Abstract:
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.
