Extremely Elevated Myoglobin Contents in the Pelagic Melon-Headed Whale (Peponocephala electra) after Prolonged Postnatal Maturation

Muscle biochemistry of aquatic birds and mammals varies in accordance with swimming and diving performance, as well as with ontogeny. Similar to other odontocetes, the locomotor muscles (longissimus dorsi) of neonatal melon-headed whales (Peponocephala electra) have low myoglobin content (Mb; 1.06 +/- 0.20 g Mb/100 g wet muscle mass; mean +/- SE; n=2] and low muscle nonbicarbonate buffering capacity (37.78 +/- 3.75 slykes; n=2), representing only 16% of adult Mb (6.64 +/- 0.33 g Mb/100 g wet muscle mass; n=5) and 56% of adult muscle nonbicarbonate buffering capacities (66.90 +/- 4.80 slykes; n=5). By the juvenile stage, Mb (2.75 +/- 0.80 & x2062; g Mb/100 g wet muscle mass; n=3) is still only 41% of adult levels, but nonbicarbonate buffering capacity (65.61 +/- 2.62 slykes; n=3) has matured. Despite the observation that Hawaiian melon-headed whales are not deep divers or long-duration divers, their Mb rivals that found in ziphiids that forage in the bathypelagic zone and monodontids that forage under sea ice. The pelagic lifestyle of melon-headed whales likely requires sustained swimming, such that endurance training could elevate Mb in the locomotor muscle. Indeed, elevated Mb in the locomotor muscles of other pelagic odontocetes has been observed. Unlike deep-diving and Arctic-dwelling odontocetes, melon-headed whales do not achieve mature muscle characteristics before nursing. It is likely that early in life, the hydrodynamic benefits of swimming in echelon position with their mothers minimizes the endurance training of the calves that would otherwise promote rapid elevations in Mb.