The evolution of sex and recombination in a varying environment.

Theoretical models of the evolutionary advantages of sex and genetic recombination in a temporally varying environment are analyzed. The models assume a quantitative trait controlled by many additive genes and subject to nor-optimal selection. The optimal value of the trait is assumed either to move steadily in one direction or to follow an autocorrelated linear Markov process. The consequences for population mean fitness of a reduction in genetic variance, due to a shift from sexual to asexual reproduction, are examined. It is shown that a large reduction in mean fitness can result from such a shift in the case of a steadily moving optimum, under light conditions. The conditions are much more stringent with a randomly varying environment, especially if the autocorrelation is low. The conditions for spread of a rare modifier affecting the rate of genetic recombination are also examined, and the strength of selection on such a modifier is determined. Again, the case of a steadily moving optimum is more favorable than a random optimum for the evolution of increased recombination.