Intraspecific variation in male mating strategies in an African ground squirrel (Xerus inauris)

Male mating strategies respond to female availability such that variation in resources that affect spatial distribution can also alter cost-benefit tradeoffs within a population. In arid-adapted species, rainfall alters reproduction, behavior, morphology, and population density such that populations differing in resource availability may also differ in successful reproductive strategies. Here, we compare two populations of Cape ground squirrels (Xerus inauris), a sub-Saharan species with year-round breeding and intense mating competition. Unlike most mammals where males resort to aggressive interactions over females, male X. inauris are tolerant of one another, relying instead on other nonaggressive pre- and postcopulatory strategies to determine reproductive success. Our findings suggest that differences in resource availability affect female distribution, which ultimately leads to intraspecific variation in male reproductive tactics and sexual morphology. Sperm competition, assessed by reproductive morphometrics, was more pronounced in our high resource site where females were distributed evenly across the landscape, whereas dominance seemed to be an important determinant of success in our low resource site where females were more aggregated. Both sites had similar mating intensities, and most males did not sire any offspring. However, our low resource site had a higher variance in fertilization success with fewer males siring multiple offspring compared with our high resource site where more individuals were successful. Our results lend support to resource models where variations in female spatial distribution attributed to environmental resources ultimately impact male reproductive behaviors and morphology.