An integrative approach to examining the influences of size, phylogeny, and locomotion on os coxae shape variation in primates

Abstract

Objectives: Aspects of three-dimensional (3D) pelvis shape are associated with body size and adaptations to locomotor behaviors in primates, while the effect of phylogeny is less well understood. This study examines 3D os coxae shape in primates using an integrated, phylomorphospace approach to investigate the relationships among shape, phylogeny, locomotor function, and size. Materials and Methods: 3D landmarks (N = 20) were collected on a large sample of primate pelves (736 individuals, 60 species) and standard geometric morphometric methods were used to examine shape variation. Phylogenetic and non-phylogenetic generalized least squares models were constructed with Procrustes coordinates as dependent variables and locomotor behavior and size as independent variables; analyses were conducted on all primates and on a nonhuman primate subsample. Results: The degree of phylogenetic signal in these models was statistically significant, but less than would be expected under a Brownian motion model of evolution. Among all primates, both size and locomotion have significant effects on os coxae shape while accounting for the effects of phylogeny. However, these group differences are relatively small and as a result, locomotion is not significantly related to os coxae shape among the nonhuman primate sample when accounting for phylogeny. Discussion: Although closely related primate taxa share locomotor behavior, there are size and locomotor differences in os coxae shape that cannot be solely accounted for by phylogeny alone and must be considered alongside previously identified mechano-functional morphological differences. Phylogenetic comparative methods make it difficult to identify adaptation when locomotion and phylogeny are closely linked.