Capturing the Effects of Domestication on Vocal Learning Complexity

Domesticated and vocal learning species can serve as informative model organisms for the reduction of reactive aggression and emergence of speech in our lineage. Amidst mounting evidence that domestication modifies vocal repertoires across different species, we focus on the domesticated Bengalese finch, which has a more complex song than the wild-type white-rumped munia. Our explanation for this effect revolves around the glutamate neurotransmitter system. Glutamate signaling (i) is implicated in birdsong learning, (ii) controls dopamine activity in neural circuits crucial for vocal learning, (iii) is disproportionately targeted in the evolution of domesticates, and (iv) regulates stress responses and aggressive behaviors attenuated under domestication. We propose that attenuated excitation of stress-related neural circuits potentiates vocal learning via altered dopaminergic signaling. Signals of positive selection across domesticated species and in modern humans disproportionately fall on glutamatergic signaling genes that attenuate stress responses and differentially modulate dopamine release in the dorsal and ventral striatum.The Bengalese finch, a domesticated songbird that shows evidence for attenuated stress signaling, produces a more varied and syntactically complex song than the stereotyped songs of the wild-type white-rumped munia.Multiple studies implicate midbrain–striatal dopamine release and domestication-associated glutamatergic signaling genes in the vocal learning abilities of songbirds and in stress disorders marked by stereotypies and tics.We propose that attenuated stress signaling under domestication can bring about alterations to glutamate–dopamine interactions in the striatum, supporting more variable vocalizations.