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MBE Advance Access published online on January 6, 2009
Molecular Biology and Evolution, doi:10.1093/molbev/msn296
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© The Author 2009. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Article

Balancing and directional selection at exon-2 of the MHC DQB1 locus among populations of Odontocete cetaceans

Demetrios Vassilakos*,1, Ada Natoli*, Marilyn Dahlheim{dagger} and A. Rus Hoelzel*

* School of Biological and Biomedical Sciences, University of Durham, DH1 3LE, UK
{dagger} National Marine Mammal Laboratory, National Marine Fisheries Service, Seattle, Washington

Corresponding author: A. Rus Hoelzel, School of Biological and Biomedical Sciences, University of Durham, South Road, Durham, DH1 3LE, UK; phone: +44-(0)191-334-1325; fax: +44-(0)191-334-1201; email: a.r.hoelzel{at}dur.ac.uk

Received for publication April 9, 2008. Revision received November 6, 2008. Accepted for publication December 16, 2008.

The diversity of exon-2 (peptide binding region) of the DQB1 locus (Class II, MHC) was investigated on an extended sample of populations of three focal cetacean species (two sibling delphinid species, and another in the same family). We tested the hypothesis that dolphin populations with a world-wide distribution across different habitats and geographic regions will be under differential selective pressure by comparing DQB1 variation with variation at neutral markers, and by investigating putative functional residues within the exon-2 sequence at the population level. Variation at the DQB1 locus was not correlated to neutral differentiation (assessed by comparison with microsatellite DNA markers), and overall FST values were significantly lower for the MHC locus, consistent with expectations for balancing selection. Measures of heterozygosity and dn/ds ratios were also consistent with balancing selection. However, outliers in the FST comparisons and the analysis of putative functional residues suggested incidences of directional selection in local populations.

Key Words: Evolution • Population Genetics • Marine Mammal • MHC • Immune System

1 Present address: Division of Molecular Immunology, MRC National Institute for Medical Research, London, UK, NW7 1AA


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