Ontogeny and the evolution of adult body size dimorphism in apes
Article first published online: 3 JUN 2005
Copyright © 1995 Wiley-Liss, Inc., A Wiley Company
American Journal of Primatology
Volume 36, Issue 1, pages 37–60, 1995
How to Cite
Leigh, S. R. and Shea, B. T. (1995), Ontogeny and the evolution of adult body size dimorphism in apes. Am. J. Primatol., 36: 37–60. doi: 10.1002/ajp.1350360104
- Issue published online: 3 JUN 2005
- Article first published online: 3 JUN 2005
- Manuscript Revised: 8 SEP 1994
- Manuscript Received: 23 NOV 1993
- growth and development;
- sexual size dimorphism;
This analysis investigates the ontogeny of body size dimorphism in apes. The processes that lead to adult body size dimorphism are illustrated and described. Potential covariation between ontogenetic processes and socioecological variables is evaluated. Mixed-longitudinal growth data from 395 captive individuals (representing Hylobates lar [gibbon], Hylobates syndactylus [siamang], Pongo pygmaeus [orangutan], Gorilla gorilla [gorilla], Pan paniscus [pygmy chimpanzee], and Pan troglodytes [“common” chimpanzee]) form the basis of this study.
Results illustrate heterogeneity in the growth processes that produce ape dimorphism. Hylobatids show no sexual differentiation in body weight growth. Adult body size dimorphism in Pongo can be largely attributed to indeterminate male growth. Dimorphism in African apes is produced by two different ontogenetic processes. Both pygmy chimpanzees (Pan paniscus) and gorillas (Gorilla gorilla) become dimorphic primarily through bimaturism (sex differences in duration of growth). In contrast, sex differences in rate of growth account for the majority of dimorphism in common chimpanzees (Pan troglodytes).
Diversity in the ontogenetic pathways that produce adult body size dimorphism may be related to multiple evolutionary causes of dimorphism. The lack of sex differences in hylobatid growth is consistent with a monogamous social organization. Adult dimorphism in Pongo can be attributed to sexual selection for indeterminate male growth. Interpretation of dimorphism in African apes is complicated because factors that influence female ontogeny have a substantial effect on the resultant adult dimorphism. Sexual selection for prolonged male growth in gorillas may also increase bimaturism relative to common chimpanzees. Variation in female growth is hypothesized to covary with foraging adaptations and with differences in female competition that result from these foraging adaptations. Variation in male growth probably corresponds to variation in level of sexual selection. © 1995 Wiley-Liss, Inc.