Phylogenetic correlograms and the evolution of body size in South Americanowls (Strigiformes)

During the last few years, many models have been proposed to link microevol utionary processes to macroevolutionary patterns, defined by comparative da ta analysis. Among these, Brownian motion and Ornstein-Uhlenbeck (O-U) proc esses have been used to model, respectively, genetic drift or directional s election and stabilizing selection. These models produce different curves o f pairwise variance between species against time since divergence, in such a way that different profiles appear in phylogenetic correlograms. We analy zed Variation in body length among 19 species of South American owls, by me ans of phylogenetic correlograms constructed using Moran's I coefficient in four distance classes. Phylogeny among species was based an DNA hybridizat ion. The observed conelogram was then compared with 500 correlograms obtain ed by simulations of Brownian motion and O-U over the same phylogeny, using discriminant analysis. The observed correlogram indicates a phylogenetic g radient up to 45 mya, when coefficients tend to stabilize, and it is simila r to the correlograms produced by the O-U process. This is expected when we consider that body size of organisms is correlated with many ecological an d life-history traits and subjected to many constraints that can be modeled by the O-U process, which has been used to describe evolution under stabil izing selection.