Concerted evolution reveals co-adapted amino acid substitutions in Na+K+-ATPase of frogs that prey on toxic toads.

ABSTRACT Gene duplication is an important source of evolutionary innovation, but the adaptive division-of-labor between duplicates can be opposed by ongoing gene conversion between them. Here we document a tandem duplication of Na + ,K + -ATPase subunit α1 (ATP1A1) shared by frogs in the genus Leptodactylus , a group of species that feeds on toxic toads. One ATP1A1 paralog evolved resistance to toad toxins while the other paralog retained ancestral susceptibility. We show that the two Leptodactylus paralogs are distinguished by 12 amino acid substitutions that were maintained by strong selection that counteracted the homogenizing effect of gene conversion. Protein-engineering experiments show that two major-effect substitutions confer toxin resistance, whereas the 10 additional substitutions mitigate deleterious pleiotropic effects on enzyme function. Our results highlight how trans-specific, neofunctionalized gene duplicates can provide unique insights into interactions between adaptive substitutions and the genetic backgrounds on which they arise. One Sentence Summary Selection counteracts gene conversion to maintain an adaptive division-of-labor between tandemly duplicated genes.