Meeting Abstract
Currently, the role, if any, of the primarily slow-twitch (65%) diaphragm in the explosive inhalation (< 0.03 seconds) of bottlenose dolphins, is still unknown. In other mammals, the diaphragm has been shown to exhibit regional variation in fiber-type profile, and these differences in fiber composition have been related to other functions of the diaphragm. Thus, the purpose of this study is to investigate regional variation in the fiber-type profile of the bottlenose dolphin diaphragm, in order to better understand the functions of this muscle. To achieve this goal, sections of the dolphin diaphragm from the middle (M) and lateral edge (L) of the costal region, ventral to the esophagus (E), ventral to the caval foramen (C), and near to the dorsal edge (D) were cut and stained for their myosin ATPase activities. Digital images of the stained sections were captured and printed, and the numbers of slow- and fast-twitch fibers were counted on each image. These data were used to calculate the average percentage of slow-twitch fibers in each region of the diaphragm. A mixed statistical model demonstrated that there is significant variation in fiber-type profile between the different diaphragm regions. The E region possessed significantly more slow-twitch fibers by count than the C, L, and M regions, a result that suggests this region of the diaphragm acts as a sphincter to prevent regurgitation of prey. However, overall, the diaphragm of bottlenose dolphins is composed primarily of slow-twitch fibers (range: 63% to 82%). Thus, the regions of this muscle may work together to play a role in ventilation by acting as a spring or to decouple ventilation and locomotion while these animals dive on a breath-hold.
