Rules of amino acid convergence: Not how many, but who in avian vocal learning clades

Abstract Single amino acid variants (SAVs) may provide clues to understanding evolution of traits. A complex trait that has evolved convergently among species is vocal learning, the rare ability to imitate sounds heard and an important component of spoken-language. Here we assessed whether convergent vocal learning bird species have convergent SAVs (CSAVs) that could be associated with their specialized trait. We analyzed avian genomes and identified CSAVs in vocal learners, but also in most species combinations tested. The number of CSAVs among species was proportional to the product of the most recent common ancestor (MRCA; origin) branch lengths of the species in question, and vocal learning birds did not exceed the overall proportion in most test. However, genes with identical CSAVs (iCSAVs) in vocal learning species were uniquely enriched in ‘learning’ functions, and a subset of iCSAV genes were under positive selection and had enriched specialized regulation in vocal learning and their adjacent brain subdivisions. Several top candidate genes converge on the cAMP signaling pathway, including DRD1B and PRKAR2B. Our findings suggest a complex mechanism of amino acid convergences and specialized gene regulation upon which selection acts for specialized convergent traits.