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Positive Darwinian evolution in human influenza A viruses
W M Fitch1, J M Leiter, X Q Li
1Department of Ecology and Evolutionary Biology, University of California, Irvine 92717.
Summary
Type A influenza virus evolves through positive Darwinian selection, driven by immune surveillance. Survivors show more beneficial mutations in antigenic sites than extinct lineages, indicating rapid viral evolution.
Area of Science:
- Evolutionary biology
- Virology
- Molecular biology
Background:
- Type A influenza viruses are subject to immune surveillance.
- Previous work suggested positive Darwinian selection in influenza virus genes.
Purpose of the Study:
- To demonstrate positive Darwinian evolution in type A human influenza virus.
- To analyze amino acid replacements in antigenic sites of surviving versus extinct lineages.
Main Methods:
- Comparative analysis of amino acid replacements in viral hemagglutinin genes.
- Distinguishing between surviving (trunk) and extinct (branch) lineages in the evolutionary tree.
Main Results:
- Viral hemagglutinins fix more amino acid replacements in antigenic sites in surviving lineages compared to extinct ones.
- The hemagglutinin gene evolves three times faster than the nonstructural gene.
- Extinction of influenza lineages is rapid, with an average age of only 1.6 years for nonsurvivors.
Conclusions:
- Type A human influenza virus undergoes positive Darwinian evolution.
- Immune surveillance drives the fixation of favorable amino acid replacements in antigenic sites.
- Influenza virus evolution is characterized by rapid extinction and selection for advantageous mutations.