Rivera Gabriel, Rivera Angela R V, Dougherty Erin E, Blob Richard W
Department of Biological Sciences, Clemson University, 132 Long Hall, Clemson, SC 29634, USA.
J Exp Biol. 2006 Nov;209(Pt 21):4203-13. doi: 10.1242/jeb.02488.
The ability to capture prey and avoid predation in aquatic habitats depends strongly on the ability to perform unsteady maneuvers (e.g. turns), which itself depends strongly on body flexibility. Two previous studies of turning performance in rigid-bodied taxa have found either high maneuverability or high agility, but not both. However, examinations of aquatic turning performance in rigid-bodied animals have had limited taxonomic scope and, as such, the effects of many body shapes and designs on aquatic maneuverability and agility have yet to be examined. Turtles represent the oldest extant lineage of rigid-bodied vertebrates and the only aquatic rigid-bodied tetrapods. We evaluated the aquatic turning performance of painted turtles, Chrysemys picta (Schneider, 1783) using the minimum length-specific radius of the turning path (R/L) and the average turning rate (omega(avg)) as measures of maneuverability and agility, respectively. We filmed turtles conducting forward and backward turns in an aquatic arena. Each type of turn was executed using a different pattern of limb movements. During forward turns, turtles consistently protracted the inboard forelimb and held it stationary into the flow, while continuing to move the outboard forelimb and both hindlimbs as in rectilinear swimming. The limb movements of backward turns were more complex than those of forward turns, but involved near simultaneous retraction and protraction of contralateral fore- and hindlimbs, respectively. Forward turns had a minimum R/L of 0.0018 (the second single lowest value reported from any animal) and a maximum omega(avg) of 247.1 degrees. Values of R/L for backward turns (0.0091-0.0950 L) were much less variable than that of forward turns (0.0018-1.0442 L). The maneuverability of turtles is similar to that recorded previously for rigid-bodied boxfish. However, several morphological features of turtles (e.g. shell morphology and limb position) appear to increase agility relative to the body design of boxfish.
在水生栖息地中捕获猎物和躲避捕食的能力很大程度上取决于进行非稳态机动（如转弯）的能力，而这又强烈依赖于身体的灵活性。之前两项关于刚体类群转弯性能的研究，要么发现了高机动性，要么发现了高敏捷性，但并非两者兼具。然而，对刚体动物水生转弯性能的研究在分类学范围上有限，因此，许多身体形状和设计对水生机动性和敏捷性的影响尚未得到研究。海龟代表了现存最古老的刚体脊椎动物谱系，也是唯一的水生刚体四足动物。我们以转弯路径的最小特定长度半径（R/L）和平均转弯速率（ωavg）分别作为机动性和敏捷性的指标，评估了彩龟（Chrysemys picta，施耐德，1783年）的水生转弯性能。我们拍摄了海龟在水生场地中进行向前和向后转弯的过程。每种转弯类型都采用不同的肢体运动模式执行。在向前转弯时，海龟持续伸展内侧前肢并使其在水流中保持静止，同时像直线游泳一样继续移动外侧前肢和两条后肢。向后转弯的肢体运动比向前转弯更复杂，但分别涉及对侧前肢和后肢几乎同时的收缩和伸展。向前转弯的最小R/L为0.0018（这是从任何动物报道的第二低的单一值），最大ωavg为247.1度。向后转弯的R/L值（0.0091 - 0.0950L）的变化远小于向前转弯（0.0018 - 1.0442L）。海龟的机动性与之前记录的刚体箱鲀相似。然而，海龟的几个形态特征（如壳形态和肢体位置）相对于箱鲀的身体设计似乎增加了敏捷性。
