Songbirds sing species-specific songs

Learning of most complex motor skills, such as birdsong and human speech, is constrained in a manner that is characteristic of each species, but the mechanisms underlying species-specific learned behaviors remain poorly understood. Songbirds acquire species-specific songs through learning, which is also thought to depend on species-specific patterns of gene activity in song nuclei -- brain regions known to be specialized for vocal learning and production.

In the new study, Wada and colleagues made use of two closely related songbird species -- the zebra finch (Taeniopygia guttata) and the owl finch (Taeniopygia bichenovii) -- and also the hybrid offspring of matings between these two species. This allowed them to examine the relationship between inter-species differences in gene expression and the production of species-specific song patterns.

The researchers compared the songs of birds that had been taught the same species' song versus those that had only heard the other species' song; this showed that the song learning was mostly regulated by species-specific genetic differences. They then identified genes whose activity in song nuclei is regulated in a species-specific fashion, either by changes in the genes' own regulatory regions ("cis-regulation") or by changes in other proteins that affect a gene's activity ("trans-regulation").

They found that trans-regulatory changes were more prevalent than cis-regulatory changes and tended to primarily affect the activity of genes involved in the formation of nerve connections and transmission of information between neurons in one particular song nucleus, "RA" -- considered as birds' counterpart to the mammalian laryngeal motor cortex.

They identified a signaling molecule called BDNF as a mediator of changes in trans-regulated of genes in RA, with a significant correlation between individual variation in the amount of BDNF and species-specific song properties. This was supported by the fact that the use of a drug to over-activate BDNF receptors altered the activity of trans-regulated genes in the RA and disrupted the structures of learned songs in the adult zebra finch.

These results demonstrate functional neurogenetic associations between inter-species differences in gene regulation and species-specific learned behaviors. According to the authors, future research building on these findings could reveal the specific gene regulatory changes that underlie the evolution of species-specific learned behaviors.

"We believe that this isn't just about bird songs," the lead author, Kazuhiro Wada said. "Our study is a promising step to understand how the changes in gene regulation could eventually lead to the evolution of species-specific animal behaviors."