Osteo-cranial variation in CB snakes...

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Posted by Chris_Harper2 on January 29, 2003 at 09:38:14:

In Reply to: Anyone else ever noticed round snouts in captive Elaphe? posted by chrish on January 29, 2003 at 01:18:56:

Snakes born and raised in captivity often show significant variation from their wild counterparts in cranial development. The differences often show up in relative cranial size (with CB snakes have smaller heads relative to body size than wild-caught specimens) but shape is also thought to be affected.

And there are numerous anecdotes regarding this. Enough that it has been studied empirically.

The study I'm aware of was flawed but still interesting. The researchers took a group of CB Nerodia spp. (from a field inseminated female, I believe) and fed one group feeder-fish that were some percentage larger than the snakes head and the other group was fed fish that were a percentage smaller or the same size as the snakes head. With both groups the size of the feeder fish increased as the study specimen grew.

I read this study years ago so I may have the details slightly wrong.

At any rate, the group fed the larger prey items developed heads larger relative to body size than the group fed smaller prey items. The researchers suggested this was a facultative response to eating larger/smaller prey items. I assume the mechanism suggested was a gene-by-environment interaction (aka 'reaction norm') but they may not have even brought this up.

The study was flawed primarily because they did not correct for nutritional variation in different sized fish. So one group may have recieved a diet with a different calcium/phosphourous ratio not to mention other critical differences known to effect bone development in captive reptiles. The study fed each group the same weight of fish, but the nutritional quality probably varied greatly among the groups.

The chance of multiple paternity in the clutch is also a potential problem.

Regardless, the results are interesting and do fit with anecdotal observations by hobbyists and zoo professionals.

For what it is worth, this was discussed a lot more back in the 80's when CB snakes first became common. Many hobbyists were so used to dealing with WC snakes primarily that the differences in CB snakes were much more apparent. In today's day and age where there are so many CB snakes it is not noticed as much.

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