Ontogenetic Development of Sexual Dimorphism in Body Mass of Wild Black-and-White Snub-Nosed Monkey ( Rhinopithecus bieti ) Animals : an Open Access Journal from MDPI
Abstract Simple Summary Sexual dimorphism widely exists in animals and is reflected in different forms; of these, body mass dimorphism is the most prominent. Studies on the development and adaptation mechanism of sexual dimorphism in body mass can help us to understand how animals adapt to their environment via sexual dimorphism. As this has not been widely reported in Rhinopithecus , this study explores the ontogenetic development pattern of sexual dimorphism in the body mass of R. bieti , and interprets the causes resulting in extreme sexual dimorphism. The results showed that a significant dimorphism appears when females enter the reproductive period, reaching the maximum when males are mature for reproduction. It was determined that a period of decline begins after 8 years of age, and that males had a longer growth period than females. The large sexual dimorphism in body mass in R. bieti can be explained by both Bergmann’s and Rensch’s rules; however, the females’ choice for males may not be significantly related to it. Overall, environmental adaptation, a distinctive alimentary system, and complex social structure have allowed R. bieti to have remarkable sexual dimorphism in body mass compared to other colobines. This study will undoubtedly highlight the same issues on the other 26 primate species in China, particularly the colobines, which will enrich research designs and enlarge research focus on China’s primatology. Abstract Sexual dimorphism exists widely in animals, manifesting in different forms, such as body size, color, shape, unique characteristics, behavior, and sound. Of these, body mass dimorphism is the most obvious. Studies of evolutionary and ontogenetic development and adaptation mechanisms of animals’ sexual dimorphism in body mass (SDBM), allow us to understand how environment, social group size, diet, and other external factors have driven the selection of sexual dimorphism. There are fewer reports of the ontogenetic development of sexual dimorphism in body mass in Rhinopithecus . This study explores the ontogenetic development pattern of SDBM in wild black-and-white snub-nosed monkeys ( R. bieti ), and the causes resulting in extreme sexual dimorphism compared to other colobines. A significant dimorphism with a ratio of 1.27 ( p < 0.001) appears when females enter the reproductive period around six years old, reaching a peak (1.85, p < 0.001) when males become sexually mature. After the age of eight, the SDBM falls to 1.78, but is still significant ( p < 0.001). The results also indicate that males had a longer body mass growth period than females (8 years vs. 5 years); females in larger breeding units had a significantly higher SDBM than those in smaller ones (2.12 vs. 1.93, p < 0.01). A comparative analysis with other colobines further clarifies that Rhinopithecus and Nasalis , which both have multilevel social organization, have the highest degree of SDBM among all colobines. The large SDBM in R. bieti can be explained through Bergman’s and Rensch’s rules. Overall, environmental adaptation, a distinctive alimentary system, and a complex social structure contribute to R. bieti having such a remarkable SDBM compared to other colobines. In addition, we found that females’ choice for males may not be significantly related to the development of SDBM. Keywords: Rhinopithecus bieti , sexual bimaturism, environmental adaptation, multilevel social organization, sexual selection
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Yan-Peng Li, Zhi-Pang Huang, Yin Yang et al.. Ontogenetic Development of Sexual Dimorphism in Body Mass of Wild Black-and-White Snub-Nosed Monkey (Rhinopithecus bieti). Animals : an Open Access Journal from MDPI. (2023). https://doi.org/10.3390/ani13091576 Yan-Peng Li, Zhi-Pang Huang, Yin Yang, Xiao-Bin He, Ru-Liang Pan, Xin-Ming He, Gui-Wei Yang, Hua Wu, Liang-Wei Cui, Wen Xiao
1School of Life Sciences, Central China Normal University, Wuhan 430079, China; [email protected] 2Institute of Eastern-Himalaya Biodiversity Research, Dali University, Dali 671003, China 3International Centre of Biodiversity and Primate Conservation, Dali University, Dali 671003, China 4Institute of International Rivers and Eco-Security, Yunnan University, Kunming 650091, China 5Administration of Baimaxueshan National Nature Reserve, Diqing 674500, China 6School of Anatomy, Physiology and Human Biology, The University of Western Australia, Perth WA 6009, Australia 7Administration of Gaoligongshan National Nature Reserve in Nujiang, Nujiang 673200, China 8Key Laboratory of Wildlife Conservation for Minimal Population in Universities of Yunnan Province, Southwest Forestry University, Kunming 650224, China 