Abstract
In marine mammals, muscular development has been identified as a rate-limiting factor in achieving adult dive capacities. This study investigates the rate that myosin heavy chain (MHC) composition matures in a postural and locomotor skeletal muscle for four pinniped species with different lactation lengths: hooded seals, Cystophora cristata; harp seals, Pagophilus groenlandicus; northern fur seals, Callorhinus ursinus, and Steller sea lions, Eumetopias jubatus. The ontogeny of MHC isoform expression was compared with developmental rates of myoglobin concentrations, and aerobic (citrate synthase, β-hydroxyacyl-CoA dehydrogenase) and anaerobic (lactate dehydrogenase) enzyme activities. Within taxonomic families, species with shorter lactation periods had more mature muscles biochemically at birth, and fiber types differentiated earlier during ontogeny (Phocidae: hooded > harp seals, Otariidae: northern fur seals > Steller sea lions). Northern fur seal neonates had the most phenotypically-mature muscles in this study, with no immature MHC isoforms. The relationship between muscle biochemistry and MHC composition became more pronounced with age, and developed to reflect swimming mode and activity levels. In adults, phocids had more slow-twitch oxidative protein in their primary locomotor muscle, the Longissimus dorsi (LD), than otariids which likely reflects oxygen-sparing strategies for the phocids’ longer dives. Conversely, northern fur seal muscles had higher proportions of fast-twitch MHCs in the Pectoralis and LD, likely indicative of this species’ smaller size and higher mass-specific metabolic rates. Thus, muscle phenotype is linked with species life history, and a mismatch between muscle biochemistry and MHC composition at weaning has important implications for the first year of independent foraging in pinniped pups.
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Abbreviations
- CS:
-
Citrate synthase (IU g−1 wet tissue)
- FOG:
-
Fast-twitch oxidative glycolytic
- HOAD:
-
β-Hydroxyacyl-CoA dehydrogenase (IU g−1 wet tissue)
- LD:
-
Longissimus dorsi
- LDH:
-
Lactate dehydrogenase (IU g−1 wet tissue)
- Mb:
-
Myoglobin (mg g−1 wet tissue)
- MHC:
-
Myosin heavy chain
- O2 :
-
Oxygen
- Pec:
-
Pectoralis
- PWF:
-
Post-weaning fast
- SO:
-
Slow-twitch oxidative
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Acknowledgements
Samples were collected with the Canadian Department of Fisheries and Oceans (harp and hooded seals; sampling conducted under IML-2007-004 to Canadian DFO, import under NMFS MMPA No. 782-1694-02), the Alaska SeaLife Center and North Pacific Wildlife Consulting LLC (northern fur seal samples; research authorized by permit No. 04-1370 from the Sakhalin-Kuril Territorial Department of the Federal Committee of Fisheries of Russia, import under NMFS MMPA No. 881-1724), and the Alaska Department of Fish and Game and National Marine Mammal Laboratory (Steller sea lions; sample collection under NMFS MMPA No. 358-1564 (ADF&G) and 782-1532 (NMML)), and respective Institutional Animal Care and Use Committees. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1242789 to M.R.S., the Research Experience for Undergraduates program to L.S. under DBI-1263415, and material is based upon work, while J.M.B. was serving at the National Science Foundation. Any opinion, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
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Shero, M.R., Reiser, P.J., Simonitis, L. et al. Links between muscle phenotype and life history: differentiation of myosin heavy chain composition and muscle biochemistry in precocial and altricial pinniped pups. J Comp Physiol B 189, 717–734 (2019). https://doi.org/10.1007/s00360-019-01240-w
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DOI: https://doi.org/10.1007/s00360-019-01240-w