FEMALE PREFERENCE AND VARIABILITY AMONG T-HAPLOTYPES IN WILD HOUSE MICE

Many wild house mice are heterozygous (+/t) for a t-haplotype at the t-complex. Most t-haplotypes carry recessive lethal factors causing embryonic mortality of homozygotes. Many different t-haplotypes coexist in mouse populations. Fetal death occurs when mice are homozygous for lethal haplotypes from the same complementation group. If the mouse carries two t-haplotypes from different complementation groups, it survives, but all such males are sterile. We gave +/t(w12) and +/t(w32) females a choice between +/t(w12) and +/t(w32) males. Females preferred the male carrying a t-haplotype different from their own. This disassortative preference was stronger for +/t(w12) than for +/t(w32) females. We paired +/t(w12) and +/t(w32) females to males of each genotype and measured the number of fertile progeny produced. Fitness of +/t(w32) females was slightly higher when they were mated to males of the opposite genotype; fitness of +/t(w12) females was much higher when they were mated to +/t(w32) than when mated to +/t(w12) males. Hence, female preferences for genetically based male cues may track fitness consequences of mating. Female preference combined with a fitness advantage for disassortative mating among haplotypes may maintain the high degree of genetic variability in this region.