Levels of Intraspecific Variation Within the Catarrhine Skeleton

Abstract

The amount of phenotypic variation between conspecifics is largely a result of the opposing forces of constraint and plasticity. Because selection is the product of competition between individuals of the same species, understanding the interactions between these forces is vital to understanding evolution. We investigated levels of intraspecific variation in the catarrhine skeleton using a morphometric analysis of 245 crania and 189 appendicular postcranial skeletons. We identified regions of interest from the literature and made comparisons of intraspecific variation between the appendicular postcranium and cranium, the forelimb and hind limb, the diaphyses and epiphyses of long bones, and the diaphyses of the proximal and distal segments of the limbs. We confirmed that variation is significantly higher in the appendicular postcranium than in the cranium, in the forelimb compared to the hind limb, and in the diaphyses compared to the epiphyses. Further, we found that this pattern was repeated in 12 species spanning the infraorder, suggesting a characteristic of catarrhines in general. The relatively low level of variation in the cranium suggests that constraint is more widespread in this region compared to the appendicular postcranium, which is more plastic, especially in the diaphyses of the forelimb. In contrast to previous studies, we found the diaphyses of the distal segment to be more variable than the diaphyses of the proximal segment. The results from this study, which show regional differences in intraspecific variation, will aid the interpretation of evolutionary and plastic influences on morphological variation and inform decisions about which skeletal regions are suitable for answering specific evolutionary questions.