Collaborative Research: Evolution of the hyoid, pharynx and swallowing biomechanics in mammals

All mammals, including humans, have a bone at the base of the tongue called the hyoid bone. The hyoid bones vary in shape, size and position relative to the skull, jaws, and the muscles of the throat, but we do not know why the hyoid bones show such wide variation, how it evolved, what it means for normal swallowing function in humans, for medical disorders involving difficulty swallowing, and for swallowing function in domesticated animals (including pets and farm animals). This research will use innovative imaging and computational methods to measure the variation in hyoid and throat anatomy in mammals, as well as to study how the hyoid moves during swallowing. The research will create novel databases of three-dimensional static hyoid anatomy and of hyoid and tongue movements during chewing and swallowing in several species of mammals. The NSF-supported work will accelerate research into swallowing disorders in humans, their pets and in farm animals. It will provide opportunities for research experiences for undergraduate and graduate students traditionally under-represented in STEM fields. It will also engage in public science education and outreach, through museums and online platforms, to underserved urban and rural communities in Chicago and Ohio. The hyoid apparatus of mammals varies in shape, position, and the degree to which its connection to the cranium is composed of bones and ligaments. However, the evolutionary and functional significance of this variation is unknown because we lack basic information on the full range of variation in hyoid and pharynx morphology among mammals, and its relationship to variation in hyoid function during feeding. Hyoid movement is thought to play an important role in swallowing, but whether mammals with different hyoid anatomy employ the same or different swallowing mechanisms remains to be established. The proposed research aims to (1) document the full range of hyoid chain variation in the mammal clades Euarchontoglires and Laurasiatheria, (2) quantify relationships between hyoid chain anatomy and anatomy of the soft tissues of the tongue and pharynx (throat) in species with diverse hyoid chain morphologies, and (3) determine whether interspecific variation in hyoid, lingual and pharyngeal anatomy is associated with significant differences in hyolingual biomechanics during swallowing. Aims (1) and (2) will be addressed using micro-computed tomography (CT) and diffusible-iodine contrast enhanced CT of the skulls, hyoids and pharynges of representative species of our focal clades that show the full range of hyoid anatomy. Aim (3) will be addressed using the XROMM (X-Ray Reconstruction of Moving Morphology) workflow to collect high-resolution 3D musculo-skeletal kinematics of hyolingual function in three species of Euarchontoglires and three species of Laurasiatheria. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.