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RE: Rattleless Crotalus questions
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by CanadianSnakeMan on October 27, 2010
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Thanks to all for providing some answers. I had heard some reports on and off and thought it would be a good idea to verify them. Very sensible answers from all.
John, do you have a link to your references regarding snakes losing rattling behaviour?
Also, Wolfgang Wuster was kind enough to provide some insight for me in a discussion on another venomous reptiles website. Here's what he had to say about the 'hoofed animal' theory of rattle evolution:
"Hard to know whether it would an advantage to lack a rattle. I can certainly imagine that there may be places where it might be advantageous to lose the behavioural inclination to use a rattle, namely anywhere with a lot of people who don't like snakes. It simply depends on the balance between predation from predators that might be deterred by the rattle and humans that will use the rattling as a cue to kill the snake.
The large hoofed mammal hypothesis for the evolution of the rattle is almost certainly wrong. The most likely place of origin of rattlesnakes is in the mountains of Mexico, or possibly various other places - basically pretty much anywhere OTHER than the great prairies. The other point to make is that the scenario of a rattlesnake caught out in the open by a herd of buffalo without any kind of shelter is pretty unlikely. Most rattlesnakes live in considerably more varied terrain, and even a prairie that looks flat, featureless and without any shelter to something our size is actually full of holes and nooks and crannies if your diameter is only 5 cm. So I really doubt that trampling by large ungulates was ever a major selection factor in the evolution of rattlesnakes.
It is probably misleading to assume that the rattle necessarily evolved due a specific set of circumstances. It is just as plausible to suggest that it evolved pretty much by chance in a particular lineage of pitvipers that had the necessary predisposing features. As it happens, most pitvipers have two key predisposing features: defensive tail vibration behaviour, and a terminal tail spine, i.e., a conical scale covering the entire tail tip. Most pitvipers vibrate their tails when in defensive mode, causing rustling in the leaf litter. If that has any deterrent effect on predators (it needn't be on all predators - it just needs to increase the overall survival rate of the snakes), then those snakes possessing the relevant genes will be at a selective advantage. Moreover, any further mutation that amplifies the effect will gain an additional advantage - e.g., stronger tail muscles, or indeed anything that increases the sound volume - like say a retained terminal tail scale that rattles against the one below it. If the increased sound volume increases survival, then the gene will spread, and more snakes will have the novelty in subsequent generations. All it takes is (i) a chance mutation and (ii) the right level of natural selection."
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RE: Rattleless Crotalus questions
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by AquaHerp on October 27, 2010
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Rattlesnakes lacking rattles do indeed show up often. As do rat snakes missing most of the tail....stub-tailed garter snakes...crop-tailed racers......
Rattlesnakes without rattles have been recorded for the course of field herpetology from the beginning.
The rattlesnake/bison theory is questionable as well.
DH
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RE: Rattleless Crotalus questions
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by Cro on October 27, 2010
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Luke, as far as references regarding snakes losing rattling behavior, you can find some about that in both of these books:
Timber Rattlesnakes in Vermont & New York: Biology, History, and the Fate of an Endangered Species (Jon Furman)
and in:
Landscape with Reptile: Rattlesnakes in an Urban World (Thomas Palmer)
Best Regards
John Z
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RE: Rattleless Crotalus questions
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by CanadianSnakeMan on October 27, 2010
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Thanks Doug,
That is what I was looking for!
What causes these species to have shortened tails? Are the rattlesnakes which lack rattles congenitally so or have they lost them for some other reason (i.e. trauma)?
Is there anything in peer-reviewed literature about species that normally have rattles being found without them?
On a side-note; in your opinion, would the loss of a ratle (or rattling behaviour for that matter) prove advantageous to snakes for surviving persecution from people? Do you think such adaptations be occurring?
Thanks!
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RE: Rattleless Crotalus questions
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by CAISSACA on October 28, 2010
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John,
I don't have either of the two books you cite. Do they provide real data on reduction of rattling behaviour, or is it just anecdotal stories?
Another interesting comment you made, concerning widespread tail vibrations in snakes: pitvipers (and their sister group Azemiops) mostly vibrate their tails when molested. Viperines don't. Many colubrids do vibrate their tails. Where it gets interesting is in the fact that most colubrids known to vibrate their tails are from either Asia or the Americas, i.e., they are sympatric with pitvipers! Few or no African, European or Australasian colubrids vibrate their tails. Although I don't think this has ever been analysed rigorously, it is certainly consistent with the hypothesis that tail vibration in colubrids is a form of pitviper mimicry.
There is even a species of false coral snake in S. America (Simophis rhinostoma) that usually just raises its tail during the day (mimicking real coral snakes), but will vibrate its tail at night, when its colours are difficult to see, but the noise mimics that caused by tail vibrations in pitvipers.
Cheers,
WW
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RE: Rattleless Crotalus questions
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by AquaHerp on October 28, 2010
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Ditto what WW replied.
My original answer was not to ride along with the “rattle-less bandwagon” but rather to point out the opposite. Many environmental factors come into play here. Attempted predation, injuries, frostbite, limited blood circulation et al can result in the tail loss (or rattle loss). Are some on occasion born rattle-less? Sure. Some are born with two heads, patternless, albino…… this isn’t to say that any of these traits is going to be a driving focus in such a short time span (or at all).
I keep hearing all the new conjecture as of late. Rattlesnakes are quickly becoming more venomous as a result… Rattlesnakes are no longer rattling as a result….. Rattlesnakes are losing their rattle as a result….. My theory, or personal opinion rather is that society has become saturated with many things as of late; two of these being instant communication and another being herp enthusiasts. We take the good and the bad. “I’ve discovered the key to keeping and breeding Fea’s vipers, and here’s how….” Good. “I found a rattlesnake with no rattle”… Ten thousand people jump in with an opinion, most not grounded in science….not so good. This is why we have 12 foot rattlesnake photos, toilet spiders, brown recluse bites in Alaska, photos of reticulated pythons eating people in the wilds of South America….you get the point.
My opinion, for what it’s worth is that we are not seeing any dramatic overnight changes in these snakes. I have seen thousands of rattlesnakes from the wild, some rattle, some don’t. Some are stub-tailed, some are not. Some venom is more hemorrhagic, some is not. It is what it is. Will they change over the next geologic blip? If they survive I suppose they will. Are they doing it over a generation or two? Probably no more than an albino opossum is a sign that they are adapting to exist remora-style with the yeti.
DH
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RE: Rattleless Crotalus questions
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by pictigaster1 on October 28, 2010
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Doug my colony of yeti only feed on snow lepords .Every once in awhile one will eat a yack .The problem I am haveing is how much room these feeder racks are taking up.Do you know of any alternate food source that may be a little less to take care of.Thanke in advance ..Archie//
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RE: Rattleless Crotalus questions
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by theemojohnm on October 28, 2010
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Archie, I feed my yeti's all the troublesome neihborhood kids, and my male is a vegetairian.. =)
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RE: Rattleless Crotalus questions
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by CanadianSnakeMan on October 28, 2010
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Thanks Doug, John and Wolfgang,
This definitely answers my question. Also FYI, I wasn't necessarily assuming that this was an evolutionary adaptation, that's why I was asking the questions in my first post - to see if there was any kind of pattern or if there was no basis to it at all.
I certainly understand now that it's completely unfounded... I'll make sure to improve my lines of questioning in the future, I promise!
The loss of rattling behaviour as a potential evolutionary advantage is very interesting. Has it been substantially studied or recorded in peer-reviewed literature? How would such a finding be measured (i.e. would the rattling frequency/intensity of snakes in built-up areas be compared to more remote populations)?
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