Toxin resistance mechanisms span biological scales in the Royal Ground Snake (Colubridae: Erythrolamprus reginae)

Valeria Ramírez-Castañeda , Samantha Nixon, Dario Alarcón-Naforo, Fayal Abderemane-Ali, Richard Fitch, David Salazar-Valenzuela, Daniel Minor, Rebecca Tarvin

All predators of poisonous prey deal with toxins, yet we often lack an understanding of how the predators integrate various physiological adaptations to toxins. Here we investigate multiple complementary toxin resistance mechanisms in the pan-Amazonian snake Erythrolamprus reginae (Squamata: Colubridae), which consumes multiple species of poisonous frogs. We find that the toxin resistance mechanisms employed by E. reginae integrate novel behaviors, mutations in gene families, and plasticity in organ systems that help dampen possible costs of toxin exposure. Specifically, E. reginae exhibited longer handling times and aversion toward the poison frog Ameerega trivittata, demonstrating additional foraging costs and bringing into question prior assumptions about the species’ propensity to consume toxic prey. In the liver, upregulation of transporters likely helps clear toxins following A. trivittata ingestion; additionally, protein extracts from the liver partially restored the activity inhibited by various small molecule toxins, including some toxins from A. trivittata and, unexpectedly, by neosaxitoxin, a guanidinium neurotoxin not known in the snake’s diet. Further, mutations in the E. reginae voltage-gated sodium channel NaV1.4 provide resistance to guanidinium toxins including TTX, STX, neoSTX. These findings indicate that a chemically diverse prey community can drive multi-scale evolutionary responses, with distinct mechanisms acting on distinct toxin classes and, in some cases, complementary mechanisms converging on the same compound. Together our results demonstrate a comprehensive assessment of toxin resistance, establishing that resistance to toxic prey necessitates adaptations across biological scales, and providing a roadmap for future studies of toxin resistance in emerging model species.