Intraspecific variation of long bone cross-sectional properties in Pan troglodytes troglodytes and Gorilla gorilla gorilla

Objectives: Morphological intraspecific variation is due to the balance between skeletal plasticity and genetic constraint on the skeleton. Osteogenic responses to external stimuli, such as locomotion, have been well documented interspecifically across the primate order, but less so at the intraspecific level. Here, we examine the differences in cross-sectional variability of the femur, humerus, radius, and tibia in Pan troglodytes troglodytes versus Gorilla gorilla gorilla. We investigate whether there are sex, species, bone, and trait differences in response to variable body size and locomotion.

Materials and methods: Adult male and female P. t. troglodytes and G. g. gorilla long bones from the Cleveland Museum of Natural History were scanned with a peripheral quantitative computer tomography system. Scans were taken at the midshaft of each bone according to functional bone length. Coefficients of variation were used to provide a size-independent measure of variation. We applied a Bonferroni correction to account for the multiple pairwise tests.

Results: There were limited significant differences between males and females, however, females tended to be more variable than males. Variation in Gorilla, when significant, was greater than in Pan, although significant differences were limited. There were no differences between bone variability in male and female Gorilla, and female Pan.

Discussion: Increased female variability may be due to more variable locomotor behavior, particularly during periods of pregnancy, lactation, and caring for an offspring compared to consistent locomotion over the life course by males. Body size may be a contributing factor to variability; more work is needed to understand this relationship.