Reptile & Amphibian Forums

Hey Shannon and Aaron,

Thanks for posting the pics liked I asked. I just now saw the ones Aaron put up (I forgot to look!! getting old here).

That area north of Study Butte is ripe with atrox X scutulatus hybrids. I was thinking you may have found one there, but I have not seen one with that color. However, after seeing Aaron's photos, I think it is an atrox just exhibiting good old atrox variability. It could also be an F2 or greater backcross, but the head scalation makes me stick with atrox.

Thanks for sharing. Sorry about the rattler post on the alterna page - at least it is winter!!

I'm curious about this because at least several times a year I hear someone mention the rampant overun of hybrid rattlesnakes in west Texas...

What is it that determines a genuine hybrid? I've found my share of scutulatus and atrox throughout the trans-Pecos, southern New Mexico, and southern Arizona. I have seen west Texas atrox with low band counts and strange patterns on their tails and scutulatus with higher caudal band counts. I've spent a significant amount of time in high prairie where scutulatus and atrox occur together (and in pretty substantial density). I have never seen even a marginal specimen that upon close inspection did not yield a definitive identification as one or the other. The scutulatus and atrox in west Texas are certainly different from other populations and may have some abberencies that typically serve to easily distinguish one from the other, but scutulatus still have only two scales between the supraoculars.

Does anyone have photos of any hybrid scutulatus X atrox?

I've attached a link to some research but here's the abstract:

An Evaluation of the Possibility of Hybridization between the Rattlesnakes Crotalus atrox and C. scutulatus in the Southwestern United States - James S. Jacob

Abstract
The possibility that Crotalus atrox and C. scutulatus might hybridize in southeastern Arizona-southwestern New Mexico or in the Big Bend region of Texas was analyzed morphometrically and electrophoretically. Intraspecific variation and interspecific overlap in key morphological characters has led to the incorrect assumption that these species hybridize. Even though they are syntopic primarily in an unstable desert-grassland ecotone where habitat differences are not evident, C. atrox and C. scutulatus are morphologically and biochemically distinct.

Link to paper

Damon,
First the paper you cited was authored in 1977.
Secondly, there is no doubt in my mind that atrox, scutulatus, AND molossus hybridize on that prairie you mention. As sure as I am that they do, how could either of us be so sure just by looking anyway? At the very least I've seen some up there that would generate some healthy discussion (possible molosuss x scutulatus).

Like Hugh said, once an hybrid is back crossed it gets really difficult sometimes. FR just posted an interesting photo on the kingsnake forum, you should check it out.

The grasslands are a mere shadow of what they were 200 hundred years ago. The habitat alteration has untold effect on populations including displacement and hybridization. IMO it happens in at least three localities in Texas with regularity.
-----
http://www.hcu-tx.org

I realize that hybrids have occurred. I'm not arguing that (although I do consider it to be more of a rarity). My argument is that just because a snake looks a little different doesn't mean that it and its relatives have been buggering their way around the prairie. Shannon's snake below is a good example. That snake says nothing to me other than "atrox". If atrox and scutulatus are hybridizing why don't people see animals with some median number of scales between the supraoculars? I've had so many people show me "hybrids" that are simply misidentified that I really question the idea (not of hybridization, but of wide-scale hybridization).

I saw Frank's photo... one of very few photographs I've seen that looks to in fact be a hybrid (the published shots of the willardi X klauberi from the Peloncillos looked obvious too). That's very different than the "it looks weird so it must be a hybrid" idea. In most cases, the simplest biological hypothesis is often the correct one. Could west Texas simply be imposing some sort of convergent crypsis or is there a big Crotalus orgy going on? I just can't buy the second theory and certainly haven't seen enough evidence to budge my impressions.

I realize the paper research is old, but at least it's research and not "gut feeling". I'd love to see some photos of questionable animals and since so many of the folks who post here spend time in the field I figured it would be a good time to solicit for photos. I'll dig up some of mine and post them later tonight. Gotta go start dinner

Here's a handful from the cobweb covered recesses of my hard drive.

Any guesses?

#1

#2

#3

#4

#5

#6

#7

#8

1-6 atrox
7-8 scut

I'll look again, but that's what I see off the top of my head.
-----
http://www.hcu-tx.org

"Something can be rarely observed without being rare."

