Terrestrial apnea in northern elephant seals, Mirounga angustirostris: Development and role in water economy.

摘要

During prolonged fasts on land, northern elephant seals (Mirounga angustirostris) have an irregular breathing pattern, alternating between bouts of breathing (eupnea) and periods of breath-holding (apnea). The development of this behavior was investigated in free-ranging seals and compared to the development of diving ability. Elephant seals have an unusual breath-holding ability, probably acquired for procuring prey at sea. The hypothesis that they use this breath-holding ability for water conservation on land was tested by comparing the respiratory water loss of a weaned pup breathing apneustically with that of a hypothetical animal, similar in every way but not showing any terrestrial apneas.; Behavioral observations of breathing during apparent sleep were done on 163 seals ranging in age from newborns to adults. Sixteen weaned pups and 8 yearlings were fitted with data loggers, which recorded heart rate, from which time in apnea was inferred, as well as gross motor activity, ambient temperature and whether the animals were in the water or on land. Water flux was measured in 4 weanlings using the tritiated water method.; Mean length of apnea and percentage time spent in apnea during sleep increased from 1.8 min. and 37% in suckling pups to about 8.0 min. and 60% in adults of both sexes. Sleep apnea duration and time spent in sleep apnea increased most markedly during the post-weaning fast, when weanlings also develop their diving ability. Daily total time spent in apnea was very similar in weanlings and yearlings, averaging about 55%. The number of breaths taken per day would increase by 50% in weanlings and 76% in yearlings without the use of terrestrial apnea. Water turnover rates were extremely low, rivaling those of desert animals. The contribution of respiratory water loss to the animal's total water budget would increase from 63% to 88% without the use of terrestrial apnea. Apneustic breathing saves weanlings the equivalent of about 40% of their daily respiratory water loss. Northern elephant seals use several adaptations for water economy, several of which are also found in arid-adapted mammals. These allow them lengthy fasts, which are part of their unusual life-history.