Meeting Abstract
Among amniotic animals, birds evolved a variety of egg shapes. Two mayor types of hypotheses have been proposed to explain the morphologic diversity of this key avian feature: 1 adaptive hypotheses, which include life history pressures and breeding ecology as major drivers of egg shape, and 2 an indirect hypothesis, stating that egg shape evolves in correlation with skeletal and muscular features because of the physical pressures they exert during egg formation. The latter has recently been backed by evidence showing that at broad taxonomic scales, egg shape is associated with flight capacity, arguing that species with an aerial lifestyle have skeletal and muscular adaptations that differ from those of birds that spend more time on the ground. Studies that test adaptive hypotheses at the intraspecific level have focused on species with highly asymmetric eggs and that nest in cliffs, for which shape adaptations are clearly important. We test the hypothesis of egg shape evolving in association with flight capacity between closely related species and at the intraspecific level. Numerous species of birds have populations that are migratory and others that are sedentary, two behavioral strategies that have been shown to result in differences in wing shape across different families of birds. To test whether egg shape evolves in correlation with flight capacity, we studied egg shape within species of Kingbirds (Tyrannus) that have migratory and sedentary birds. We also developed a novel mathematical description of egg geometry and a computer app to measure egg shape. We find that eggs from migratory individuals are more elongated as was found at higher taxonomic levels, but that eggs from sedentary species are more asymmetrical, contrasting higher taxonomic trends.
