Meeting Abstract
The hoatzin (Opisthocomus hoazin) is one of the only strictly folivorous birds and has a unique digestive physiology. Due to the foregut fermentation, their crop is hypertrophied which implies modifications of the scapular girdle. It has been hypothesized that it could have functional implications by greatly reducing the sternal carina thus reducing the insertion site for the flight muscles. However, this hypothesis remains to be tested. This study aims to quantify the morphology of bones that are functionally important during flight: the sternum, the scapular girdle, and the humerus. To do so, a 3D surface geometric morphometric study was performed on each bone for more than 50 species of birds with different locomotor abilities and diet. Basal metabolic rates from the literature were also used in order to test for possible functional trade-offs between physiological parameters, flying ability, and the shape of each bone. Morphological differences in relation to diet and flying ability were explored using a Principal Component Analyses, phylogenetic multivariate analysis of variance and phylogenetic partial least square regression. Our results show morphological differences for the bones of the scapular girdle depending of the type of flight and diet. No relationship was found between the metabolism and flight type and the shape of each bone even when body mass and phylogeny were taken into account. In summary, the shape of scapular girdle of birds seems a very good indicator of adaptations for flight, its shape distinguishing good and poor flyers. The sternum is an exception in being mainly impacted by centroid size. This can highlight its multiple roles ranging from the protection of the internal organs to the insertion of flight muscles.
