How the rattlesnake got its rattle

[Oolon Colluphid]

BMC Evolutionary Biology 2009, 9:35 (10 February 2009)

Evolutionary morphology of the rattlesnake style (http://www.biomedcentral.com/1471-2148/9/35)

Meik and Pires-daSilva



Background

The rattlesnake rattling system is an evolutionary novelty that includes anatomical, behavioral, and physiological modifications of the generalized pitviper tail. One such modification, the formation of a bony clublike style [stalk] at the terminal region of the caudal [tail] vertebrae, has not previously been examined in a phylogenetic context. Here we used skeletal material, cleared and stained preparations, and radiographs of whole preserved specimens to examine interspecific variation in style morphology among 34 rattlesnake species.

Results

Evolutionary Principal Components Analysis [which reconstructs changes along branches of a tree] revealed an inverse relationship between caudal segmental counts and style size , supporting the hypothesis that bone from caudal vertebral elements was reallocated to style formation during the evolution of this structure.

Most of the basal rattlesnake species have small styles consisting of few compacted vertebral elements; however, early in the rattlesnake radiation there appears to have been two independent transitions to relatively large, pronged styles consisting of multiple coalesced vertebrae (once in [I]Sistrurus catenatus, and once in Crotalus following the divergence of the Mexican long-tailed rattlesnakes). In terms of style shape, the two most divergent species, C. catalinensis and C. ericsmithi, provide insight into the possible relationship between style and rattle matrix morphology and lineage-specific evolutionary strategies for retaining rattle segments.

Conclusion

The considerable interspecific variation in rattle morphology appears to correspond to variation in the bony style. We hypothesize that style morphology evolves indirectly as an integrated module responding to adaptive evolution on matrix morphology.

[Oolon Colluphid]

Had to laugh at C ericsmithi... :D

[Garrett]

So what did we learn, exactly? I mean, for those of us who aren't shocked that things evolve.

[Garrett]

Make noise when hiking through socal brush. srsly

[Free in Freeport]

Fascinating! I always thought they stole them from babies.

[Worldtraveller]

Make noise when hiking through socal brush. srsly

Heh. I used to live in Tucson, Az, and my house was on about 3/4 acre. Most of that was wild desert (and about 80 acres of undeveloped desert behind), and I had a grocery store within walking distance, through said wild desert. I can't tell you how many times I have been walking back from the store, expecially after dark, or near dusk, and heard the familiar sound of a rattle from somewhere ahead. :) I always appreciated the warning and just found an alternate route.

[Redshirt]

God just wanted a snake that will be courteous enough to let you know it's there .

[Faid]

So what did we learn, exactly? I mean, for those of us who aren't shocked that things evolve.Well I'm not sure, but I always thought that it actually is a "don't tread on me" signal.

You know, like the bright colours in poisonous animals. Only instead of "eat me and die", it's a "step on me and I'll bite you, and I gots venom" warning.

I'm probably wrong, though.

[lpetrich]

Faid, the warning (aposematic) hypothesis is the favorite hypothesis that I've seen, and IMO it is a very reasonable one.

I don't know if anyone has tried to test it, but doing so is potential violation of animal-research ethics.

I imagine someone doing so on dogs from a dog pound, to try to see how fast they learn not to play with rattlesnakes. But even that would provoke the animal-rights activists, I'm sure.

[Jobar]

It would seem you could test for any inborn aversion that dogs (or any other animals) have to rattlesnake rattling by just using the rattle and a rubber snake, couldn't you?

[lpetrich]

One could certainly do so, but I had in mind testing how fast dogs learn to associate rattlesnake rattling with the possibility of being bitten by one. One would have to be careful about which breeds one uses, since some are much more trainable than others, and thus may find it easier to make such an association than others.

So dog-pound dogs are not a good choice, unless one is willing to (1) select only those from certain breeds, or else (2) test a lot of them.

[Jobar]

Ah, I see.

I think that it's possible that there might be a genetic component to the response to the noise of the rattle, like a chicken's to the silhouette of a hawk or owl. That was what I was referring to.

I've seen dogs that attacked snakes on sight, and others that were deathly afraid of even small ones- but mostly those were either moccasins or non-poisonous, in the area I grew up. So I don't recall ever seeing a dog respond to a rattler's warning.

