Individual reproductive strategies shape the mating system of tree sloths

Abstract

While polygyny is the dominant mating system in mammals, it is increasingly recognized that promiscuity occurs in most species. Using a long-term genetic and space-use data set, we documented the mating system for 2 sedentary and uniparous species of tree sloths, brown-throated three-toed (Bradypus variegatus) and Hoffmann's two-toed (Choloepus hoffmanni) sloths. We predicted that the life history of these species facilitates female strategies that promote mating with multiple males across breeding seasons, and shape central features of the mating system in tree sloths. We found that many female sloths mated with different males during our study: 70% of female B. variegatus and 50% of female C. hoffmanni switched mates among years at least once during our study. Our observations of individual movements suggested that females employed 2 strategies that appeared to influence mate switching across breeding seasons: 1) selecting a male from a pool of males in their activity center, and 2) mating with different males by shifting their home ranges during estrus. Collectively, our findings suggest that individual variation in female reproductive strategies contributes to shaping the mating systems for a sedentary mammal like sloths, and highlights the need for long-term studies to effectively capture the mating systems of mammals with slow life histories.