Female mice mate preferentially with non-parasitized males.

If parasitic infection is a driving force in female mate choice, then females should preferentially select parasite-free males. The role of infection on female mate choice in mammals was assessed using a 3-chambered apparatus. A female CD-1 mouse was allowed to choose between 2 tethered male mice, 1 uninfected and 1 infected with 200 larvae (L3) of the intestinal nematode Heligmosomoides polygyrus. Both uninfected and infected males were equally receptive to the oestrous females, and females did not differ in the number of visits and time spent exploring the 2 males. Female time preference was not a useful predictor of ultimate mate choice, whereas first mount preference of the female was a reliable indicator. Results indicate that female mice preferentially mated with uninfected males as evidenced by first ejaculation choice, but that male infection status did not significantly affect female reproductive success. Interestingly, litters sired by infected males contained a significantly higher percentage of females suggesting that parasite-induced hormonal changes may alter the sex ratio of the offspring. This study provides the first direct evidence of the impact of parasitic infection on mammalian mate choice.