Parrots are one of only three avian orders known to be vocal learners, the others being songbirds and hummingbirds. Considering the 65 million years of evolutionary history that separates songbirds and parrots from their common ancestor, if their vocal nuclei evolved independently, then convergence on similar molecular and anatomical substrates would suggest that vertebrate brain organization and possible epigenetic factors place strong constraints on how such structures could evolve.
Auditory and vocal regulation of gene expression occurs in separate discrete regions of the songbird brain. We demonstrate that regulated gene expression also occurs during vocal communication in a parrot, which belongs to an order whose ability to learn vocalizations is thought to have evolved independently of songbirds.
Adult male budgerigars (Australian parakeets) were stimulated to vocalize with playbacks of conspecific vocalizations (warbles), and their brains were analyzed for expression of the transcriptional regulator ZENK. The results showed that there was distinct separation of brain areas that had hearing- or vocalizing induced ZENK expression.
When budgerigars hear conspecific warbles, ZENK is induced in the caudomedial forebrain and within the midbrain, but not elsewhere, in a pattern highly reminiscent of that observed in songbirds. In contrast, when budgerigars engage in active vocalizing, ZENK is induced in nine other distinct brain structures, with a pattern only partially reminiscent of that observed in songbirds.
These results allowed us to generate a functional brain map of areas involved in parrot vocal communication and to address further the neurobiological basis of the evolution of vocal learning. Our results indicate that, whether or not vocal learning evolved independently, some of the gene regulatory mechanisms that accompany learned vocal communication are similar in songbirds and parrots.
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