1Anthropology, University of California, Santa Barbara, 2Biology, Saint Mary's College of California
April 16, 2020 , Platinum Ballroom
Gorillas live at a wide range of altitudes, with taller trees and more tree fruits at lower altitudes. Observations suggest that lower-altitude gorillas are more arboreal and female gorillas spend more time in trees than males. Our previous work identified altitude-related variation in the gorilla scapula, which includes attachments for muscles used in climbing. In this study, we tested the hypothesis that sexual dimorphism in scapula shape is greater at lower altitudes. We collected 3D landmarks from the scapulae of 174 gorillas, including Gorilla beringei graueri (low and high altitude), G. b. beringei (very high altitude), and G. gorilla gorilla (low altitude). Linear measurements of the coracoid process, acromion process, supraspinous fossa, and infraspinous fossa were calculated, size-adjusted, and analyzed using univariate and multivariate statistics. Within G. beringei, discriminant function analysis found sexual dimorphism to be greatest within low-altitude G. b. graueri and least within G. b. beringei, as predicted; however, separation between male and female G. g. gorilla, at low altitude, was between that of high-altitude G. b. graueri and G. b. beringei. In univariate analyses, the acromion process was consistently dimorphic and showed greater dimorphism at lower altitudes, but it was relatively larger in males, although males are less arboreal. The supraspinous fossa showed a similar pattern in G. beringei. Sexual dimorphism in scapula shape varies across altitudes and taxa in gorillas, but this variation may reflect factors other than habitat and locomotion. These findings have implications for interpreting variation in the hominoid fossil record.
Wenner-Gren Foundation, Leakey Foundation, Sigma Xi, City University of New York, New York Consortium in Evolutionary Primatology, and Saint Mary’s College Faculty Research Grant.