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, 7 (12), e51389

Unexpected Strong Polygyny in the Brown-Throated Three-Toed Sloth


Unexpected Strong Polygyny in the Brown-Throated Three-Toed Sloth

Jonathan N Pauli et al. PLoS One.


Promiscuous mating strategies are much more common than previously appreciated. So much so, that several authors have proposed that promiscuity is the "rule" rather than the exception in vertebrate mating systems. Decreasing species mobility and increasing habitat fragmentation have both been suggested to reduce the "polygyny potential" of the environment and promote other mating strategies like promiscuity in females. We explored the social and genetic mating system for one of the most sedentary extant mammals, the brown-throated three-toed sloth (Bradypus variegatus), within a highly fragmented Neotropical habitat. Surprisingly, we found that three-toed sloths were strongly polygynous, with males excluding male competitors from their core ranges, and exhibiting strong reproductive skew. Indeed, only 25% of all resident adult males sired offspring and one individual sired half of all sampled juveniles. Paradoxically, a sedentary life-history strategy seems to facilitate polygyny in fragmented landscapes because multiple females can persist within small patches of habitat, and be monopolized by a single male. Our work demonstrates that strong polygyny can arise in systems in which the polygyny potential should be extremely low, and other strategies, including promiscuity, would be favoured. Mating systems can be influenced by a multitude of factor and are dynamic, varying among taxa, over time, and across habitats; consequently, mating systems remain difficult to predict based on general ecological principles.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Figure 1
Figure 1. Four dominant cover types present at our study site in northeastern Costa Rica, 2010–2012.
A. shade grown cacao (Theobroma cacao) plantation; B. intact strips of tropical rainforest along riparian corridors; C. cattle pasture and; D. monocultures of pineapple (Ananas comosus; shown) and banana (Musa spp).
Figure 2
Figure 2. Distribution of reproductive success for adult male (n = 20) brown-throated three-toed sloths (Bradypus variegatus), and home ranges (90% fixed kernel) of all adult sloths across the four dominant cover types in northeastern Costa Rica, 2010–2012.
Males that were assigned paternity to juveniles are represented with colours. Black outlines represent the home ranges of females that were reproductively active. White and grey lines represent adult females and males respectively that did not sire offspring during our study. The home range of one female that dispersed north and out of the study area is depicted prior to her dispersal.
Figure 3
Figure 3. Frequency distribution of A. the number of adult male home ranges in which females overlapped or occurred within and; B. a pairwise index of home range overlap (utilization distribution overlap index or UDOI) for adult male brown-throated three-toed sloths in northeastern Costa Rica, 2010–2012.
Figure 4
Figure 4. Mean relatedness coefficients for pairs of brown-throated three-toed sloths as a function of geographic distance between pair members in northeastern Costa Rica, 2010–2012.

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Grant support

Funding was provided by the Milwaukee Public Museum, the University of Wisconsin-Madison, and through a fellowship awarded by the American Society of Mammalogists. Publication costs were paid for by the Department of Forest and Wildlife Ecology at the University of Wisconsin-Madison. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.