A group from Hokkaido University, University of Hyogo, the National Institute of Natural Sciences' Center for Exploration of Life and Environmental Sciences, and the National Institute for Physiological Sciences has revealed that hybrid individuals resulting from the crossing of two species of songbirds can learn the songs of not only their own species but also those of other species.

 Songbirds (passerines) are said to have species-specific learning constraints (biases in ease of learning) in song learning, and they tend to learn their own species' songs better than those of other species. For example, zebra finches cannot imitate the song of the cherry sparrow well when exposed to it, and vice versa.

 However, this study found that hybrid individuals resulting from crosses between the two species can learn the songs of both parent species. When zebra finches, cherry sparrows, and hybrid chicks were raised in as identical an environment as possible for learning songs, and were given the songs of the two parent species as examples, the hybrid chicks learned the songs of both species. On the other hand, the zebra finches and cherry sparrows chicks mainly learned the songs of their own species, and no individuals were able to reproduce the songs of the other species.

 In addition, we investigated whether hybrid individuals could learn the songs of genetically distant species such as the Japanese bush warbler, the Bengalese finch, and the canary, and found that they were able to learn these songs well. This phenomenon in which the abilities of hybrid individuals exceed those of their parent species is called hybrid vigor, and this is the first report of hybrid vigor in learning ability, especially in vocal learning.

 In a neuroscientific study, the researchers compared the brain structures of the two parent species and the hybrids. As a result, they found no significant differences in the song nuclei that control vocal learning in songbirds, but single-cell gene expression analysis revealed that the glutamate excitatory neuron group in the vocal motor nucleus of the hybrids had a high number of non-additively expressed genes with biased gene expression levels, rather than intermediate between the parent species. As there was a significant correlation between the expression levels of these gene groups and the number of phonemes learned by the hybrids, they suggest that gene expression patterns may be involved in the background of the findings of this study, which can be seen as an example of "black kites giving birth to hawks."

Paper information:[Science Advances] Expansion of learning capacity elicited by interspecific hybridization

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