Meeting Abstract
After capturing food, there are at least two equally important steps in feeding: food transport and food swallowing. Previous studies in aquatic vertebrates have found that water currents transport food from the mouth towards the esophagus (i.e. the hydrodynamic tongue), and that oral cavity expansion generates this flow. They were, however, limited by technology and unable to visualize the food position within the animal. We used X-ray Reconstruction of Moving Morphology (XROMM) to track the pathway of food in 3D in three white-spotted bamboo sharks, allowing us to measure food and cartilage movement during transport and swallowing. Gape width, ceratohyal and pectoral girdle elevation, and food displacement were analyzed for each feeding bout. We found that food moves with a ratchet-like motion once inside the oropharynx. Caudally-directed motion of the food occurs during hyoid elevation, and the food appears to be stationary during ceratohyal depression, perhaps held in place by branchial basket compression. Hyoid elevation compresses the oral cavity, so the shark likely generates water currents through the oropharynx to push food backwards. Food is pushed into the esophagus by hydrodynamics as well. Despite a smaller range of motion of the ceratohyal and pectoral girdle, food velocity is higher. This indicates that branchial basket compression might push food into the esophagus. Hence, water currents generated by cranial cartilages and branchial basket compression are key elements in moving food towards and into the esophagus. These actions are as important as food capture for animal survival.
