Mate choice, monogamy and mutational load.

The classical Haldane mutational load for dominant mutations is 1 - e-alpha (where alpha = the mutation rate of the genome). This is independent of the fitness of the mutant heterozygotes. As alpha may be between 0.9 and 1.8 this may be too high for low fecundity species to bear. The load may be greatly reduced for mildly deleterious mutations if female choice (for males with few or no mutations) is present in a polygamous species. It is shown here that if females and males prefer partners with few or no mutations then the load may also be reduced in monogamous species. As in the polygamous model the effect is greatest if mutations are mildly deleterious.