EAPSI: Investigating the Mechanisms of Toxin Resistance in Specialized Toad-Eating Snakes

Mohammadi Shabnam, Logan UT

Investigators

Abstract

Toads are chemically defended by potent steroid toxins, which are lethal if ingested. Consequently, most predators avoid consuming toads. However, several species of snakes have evolved resistance to the toxins and actively prey on toads. The Japanese snake Rhabdophis tigrinus has further evolved the ability to store the acquired dietary toxins for use in its own defense. The mechanisms responsible for resistance and physiological consequences of that resistance remain unknown. This research will be conducted in collaboration with Dr. Akira Mori at Kyoto University, a noted expert on Japanese toad-eating snakes, to explain the unknown physiological mechanisms and determine their occurrence among various lineages of snakes, including the uniquely specialized R. tigrinus. This research will provide a better understanding of the evolution of toxin resistance in snakes. Toads are chemically defended by cardiotonic steroid toxins known as bufadienolides, which exert their lethal effects by binding to, and inhibiting, Na+,K+-ATPases on cell membranes. Although select lineages of snakes from several geographic regions actively prey on toads, the Japanese snake Rhabdophis tigrinus has further evolved the ability to sequester toad toxins for redeployment in its own defense. The researcher will pursue an integrative approach to determine the molecular mechanisms and physiological trade-offs underlying tolerance of toad toxins by clarifying the genetic basis for resistance and quantifying the physiological responses to bufadienolides in snakes. Ultimately, character mapping of molecular and physiological results will determine the extent of convergent evolution of toad-eating adaptations in snakes. The expansion of sampling to include Rhabdophis tigrinus will contribute directly to this goal by expanding phylogenetic comparisons to a lineage of toad-eating snakes distinct from others that the researcher has studied and by including the only species demonstrated to sequester toad toxins. This NSF EAPSI award is funded in collaboration with the Japan Society for the Promotion of Science.