The mating system of a ‘lazy’ mammal, Hoffmann's two-toed sloth

Theory predicts that mating systems are influenced by sex-specific selection pressures and the dispersion of females, but potential constraints imposed by a species' life history and physiology are rarely considered. Sloths, or ‘perezosos’ (the ‘lazies’) in Spanish, are one of the most sedentary terrestrial mammals on Earth, and we hypothesized that their low mobility would constrain the ability of males to take advantage of the ‘polygamy potential’ of their environment. We characterized the reproductive strategy of Hoffmann's two-toed sloths, Choloepus hoffmanni, in an agro-ecosystem in northeastern Costa Rica by assigning paternity, characterizing the spatial distribution of related individuals and describing the space use of 157 individuals. Spatial patterns of relatedness suggested that natal dispersal was female biased and sufficient to avoid inbreeding. Five (36%) adult males sired offspring with more than one female, and we observed three apparent extraterritorial matings, indicating that sloths were not strictly monogamous. Generally, adult males were segregated and appeared to show some territoriality in core areas, although home ranges of adjacent males overlapped in areas of low use. On average, male home ranges encompassed more than three females, and females usually occurred within the home range of more than one male. These patterns of space use and relatedness suggest males monopolize space more than they do females, and that the mating system of Hoffmann's two-toed sloth involves a mixture of polygyny and promiscuity. Neighbouring males were more closely related than expected, suggesting that a certain level of tolerance among males may stem from the benefits of kin selection and the limited ability of males to monopolize breeding opportunities.

► We characterized the mating system of Hoffmann's two-toed sloths with genetic and movement data.
► Adult male sloths were spatially segregated and appeared to show territoriality in core areas.
► Sloths were not strictly monogamous and showed a mixture of polygyny and promiscuity.
► Tolerance among males may stem from their limited mobility and the benefits of kin selection.