Body size, developmental instability and climate change

Development is often temperature-dependent. We hypothesized smaller size and larger asymmetry with increasing temperatures. However, we also predicted associations with asymmetry to differ among traits that differ in their degree of functional importance (especially the functional wings in migratory birds were predicted to be more canalized), timing of development (skeletal (femur, tarsus and humerus) vs feather (wing and tail traits). We analyzed a large dataset of which we included species with at least 20 specimens resulting in 5533 asymmetry values in 1593 individuals from 66 species. There was a consistent significant decrease in size with temperature across all traits. Fluctuating asymmetry for wings and femur was on average lower, suggesting higher canalization, and it decreased with migration distance, while that was not the case for the other traits. Fluctuating asymmetry increased with increasing temperature for wings, but not for the other characters, where the different resp...