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quote~ some populations have very potent venom

I recently read an intresting story about geographic varience in the potency and composition of venom, from "Australian nature magazine" Autumn 97

If bitten by the Malayan pitviper (calloselasama rhodostoma) , The exact nature of the symptoms often depends on where you are when you are bitten, suggesting the composition of pitviper venom varies between geographic locations.
Biologist Jennifer daltry and coolegues from the university of wales, UK, collected the venom of wild adult malayan pitvipers from locations across Vietnam, Malaysia, thailand and java.
venom analysis revealed that composition variations were closly related to dietry differences.
The principle function of venom being to immobilise and digest prey, and different prey animals may vary in their suseptability to toxins. The researchers suggested that in malayan pitvipers, and perhaps other species, natural selection fine tunes the venom in different populations in line with their main food sources.
They found that venom from captive bred pitvipers varied according to geographic location of their wild counterparts and not according to their natural diet, which they were fed in captivity. This indicates that the venom/prey associationis inherited within populations and is not a direct consequence of of the enviroment.