Meeting Abstract
P1.97 Thursday, Jan. 3 Divergent Locomotor Muscle Design Among Thresher Sharks BERNAL, Diego*; MCGILLIVRAY, Dave; AALBERS, Scott; DONLEY, Jeanine; SYME, Douglas; SEPULVEDA, Chugey; University of Massechusetts, Dartmouth; University of Calgary; Pfleger Institute of Environmental Research; MiraCosta College; University of Calgary; Pfleger Institute of Environmental Research chugey@pier.org
This study presents the first phase of a collaborative research project that investigates several aspects of locomotor muscle function and design in the thresher sharks (Alopiidae). Threshers are a group of large, pelagic sharks easily recognized by their elongate upper caudal lobe. The alopiids represent the only genus to contain species with both lateral and medial positions of the red aerobic locomotor muscle (RM). Thus, the alopiids provide the ideal system in which to test the hypothesis that the medial RM position in the common thresher shark (Alopias vulpinus) provides the basis for a propulsion mechanism similar to that found in the lamnid sharks and different from sharks with lateral RM. Sonomicrometry was used to quantify the in-vivo muscle dynamics during sustained swimming. Field studies on the red and white muscle (WM) of six common threshers were performed off the coast of Southern California in June of 2007. At a tailbeat frequency of 0.5Hz, RM strain (at first dorsal fin) was consistently greater than that of the WM and decreased significantly during simulated swimming movements (when the RM was not stimulated; i.e., passive swimming). By contrast WM strain did not differ between active and passive swimming. A comparison of RM and WM phase during swimming showed instances in which RM shortening both led and trailed that of the surrounding WM, with no phase difference observed during the passive swimming experiments. This finding suggests that, similar to lamnid sharks, the common thresher RM sheers relative to the WM. Therefore, these results suggest that the common thresher may exhibit a similar uncoupling of RM shortening and local body bending as seen in the thunniform lamnids.
