title: Toxin-resistant isoforms of Na+/K+-ATPase in snakes do not closely track dietary specialization on toads.
abstract: Toads are chemically defended by bufadienolides, a class of cardiotonic steroids that exert toxic effects by binding to and disabling the Na+/K+-ATPases of cell membranes. Some predators, including a number of snakes, have evolved resistance to the toxic effects of bufadienolides and prey regularly on toads. Resistance in snakes to the acute effects of these toxins is conferred by at least two amino acid substitutions in the cardiotonic steroid binding pocket of the Na+/K+-ATPase. We surveyed 100 species of snakes from a broad phylogenetic range for the presence or absence of resistance-conferring mutations. We found that such mutations occur in a much wider range of taxa than previously believed. Although all sequenced species known to consume toads exhibited the resistance mutations, many of the species possessing the mutations do not feed on toads, much less specialize on that food source. This suggests that either there is little performance cost associated with these mutations or they provide an unknown benefit. Furthermore, the distribution of the mutation among major clades of advanced snakes suggests that the origin of the mutation reflects evolutionary retention more than dietary constraint.
authors.affiliation: Department of Biology, Utah State University, Logan, UT 84322, USA shab.mohammadi@gmail.com.|The Ecology Center, Utah State University, Logan, UT 84322, USA.
authors.forename: Shabnam
authors.identifier: 0000-0003-3450-6424
authors.initials: S
authors.lastname: Mohammadi
authors.affiliation: Department of Biology, Utah State University, Logan, UT 84322, USA.|The Ecology Center, Utah State University, Logan, UT 84322, USA.
authors.forename: Zachariah
authors.identifier: 0000-0003-2248-2488
authors.initials: Z
authors.lastname: Gompert
authors.affiliation: Department of Biology, Utah State University, Logan, UT 84322, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Gonzalez
authors.affiliation: Department of Zoology, Kyoto University, Sakyo, Kyoto 606-8502, Japan.|Seto Marine Biological Laboratory, Field Science Education and Research Center, Kyoto University, 459 Shirahama, Wakayama 649-2211, Japan.
authors.forename: Hirohiko
authors.initials: H
authors.lastname: Takeuchi
authors.affiliation: Department of Zoology, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Mori
authors.affiliation: Department of Biology, Utah State University, Logan, UT 84322, USA savitzky@usu.edu.|The Ecology Center, Utah State University, Logan, UT 84322, USA.
authors.forename: Alan H
authors.identifier: 0000-0002-3172-9924
authors.initials: AH
authors.lastname: Savitzky
mesh_terms: D000818:Animals; D002025:Bufonidae; D004032:Diet / Q000662:veterinary*; D009154:Mutation; D010802:Phylogeny; D011235:Predatory Behavior; D020033:Protein Isoforms / Q000235:genetics; D012911:Snakes / Q000235:genetics*; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics*; D014118:Toxins, Biological / Q000737:chemistry
chemical_list: D020033:Protein Isoforms; D014118:Toxins, Biological; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Na+/K+-ATPase; bufadienolide; cardiotonic steroids; chemical ecology; toxin resistance