The relationship between fluctuating asymmetry and environmental variance in rhesus macaque skulls

This study measures the correlation between within- and among-individual variance to gain a greater understanding of the relationship of the underlying mechanisms governing developmental stability and canalization. Twenty-six landmarks were digitized in three dimensions from the crania of 228 adult macaques from Cayo Santiago. The phenotypic variance between individuals was measured and divided into its genetic and environmental components using matriline information. Within-individual variance was measured as the fluctuating asymmetry between bilateral landmarks. We found positive and significant correlations between the phenotypic, environmental, and fluctuating asymmetry variances for interlandmark distances. We also found low but significant correspondences between the covariation structures of the three variability components using both Procrustes and interlandmark distance data. Therefore, we find that in macaque skulls traits that exhibit greater levels of asymmetry deviations also exhibit greater levels of environmental variance, and that the covariances of absolute symmetry deviations partly correspond to covariances of mean deviations at the individual level. These results suggest that the underlying processes that determine canalization and developmental stability are at least partly overlapping. However, the low correlations reported here are also evidence for a degree of independence between these variability components.