AXIAL MUSCULATURE IN THE DOLPHIN (TURSIOPS TRUNCATUS): SOME ARCHITECTURAL AND HISTOCHEMICAL CHARACTERISTICS

Abstract

In view of the supposition that a dolphin can swim faster than would be predicted based on its physical features and presumed muscle power potential, studies were initiated to reevaluate the assumptions made in reaching these conclusions. Several previous studies have shown that the architectural and histochemical properties of a skeletal muscle dictate its force, velocity and displacement properties. This study examined the muscle fiber lengths and tendon arrangements of the dorsal and ventral axial muscles in dolphins (Tursiops truncatus). Fiber type and fiber size distributions were determined to reflect the general biochemical characteristics of the musculature. The dorsal muscles had a higher mean fiber length (167 Vs. 90 mm) and the range within and across different dorsal muscles was less (141–199 vs. 37–185 mm) than in the ventral muscles. Both the dorsal and ventral muscles consisted of an overall mean of 50 percent slow twitch and 50 percent fast twitch fiber types. The fast twitch fibers were 67 percent larger (2,200 vs. 1,317 μm2) than the slow twitch fibers in the ventral and 38 percent larger (1,213 Vs. 879 μm2) in the dorsal muscles. In addition, the mean cross sectional area of the fibers in the ventral muscles was approximately 65 percent greater (1,750 vs. 1,072 μm2) than those in the dorsal muscles. The shorter, larger‐diameter fibers of the ventral musculature give it a greater potential for force production for a given amount of muscle mass. In contrast, the dorsal muscles appear to be designed to optimize velocity and displacement, (i.e., longer fibers). These findings contribute to the information necessary for the determination of the power potential of the musculature of the dolphin.

Extreme physiological adaptations as predictors of climate‐change sensitivity in the narwhal,Monodon monoceros

“…Values for narwhals in the present study are compared to those of similar muscles powering the flukes of other odontocetes (upper bars) as well as swimming and running skeletal muscles of pinnipeds and terrestrial mammals, respectively (lower bars). Data for fiber composition are from (1) odontocetes: Pacific white‐sided dolphin ( Lagenorhynchus obliquidens ), erector spinae (epaxial) (Ponganis and Pierce 1978); bottlenose dolphin ( Tursiops truncatus ), longissimus dors i (Bello et al 1985); common dolphin ( Delphinus delphis ), longissimus dorsi (Suzuki et al 1983); narwhal ( Monodon monoceros )‐ longissimus dorsi (present study); (2) pinnipeds: harbor seal ( Phoca vitulina ), longissimus dorsi (Reed et al . 1994, Watson et al .…”

“…obliquidens), erector spinae (epaxial) (Ponganis and Pierce 1978); bottlenose dolphin (Tursiops truncatus), longissimus dorsi (Bello et al 1985); common dolphin (Delphinus delphis), longissimus dorsi (Suzuki et al 1983); narwhal (Monodon monoceros)-longissimus dorsi (present study); (2) pinnipeds: harbor seal (Phoca vitulina), longissimus dorsi (Reed et al 1994, Watson et al 2003; Weddell seal (Leptonychotes weddellii), longissimus dorsi (Kanatous et al 2002); gray seal (Halichoerus grypus), longissimus dorsi (Reed et al 1994); and (3) terrestrial mammals: greyhound (Canis familiaris), semitendinosus (Gunn 1978); African cheetah (Acinonyx jubatus), vastus lateralis (Williams et al 1997); human sprinter (Homo sapiens), gastrocnemius (Wilmore and Costill 2004); mongrel dog (Canis familiaris), tibialis anterior (Kuzon et al 1989); hound dog (Canis familiaris), tibialis anterior (Kuzon et al 1989); human elite marathoner (Homo sapiens), gastrocnemius (Wilmore and Costill 2004). Kooyman (1989).…”

Intramuscular morphology and tendon geometry of the epaxial swimming muscles of dolphins

“…Although there exists a rich literature on the intramuscular morphology of mammalian appendicular locomotor muscles (e.g. Spector et al, 1980;Sacks & Roy, 1982;McClearn, 1986;Lieber & Blevins, I989), only two studies to date have measured intramuscular morphological features of cetacean axial locomotor muscles (Bello et al, 1985;Bennett, Ker & Alexander, 1987). Because neither study compared the morphologies of the m. multifidus and the m. longissimus, no information exists on the relative force and excursion potentials of the major dorsal swimming muscles of cetaceans.…”

Precocial development of axial locomotor muscle in bottlenose dolphins (Tursiops truncatus)

“…However, cetaceans (whales, dolphins, and porpoises) define an extreme in precocial locomotion in that neonates must be effective swimmers at the instant of birth. Although the adult fiber-type profiles of the axial locomotor muscles from two delphinid species (Tursiops truncatus and Delphinus delphis) have been described to be mixed (Tulsi, 1975;Suzuki et al, 1983;Bello et al, 1985), thus far no study has investigated the histochemical properties of developing dolphin muscle.…”