Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Center for Ocean Health, 100 Shaffer Road, Santa Cruz, CA 95060, USA.
J Exp Biol. 2012 Aug 15;215(Pt 16):2735-41. doi: 10.1242/jeb.069583.
A hallmark of the dive response, bradycardia, promotes the conservation of onboard oxygen stores and enables marine mammals to submerge for prolonged periods. A paradox exists when marine mammals are foraging underwater because activity should promote an elevation in heart rate (f(H)) to support increased metabolic demands. To assess the effect of the interaction between the diving response and underwater activity on f(H), we integrated interbeat f(H) with behavioral observations of adult bottlenose dolphins diving and swimming along the coast of the Bahamas. As expected for the dive response, f(H) while resting during submergence (40±6 beats min(-1)) was significantly lower than f(H) while resting at the water surface (105±8 beats min(-1)). The maximum recorded f(H) (f(H,max)) was 128±7 beats min(-1), and occurred during post-dive surface intervals. During submergence, the level of bradycardia was modified by activity. Behaviors such as simple head bobbing at depth increased f(H) by 40% from submerged resting levels. Higher heart rates were observed for horizontal swimming at depth. Indeed, the dolphins operated at 37-58% of their f(H,max) while active at depth and approached 57-79% of their f(H,max) during anticipatory tachycardia as the animals glided to the surface. f(H) was significantly correlated with stroke frequency (range=0-2.5 strokes s(-1), r=0.88, N=25 dives) and calculated swim speed (range=0-5.4 m s(-1), r=0.88, N=25 dives). We find that rather than a static reflex, the dive response is modulated by behavior and exercise in a predictable manner.
潜水反应的一个标志是心动过缓，这有助于保存船上的氧气储备，并使海洋哺乳动物能够长时间潜水。当海洋哺乳动物在水下觅食时，就会出现一个悖论，因为活动应该会导致心率升高（f(H)），以支持新陈代谢需求的增加。为了评估潜水反应和水下活动之间的相互作用对 f(H)的影响，我们将心率与成年宽吻海豚在巴哈马海岸潜水和游泳时的行为观察结果相结合。与潜水反应预期一致，潜水时休息时的 f(H)（40±6 次/分钟）明显低于水面休息时的 f(H)（105±8 次/分钟）。记录到的最大 f(H)（f(H,max)）为 128±7 次/分钟，发生在潜水后水面间隔期间。在潜水过程中，活动改变了心动过缓的程度。例如，在深处简单地摇头等行为使 f(H)从潜水时的静息水平增加了 40%。在深处水平游泳时观察到更高的心率。事实上，当海豚在深处活动时，它们的心率在 37-58%的 f(H,max)范围内，当动物滑行到水面时，它们会经历预期性心动过速，达到 57-79%的 f(H,max)。f(H)与冲程频率（范围为 0-2.5 次/秒，r=0.88，N=25 次潜水）和计算出的游泳速度（范围为 0-5.4 米/秒，r=0.88，N=25 次潜水）显著相关。我们发现，潜水反应不是一种静态反射，而是通过行为和运动以可预测的方式进行调节。
