Valeria Ramírez-Castañeda , Rebecca Tarvin, Roberto Marquez

Chemical defenses shape ecosystems by orchestrating interactions between species and promoting specialization on toxic prey. Many toxins exist in highly biodiverse tropical ecosystems, sometimes in the same prey, imposing challenges for studying toxin resistance and requiring the development of new models. Royal ground snakes (Erythrolamprus) play a significant but understudied role as predators of poisonous frogs (Bufonidae, Dendrobatidae). Several frog toxins affect the voltage-gated sodium channels (VGSCs) and sodium potassium pumps; resistance can evolve in these genes through mutations in target sites, known as target-site resistance (TSR). We investigated potential TSR in VGSC orthologs and traced their phylogenetic origin and geographic presence in six Erythrolamprus species and 15 snake outgroups from Colombia. We reveal convergent evolution of TSR in VGSCs of three Erythrolamprus snake species: E. epinephelus, E. reginae, and E. sp. We found nine sites in the VGSC pore at which neurotoxin-resistance-related amino acid changes occur in eight VGSC genes, suggesting coordinated evolution of this gene family. Amino acid substitutions at four of these positions were previously reported as conferring tetrodotoxin resistance in other species, however, the dietary source of tetrodotoxin in these snake species is unclear. Across genes, species, and populations, these sites exhibit high heterogeneity of alleles, suggestive of an evolutionary dynamic that maintains polymorphisms, such as balancing selection. These findings provide insight into the evolution of predators with a complex toxic diet, paving the way for new research models to address complex coevolutionary questions in exceptionally diverse tropical ecosystems.