Citation
Kralick, Alexandra E.; O'Connell, Caitlin A.; Bastian, Meredith L.; Hoke, Morgan K.; Zemel, Babette S.; Schurr, Theodore G.; & Tocheri, Matthew W. (2023). Beyond Dimorphism: Body Size Variation among Adult Orangutans is Not Dichotomous by Sex. Integrative and Comparative Biology, 63(4), 907-921. PMCID: PMC10563650Abstract
Among extant great apes, orangutans are considered the most sexually dimorphic in body size. However, the expression of sexual dimorphism in orangutans is more complex than simply males being larger than females. At sexual maturity, some male orangutans develop cheek pads (flanges) while other males remain unflanged even after becoming reproductively capable. Sometimes flange development is delayed in otherwise sexually mature males for a few years. In other cases, flange development is delayed for many years or decades, with some males even spending their entire lifespan as unflanged adults. Thus, unflanged males of various chronological ages can be mistakenly identified as 'subadults'. Unflanged adult males are typically described as "female-sized", but this may simply reflect the fact that unflanged male body size has only ever been measured in peri-pubescent individuals. In this study, we measured the skeletons of 111 wild adult orangutans (Pongo spp.) including 20 unflanged males, 45 flanged males, and 46 females, resulting in the largest skeletal sample of unflanged males yet studied. We assessed long bone lengths (as a proxy for stature) for all 111 individuals and recorded weights-at-death, femoral head diameters, bi-iliac breadths, and long bone cross-sectional areas (as proxies for mass) for 27 of these individuals, including seven flanged males, three adults confirmed-unflanged males, and three young adult likely-unflanged males. ANOVA and Kruskal-Wallis tests with Tukey and Dunn post-hoc pairwise comparisons, respectively, showed that body sizes for young adult unflanged males are similar to those of the adult females in the sample (all pURL
http://dx.doi.org/10.1093/icb/icad015Reference Type
Journal ArticleYear Published
2023Journal Title
Integrative and Comparative BiologyAuthor(s)
Kralick, Alexandra E.O'Connell, Caitlin A.
Bastian, Meredith L.
Hoke, Morgan K.
Zemel, Babette S.
Schurr, Theodore G.
Tocheri, Matthew W.