Hamilton's indicators of the force of selection.
To quantify the force of selection, Hamilton [Hamilton, W. D. (1966) J. Theor. Biol. 12, 12-45] derived expressions for the change in fitness with respect to age-specific mutations. Hamilton's indicators are decreasing functions of age. He concluded that senescence is inevitable: survival and fertility decline with age. I show that alternative parameterizations of mutational effects lead to indicators that can increase with age. I then consider the case of deleterious mutations with age-specific effects. In this case, it is the balance between mutation and selection pressure that determines the equilibrium number of mutations in a population. In this balance, the effects of different parameterizations cancel out, but only to a linear approximation. I show that mutation accumulation has little impact at ages when this linear approximation holds. When mutation accumulation matters, nonlinear effects become important, and the parameterizations of mutational effects make a difference. The results also suggest that mutation accumulation may be relatively unimportant over most of the reproductive lifespan of any species.
Baudisch
Annette
A
Laboratory of Survival and Longevity, Max Planck Institute for Demographic Research, Konrad-Zuse-Strasse 1, Rostock, Mecklenburg D-18057, Germany. abaudisch@demogr.mpg.de
D000375:Aging / Q000235:genetics*; D005075:Biological Evolution; D005298:Fertility / Q000235:genetics; D008136:Longevity / Q000235:genetics; D008957:Models, Genetic; D009154:Mutation / Q000235:genetics*; D012098:Reproduction / Q000235:genetics; D012641:Selection, Genetic; D015996:Survival Rate