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 +/tw12 and +/tw32 females a choice between +/tw12 and +/tw32 males Females preferred the male carrying a t-haplotype different from their own. This disassortative preference was stronger for +/tw12 than for +/tw32 females. We paired +/tw12 and +/tw32 females to males of each genotype and measured the number of fertile progeny produced. Fitness of +/tw32 females was slightly higher when they were mated to males of the opposite genotype; fitness of +/tw12 females was much higher when they were mated to +/tw32 than when mated to +/tw12 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.