I totally agree, but rare observations are not the issue here. Sample sizes of rattlesnake sightings in west Texas are far from small and yet no one's provided any proof that hybrids are anything less than very rare.

Find me a scut with more than two scales between the supraoculars or an atrox with just two. In west Texas, atrox and scutulatus both occur with "abberencies" (relative to conspecific counterparts from other regions) in tail markings, eye-striping, and pattern. Just because scuts from west Texas look more like atrox than they do scuts from southern Arizona doesn't mean the scuts in west Texas are breeding with atrox.

Frank's photo of the "molossus x atrox" is neat because it's novel. I've never seen another photo of a coon-tailed molossus. I've certainly never seen a Crotalid in the wild that looks as much like a hybrid as Franks. The argument that a backcross suddenly disguises 90% of the traits that would diagnose a specimen as a hybrid seems to be a little convenient.

I don't think we are far off from each other.
It's obviously not the norm or there would be many more observations.
-----
http://www.hcu-tx.org

Damon,
did you notice this citation?
Venoms and Morphology of Western Diamondback/Mojave Rattlesnake Hybrids
Steven D. Aird, Luke J. Thirkhill, Corrine S. Seebart, Ivan I. Kaiser
Journal of Herpetology, Vol. 23, No. 2 (Jun., 1989), pp. 131-141

I don't have the whole citation, but I bet you know where I'm going with this one (venom).
-----
http://www.hcu-tx.org

I think those hybrids were produced in captivity... different beast entirely.

Search that abstract and see the first page of the paper on J-stor. He (criticized) Jacobs for incomplete data. You have to have tons and tons of data to tell the whole story.

The only thing absolute is that is does occur. The frequency is debatable. It happens in certain places for various reasons. It happens in a multitude of species. I even read somewhere that hybridization has resulted in speciation more than once.
-----
http://www.hcu-tx.org

males just want to mate, even if it's with a dead atrox

-----
http://www.hcu-tx.org

How do you know she / he wasn't just playing dead???

"Males just want to mate." That is probably the most unrefutable statement on the forums!!

Jacob had incomplete data only in so much as he wasn't aware of the type B venom monologue. There was nothing lacking in his scientific design or the results he acheived with the type A animals.

The paper indicates that the type B monologue in scutulatus (which is found predominantly in Texas) is qualitatively very similar to atrox venom. Are you insinuating that's due to hybridization there? I'd assert that scutulatus and atrox are more syntopic in west Texas and habitat utilization seems to be more homogenous there than in other areas where the two species seem to be occupying adjacent or slightly overlapping areas with fringe intermingling. In areas where scutulatus and atrox occupy and use the same areas of the same prairie wouldn't you expect a similar monologue considering the shared prey base?

Again... I'm not saying hybridization doesn't very occasionally occur, but from what I've seen west Texas isn't full of scutrox, atrossus.

The end of the first paragraph of Aird et.al. says volumes with regard to this issue-
"Because of their similar blotch patterns and their black and white banded tails, the two are frequently confused by inexperienced persons."

>>Are you insinuating that's due to hybridization there?

Several hypotheses are offered by Aird et al to explain the origin of type B venom populations within scutulatus, though at this point I don't know what those are. If I did insinuate that, could you refute it beyond the shadow of doubt?

>>>>I'd assert that scutulatus and atrox are more syntopic in west Texas and habitat utilization seems to be more homogenous there than in other areas where the two species seem to be occupying adjacent or slightly overlapping areas with fringe intermingling. In areas where scutulatus and atrox occupy and use the same areas of the same prairie wouldn't you expect a similar monologue considering the shared prey base?

I would assert that scutulatus x atrox hybridization is more common in recently altered habitat (south county Creosote flats) than in (north county) grasslands.

>>
>>Again... I'm not saying hybridization doesn't very occasionally occur, but from what I've seen west Texas isn't full of scutrox, atrossus.

I'm not sure what you are really arguing since we have already established that we do not have hard data to establish frequency. At any rate, I'll go on because IMO this is really interesting to me (I always jump in on the scut conversations).

