Holzman Roi, Day Steven W, Wainwright Peter C
Section of Evolution and Ecology, University of California, One Shields Avenue, Davis, CA 95616, USA.
J Exp Biol. 2007 Oct;210(Pt 19):3328-36. doi: 10.1242/jeb.008292.
During aquatic suction feeding, the predator opens its mouth and rapidly expands its buccal cavity, generating a flow field external to the mouth. The rapid expansion of the buccal cavity produces high fluid velocities and accelerations that extend only a short distance from the mouth (about half of one mouth diameter), and only persist for several milliseconds. Therefore, the predator must precisely time its strike to locate the prey within the narrow region of high flow, during the brief period when flow is at its peak. With flow being the agent for transferring force to the prey, the predator may enhance these forces by producing higher water velocities and faster acceleration at the mouth, but also through increasing the strike's accuracy, i.e. locating the prey closer to the mouth at the instant of peak flow speed. The objectives of this study were to directly measure forces exerted by bluegill Lepomis macrochirus on their prey and to determine how bluegill modify force output. Bluegill were offered ghost shrimp tethered to a load cell that recorded force at 5000 Hz, and feeding sequences were synchronously recorded using 500 Hz video. Peak forces exerted on attached 20 mm shrimp ranged from 0.005 N to 0.506 N. In accordance with the short duration of the strikes (average time to peak gape of approximately 13 ms), the forces recorded were brief (approximately 12 ms from initiation to peak force), and force magnitude declined rapidly after peak force. Statistical analysis indicated that rate of buccal expansion, and prey size, but not strike initiation distance, significantly affected peak force. These observed variables were used with results from flow visualization studies to estimate the flow at the prey's location, which allowed the calculation of drag, pressure gradient force and acceleration reaction force. The relationship between these calculated forces and the measured forces was strong, indicating that the model can be used to estimate forces from strike kinematics. This model was then used to study the effects of strike initiation distance on peak force and on the rate of increasing force. Comparisons of model output to empirical results indicated that bluegill time their strike so as to exert an average of approximately 70% of the peak possible force on the prey, and that the observed strike initiation distance corresponded to the distance that maximized modeled force on an attached prey. Our results highlight the ability of bluegill to produce high forces on their prey, and indicate that precision and visual acuity play important roles in prey acquisition, beyond their recognized role in prey detection.
在水生吸食摄食过程中，捕食者张开嘴巴并迅速扩张口腔，在嘴外产生一个流场。口腔的快速扩张会产生高流体速度和加速度，这些仅在离嘴很短的距离内（约为一个嘴直径的一半）存在，并且仅持续几毫秒。因此，捕食者必须精确地把握攻击时机，以便在水流达到峰值的短暂时期内，在狭窄的高流速区域内定位猎物。水流是将力传递给猎物的媒介，捕食者可以通过在嘴部产生更高的水流速度和更快的加速度来增强这些力，还可以通过提高攻击的准确性来增强，即在水流速度峰值瞬间将猎物定位在更靠近嘴的位置。本研究的目的是直接测量蓝鳃太阳鱼（Lepomis macrochirus）对其猎物施加的力，并确定蓝鳃太阳鱼如何改变力的输出。给蓝鳃太阳鱼提供系在称重传感器上的幽灵虾，该传感器以5000赫兹的频率记录力，同时使用500赫兹的视频同步记录摄食序列。对附着的20毫米虾施加的峰值力范围为0.005牛至0.506牛。与攻击持续时间较短（平均达到最大张口的时间约为13毫秒）一致，记录到的力很短暂（从开始到峰值力约为12毫秒），并且在峰值力之后力的大小迅速下降。统计分析表明，口腔扩张速率和猎物大小，但不是攻击起始距离，显著影响峰值力。将这些观察到的变量与流动可视化研究的结果结合起来，以估计猎物位置处的水流，从而可以计算阻力、压力梯度力和加速度反作用力。这些计算出的力与测量到的力之间的关系很强，表明该模型可用于根据攻击运动学来估计力。然后使用该模型研究攻击起始距离对峰值力和力增加速率的影响。将模型输出与实验结果进行比较表明，蓝鳃太阳鱼把握攻击时机，以便对猎物施加平均约为峰值可能力的70%的力，并且观察到的攻击起始距离对应于使附着猎物上的模型力最大化的距离。我们的结果突出了蓝鳃太阳鱼对其猎物产生高力的能力，并表明精度和视敏度在猎物捕获中发挥着重要作用，这超出了它们在猎物检测中公认的作用。
