Decoupling morphological development from growth in periodically cooled zebra finch embryos

Temperature affects growth and development, and morphometry can provide a quantitative description of how temperature changes affect the resulting phenotype. We performed a morphometric analysis on zebra finch (Taeniopygia guttata) embryos that were either exposed to periodic cooling to 20 or 30 degrees C throughout incubation over a background temperature of 37.5 degrees C, or were incubated at a constant temperature of 37.5 degrees C. Using a principle components analysis, we found that the relationship between the multivariate size (first principle component) and dry embryo mass depended upon the thermal treatment to which the developing embryos were exposed. Periodic cooling resulted in a smaller embryo mass, but had no effect on the multivariate size of the embryo. This suggests that the growth of phenotypic traits such as the length of long bones and the skull are less affected by temperature than is growth of other soft tissues such as muscle and organs that contribute to body mass.