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First published online February 27, 2009
Journal of Experimental Biology 212, 790-796 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.025387

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Diving into old age: muscular senescence in a large-bodied, long-lived mammal, the Weddell seal (Leptonychotes weddellii)

Allyson G. Hindle^1,2,*, Markus Horning^1,3, Jo-Ann E. Mellish⁴ and John M. Lawler⁵

¹ Department of Marine Biology, Texas A&M University at Galveston, 5007 Avenue U, Galveston, TX 77551, USA
² Marine Mammal Research Unit, University of British Columbia, Room 247, 2202 Main Mall, Vancouver, BC, Canada V6T 1Z4
³ Department of Fisheries and Wildlife, Marine Mammal Institute, Oregon State University, 2030 SE Marine Science Drive, Newport, OR 97365, USA
⁴ School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Alaska SeaLife Center, 301 Railway Avenue, Seward, AK 99664, USA
⁵ Department of Health and Kinesiology, Intercollegiate Faculty of Nutrition, Texas A&M University, College Station TX 77843, USA

^* Author for correspondence (e-mail: a.hindle{at}fisheries.ubc.ca)

Accepted 6 January 2009

Classic aging theory postulates the absence of pronounced organismal senescence in wild animals since mortality probably occurs first. Large-bodied, long-lived mammals are a recognized exception to this tenet, yet organismal senescence has not been investigated to date in such mammals in the wild. Furthermore, oxidative stress theory of aging supports the suggestion that exercise hypoxia, as regularly incurred during apneustic foraging in diving mammals might lead to cellular dysfunction and accelerated aging. To determine if an aspect of organismal senescence occurs in wild marine mammals, we examined the pattern of skeletal muscle aging (contractile and connective tissue components of longissimus dorsi and pectoralis muscles) in free-ranging adult Weddell seals (9–26 years). The average myocyte cross-sectional area was 22% greater with age in the longissiums dorsi, but no significant increase occurred in the pectoralis. Cross-sectional area was not related to body mass. Changes in myocyte number per area were consistent with the 35–40% age-increase in extracellular space in both muscle groups. Also consistent with extracellular space remodeling, total and relative collagen contents were significantly elevated in older seals (115% in longissimus dorsi; 65% in pectoralis). The ratio of muscle myocyte to collagen declined with age (50–63%) at both sites. Additionally, a shift towards a higher ratio of type I to type III collagen occurred with advancing age in both muscle groups (79% increase in pectoralis; 49% in longissimus dorsi). We reject the classic tenet and null-hypothesis that Weddell seals do not survive to an age where muscular senescence becomes detectable.

Key words: muscle morphology, collagen, diving, aging

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