Burns J M, Costa D P, Frost K, Harvey J T
Department of Biological Sciences, University of Alaska, Anchorage, AK, 99508, USA.
Physiol Biochem Zool. 2005 Nov-Dec;78(6):1057-68. doi: 10.1086/432922. Epub 2005 Sep 8.
Harbor seal pups are highly precocial and can swim and dive at birth. Such behavioral maturity suggests that they may be born with mature body oxygen stores or that stores develop quickly during the nursing period. To test this hypothesis, we compared the blood and muscle oxygen stores of harbor seal pups, yearlings, and adults. We found that pups had smaller oxygen stores than adults (neonates 57%, weaned pups 75%, and yearlings 90% those of adults), largely because neonatal myoglobin concentrations were low (1.6+/-0.2 g% vs. 3.8+/-0.3 g% for adults) and changed little during the nursing period. In contrast, blood oxygen stores were relatively mature, with nursing pups having hematocrit (55%+/-0.2%), hemoglobin (21.7+/-0.4 g%), and blood volume (12.3+/-0.5 mL/kg) only slightly lower than the corresponding values for adults (57%+/-0.2%, 23.8+/-0.3 g %, and 15.0+/-0.5 mL/kg). Because neonatal pups had relatively high metabolic rates (11.0 mL O2/kg min), their calculated aerobic dive limit was less than 50% that of adults. These results suggest that harbor seals' early aquatic activity is primarily supported by rapid development of blood, with immature muscle oxygen stores and elevated use rates limiting aerobic diving ability.
港海豹幼崽出生时就高度早熟，能够游泳和潜水。这种行为上的成熟表明，它们可能天生就拥有成熟的身体氧气储备，或者在哺乳期内储备迅速发育。为了验证这一假设，我们比较了港海豹幼崽、一岁幼兽和成年海豹的血液和肌肉氧气储备。我们发现，幼崽的氧气储备比成年海豹少（新生幼崽为成年海豹的57%，断奶幼崽为75%，一岁幼兽为90%），这主要是因为新生幼崽的肌红蛋白浓度较低（成年海豹为3.8±0.3 g%，而新生幼崽为1.6±0.2 g%），并且在哺乳期内变化不大。相比之下，血液氧气储备相对成熟，哺乳幼崽的血细胞比容（55%±0.2%）、血红蛋白（21.7±0.4 g%）和血容量（12.3±0.5 mL/kg）仅略低于成年海豹的相应值（57%±0.2%、23.8±0.3 g%和15.0±0.5 mL/kg）。由于新生幼崽的代谢率相对较高（11.0 mL O2/kg·min），其计算得出的有氧潜水极限不到成年海豹的50%。这些结果表明，港海豹的早期水上活动主要由血液的快速发育来支持，肌肉氧气储备不成熟以及使用率升高限制了有氧潜水能力。
