Size as a complex trait and the scaling relationships of its components across teleosts.

Body size influences nearly every aspect of an organism's biology and ecology. When studying body size, researchers often focus on a single dimension, such as length, despite the fact that size can evolve by altering multiple body dimensions. The distinct ways organisms change their size can have profound consequences on evolutionary and ecological processes. Here, we investigate the evolution of size as a complex trait by exploring the interaction between body length, depth, and width across 42 orders of teleost fishes. Using Ornstein-Uhlenbeck models, we compare shifts in the adaptive landscapes of each of the three size components, and in the scaling relationships between them. We find that fishes change their size in a myriad of ways: changes in length, depth and width rarely co-occur on the phylogeny or in accordance with composite measures of size (body mass or the geometric mean). Body size diversity tends to accumulate along trajectories close to isometry but there is also some variation in the allometric regimes. Finally, orders with scaling shifts are more species rich than those without shifts, suggesting that body size diversity trajectories have the potential to be associated with distinct diversification scenarios in teleosts. Based on the evolutionary relationships we found between size components, we recommend that researchers treat body size as a complex trait to properly evaluate the patterns and processes of size variation in nature. [ABSTRACT FROM AUTHOR]