Mating behavior of Columbian ground squirrels .1. Multiple mating by females and multiple paternity

Patterns of multiple mating by female Columbian ground squirrels (Spermophilus columbianus) were investigated by observing mating behavior intensively over 5 years. Paternity of litters was assessed through electrophoretic analyses of blood proteins in samples collected from females, offspring, and putative fathers. On average, females mated with four males, and all mated with more than one male. Sixteen percent of 165 litters were multiply sired, but that is probably an underestimate of the rate of multiple paternity. Neither age of the female nor a crude estimate of the operational sex ratio affected number of mates. Litter size did not vary with the number of mates a female had. However, numbers and proportion of juveniles surviving to yearling age tended to increase (nonsignificantly) with the number of mates for mothers. These data suggest that mate choice for ''good genes'' via sperm competition is the most plausible benefit of multiple mating for females. Other possible benefits of multiple mating are either not plausible or untested with current data.