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Medline Abstract
Department of Biology, University of California San Diego 92093, USA. lchao@biomail.ucsd.edu
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Conventional models predict that low genetic
relatedness among parasites that coinfect the same host leads to the
evolution of high parasite virulence. Such models assume adaptive
responses to hard selection only. We show that if soft selection is
allowed to operate, low relatedness leads instead to the evolution of
low virulence. With both hard and soft selection, low relatedness
increases the conflict among coinfecting parasites. Although parasites
can only respond to hard selection by evolving higher virulence and
overexploiting their host, they can respond to soft selection by
evolving other adaptations, such as interference, that prevent
overexploitation. Because interference can entail a cost, the host may
actually be underexploited, and virulence will decrease as a result of
soft selection. Our analysis also shows that responses to soft
selection can have a much stronger effect than responses to hard
selection. After hard selection has raised virulence to a level that is
an evolutionarily stable strategy, the population, as expected, cannot
be invaded by more virulent phenotypes that respond only to hard
selection. The population remains susceptible to invasion by a less
virulent phenotype that responds to soft selection, however. Thus, hard
and soft selection are not just alternatives. Rather, soft selection is
expected to prevail and often thwart the evolution of virulence in
parasites. We review evidence from several parasite systems and find
support for soft selection. Most of the examples involve interference
mechanisms that indirectly prevent the evolution of higher virulence.
We recognize that hard selection for virulence is more difficult to
document, but we take our results to suggest that a kin selection model
with soft selection may have general applicability. Publication Types:
MeSH Terms:
PMID: 11008699 |
This article has been cited by other articles:
why? |
INVESTIGATIONS: Laurence Mouton, Franck Dedeine, Hélène Henri, Michel Boulétreau, Nérina Profizi, and Fabrice Vavre Virulence, Multiple Infections and Regulation of Symbiotic Population in the Wolbachia-Asobara tabida Symbiosis Genetics, September 1, 2004; 168: 181 - 189. |
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why? |
VIEWPOINT: Andrew F. Read and Louise H. Taylor The Ecology of Genetically Diverse Infections Science, May 11, 2001; 292: 1099 - 1102. |
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