>>
>>The end of the first paragraph of Aird et.al. says volumes with regard to this issue-
>>"Because of their similar blotch patterns and their black and white banded tails, the two are frequently confused by inexperienced persons."
>>

Are you suggesting that I am inexperienced? I hope not. This year I observed over 2000 Rattlesnakes in north county alone. I do agree with Aird's statement though, and if folks have that much trouble with atrox and scut, how would you expect them to identify a F2 or F3 back-crossed hybrid? Once a hybrid occurs, if it lives to breed, then it back-crosses one way or another, however convenient you find that explanation.

Finally, I would refer to Hughs post and suggest that it's possible some of those "atrox" that you observe in north county could in fact be f2 or F3 back-crossed hybrids and you'd never know it by looking.

-----
http://www.hcu-tx.org

I'm pushing this topic because I find it interesting as well... I'm glad you're enjoying it too.

My reference to the Aird et. al. quote was rooted in my opinion that the majority of the scut/atrox hybridization theory is a direct result of many herpers who have trouble correctly differentiating scuts and atrox. Just because the scuts in west Texas phenotypically have more in common with west Texas atrox than southern NM/AZ scuts do with southern NM/AZ atrox doesn't mean west Texas scuts and west Texas atrox are hybridizing. That's a loooooong way to go to solve a problem with a much more simple answer. To say that they look similar and have similar venom monologues because of localized wide-scale hybridization that can't currently be demonstrated in wild observations because they're all backcrossed and the visual evidence of hybridization is masked is a much more complex and to my way of thinking unlikely theory.

I do agree with you that environmental stresses and substandard or altered habitats create scenarios where opportunities for hybridization are more enticing. The obscurus/klauberi hybrid is a good example here... it's not as through the Peloncillos are particularly supportive to the habitat preferences of willardi. When a snake can't find a mate it's more likely to mate with what it can find. I still see this as an edge effect rarity and not a regular occurence.

I would still love to see some photos of "intermediate" animals. I've heard people refer to using the postocular striping trait, white width on the tail, tail band count etc. as diagnostics, but I still have never seen a scut or atrox in west Texas that I felt wishy-washy about. I've never seen one that keyed (on hard traits and not "feel" ) as intermediate. If anyone has photos I'd love to see them. I'd like the opportunity to change my mind. I'm not staunch in my stances. I just have seen nothing to dissuade me.

Did you hit one too many zeros on the crot numbers?

>>Did you hit one too many zeros on the crot numbers?

I was being conservative. I saw 200 crotes in one three night span. When you're looking at those kinds of numbers you will see some odd balls - if you take the time to look at them.

I thought we already established that it occurs? Just for fun let's say I saw 3, out of 2000 crotes, that's .0015 or roughly one sixth of one percent. Also this is the habitat where I said I felt it was a less likely to occur. I also saw what I believed to be a scut x molossus in the same habitat.
-----
http://www.hcu-tx.org

I'd agree with you but of the 1,283 mating pairs of rattlesnakes I observed in the wild this past year all of them were conspecific pairings.

>>I'd agree with you but of the 1,283 mating pairs of rattlesnakes I observed in the wild this past year all of them were conspecific pairings.

I spent an inordinate amount of time. That is all that is required.
I don't dispute that you haven't seen one you would attribute to being a hybrid. Besides, there are three or four other things I've seen up there that you haven't
-----
http://www.hcu-tx.org

Just for fun let's say that hunting Friday, Saturday, and Sunday nights every weekend from the beginning of March through the end of November and five full weeks throughout the course of the year would yield roughly 125 hunting nights. At 2000 observations (conservatively) that averages 16 Crotalids per day/night. That's just Crotalids. Considering typical observation ratios you'd also have found roughly 250 splendida, 550 bullsnakes, 400 night snakes, 300 garter snakes, 200 great plains ratsnakes, 200 glossy snakes, and 400 longnose (just to round out the more common stuff). That totals up to about 4300 snakes and if divided by the 125 nights would yield and average of about 34 snakes/night every night. Of course once you factor in the cold, dry, or rainy nights the average on huntable nights would have to go up. But I guess that if you're finding 200 snakes every three days it would only take 64 nights to pull that off.

"Besides, there are three or four other things I've seen up there that you haven't"

Let me guess... a sasquatch, a chupacabra, and ALIENS!?

