Meeting Abstract
The avian sternum anchors the main muscles powering flight and is highly disparate in morphology. For instance, some birds feature long, narrow sternal plates with deep keels, others have almost square sternal plates and shallow keels, and some have very reduced or non-existent keels. Little work has focused on the relationship between the complex sternum shape and a bird’s ecomorphology. Here, we use automated three-dimensional (3D) geometric morphometrics (auto3dgm in Matlab) on a sample of 124 isolated avian sterna to examine relationships between sternal form and function. The R package Geomorph was used to run a General Procrustes Analysis and a Principle Component (PC) Analysis to examine the sternal plate disparity across Aves. In our results, PC1 ranges between a square sternal plate and a shallow keel (e.g., owls, grebes) and a long, narrow sternal plate with a deep keel (e.g., turkeys and doves). PC2 ranges between a posteroventrally-inclined leading edge of the sternal keel (e.g., owls, turkeys) and an anteroventrally-inclined leading edge of the sternal keel (e.g., gannets, loons). PC3 ranges between an angled posterolateral margin (e.g., tropicbird, hornbill) and a rounded posterolateral margin (e.g., loons, kakapo). A 3D plot of these PCs shows that phylogeny seems to be the predominant factor driving most of the clustering in the analyses. Owls group together, pheasants and turkeys group together, and ducks and geese group together. However, convergence is also evident; for example, a cluster with doves, macaws, and terns exhibits very deep keels extending the full length of an anteroposteriorly elongate sternal plate. These observations suggest that certain sternum morphologies can be used for multiple behaviors and habitats and that sternal shape is not driven by phylogenetic relationships alone.
