Repeatability in venom expenditure during defensive bites in rattlesnakes: use of a chemical weapon deployed to generate an extended phenotype

Animal personality is characterized by consistent among-individual differences in behavior across time and contexts and can influence a wide range of ecological and evolutionary processes. Although consistent behavioral differences have been linked to variation in behaviors that create or modify extended phenotypes, their role in shaping the deployment of chemical effectors that induce phenotypic changes in other organisms remains largely unexplored. Venom provides an ideal system for addressing this question because venomous animals can regulate how much venom they deploy, and the quantity delivered can strongly influence the resulting phenotype expressed by the recipient. In this study, we subjected 48 subadult and adult southern Pacific rattlesnakes ( Crotalus oreganus helleri ) to standardized venom extractions to examine the repeatability of venomous bite characteristics across three trials. All measured bite attributes exhibited significant repeatability, including number of strikes during tubing for restraint, bite occurrence during the extraction, number of venom pulses from the fangs, volume of venom expended, and venom volume per pulse. Larger snakes expended more venom and venom expenditure increased with the number of venom pulses delivered, but consistent among-individual differences persisted in all traits after accounting for these factors. These results indicate that, similar to other defensive traits, venom deployment comprises a repeatable component of the defensive behavior of rattlesnakes. Although repeatability of venom expenditure needs to be tested in additional contexts, our study demonstrates consistent individual differences in the deployment of a chemical effector used to generate an extended phenotype, thus highlighting the importance of consistent behavioral variation in determining how organisms deploy chemical weapons and other bioactive compounds that alter the behavior, physiology, or fitness of other organisms.