Postural role of lateral axial muscles in developing bottlenose dolphins (Tursiops truncatus)

Abstract

Foetal dolphins (Tursiops truncatus) are bent ventrolaterally, such that the tailflukes and lower jaw are juxtaposed. The lateral flexibility required en utero may compromise the efficiency of the dorsoventral oscillations required of the swimming neonate. The m. intertransversarius caudae dorsalis (IT) is the most laterally placed epaxial muscle. Bilateral contractions of the IT could limit lateral deformations of the flexible tailstock of the early neonate. We test the hypothesis that the IT is functioning as a postural muscle in neonates by examining its morphological, histological and biochemical properties. The neonatal IT has a relatively large cross-sectional area and bending moment, as well as a large proportion of slow-twitch fibres and elevated myoglobin concentrations. Our results demonstrate that the IT is functionally capable of performing this specific postural function in neonatal dolphins. In later life-history stages, when postural control is no longer needed, the IT serves to fine-tune the position of the tailstock during locomotion. The changing function of the adult IT is concomitant with changes in morphology and biochemistry, and most notably, with an increase in the proportion of fast-twitch fibres. We suggest that these changes reflect strong selective pressure to improve locomotor abilities by limiting lateral deformations during this critical life-history stage.

Ontogeny of swim performance and mechanics in bottlenose dolphins(Tursiops truncatus)

“…Combined, these factors undoubtedly limit sustainable muscular power production for fluke movements through the viscous, dense seawater. At the same time, extreme skeletal and muscular flexibility (Etnier et al, 2003) and floppy dorsal fins and flukes (McBride and Kritzler, 1951;Tavolga and Essapian, 1957;Cockcroft and Ross, 1990) can further compromise swimming efficiency during early development.…”

Infant position in mother-calf dolphin pairs: formation locomotion with hydrodynamic benefits

“…Immature dolphins have lower aerobic and anaerobic capacities in the muscle (reviewed by Noren & Edwards 2007) and proportionally smaller muscle mass (reviewed by McLellan et al 2002) than adult conspecifics. At the same time, extreme skeletal and muscular flexibility (Etnier et al 2004) and floppy (hydrodynamically ineffective) dorsal fins and flukes (McBride & Kritzler 1951, Tavolga & Essapian 1957, Cockcroft & Ross 1990 compromise the swimming efficiency of newborns, while small body size throughout ontogeny limits swimming performance as swimming speed is proportionate to body size across cetaceans (Fish 1998). Underdeveloped physiology correlates with the reduced swim performance of calves <1 yr postpartum (Noren et al 2006).…”

Novel locomotor muscle design in extreme deep-diving whales

“…Dearolf et al, 2000;Etnier et al, 2004;Cotten et al, 2008;Kielhorn et al, 2013), were used. Approximately 1cm 3 blocks of m. longissimus dorsi were cut from a position just ventral to the superficial tendon (Pabst, 1990), coated with Optimal Cutting Temperature compound (Sakura Finekek, Torrance, CA, USA), rapidly frozen in isopentane cooled by liquid nitrogen, and sectioned at 10μm thickness in a cryostat (Leica Microsystems, Wetzlar, Germany) at −19°C.…”