[Oolon Colluphid]

I imagine the animals most likely to have innate aversions to rattles would be whatever the native large mammal species are in the areas where the crotalines are. Deer? Raccoons, wolves, coyotes, bobcats, bison? (Not sure what else is large and native...)

It's certainly possible for mammals to have instinctive snake-aversion. The two main predators of chinchillas are birds of prey and snakes, and our pet one used to freak out if we hoovered near him -- the swish of the black electric cable, y'see. (Sudden overhead shadows had the same effect.)

[Puck]

I've had dogs that instinctively shied and barked at a rattler in the bushes. We'd be walking and all of a sudden the dog would stop, face the direction of a shrub, and start barking to me, clearly agitated. The dog was bred by us (German Short Haired Pointers), and had never been around a rattler before that.

My Conure freaks out over hawks outside, screaming and taking flight in a burst of feathers and going into another room. If it's just a large non-predator bird, she might scream, but not freak out.

[Berthold]

It's certainly possible for mammals to have instinctive snake-aversion.
There was one thread a long time ago, quoting a technical paper, that certain aversions (among them for snakes) are very easily learned, and very hard to unlearn. If I recall correctly, it was about primates. Just one adult alarm cry when seeing one was enough.

This is quite interesting in the context of how hard it is to teach children an aversion against electric sockets etc.

[Occam's Aftershave]

Kinda on topic story:

My first engineering job out of college was working for a company that made radar threat warning receivers. These are electronic devices that go on military planes and alert the pilot when he is being scanned or locked up by an enemy fire control radar. They were first developed during the Vietnam war, where they saved the lives of numerous pilots who otherwise would have taken a radar guided missile up the tailpipe. The boxes have quite a bit of smarts, and can ID many different kinds of radars, multiple emitters, and prioritize the ones that are most dangerous.

Many different means of alerting the pilot when he was in danger were tested - flashing lights, audible alarms like beeps, klaxons, whistles, etc. The one sound that consistently got the pilots' immediate attention no matter how distracted they were, and the sound that is still used today AFAIK is a loud rattlesnake's rattle.

Whether it was some primeval subliminal signal or a learned behavior I have no idea. But when that rattle goes off in a fighter pilot's ear you can bet he'll hit the chaff, or wet his flight suit, or both.

[Steviepinhead]

Okay, since we're starting to stray ever so slightly, I'll take that as absolute license:

One of my great-grandfathers was a farmer and barber in Eastern Washington. Great-grandpa was also a local musician who used to play the fiddle for the Grange Hall get-togethers (hoe-downs, hootenannies...) atop Steptoe Butte*.

My grandmother inherited the fiddle. She didn't play, so she hung it on the wall.

I inherited the fiddle from my grandmother. Since I play guitar a little, I gave some thought to having the fiddle reconditioned and restrung, and maybe -- "someday" -- learning how to play. Anyway, while messing about with this family heirloom, I heard something rattling about inside the sound chamber. Shaking the fiddle gently, I eventually coaxed the small object over to the vicinity of the f-hole, so that I could see what it was.

Having grown up in the red-clay country of rural Georgia, I instantly recognized a rattlesnake's rattle. While Western Washington, where I now live, is -- like Ireland -- free of poisonous snakes, Eastern Washington is rattlesnake country. Thus, my great-grandpa would have had no difficulty acquiring a rattler's rattle. The question was why would he want to stow the rattle inside of a working violin.

It turns out that some old-time country fiddlers enjoyed the slight resonant buzz that the rattle gave to the sound of the fiddle when played, a "country" burr or slur or twang, as opposed to the concert violin's purity of note...
__________
Just to make this a little scientifical, I'll note that Steptoe Butte is an outlier of the NA continental craton. Everything west of there is a tectonic tack-on of one kind or another....

While I have not investigated closely, I'm presuming that the rattle in the violin is most likely that of the Western Rattlesnakes or Crotalus viridis. There are several western rattler subspecies, but Steptoe Butte is in the core range of the Northern Pacific Rattlesnake or Crotalus viridis oreganus.

[Steviepinhead]

Technical glitch, sorry... :bang:

[Steviepinhead]

Ah, here's what I was looking for:

How can we leave the topic of "dangerous" snakes without one fond farewell glance at this immortal YouTube offering:
http://www.youtube.com/watch?v=rebnrnGLKh0