I understand you doubt the numbers, but I gave it one last hooray before the road hunting ban. With gas prices and legislation I don't ever expect to repeat 2007, but that was the point. To put it in perspective for you, I spent more time looking than you did at work this summer. Luck and timing played a part I'm sure, you might know something about that.

I didn't see as many colubrids as you estimate, with a few exceptions
-----
http://www.hcu-tx.org

NO offense, but your missing a very important concept. Your studies are in one locality. Which apparently does not have hybrids. But that area is NOT the area that HKM and have seen lots of them.

I would imagine, that if you spend that much time in the area we find them. You would see far more then us.

This concept is not all that scientific, its more about common sense, its called context. No one said, all populations have hybrids. In fact, very much the opposite. We have a few sites that do, and hundreds that do not.

While your trying to rationalize your thoughts with numbers, your numbers are useless, unless you are in an area where they occured.

To make it even worse, its also about timing as well as location. In the area we see lots of Mohave/atrox crosses, we have surveyed this area for about forty years. There have only seen hybrids for about five years or so.

Again, no offense, but your arguements so far seem very narrow. I say that because it really bothers me when biologists tell me what is and what is not, by what they HAVE NOT SEEN. The point is, what we HAVE seen. Sorry but I hold no validity in what you have not seen. Whats important is what you have seen.

I will take the blame for not taking pics of GOOD mohave/atrox crosses, because I was the one who had the camera and did not take pics. The reason is, we did not care. That is, until we started seeing more and more.

The reality is, one is more or less meaningless. We all know that can occur. But when it becomes a pattern, we should start to pay attention. So we are. hence the pic of the atrox/mol. I asked HKM to take pics of those. If not, he most likely would have watched it go off the road, as usual.

If and when we see more, we will take pics.

About atrox variation, I have been working some congregations, oh for about 30 years on the same sites. And I have seen lots of variation. More then you can imagine. But they were all atrox, on those sites. I do have lots of pics. Including a couple odd ones. Cheers

The intent to my original post was to try to outline the notion that I've run into so many west Texas herpers over the years that claimed to have seen "mojave x diamondback" hybrids and yet never on a single occasion has one of those snakes been shown to me (in a photo or in person) that wasn't easily diagnosed as one or the other. The misdiagnosis is simply a matter of inexperience. In west Texas, the similar phenotypes of scuts and atrox make them more difficult to differentiate from one another and I was trying to draw the line between legitimate hybrids and a "hybrid by default due to misidentification". If so many of Texas' infrequent or slightly inexperienced herpers were to be believed, scut/atrox hybrids are all over the place. It's gotten to be a bit of a peeve of mine. In some way it's gotten to be the herpers version of the "bullsnakes are breeding with rattlesnakes" tale I hear from ranchers. I've said several times that it's not my contention that hybridization does not occur... simply that from what I've seen it seems to occur at very low frequency.

"NO offense, but your missing a very important concept. Your studies are in one locality."

While I've concentrated on keeping point data for the last 10 or so years and I do have a pretty good set of data from northern Brewster county, I've also spent my share of time in southern Brewster and Presidio counties where Hugh mentioned having had collected the jarful of intermediates. The northern Brewster county snakes came into the conversation because Joe and I are familiar with that spot and I've heard claims of intermediates up there too.

"I say that because it really bothers me when biologists tell me what is and what is not, by what they HAVE NOT SEEN. The point is, what we HAVE seen. Sorry but I hold no validity in what you have not seen. What's important is what you have seen."

I understand what you're saying here, but at some point sample sizes get so large that what you haven't seen starts to statistically mean something. It can never be a definite, but it's worth considering.

I'd love to see some of the oddballs you and Hugh have seen over the years. This topic intrigues me. Please keep in touch.

I kinda think your going in circles. As we(all of us)already know they are not common, or all of us would have already seen it. It would be common knowledge. Also if they commonly crossed, then they would be considered the same species.

But that is not the case. The case is, they do occur and not as rare as you would think. The problem is, its highly isolated and a timely condition.

We have found that once you find an area where it occurs, its not "one" individual.

