Genetic variability maintained in a finite population under mutation and autocorrelated random fluctuation of selection intensity.

By using the diffusion equation method, the level of genetic variability maintained under mutation pressure in a finite population is investigated, assuming autocorrelated random fluctuation of selection intensity. An appropriate mathematical model was formulated to treat the change of gene frequencies, incorporating mutation pressure and fluctuating selection. Extensive Monte Carlo simulation experiments were also performed to supplement the theoretical treatments. Excellent agreement between the two results suggests the validity of the present diffusion model for the autocorrelated selection. One of the most important findings from the simulation studies is that mutations and random sampling drift largely determine the level of genetic variability, and that the presence of autocorrelated selection can significantly lower genetic variability only when its strength, as measured by the cumulative variance of selection intensity, is larger than about 10(3) times the mutation rate. It is pointed out that the effects of both mutations and random sampling drift have to be incorporated in order to assess the role of various factors for the maintenance of genetic variability in natural populations.