Ontogenetic Development of Sexual Dimorphism in Body Mass of Wild Black-and-White Snub-Nosed Monkey (Rhinopithecus bieti)

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.

Morphometric Analysis of Growth in Captive-bred Pig-tailed macaque (Macaca nemestrina Linnaeus 1766)

“…Environmental adaptation, the digestive system's ability to absorb nutrients, and complex social structures influence the growth of sexual dimorphism (Li et al 2023). Growth hormone Growth hormone (GH)-insulin-like growth factor (IGF) is consistently associated with growth measures (Bernstein 2017).…”

Variation in monthly and seasonal elevation use impacts behavioral and dietary flexibility in Rhinopithecus bieti

“…However, the notable relationship between climate and elevation use during the winter and fall with little variation in monthly feeding times and diets during these seasons suggests the importance of behavioral flexibility within these seasons. Our R. bieti population likely spends more time at higher elevations during colder fall and winter months to capitalize on higher sunlight intensity, either through thermoregulatory behaviors like sun-basking or increases in food access (Li et al, 2023;Quan et al, 2011). Further research on R. bieti energetics could shed more light on this phenomenon.…”

“…One possibility is that these monkeys catabolize protein from their lean body mass, as seen among reindeer (Rangifer tarandus) consuming lichenbased diets (Barboza & Parker, 2006). Indeed, limited reports suggest that R. bieti adult males can weigh between 17 and 26 kg (Li et al, 2023), though more detailed physiological studies are needed to understand individual and seasonal variations in body mass .…”

Early life drought predicts components of adult body size in wild female baboons

“…This is especially true for wild primates: obtaining body size data have typically involved immobilization or provisioning, both of which present particular challenges for primates. To our knowledge, measures of growth or body size during both pre-adult and adult life stages have only been estimated for geladas, Assamese macaques, owl monkeys, black-and-white snub-nosed monkeys, anubis baboons, eastern chimpanzees, and mountain gorillas (Anzà et al, 2022;Galbany et al, 2017;Huck et al, 2011;Li et al, 2023;Lu et al, 2016;Pusey et al, 2005;Strum, 1991). Further, predictors of inter-individual differences in body size or mass have only been assessed for a handful of wild primate populations Berghänel et al, 2015Berghänel et al, , 2016Borg et al, 2014;Jarrett et al, 2020;Johnson, 2003;Pusey et al, 2005;Thompson et al, 2016;Wright et al, 2019Wright et al, , 2020.…”