title: Positive Darwinian selection results in resistance to cardioactive toxins in true toads (Anura: Bufonidae).
abstract: Members of the Family Bufonidae, true toads, are famous for their endogenously synthesized cardioactive steroids that serve as defensive toxins. Evolution of resistance to these toxins is not understood. We sequenced a key region of the toxin's binding site in the Na(+)/K(+) ATPase for relevant taxa representing Hyloidea (including bufonids), Ranoidea and Archaeobatrachia and tested for positive selection in a phylogenetic context. Bufonidae were distinct from other Hyloidea at 4-6 of 12 sites and, with one exception, had a homologous amino acid sequence. Melanophryniscus stelzneri had a distinct sequence, consistent with other independent evidence for a differentiated toxin. Tests within Bufonidae detected positive selection within the binding region, providing, to our knowledge, the first evidence of this type for positive selection within Amphibia. There was no evidence for positive selection on Bufonidae or M. stelzneri lineages. Sequence change in Leptodactylus ocellatus, a leptodactylid predator of Bufonidae, provides a molecular basis for predator resistance possibly associated with gene duplication.
authors.affiliation: School of Botany and Zoology, The Australian National University, Canberra, ACT 0200, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Moore
authors.forename: Damien C T
authors.initials: DC
authors.lastname: Halliday
authors.forename: David M
authors.initials: DM
authors.lastname: Rowell
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Robinson
authors.forename: J Scott
authors.initials: JS
authors.lastname: Keogh
mesh_terms: D000818:Animals; D001001:Anura / Q000378:metabolism / Q000502:physiology*; D001665:Binding Sites; D005075:Biological Evolution; D005091:Exons; D020440:Gene Duplication; D010802:Phylogeny; D012867:Skin / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013045:Species Specificity; D013256:Steroids / Q000378:metabolism; D014981:Xenopus; D014982:Xenopus laevis
chemical_list: D013256:Steroids; D000254:Sodium-Potassium-Exchanging ATPase