Institute of Marine Science, Center for Ocean Health, University of California at Santa Cruz, Santa Cruz, CA 95060, USA.
J Exp Biol. 2011 Dec 15;214(Pt 24):4151-9. doi: 10.1242/jeb.059121.
Constraints on locomotion could be an important component of the cost of reproduction as carrying an increased load associated with eggs or developing fetuses may contribute to decreased locomotor performance for females across taxa and environments. Diminished performance could increase susceptibility to predation, yet the mechanism(s) by which gravidity and pregnancy affect locomotion remains largely unexplored. Here we demonstrate that morphology, hydrodynamics and kinematics were altered during pregnancy, providing a mechanism for diminished locomotor performance in two near-term pregnant (10 days pre-parturition) bottlenose dolphins (Tursiops truncatus). Near-term pregnancy resulted in a 56 ± 13% [corrected] increase in frontal surface area, coinciding with dramatic increases in drag forces while gliding. For example, pregnant females encountered 80 N of drag at 1.7 m s(-1) whereas that magnitude of drag was not encountered until speed doubled for females 18 months post-parturition. Indeed, drag coefficients based on frontal surface area were significantly greater during pregnancy (C(d,F)=0.22 ± 0.04) than at 18 months post-parturition (C(d,F)=0.09 ± 0.01). Pregnancy also induced a gait change as stroke amplitude and distance per stroke were reduced by 13 and 14%, respectively, compared with non-pregnant periods (1-24 months post-parturition). This was concomitant with a 62 and 44% reduction in mean and maximum swim speeds, respectively, during the pregnancy period. Interestingly, attack speeds of known predators of dolphins surpass maximum speeds for the pregnant dolphins in this study. Thus, pregnant dolphins may be more susceptible to predation. This study demonstrates unequivocally that changes in morphology, hydrodynamics and kinematics are associated with diminished performance during pregnancy in dolphins.
运动受限可能是生殖成本的一个重要组成部分，因为携带与卵子或发育中的胎儿相关的增加的负荷可能会导致跨分类群和环境的雌性动物的运动表现下降。性能下降可能会增加被捕食的易感性，但妊娠期和怀孕如何影响运动的机制在很大程度上仍未得到探索。在这里，我们证明了形态、水动力和运动学在怀孕期间发生了改变，为两种接近分娩期（分娩前 10 天）的瓶鼻海豚（Tursiops truncatus）的运动表现下降提供了一种机制。接近分娩期导致前表面积增加了 56 ± 13%[校正]，同时滑翔时的阻力急剧增加。例如，怀孕的雌性动物在 1.7 m s(-1)时遇到 80 N 的阻力，而在分娩后 18 个月的雌性动物速度增加一倍时才遇到这种阻力。事实上，基于前表面积的阻力系数在怀孕期间（C(d,F)=0.22 ± 0.04）显著大于分娩后 18 个月（C(d,F)=0.09 ± 0.01）。怀孕还导致了步态的改变，与非怀孕期（分娩后 1-24 个月）相比，冲程幅度和冲程距离分别减少了 13%和 14%。这与怀孕期间平均和最大游泳速度分别降低了 62%和 44%是一致的。有趣的是，海豚已知捕食者的攻击速度超过了本研究中怀孕海豚的最大速度。因此，怀孕的海豚可能更容易被捕食。这项研究明确表明，形态、水动力和运动学的变化与海豚怀孕期间的运动表现下降有关。