ALso, without DNA work, I believe theres a lot missing in our understanding. As many of these tweeners may most likely be products of a questionable history. Cheers

I'll go a step further and say it's probably more common than most realize, and has been taking place for millions of years. For every animal you see, imagine the number you don't see. Something can be rarely observed without being rare - like NM alterna haha
-----
http://www.hcu-tx.org

Damon,

First of all, gut feelings or otherwise, I hope you did not take offense to my mention of atrox X scutulatus hybrids being common. Maybe that is a misnomer? And I have not done DNA work to confirm any of it. As an example of why I will now say "not unusual" - I sent 20+ preserved "apparent" crosses of the above two species to UTEP in the early eighties - they all looked like atrox. Meristically they were intermediate. Most were patterned like atrox. The curator joked with me as I had them labled as Crotalus sp? He said "Gosh Hugh, can't you even ID atrox?" I told him to run them through a key... He was stunned to see them key as intermediate. These were road kills picked up around Study Butte and Christmas Mts. over a few months down there. Road kills - random DOR's. I did not preserve all of the DOR's I found, and without going to the notes, if these were 5% of the total number of atrox and scutes found DOR, in the grand scheme of natural events that would not be deemed rare. I have always found a small percentage of these oddities in this area of West Texas (29 years in the field there). I have found them elsewhere where they are sympatric.

The picture Frank posted is a specimen I found and photographed at our Oxybelis field sight here in southern Arizona. In West Texas, I have seen a few molossus X atrox looking beasts. In Arizona they ARE common in certain areas (35 years in the field studying rattlesnake demography and social behavior).

Of the photos you posted it looks like the first six are atrox and the last two scutes - but that is gut feeling as they are not in hand.

It is not odd to me that hybridization occurs; I think it occurs very commonly. But that is just me. What is important is, does the crossing take hold when it does occur? It is clear to me that in some areas it is happening and has been for several snake generations at the F1 level. The backcross stuff I will leave to those much better versed than I in captive breeding to work out. I have been told that the species (kingsnakes for the most part) that have been crossed and crossed and recrossed and looped and partially abjunticated and then crossed some more in captivity are the ones that have shown a high degree of "return to the typical pure adult pattern" in subsequent generations. If that is truly the case, then what about these rattlesnake species; the molossus X atrox looking thing in the photo would probably be the F1 offspring of the two parental species. But what about those beasts jarred up in the UTEP collection that looked like plain old atrox but keyed intermediate??? Might they be the fruits of multi-generational crossing?

My research is demographics and social behavior. While this certainly plays right into that, it is not on my radar to fund or work out at this time - So I guess I should call it gut feeling. I eat a lot and have for many years. My guts have mostly been very good to me, and always more trustworthy than editors.

Hugh...
I absolutely was not offended. I just wanted to bring this up because it's something I find interesting and this seemed a good opportunity. Most of the time the tone of a forum post is not as palpable as vocal inflection would be in a personal conversation. I apologize if my wording allowed the implication by me or the inference by you that I was offended. I just wanted to chew on some ears and find out what other people were thinking.

I'm intrigued by this topic but I'm biased to the extent that on many occasions I've seen actual animals or photos of animals from west Texas that were labeled incorrectly due to inexperience on the part of the observer. Separating those observations from legitimate observations of hybrids is very difficult. It's not that I think hybridization doesn't occur, but I'm having issues with the idea that it's widespread. You mentioned key characteristics and the keyed Crots you sent to UTEP, but many of the keys that were initially created for the differentiation of scuts and atrox have the same flaws as the Jacob paper. They excluded some of the west Texas specimens. The postocular stripe/tail banding/blotching traits don't act as solid characters in those areas.

I hope that makes sense. Sometimes I get to rambling and everything runs together.

Cool Damon.

Here's another question (scutes / atrox): In my experience, color pattern characterisitics are much more variable for both species in sympatric populations or in contact zones between allopatric popululations. There, as you inferred, one finds atrox with thin tail bands, scutes with atrox blotches, etc etc. Yet, color pattern characteristics (not ground color) remain quite static where one species occurs without the other.

Why?

