Opossums and pitvipers are sympatric throughout most of the New World, but trophic relationships between these speciose clades have only recently attracted the attention of researchers. Although it is now known that some venom-resistant opossums prey on pitvipers, a review of the literature on diets shows that some Neotropical pitvipers prey on opossums. Interestingly, some pitviper species prey on opossums known or suspected to be venom resistant. If venom resistance and venom potency are coevolved traits, then these observations suggest that alternative outcomes may result in role-switching between victims and exploiters. Because molecular antagonists (e.g., venom toxins and toxin-neutralizing serum proteins) that could mediate such outcomes have been plausibly identified, this system is a potentially fruitful field for evolutionary research.
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