Rapid maturation of the muscle biochemistry that supports diving in Pacific walruses (Odobenus rosmarus divergens)
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Full Publication: https://doi.org/10.1242/jeb.125757Product Type: Journal Article
Year: 2015
Authors: Noren, S. R., C. V. Jay, J. M. Burns, and A. S. Fischbach
Suggested Citation:
Noren, S. R., C. V. Jay, J. M. Burns, and A. S. Fischbach. 2015. Rapid maturation of the muscle biochemistry that supports diving in Pacific walruses (Odobenus rosmarus divergens). Journal of Experimental Biology 218:3319-3329. doi:10.1242/jeb.125757
Abstract
Physiological constraints dictate animals' ability to exploit habitats. For marine mammals, it is important to quantify physiological limits that influence diving and their ability to alter foraging behaviors. We characterized age-specific dive limits of walruses by measuring anaerobic (acid-buffering capacity) and aerobic (myoglobin content) capacities of the muscles that power hind (longissimus dorsi) and fore (supraspinatus) flipper propulsion. Mean buffering capacities were similar across muscles and age classes (a fetus, five neonatal calves, a 3 month old and 20 adults), ranging from 41.31 to 54.14 slykes and 42.00 to 46.93 slykes in the longissimus and supraspinatus, respectively. Mean myoglobin in the fetus and neonatal calves fell within a narrow range (longissimus: 0.92–1.68 g 100 g-1 wet muscle mass; supraspinatus: 0.88–1.64 g 100 g-1 wet muscle mass). By 3 months post-partum, myoglobin in the longissimus increased by 79%, but levels in the supraspinatus remained unaltered. From 3 months post-partum to adulthood, myoglobin increased by an additional 26% in the longissimus and increased by 126% in the supraspinatus; myoglobin remained greater in the longissimus compared with the supraspinatus. Walruses are unique among marine mammals because they are born with a mature muscle acid-buffering capacity and attain mature myoglobin content early in life. Despite rapid physiological development, small body size limits the diving capacity of immature walruses and extreme sexual dimorphism reduces the diving capacity of adult females compared with adult males. Thus, free-ranging immature walruses likely exhibit the shortest foraging dives while adult males are capable of the longest foraging dives.
Keywords: Pacific walrus, foraging, Arctic, aerobic dive limit
Annotation
The rate of change within Arctic ecosystems, including changes in sea ice cover, sea level, water temperature, and ocean currents, is exceeding trends recorded over the past several millennia. As long-lived species with slow reproductive rates, Pacific walruses are poorly equipped to respond to sudden alterations in climate. Walruses are unique among marine mammals because they are born with a mature muscle acid-buffering capacity and attain mature myoglobin content early in life, meaning that walruses are physiologically capable of swimming, diving, and foraging for benthic food at young ages. However, younger, smaller walruses cannot dive as deep or as long as larger, mature males. These physiological constraints limit the ability of immature walruses to exploit available foraging grounds. Human activities such as shipping that impact walrus foraging may have more significant impacts on immature and female walruses.