The development of diving in marine endotherms: preparing the skeletal muscles of dolphins, penguins, and seals for activity during submergence

Myoglobin is an important oxygen store for supporting aerobic diving in end otherms, yet little is known about its role during postnatal development. T herefore, we compared the postnatal development of myoglobin in marine endo therms that develop at sea (cetaceans) to those that develop on land (pengu ins and pinnipeds). We measured myoglobin concentrations in the major locom otor muscles of mature and immature bottlenose dolphins (Tursiops truncatus ) and king penguins (Aptenodytes patagonicus) and compared the data to prev iously reported values for northern elephant seals (Mirounga angustirostris ). Neonatal dolphins, penguins, and seals lack the myoglobin concentrations required for prolonged dive durations. having 10%, 9%, and 31% of adult va lues, respectively. Myoglobin contents increased significantly during subse quent development. The increases in myoglobin content with age may correspo nd to increases in activity levels, thermal demands, and time spent in apne a during swimming and diving. Across these phylogenetically diverse taxa (c etaceans, penguins, and pinnipeds), the final stage of postnatal developmen t of myoglobin occurs during the initiation of independent foraging, regard less of whether development takes place at sea or on land.