Frank , S . A . 1992 . A kin selection model for the evolution
نویسنده
چکیده
SUMMARY The costs and benefits of parasite virulence are analyzed in an Evolutionarily Stable Strategy (ESS) model. Increased host mortality caused by disease (virulence) reduces a parasite's fitness by damaging its food supply. The fitness costs of high virulence may be offset by the benefits of increased transmission or ability to withstand the host's defenses. It has been suggested that multiple infections lead to higher virulence because of competition among parasite strains within a host. A quantitative prediction is given for the ESS virulence rate as a function of the coefficient of relatedness among coinfecting strains. The prediction depends on the quantitative relationship between the costs of virulence and the benefits of transmission or avoidance of host defenses. The particular mechanisms by which parasites can increase their transmission or avoid host defenses also play a key role in the evolution of virulence when their are multiple infections. Parasites face a tradeoff between damaging their hosts (virulence), which destroys their food supply, and the benefits of rapid growth and transmission. Levin and Pimental (1981) showed that intermediate levels of virulence are often favored when the advantages of high transmission rate are offset by the costs of high virulence. showed that a tradeoff between virulence and the host's ability to purge itself of infection (recovery rate) can favor the evolution of intermediate levels of virulence. Finally, Bremermann and Pickering (1983) and Knolle (1989) have shown that competition among parasites within a host can favor the evolution of increased virulence. In this case the group of coinfecting parasites may gain by sparing the host, but competition among parasites within the group favors high transmission and greater virulence. I present a simple model for the evolution of virulence. This model is useful in two ways. First, specific quantitative predictions are given for the relationship between the genetic variability among coinfecting strains and the evolution of virulence. This is important because genetic variability, rather than the number of coinfecting strains (Bremermann and Pickering 1983; Knolle 1989), determines how virulence evolves. In addition, genetic variability of parasites within a host is easier to measure than the number of coinfecting strains. The second contribution of this model is that it focuses attention on the mechanisms by which a parasite increases its transmission or avoids the host's defenses. For example, if the mechanism of transmission is a sneeze, and all parasites within a host gain equally from an …
منابع مشابه
A kin selection model for the evolution of virulence.
The costs and benefits of parasite virulence are analysed in an evolutionarily stable strategy (ESS) model. Increased host mortality caused by disease (virulence) reduces a parasite's fitness by damaging its food supply. The fitness costs of high virulence may be offset by the benefits of increased transmission or ability to withstand the host's defences. It has been suggested that multiple inf...
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