Functional venom activity and antivenom neutralization in rattlesnakes across Baja California and Gulf of California islands.

Snake venoms are complex biochemical phenotypes whose composition can diverge dramatically among taxa, yet the functional and biomedical consequences of such variation remain understudied for many lineages. Here, we characterized the functional activities of venom from multiple rattlesnake species distributed across insular and mainland localities in the Baja California Peninsula and Gulf of California. We quantified phospholipase A2 (PLA2), proteolytic, and fibrinogenolytic activities as well as median lethal doses (LD50) for 55 individuals across Crotalus enyo, C. mitchellii, C. pyrrhus sensu lato, and C. ruber. We also evaluated the neutralization efficacy of the commercial polyvalent antivenom Antivipmyn®. Venom functional activities differed significantly among species. Crotalus mitchellii expressed a neurotoxic phenotype characterized by the highest PLA2 activity, the lowest LD50 values, and minimal proteolysis. Crotalus pyrrhus and C. ruber expressed proteolytic phenotypes with high enzymatic activity and ubiquitous dual-chain fibrinogenolysis. Crotalus enyo exhibited intermediate functional activities with moderate enzymatic output and the most efficient antivenom neutralization among species. Although Antivipmyn® neutralized the lethal activity of all venoms, efficacy differed significantly among species in both mass-normalized (mgAV/mgV) and potency-scaled (LD50-equivalents per vial) metrics. Notably, insular and mainland populations within species showed qualitative variation in both functional activities and antivenom responses. These results establish that the focal species possess functionally distinct venom phenotypes with species-specific consequences for antivenom neutralization, underscoring the relevance of venom functional characterization for clinical management of envenomation across the Baja California region.