dolphin projects



Bottlenose dolphins (Tursiops truncatus) can exhale and inhale in 0.6 seconds. They then hold their breath for one to two minutes while they are at rest, or for periods up to eight minutes while they are diving. I am interested in determining which muscles power this unique combination of an explosive exchange of respiratory gases with periods of breath-hold. To identify the breathing muscles of dolphins, I am investigating muscles that have been implicated in the breathing mechanics of terrestrial mammals - diaphragm, intercostals, scalenus, and rectus abdominus.
 

 
 
 

For my Ph.D. thesis, I completed a study of the bottlenose dolphin diaphragm. Unlike the manatee diaphragm (Rommel and Reynolds, 2000), the anatomical connections of the diaphragm in these animals have not been well described. Thus, through detailed dissections, I determined the skeletal attachments of the diaphragm in dolphins. I also described the anatomical features of the diaphragm muscle itself.
 

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In addition, I looked at the fiber-type profile of the dolphin diaphragm using histochemical and biochemical techniques and found this muscle to be primarily composed of slow-twitch fibers. This characteristic does not seem to fit with the quick inhalation of dolphins. However, the construction of the dolphin diaphragm suggests that it acts as a spring, being loaded during exhalation and recoiling caudally to cause inhalation. In addition, two of the myosin isoforms expressed by this muscle are different from those found in rat diaphragm. To date, the contractile abilities of these unique myosins are unknown, but they may allow the dolphin diaphragm to contract more quickly than its histochemical profile would suggest.
 
To better understand how cetaceans (whales, dolphins, and porpoises) are able to inhale so quickly, my students and I have undertaken studies to examine one of the other muscles involved in inspiration, the scalenus muscle. Evan Brickell and Eric Traister studied the scalenus muscle of harbor porpoises (Phocoena phocoena) and Brandon Thurow studied this muscle in bottlenose dolphins.
 

Brandon Thurow joined the lab in the summer of 2004. He studied the scalenus muscle of bottlenose dolphins to determine if there was variability in the fiber-type profile of this muscle across the muscle's cross-section. His project has lent insight into the function of this muscle in bottlenose dolphins and assisted in the design of other projects examining the scalenus muscle in cetaceans. Brandon presented his project at the 89th Annual Arkansas Academy of Science meeting held at Hendrix College on April 8 - 9, 2005.
 

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