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First published online August 8, 2008
Journal of Experimental Biology 211, 2559-2565 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.018119

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The ontogeny of aerobic and diving capacity in the skeletal muscles of Weddell seals

S. B. Kanatous^1,*, T. J. Hawke², S. J. Trumble³, L. E. Pearson¹, R. R. Watson⁴, D. J. Garry⁵, T. M. Williams⁶ and R. W. Davis⁷

¹ Department of Biology, Colorado State University, Fort Collins, CO 80523-1878, USA
² School of Kinesiology and Health Science, York University, Toronto, ON, Canada M3J 1P3
³ Department of Biology, University of Michigan Flint, Flint, MI 48502, USA
⁴ Biological Sciences Department, California State Polytechnic University, Pomona, CA 91768, USA
⁵ Lillehei Heart Institute, University of Minnesota, Minneapolis, MN 55455, USA
⁶ Department of Ecology and Evolutionary Biology, University of California at Santa Cruz, Santa Cruz, CA 95060, USA
⁷ Department of Marine Biology, Texas A&M University at Galveston, Galveston, TX 77551, USA

^* Author for correspondence (e-mail: kanatous{at}lamar.colostate.edu)

Accepted 4 June 2008

Our objective was to determine the ontogenetic changes in the skeletal muscles of Weddell seals that transform a non-diving pup into an elite diving adult. Muscle biopsies were collected from pups, juveniles and adults and analyzed for changes in fiber type, mitochondrial density, myoglobin concentrations and aerobic, lipolytic and anaerobic enzyme activities. The fiber type results demonstrated a decrease in slow-twitch oxidative (Type I) fibers and a significant increase in fast-twitch oxidative (Type IIA) fibers as the animals mature. In addition, the volume density of mitochondria and the activity of lipolytic enzymes significantly decreased as the seals matured. To our knowledge, this is the first quantitative account describing a decrease in aerobic fibers shifting towards an increase in fast-twitch oxidative fibers with a significant decrease in mitochondrial density as animals mature. These differences in the muscle physiology of Weddell seals are potentially due to their three very distinct stages of life history: non-diving pup, novice diving juvenile, and elite deep diving adult. During the first few weeks of life, pups are a non-diving terrestrial mammal that must rely on lanugo (natal fur) for thermoregulation in the harsh conditions of Antarctica. The increased aerobic capacity of pups, associated with increased mitochondrial volumes, acts to provide additional thermogenesis. As these future elite divers mature, their skeletal muscles transform to a more sedentary state in order to maintain the low levels of aerobic metabolism associated with long-duration diving.

Key words: diving, hypoxia, ontogeny, seals, skeletal muscle

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