Natural Selection

Abstract

Genetic variation due to the segregation of known Mendelian genes provides a way to study the synthesis of population growth and natural selection. One such allelic polymorphism in Tribolium is associated with the utilization of unsaturated fatty acids, where the metabolism or lack of metabolism is essentially due to a single autosomal locus with two alleles (Costantino et al. 1966,1967,1968). In a population genetic analysis, interest in this sort of fitness-related physiological mutant is focused on the dynamics of both allele frequency and population size. While selection in the context of Malthusian growth is the more traditional approach (Moran 1962, Crow and Kimura 1970), an extensive literature on non-Malthusian growth is available (MacArthur 1962, Anderson 1971, Roughgarden 1971, Charlesworth 1971, Clarke 1972,1973, Ginzburg 1977a, Asmussen andFeldman 1977, Hastings 1978, Leon and Charlesworth 1978, Gregorius 1979, Slatkin and Maynard Smith 1979, Desharnais and Costantino 1983, Ginzburg 1983, Selgrade and Namkoong 1984). New questions arise. With selection and non-Malthusian growth, the equilibrium allele frequency no longer corresponds to the maximization of the population’s growth rate but rather leads to the maximization of the equilibrium population size. In laboratory experiments with the flour beetle, is population size maximized? Do cultures with different initial allele frequencies all converge to a common allele frequency? Do they converge to a common population size? How is the concept of a stochastic equilibrium, as discussed in Chapters 4 and 5, to be viewed? In this chapter we look at the long term or stationary dynamics while in the next chapter we emphasize the dynamics of the approach to equilibrium.