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head sizes correlated to prey size?
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by asud on December 21, 2009
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okay, maybe a naive question but here goes: i was talking with an ornithologist at cornell the other day and she was enthusing about a skull of a big retic they had up there, about how much bigger it was than anything you'd find in a zoo simply because it was from the wilds of borneo where it presumably had to eat bigger fare than little rodents.
so, is it fair to generalize and say that wild caught - particularly bigger bodied species - will have broader heads than their captive bred brethren?
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RE: head sizes correlated to prey size?
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by FSB on December 21, 2009
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Not the question I was expecting... I thought this was going to be about head size varying across different species - not within a single species.The size of a retic's head is genetically determined, and will not at all be affected in a single snake's lifetime by what it eats. [I am rather surprised that any modern scientist, especially at Cornell, would even entertain such an idea]. Head size will also be proportional to the overall size of the snake, so, the bigger the retic, the bigger the head. Just because large snakes are capable of eating large prey doesn't mean they always do so. They will eat whatever they can catch, and many large, wild retics subsist very well on rats, while others might eat sun bears - whatever's available. I suspect that the skull at Cornell is rather an old specimen, collected back when wild retics still reached prodigious sizes. These days, thanks largely to overharvesting for the skin and meat trade, wild retics of even 5 meters are rare, whereas in the early to mid 20th century 7-8 meter specimens were commonly collected for zoos. I would invite your friend to come visit us at the Catoctin Zoo in MD and view the head of our largest female if she has any doubts about the ability of retics in zoos to grow impressively large heads. [By the way, I hope she realizes that, since birds are now classified as reptiles, that she's actually a herpetologist?]
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RE: head sizes correlated to prey size?
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by asud on December 21, 2009
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i may've misunderstood her (particularly as i'm a humanities type with an iffy science background - which is why i come here). anyhow, yes, you're right. it was shot in borneo back in 1909, back in a time which, while not being necessarily more enlightened, at least had considerably fewer of us.
thanks for the correction. hopefully will make it down to catoctin someday myself...
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RE: head sizes correlated to prey size?
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by pictigaster1 on December 21, 2009
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A bit off topic ,but I remember in the 80s seeing a few burms we called pinheaded.These guys were chain fed rats all the time and got 10 11 0r 12 foot.There bodies were very large but there heads were too small for a snake that size.If you kept one for awhile you could watch as the head would sometimes catch up but not always.Some of them looked very funny.
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RE: head sizes correlated to prey size?
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by yoyoing on December 22, 2009
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This is interesting. I used to live right down the street from Sapsucker Woods, the Cornell Ornithology Lab. They used to have a colony of wolves, so when one escaped that was big news, and I remember looking for it. If a Cornell scientist said it, trust that there is no ignorance lurking below. The comment may have been miscommunicated.
Regarding the information about pinhead Burms, that really is cool. Everybody knows body dimensions are generally dictated by genetics. Human intervention can also influence these dimensions. If not, I want my money back from the kids' orthodontist.
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RE: head sizes correlated to prey size?
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by stopgetinpopped on December 22, 2009
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I absolutely disagree with the previous. Head size is directly proportionate to size of food availability. Absolutely, no question about it. It is not genetically predetermined. Wild Retics do in fact have much larger heads than most Captive specimens.
Put simply, when only extreme sized food is available the skull and the musculature must adapt to be able to feed opportunistically on whatever food is available.
You will find this is very true for Rattlesnakes as well. Western Diamondbacks from many south Texas populations where diet consists mainly of cottontail rabbits have extreme heads compared to other populations.
Think of it like this, it's much like weight lifting in humans. If your average man curls 5 pounds a hundred times he will maintain good muscle tone but will not really gain any muscle mass. If he were to curl just slightly more than physically comfortable he will gain muscle and his skeletal system will have to adapt to support that weight...
A 180 pound Retic fed 30-50 pound pigs or goats 3 or 4 times per year compared to a 180 pound Retic fed 10 pound rabbits weekly will be much larger, more toned and a hell of a lot stronger, with a head twice the size....
Cheers!
Terry
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RE: head sizes correlated to prey size?
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by squigy on December 22, 2009
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I would have to agree to the prey size explaination. In western diamond backs I have seen this or freaks at least. Quite a few extra large headed atrox have been taken out of the Hollis and Texas panhandle area over the years. A biologist friend of mine has been catching them for over 50 years and calls them loggerheads. About a 3 foot snake with a 5 footer head on them. Interesting thing to think of.
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RE: head sizes correlated to prey size?
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by theemojohnm on December 23, 2009
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Cool, a debate. ;)
Head size of any natural species IS genetically predetermined, absolutely.
Where it is true that populations of the same species that are isolated from each other, sometimes evolve unique physical traits. For instance, the Timber/Canebrake Rattlesnakes. Also note other types of phenotypical differences, such as body shape, etc. We even see venom composition differ fairly dramatically in some American Rattlesnake species.
The only educated explanation for this, is food availability over the natural history of a species existence, and utilizing the most appropriate form of venom, being the most efficient to catch food.
In areas where rodents have become scarce, some Crotalus species have evolved varying venom compounds, some neurotoxic, better geared it seems, to target the lizards and other prey items these animals then begin feeding on, in place of the diminishing rodent populations in that area.
We see many examples of this, and it really is quite fascinating. However, it takes generations upon generations for these dramatic adaptations to develop.
And, they are genetically predetermined. Also environmentally influenced, but over the course of many years and many generations. Thousands of years of evolution have made these animals what they are.
There is no individual retic that, not matter how long it may live, can simply "evolve" a larger head to best suit its independent needs. Not in its lifetime.
Nor does simply feeding on bigger prey items "stretch" a snakes head to a larger size. Ridiculous.
Simply put, some retics may have larger heads than others. And, if this is an evolutionary adaptation, it is CERTAINLY genetically pre-determined, simply because physical differences ARE genetic. That is how it works.
If I have a retic with a small head, and my friend owns a different specimen with a much larger head than mine, is it accurate to say that his animal may have come from an area with much larger prey items and has a bigger head simply because it is "used to" growing up eating larger prey items? Of course not.
What is highly plausible is that his animal may have come from an area where exceptionally large prey items are the only ones available for a long period of time, where local populations have refined genetic adaptations, to solve this problem. The same evolutionary adaptations, passed down, throughout many generations of a local population exposed to the same conditions, over a great period of time.
An embryo developed into that retic with a GENETICALLY pre-determined blueprint.
Over exposure to similar environmental factors over long periods of time, some truly unique evolutionary adaptations can be found. But NO one animal over the course of its life, accomplish this.
Merry Christmas All.
Take Care,
-John Mendrola.
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RE: head sizes correlated to prey size?
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by pictigaster1 on December 23, 2009
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.Life offers many variables once you have lived long enough to see some of them you will know.Predisposition to a given trait may be triggered by many variables .When I have time I will list a few .Good post tho john.It makes us think I like that.
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by FSB on December 23, 2009
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Well, I've been waiting for a chance to get back on here and respond, but John M. seems to have covered it pretty well in the meantime. I was going to say that most of the instances cited seem based upon anecdotal rather than scientific evidence, and that the tendency of a population of animals to develop a new trait over time is quite different from individual animals reconfiguring their body parts in response to a given behavior or environmental stimulus. That sounds all too much like the Lamarckian idea that the giraffe developed a long neck by continually reaching higher and higher for leaves. Finger length is genetically determined, and a person born with short fingers is not going to develop long fingers by playing piano for ten hours a day.
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