Meeting Abstract
Aquatic feeding vertebrates must balance risks of food escape with requirements for food processing before swallowing. Food control in water depends on the tongue (hyoid) acting as a hydrodynamic piston to produce fine-scale intraoral water flows and control food positioning before a processing power stroke is initiated. However, the deep, hidden placement of the musculoskeletal elements involved has challenged measurements of tongue and food movements during feeding. We used biplanar fluoroscopy to record skeletal movements (XROMM), muscle strains, and food movements (fluoromicrometry) during chewing in Axolotls. We tested an idea arising from prior EMG studies; that muscle-driven motion of the tongue moves food caudally during gape opening, likely to prevent its escape. During gape opening, in preparation for the power stroke, we measured shortening of the hyoid retractor in the majority of cycles, resulting in caudoventral hyoid and food excursion. However, other cycles involved lengthening of sternohyoid, or alternatively shortening of both the hyoid pro- and retractor, resulting in elevation and/or rostrad excursion of the hyoid during, and even prior to gape opening. Whereas contractions of the hyoid pro- and retractor are tightly integrated and coordinated, consistent with the idea that the tongue moves water to exert food displacement, there is considerable temporal variation in hyoid movement with respect to jaw muscle action and jaw cycle. These results underscore problems associated with predicting hidden motion based on EMG, suggest the presence of elastic elements within the hyoid musculature, and document an unappreciated diversity in salamander chewing function.
