Influence of scramble competition for mates upon the spatial ability of male meadow voles

Scramble competition for mates selects for traits that increase an individual's ability to efficiently locate mates. We tested the hypothesis that scramble competition for mates is the cause of sex differences in spatial ability among meadow voles, Microtus pennsylvanicus. Specifically, we tested the predictions that males with better spatial ability have larger home ranges, visit more females' nests, and achieve greater reproductive success. We also tested the prediction that receptive females would mate with the first male that they contacted. The spatial ability of wild-caught males was quantified using the Morris water maze. Males with known spatial ability were released into enclosures for two field experiments. In the first experiment, we determined the males' home range sizes using radiotelemetry. In the second experiment, we quantified males' visits to nests by housing females in nestboxes with one-way doors and checking the boxes for male visitors twice daily. Paternity was determined by amplifying polymorphic loci using nine microsatellite primers. We found that males with better spatial ability had larger home ranges and made more visits to different nestboxes than did males with poorer spatial ability. Males with better spatial ability did not, however, sire more litters or pups. This finding may have been the result of female mate choice based on traits other than spatial ability. Females also did not always mate with the first male that they encountered.