Adult rattlesnake size: Nature verses Nurture. - FaunaClassifieds
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Old 11-20-2008, 11:22 PM   #1
ChuckHurd
Thumbs down Adult rattlesnake size: Nature verses Nurture.

There are countless debates over nature verses nurture but what i am specifically interested in is opinions on the adult size of snakes given captive care conditions verses their natural conditions.

I have, for many years, been on a quest to find the dwarf eastern diamondbacks. i heard a report of an inland in the Gulf of Mexico that yields a race of reduced size EDB's. after years of research, i came across someone that knows it. He took a pair off of the island in 1959. he tells me that his never exceeded 30 inches and he has never heard of one that exceeded 3 feet. obviously, something in the island conditions has stunted the growth of the snakes. i am thinking most likely reduced food intake and perhaps a shorter feeding season.

i compare these snakes to the Timber Rattlesnakes off the mountains of the far northern range. i once had breeding size female from the Adirondack Mountains that was only 18 inches. i researched the yearly average temperatures for the region and based on my knowledge of timbers, i estimate they are only feeding about 5 to 6 months out of a given year. i was searching for a dwarf sized male, but i lost the female before we could breed her. i did not know the history of this female before she came to me, so i could not tell if he had been raised on a normal captive feeding regiment or if she was held to the shortened feeding season that was natural to her. what i was interested to see with her, and with these EDB's if i can find a pair, is this: if babies captive born from the naturally dwarfed parents, will remain dwarfed if given a normal captive feeding regiment.

In term of will they remain dwarfed, i think of the dwarf retics and burms. they come from populations that have been isolated from the mainland populations for generations, and when bread and raised in captivity, they remain dwarfs. on the other side, i recall a finding couple years ago that reported most of a rattlesnakes total adult size is determined by the amount of food intake in the first 18 months of life. So, babies produced in captivity from small parents, may not remain dwarfed if feed well for the first year and a half.

i guess what is boils down to is the question, will generation after generation of reduced feeding in the wild, lead to a genetically dwarfed rattlesnake, or will these snakes reach a normal adult size when feed the same as normal snakes when they are captive produced?
 
Old 11-21-2008, 10:18 AM   #2
Mokele
IMHO, the answer is the ever-so-satisfying "it depends."

It's the basic problem of phenotypic plasticity (ability of an individual organism to change in response to the environment, such as stunting growth) vs evolution (natural selection weeding out large individuals and favoring small ones). If you drop snakes on an island, they'll simple be stunted, but over many generations, naturally smaller individuals (those who are 'less stunted', and therefore will spend energy on reproduction rather than attempting to grow to 'natural size') will be selected for until the genetically determined adult size is what is reduced to what is sustainable on the island. So it all depends on when, on an evolutionary timescale, you find these animals. If you find a population of island dwarfs that's only a few generations old, they'll likely just be stunted and grow up fine in captivity. But if they've had a few hundred generations to evolve (and there is evidence that this particular evolutionary trend can be very rapid), they'll have a small maximum size.

Oh, and I found the study about feeding early in life influencing later growth freely available: http://www.kingsnake.com/aho/pdf/Nov...madsen2000.pdf

Mokele
 
Old 11-26-2008, 12:07 AM   #3
Tim Cole
Question

Chuck,
Slightly off topic question. Don't Timbers need to be 11 or 12 years old to be sexual mature? I recall most literature stating this.
 
Old 11-26-2008, 07:49 PM   #4
ChuckHurd
well, i have never been able to monitor a wild snake to see at what point the produce. i have read that, just like you. most reports say something like 9 years on females, 5 on males. i think that is probably pretty close to right...maybe a little more for the snakes of the mtn tops of northern NY as they only eat half the year. in captivity, i have had males breed at 3 years old and females are 5 years old.

that is relevant to this question. the island edb, like the mtn top timbers are smaller because they eat less. that is a given, BUT after many generations of this, will it led to a genetic difference in the snakes? if we say the edb's are producing at about 5 years, that means about 20 generations over the past 100 years. so, if "normal" edb's made there way to that island about 1900, this is only a supposition, has 20 generations of the smallest males breeding the smallest females lead to a genetically smaller snake...OR, if we breed those snakes and feed the babies the same as the mainland snakes....will they grow to a normal mainland size?
 
Old 11-27-2008, 02:35 PM   #5
Mokele
Quote:
BUT after many generations of this, will it led to a genetic difference in the snakes?
Given sufficient time, yes.

Think of it in terms of energy budgets. When a snake is young, it dumps any energy not used for basic life functions into growth, and thus grows very fast. As it gets older, it's growth rate slows, and it becomes able to reproduce. At this point, the snake has to split energy into 3 things: basic life functions, growth, and reproduction. Because an animal obviously can't short itself on the first (or it dies), it's mostly a choice between growth and reproduction.

Imagine you have 100 WC rattlesnakes, and you feed them all the same and keep them in identical conditions, measuring and weighing them every week. After they've all grown up, you'll have a curve for each snake, which starts out with a steep slope (fast growth), which gradually flattens out, but each snake's curve will be different. Naturally smaller snakes (even if only a foot shorter than normal), will have a curve that isn't as steep at first, and flattens out sooner and at a smaller size.

Now, imagine you dumped those babies on an island, and they got stunted. Let's say, hypothetically, they were all now just 4 feet long at sexual maturity. For the babies who, under normal conditions, would have gotten quite large, they're still on that steep growth curve, and any calories from the mice they eat will be diverted much more heavily towards growth than reproduction. But for naturally small snakes, they may already be at the point where their growth is slowing, and so would spend more of their energy on reproduction.

This leads to a fairly simple system - naturally smaller snakes would reproduce more, leading to a smaller next generation. That generation would face the same issue, and the smallest of those would reproduce more. Finally, after many generations, the natural size of the snakes would be so reduced that they're no longer stunted, and if taken into captivity and fed freely, they'd stay small.

The key issue is how long this takes, and when you find the population. If only a few generations have gone by, captive ones would probably reach full, normal size. If it's been a few thousand years, it's probably genetic. If the island is an uplifted coral atoll or a volcano that only became large enough to be habitable a few hundred years ago, they're probably just stunted. If, however, the 'island' was colonized by snakes via a land bridge during the last ice age (which ended about 10,000 years ago), they've had plenty of time to adapt and become true genetic dwarfs.

Hope this helps,
Mokele
 
Old 12-26-2008, 03:15 PM   #6
Rattlesnake
To the board members.
Some months ago a picture was posted on here showing a man with a dead WDB or EDB holding the snake up and measuring its size.
From what I recall, the snake was over 6 feet long.
Does anyone remember this picture or have a picture of the snake?
I would like to use it on my homepage.
Thanks for your help.
 

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