, Volume 53, Issue 6, pp 483–489

Class I MHC polymorphism and evolution in endangered California Chinook and other Pacific salmon

  • Daniel Garrigan
  • Philip W. Hedrick
Original Paper

DOI: 10.1007/s002510100352

Cite this article as:
Garrigan, D. & Hedrick, P.W. Immunogenetics (2001) 53: 483. doi:10.1007/s002510100352


Twelve MHC class I exon 2 sequences were uncovered in a sample from the endangered Sacramento River winter-run Chinook salmon in the central valley of California. Phylogenetic analysis of the 12 sequences indicates that the alleles descend from two of six major allelic lineages found among four Pacific salmon species. Nine of the 12 alleles belong to an allelic lineage that began diversifying 8 million years ago, just prior to the estimated time of Chinook speciation. The most recent common ancestor of all 12 winter-run alleles is estimated to be 15 million years ago, approximately 5 million years before the radiation of the Pacific salmon species. The average nonsynonymous distance among the peptide binding-region codons of exon 2 for the 12 alleles is significantly higher than the average synonymous distance in these codons. We estimate the symmetrical overdominant selection coefficient against homozygotes for this exon to be 0.038. Thus, strong positive and balancing selection has maintained functional diversity in the peptide-binding region of the exon over millions of years and this variation has not yet been substantially eliminated by increased genetic drift due to the recent dramatic decline in abundance of this Chinook salmon population.

Chinook salmon Major histocompatibility complex Polymorphism Positive selection Substitution rate Trans-species evolution

Copyright information

© Springer-Verlag 2001

Authors and Affiliations

  • Daniel Garrigan
    • 1
  • Philip W. Hedrick
    • 1
  1. 1.Department of Biology, Arizona State University, Tempe, AZ 85287-1501, USA