Tune differences between bird species linked to genes: Study

The distinct tunes sung by different bird species are due to variations in the activity of their genes, according to a study that could lead to a better understanding of how changes in the regulation of the genes in an animal's body may lead to the evolution of species-specific behaviors. The researchers, including those from Hokkaido University in Japan, said species-specific songs by birds were dependent on differences in the structure and development of regions in the brain which influenced behavior, but the genetic mechanism underlying these differences remained elusive until now. They studied the bird's zebra finches and owl finches -- two closely related bird species with different songs -- and their hybrid offspring, looking at the differences in the expression of genes between the two species, and how the varying patterns of gene activity produced proteins in the birds' brains. 

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The findings of the study, published in the journal PLOS Biology, revealed that the regulation of genes differed in the two species for about 800 genes in their brain's song nucleus -- the region responsible for vocal learning and production -- which accounts for 10 percent of all genes expressed in the brains of these birds.

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Nucleus in the bird equivalent of laryngeal motor cortex

The researchers also studied the ratio in which certain genes from the zebra finch's and the owl finch's genomes present in the hybrid offspring were expressed. Using these results, the researchers were able to map how the regulation of these genes diverged between the species -- enabling them to produce species-specific songs. The researchers said changes in the genetic activity were also associated with the formation of junctions between nerve cells in the birds' brains, and the transmission of nerve signals within and between the song nucleus. The study said the song nucleus is the bird equivalent of the laryngeal motor cortex in humans, which controls speech.

"This isn't just about bird songs. Our study is a promising step to understand how changes in gene regulation could eventually lead to the evolution of species-specific animal behaviors," said Kazuhiro Wada who led the research at Hokkaido University.

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Bird gene in nerve cells change its tune

The researchers also found a gene in the nerve cells present in the birds' brains called the brain-derived neurotrophic factor (BDNF).  They said the protein BDNF was involved in the regulation of gene expression and mediated many important processes such as the growth and specialization of nerve cells to perform distinct functions and the formation of junctions between nerve cells. When the team treated adult zebra finches with drugs that over-activated the BDNF receptors for two weeks, the activity pattern of genes in their song nuclei was altered, and the birds sang unusual songs with different patterns compared to their normal tunes. Based on the findings, the researchers suggested that differences in BDNF expression between species could shape the development of neural circuits for song learning by affecting gene expression in the song nuclei. 

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