My impression is that broad habitat utilization by any species will result in more phenotypic variability within a population. Specialized habitat utilization would result in less. In places where atrox and scutulatus are more specialized and habitat utilization (and therefore activities) are more segregated, scuts are pressured towards a phenotype best suited for their microhabitat and atrox likewise. In areas where generalization occurs and scuts and atrox are truly sympatric, higher phenotypic variability in individual species (and hence more similarity across species) occurs because both atrox and scutulatus are exposed to shared pressures. The generalization of scut and atrox populations in west Texas might also explain the fact that the type B venom monologue that's unique to west Texas is similar to the monolgue of atrox there... they may be so generalized that they share a prey base that Arizona atrox and scutes don't.

I’m still pondering that either are specialists anywhere – maybe one has usurped the other in certain locals, but habitats? Lower desert creosote – atrox in west Texas / scutulatus in southern AZ. While it appears that scutes hold the higher elevation grasslands, atrox can be found up there in AZ and in the northern part of there range as well. In southern AZ, atrox rules the middle elevation palo verde / saguaro association (but not exclusively)…. Scutes are found below in the creosote and above in the grasslands. In many areas where scutes don’t occur atrox inhabits the grasslands. Depending on where you are, you can find them sympatric or not in just about every habitat type that they occur in. So what about specialized food items? Yes – anything they can fit down their throats. I can’t get into the microhabitat stuff unless we are talking individuals or family groups. Semantics more than anything else I guess, but for most crotalids that term just annoys me .

In sympatric populations with “shared pressures”, one might indeed expect to see more phenotypic similarity as you said. But occasional genetic mingling between the two species could also explain some of the similar venom monologues, pattern mush’s or other intermediate variations. My guess it is some of both.

I doubt very much there is any isolating mechanism that will keep a horny male of either away from a receptive female of either. Certainly, winter breeding / social gathering locals (I do not call them dens or hibernacula – that is another discussion) would have a huge effect if they are monospecific. Rarely is that the case. Where they are spread out among family groups or pairs, the potential for contacts between the “roving loaded gun” males and the “who gets me first” females increases all the more. There is no tie goes to the runner. Of course, I am playing devils advocate here now Damon, as I do think that in most cases, conspecifics would breed with conspecifics. BUT, I think that, I do not know that. I have also seen many individual beasts in quite a few areas that scream hybrid at me. Similarly, I think that, I do not know that.

Hugh,
What do we know about poly-paternity in Rattlesnakes, or more than one male parent for a litter?
-----
http://www.hcu-tx.org

I didn't mean to imply that scuts or atrox are specialists in general, just that on a relative scale certain localities may contain atrox and scut populations that are more segregated due to minor differences in preference for microhabitat or prey. As you know, the differentiation of microhabitat is sometimes lost to the human eye, but point data can still reveal differential habitat utilization by each species. Some areas contain somewhat discrete pockets of each species with fringe intermingling. Other areas show more homogenous usage. The prairie in northeastern Brewster county is one of those areas that has (at least to me) revealed little in the way of segregated habitat utilization. With a few exceptions (one fairly substantial one), the points I've taken over the years show no real pattern of segregated habitat utilization by atrox or scuts. Other locations reveal habitual usage of certain geographical areas by a particular species... almost as if lines were drawn in the dirt. I have no qualitative data to back up the observation, but those areas where segregation doesn't appear to be occuring seem to contain populations with phenotypical characters that fall outside the parameters typically used for specific identification.

Why some populations have segregated close-proximity habitat utilization, some have true allopatric disassociation, and others intermingle is beyond me. I have guesses, but this scenario profoundly demonstrates just how dynamic and plastic populations can be in their adaptations to particular environments.

In any case, any "normal" or "intermediate" scut I've ever seen in Brewster county still keyed as such based on head scalation. I've never seen a "structural" intermediate.

Food for thought... with as much as I hear mention of scut X atrox hybrids, the scut and atrox populations in northern Brewster county share turf with a hefty population of viridis. You're almost just as likely to find any of the three (atrox, scutulatus, and viridis) on most any given stretch of road. Is it the fact that viridis are easier to differentiate from scuts and atrox that seems to be limiting the suggestion or possibility that they might be suggested as hybrids?

I happened to come across this pic today of an atrox I found on 118 just north of the Gap cut off. Thought some of you might want to see it.

ST