Sexual size dimorphism in Asian colobines revisited

Abstract

Asian colobines exhibit a wide range of sexual dimorphism in body mass. Some species are monomorphic, whereas others are strongly dimorphic. Strong sexual dimorphism is generally viewed as the consequence of intense male contest competition over access to mates, but this idea appears not to explain variation in sexual dimorphism in Asian colobines. Our results show that modular colobines, i.e. species in which social units aggregate into higher-level bands or often associate, have significantly higher levels of sexual dimorphism in body mass than the nonmodular ones. This finding was corroborated by means of phylogenetically controlled methods and multiple regression analyses. The results suggest that living in a modular society intensifies the contest competition among males, which is further exacerbated by the continuous presence of all-male units.

Are badges of status adaptive in large complex primate groups?

“…For example, geladas, hamadryas baboons, and snub-nosed monkeys live in large bands composed of smaller social units nested therein (Grueter et al, 2012a;Kirkpatrick & Grueter, 2010;Stammbach, 1987). Generally high scores for visual trait dimorphism in these species support the prediction that multilevel social organizations lead to the elaboration of ornamental features, possibly as a result of a relatively high potential for inter-male competition (Grueter and van Schaik 2009). …”

“…Campbell et al (2011), supplemented with data from Grueter (2009Grueter ( , 2013 if not otherwise noted in Table S2). Group sizes were calculated using species means and if ranges were given we took the midpoint.…”

“…For example, mountain gorillas (Gorilla beringei beringei) live in single male and multi-male groups (Stoinski et al, 2009). In the present study we used the modal social organization for each species using data compiled from Willems et al (2013) and complemented with data from Mittermeier et al (2013) and Grueter (2009).…”

Snub‐nosed monkeys: Multilevel societies across varied environments

“…2,3,42 Male intrasexual competition is also seen in infanticide and sperm competition. While only one case of infanticide has been reported for fully wild snub-nosed monkeys, in black snub-nosed monkeys at Xiaochangdu, 43 infants are also known to disappear during male replacement in OMUs of the provisioned band of golden snub-nosed monkeys at Zhouzhi West.…”

“…68 For Asian colobines as a whole, multilevel social organization is significantly associated with a high sex ratio in OMUs, 27 as well as with high sexual dimorphism. 42 Grueter and van Schaik 27 argue that a high sex ratio in OMUs indicates a high number of extra-unit males and that sex ratio is therefore a marker of conspecific threat. OMU males can address the threat of replacement by banding together.…”