Comprising up to 50% of most species' body mass, skeletal muscle is the largest organ in many creatures' bodies. Skeletal muscle also consumes a significant proportion of the body's metabolic budget. Every tissue's metabolic rate is dramatically affected by changes in temperature, which makes metabolic adaptation in skeletal muscle especially important for creatures whose body temperatures are dictated by their environment. The review by Hans-Otto Pörtner describes functional adaptations of fish muscle to icy polar waters (p. 2217). Both Arctic and Antarctic species have compensated for their reduced aerobic function by packing their muscle tissue with mitochondria and lipid fuel at the expense of fewer contractile elements into each muscle cell. But Antarctic species, which only survive a very narrow range of temperatures, have also reduced their oxygen demand by reducing their mitochondrial metabolic rate.
Fish that face seasonal temperature variations have to adapt over a much shorter...
