enough
Reptiles

Rick:

Idle speculation can, at best, be productive, and at worst, merely interesting! Because color/pattern is such a conspicuous feature of snakes--our instincts suggest, and an extensive body of literature supports, the notion that these are the byproduct of strong selection pressures. This is more obviously true for some groups than others--high degree of substrate matching (= crypsis) in horned lizards, for example. Also, there are a number of studies that explore the relationships (in snakes)among body form (short, stout vs. long, slender), color pattern (banding vs. striping vs. unicolor, etc.), responses to danger (flight, defensive display, crypsis, and habitat type. For example, slow-moving snakes are usually blotched, ringed, or unicolored--almost never striped. Fast-moving diurnal snakes are typically striped (with stripes fading out on tail) or unicolored, almost never blotched or ringed. You can make a list of species that you are familiar with, and then think about how and where they live, how they are patterned, what sort of defensive response they employ, etc. See if common themes emerge.

Cheers,

Bob

Dan, Bob, Jason, and others lucky enough to see L. m. thayeri in the field,

Are the two different phases, Milksnake phase and Leonis, more or less prevalent than the other phase in certain types of environments? I know MSP is dominant over Leonis, so I would expect more of them but certain areas may have more Leonis phase than other areas.

I can use Cal Kings as a good example; the banded form is dominant but in grassy coastal areas in Southern California, approximately 1/3 of the Calkings found are striped. However, if you go to the desert or mountain areas, a striped individual is rarely encountered.

I am just curious; my first thought would be Leonis were more common in the lower elevation flood plains (like the arroyo you pictured) or grassy areas.

-----
Rick
Never Enough
Reptiles