MBE Advance Access published online on October 17, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn237
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Research Article |
Comparative Proteomics Reveals Evidence for Evolutionary Diversification of Rodent Seminal Fluid and Its Functional Significance in Sperm Competition
1 Mammalian Behaviour and Evolution Group, Department of Veterinary Preclinical Science, University of Liverpool, Leahurst Campus, Chester High Road, Cheshire CH64 7TE, U.K
2 Proteomics and Functional Genomics Group, Faculty of Veterinary Science, University of Liverpool, Crown Street, Liverpool L69 7ZJ, U.K
Corresponding author: Dr. P. Stockley, Mammalian Behaviour and Evolution Group, Department of Veterinary Preclinical Science, University of Liverpool, Leahurst Campus, Chester High Road, Neston CH64 7TE, U.K. Tel. +44 (0)151 794 6103; Fax +44 (0)151 794 6107; Email p.stockley{at}liv.ac.uk.
Received for publication July 16, 2008. Revision received October 10, 2008. Accepted for publication October 13, 2008.
During insemination, males of internally fertilizing species transfer a complex array of seminal fluid proteins to the female reproductive tract. These proteins can have profound effects on female reproductive physiology and behaviour, and are thought to mediate post-copulatory sexual selection and inter-sexual conflict. Such selection may cause seminal fluid to evolve rapidly, with potentially important consequences for speciation. Here we investigate the evolution of seminal fluid proteins in a major mammalian radiation, the muroid rodents, by quantifying diversity in seminal fluid proteome composition for the first time across a broad range of closely-related species. Using comparative proteomics techniques to identify and cross-match proteins, we demonstrate that rodent seminal fluid is highly diverse at the level of both proteomes and individual proteins. The striking interspecific heterogeneity in seminal fluid composition revealed by our survey far exceeds that seen in a second proteome of comparable complexity, skeletal muscle, indicating that the complement of proteins expressed in seminal fluid may be subject to rapid diversification. We further show that orthologous seminal fluid proteins exhibit substantial interspecific variation in molecular mass. Since this variation cannot be attributed to differential glycosylation or radical differences in termination sites, it is strongly suggestive of rapid amino acid divergence.
Sperm competition is implicated in generating such divergence for at least one major seminal fluid protein in our study, SVS II, which is responsible for copulatory plug formation via transglutaminase-catalysed cross-linking after insemination. We show that the molecular mass of SVS II is positively correlated with relative testis size across species, which could be explained by selection for an increased number of cross-linking sites involved in the formation of the copulatory plug under sperm competition.
Key Words: copulatory plug • proteomics • mammals • seminal fluid • sexual selection • sperm competition
3,5 These authors contributed equally to this work.