Dramatic dietary shift maintains sequestered toxins in chemically defended snakes

Abstract

Significance Animals protected by sequestered toxins must employ an alternative source of defensive chemicals when a shift in diet evolves. Snakes of the genus Rhabdophis possess defensive glands that store powerful defensive toxins known as bufadienolides. The ancestral prey of Rhabdophis consists of anuran amphibians, including toads (Bufonidae) that are the source of sequestered bufadienolides. However, members of a derived clade of Rhabdophis consume nontoxic earthworms as their primary prey, yet their integumentary glands still contain bufadienolides. We demonstrate that snakes in the worm-eating clade obtain their defensive toxins primarily by consuming larval fireflies. Our finding represents a remarkable evolutionary example in which a shift from vertebrate to nonvertebrate prey provides the same chemical class of sequestered defensive toxins.