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Motor pathway convergence predicts syllable repertoire size in oscine birds
Jordan M. Moore, Tamás Székely, József Büki and Timothy J. DeVoogd
Proceedings of the National Academy of Sciences of the United States of America
Vol. 108, No. 39 (September 27, 2011), pp. 16440-16445
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/41352817
Page Count: 6
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Behavioral specializations are frequently associated with expansions of the brain regions controlling them. This principle of proper mass spans sensory, motor, and cognitive abilities and has been observed in a wide variety of vertebrate species. Yet it is unknown if this concept extrapolates to entire neural pathways or how selection on a behavioral capacity might otherwise shape circuit structure. We investigate these questions by comparing the songs and neuroanatomy of 49 species from 17 families of songbirds, which vary immensely in the number of unique song components they produce and possess a conserved neural network dedicated to this behavior. We find that syllable repertoire size is strongly related to the degree of song motor pathway convergence. Repertoire size is more accurately predicted by the number of neurons in higher motor areas relative to that in their downstream targets than by the overall number of neurons in the song motor pathway. Additionally, the convergence values along serial premotor and primary motor projections account for distinct portions of the behavioral variation. These findings suggest that selection on song has independently shaped different components of this hierarchical pathway, and they elucidate how changes in pathway structure could have underlain elaborations of this learned motor behavior.
Proceedings of the National Academy of Sciences of the United States of America © 2011 National Academy of Sciences