Hierarchical comparison of genetic variance-covariance matrices. II. Coastal-inland divergence in the garter snake, Thamnophis elegans

The time-scale for the evolution of additive genetic variance-covariance ma trices (G-matrices) is a crucial issue in evolutionary biology. If the evol ution of G-matrices is slow enough, we can use standard multivariate equati ons to model drift and selection response on evolutionary time scales. We c ompared the G-matrices for meristic traits in two populations of garter sna kes (Thanmnophis elegans) with an apparent separation time of 2 million yea rs. Despite considerable divergence in the meristic traits, foraging habits , and diet, these populations show conservation of structure in their G-mat rices. Using Flury's hierarchial approach to matrix comparisons, we found t hat the populations have retained the principal components (eigenvectors) o f their G-matrices, but their eigenvalues have diverged. In contrast, we we re unable to reject the hypothesis of equal environmental matrices (E-matri ces) for these populations. We propose that a conserved pattern of multivar iate stabilizing selection may have contributed to conservation of G- and E -matrix structure during the divergence of these populations.