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

Exposure to multiple toxic compounds imposes selective pressures across biological levels. There are several known toxin resistance mechanisms–such as behavioral avoidance, metabolic detoxification, and target-site insensitivity but an integrative approach to consider multiple toxins and resistance strategies. Predators of amphibians, for example, must counteract multiple chemicals secreted by different species or even by the same individual prey. The pan-Amazonian snake Erythrolamprus reginae (Squamata: Colubridae) preys on multiple species of poisonous frogs, including members of the Dendrobatidae family, and is therefore exposed to a chemically diverse diet. We aimed to evaluate the process of consuming a toxic prey, from behavioral decisions to a suite of resistance mechanisms. First, feeding assays revealed that E. reginae exhibited longer handling times and aversive behaviors toward the highly toxic Ameerega trivittata, suggesting additional foraging costs. Second, we showed that soluble proteins in the liver partially restored the activity inhibited by A. trivittata alkaloids and neosaxitoxin, indicating the presence of toxin-binding proteins. Third, transcriptomic profiling across tissues revealed a complementary detoxification mechanism based on liver-specific upregulation of transporters. Finally, we showed that E. reginae voltage-gated sodium channel Na_V1.4 is highly resistant to tetrodotoxin, saxitoxin, and neosaxitoxin. However, this same Na_V1.4 channel variant did not prevent inhibition by A. trivittata alkaloids. These demonstrate that E. reginae populations may be adapting to a chemically diverse diet by evolving multiple, overlapping forms of resistance. This highlights the complexity of resistance where selection favors multiple mechanisms acting at different physiological levels, providing unparalleled insight into whole-organismal resistance.