Cummings Cloe R, Lea Mary-Anne, Morrice Margaret G, Wotherspoon Simon, Hindell Mark A
Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS 7004, Australia.
School of Life and Environmental Sciences, Deakin University, Warrnambool, VIC 3280, Australia.
Conserv Physiol. 2015 Dec 8;3(1):cov049. doi: 10.1093/conphys/cov049. eCollection 2015.
Southern elephant seal (Mirounga leonina) pups must strike a balance between conserving energy during their post-weaning fast and simultaneously developing diving abilities to attain nutritional independence. Little is known about environmental influences on cardiorespiratory patterns, hence energy use, throughout the 6 week fast. Continuous heart rates were recorded for free-ranging, newly weaned southern elephant seals using heart rate time-depth recorders for 5-9 days at Sub-Antarctic Macquarie Island, during October 1994 (n = 1), 1995 (n = 4) and 1996 (n = 1). Daytime observations of respiration and behaviour were made throughout. We present the first instance of synchronous heart rate traces recorded simultaneously for individual weaners. Generalized additive models revealed that a sinusoidal pattern of diurnal heart rate elevation and nocturnal depression was evident in all seals and, on at least one occasion, a conspicuous break in this pattern coincided with an extreme cold weather event. Seals in this study were capable of considerable cardiorespiratory control and regularly demonstrated bradycardia during periods of resting apnoea. Apnoeic duration ranged from 33 to 291 s (mean 134 s). Apnoeic heart rates (mean 67 ± 15 beats min(-1), range 40-114 beats min(-1)) were on average 19.7% lower than those exhibited during periods of eupnoea (mean 83 ± 15 beats min(-1), range 44-124 beats min(-1)). The early development of the cardiorespiratory response is characterized by arrhythmic heart and respiration rates. The strong temporal patterns observed are being driven by the opposing requirements of maximizing time spent fasting in order to develop diving capabilities and of maximizing departure mass. This pilot study has highlighted a potentially large effect of ambient weather conditions on newly weaned southern elephant seal cardiorespiratory activity. Given the increasing westerlies and more erratic and increasing storminess associated with the Southern Annular Mode predicted in the Southern Ocean, the patterns observed here warrant further investigation.
南象海豹（Mirounga leonina）幼崽必须在断奶后的禁食期保存能量与同时发展潜水能力以实现营养独立之间找到平衡。在为期6周的禁食期内，关于环境对心肺模式以及能量使用的影响，我们所知甚少。1994年10月（n = 1）、1995年（n = 4）和1996年（n = 1），在亚南极的麦夸里岛，使用心率时间深度记录仪对自由放养的、刚断奶的南象海豹连续记录心率5 - 9天。在此期间，对呼吸和行为进行了全天的日间观察。我们展示了首次为个体断奶幼崽同时记录的同步心率轨迹实例。广义相加模型显示，所有海豹的心率呈现出昼夜节律模式，即白天心率升高，夜间心率降低，并且至少有一次，这种模式的明显中断与极端寒冷天气事件同时发生。本研究中的海豹具备相当程度的心肺控制能力，在静息性呼吸暂停期间经常出现心动过缓。呼吸暂停持续时间为33至291秒（平均134秒）。呼吸暂停时的心率（平均67 ± 15次/分钟，范围40 - 114次/分钟）平均比正常呼吸期间的心率（平均83 ± 15次/分钟，范围44 - 124次/分钟）低19.7%。心肺反应的早期发展特征是心率和呼吸频率无节律。所观察到的强烈时间模式是由两个相互矛盾的需求驱动的，即最大化禁食时间以发展潜水能力和最大化离乳体重。这项初步研究突出了环境天气条件对刚断奶的南象海豹心肺活动可能产生的重大影响。鉴于南大洋预计与南半球环状模相关的西风增强以及更不稳定和增加的风暴，这里观察到的模式值得进一步研究。
