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MBE Advance Access published online on November 28, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msm260
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Published by Oxford University Press 2007.

Research Article

Duplication of Growth Hormone Gene and Accelerated Evolution in Passerine Birds

Tamaki Yuri1,2,4, Rebecca T. Kimball2, Edward L. Braun2 and Michael J. Braun1,3

1 Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, 4210 Silver Hill Road, Suitland, MD 20746, USA
2 Department of Zoology, University of Florida, Gainesville, FL 32611, USA
3 Behavior, Ecology, Evolution, and Systematics Program, University of Maryland, College Park, MD 20742, USA

4 Author for correspondence: Tamaki Yuri, Department of Zoology, University of Florida, P.O. Box 118525, Gainesville, FL 32611-8525, Phone: (352) 846-3737, Fax: (352) 392-3704, Email: tyuri{at}ufl.edu

Received for publication March 27, 2007. Revision received October 18, 2007. Accepted for publication November 21, 2007.

We report the discovery of a duplication of the growth hormone gene in a major group of birds, the passerines (Aves: Passeriformes). Phylogenetic analysis of 1.3-kb partial DNA sequences of growth hormone genes for 24 species of passerines and numerous outgroups indicates that the duplication occurred in the ancestral lineage of extant passerines. Both duplicates and their open reading frames are preserved throughout the passerine clade, and both duplicates are expressed in the Zebra Finch brain, suggesting that both are likely to be functional. The estimated rates of amino acid evolution are more than ten fold higher in passerine growth hormone genes than in those of their closest non-passerine relatives. In addition, although the 84 codons sequenced are generally highly conserved for both passerines and non-passerines, comparisons of the non-synonymous/synonymous substitution ratios and the rate of predicted amino acid changes indicate that the two gene duplicates are evolving under different selective pressures and may be functionally divergent. The evidence of differential selection, coupled with the preservation of both gene copies in all major lineages since the origin of passerines, suggests the duplication may be of adaptive significance, with possible implications for the explosive diversification of the passerine clade.

Key Words: relaxation of selection • positive selection • subfunctionalization • Passeriformes


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