Experimental Hydrodynamics and Evolution: function of median fins in ray-finned fishes

生活在水中的生物代表了生命多样性的很大一部分，了解动物如何在水中移动，对环境施加力，以及在动荡的环境中控制身体位置，对于深入了解水生生物的多样性至关重要。然而，在过去的20年里，试图研究这个问题遇到了许多困难。其中最主要的是，要量化生物在水中运动所施加的力，在技术上存在相当大的困难。在陆地上，这样的测量在技术上是容易的（例如，踩在秤上，就可以测量身体在地面上的力），但是我们无法量化水中生物施加的力，这使得我们很难理解不同身体和鳍形的功能意义。本研究从工程领域引进了一种新的流动可视化技术——数字粒子图像测速（DPIV），并对其进行了改进，以研究鱼的身体和鳍的运动。这项技术第一次提供了一种实验方法，可以量化自由游动的鱼类在尾迹中的水运动，并计算自由游动的水生生物的鳍和身体对水施加的力的大小和方向。以前NSF拨款的进展已经证明了DPIV能够提供对理解生物水中运动机制至关重要的数据，并表明如何使用这种新方法来测量水的运动，从而对水生生物的多样性产生以前意想不到的见解。本研究的总体目标是研究鱼类鳍的流体动力学功能，重点关注翻车鱼、鳟鱼和鲟鱼的背鳍和尾鳍，目的是测试文献中关于这些鳍产生力量并允许鱼类在水中机动和定位的机制的几个长期存在的假设。特别令人感兴趣的是“尾流拦截”假说：鱼类可以通过尾鳍拦截背鳍产生的水动力尾流来增强尾鳍产生的力。如果这一假说得到证实，它将代表一种重要的新的通用机制，通过这种机制，生物和人造潜水器都可以提高推进效率。该研究项目通过由首席研究员（PI）共同教授的高级本科课程的学生个人研究项目，为本科生提供动物生物力学和进化研究的新方法和技术的高级培训，为生物学研究生提供生物功能研究的工程方法的跨学科培训，并为下一代学术教师提供博士后培训。这里提出的研究将通过哈佛大学生物力学广泛的新培训计划产生更广泛的影响，该计划整合了生物力学研究生在生物学，化学，物理学和工程学方面的培训。PI是这项资助的教员之一，所提出的研究将作为学生进行强制性轮岗的项目，从而向化学、物理和工程研究生介绍他们原本不会接触到的各种各样的有机功能生物学的概念和方法。

Organisms that live in the water represent a substantial fraction of life's diversity, and understanding how animals move through water, exert forces on their environment, and control their body position in a turbulent environment is critical to developing insights into the diversity of aquatic life. However, attempts to study this question over the past 20 years have met with many difficulties. Chief among these has been the considerable technical difficulty of quantifying the forces exerted by the movement of organisms on the water. On land such measurements are technically easy (stepping on a scale, for example, gives a force measurement of the body on the ground), but our inability to quantify forces exerted by organisms in the water has made it very difficult to understand the functional significance of different body and fin shapes.This study adopts from the field of engineering a new flow visualization technique called Digital Particle Image Velocimetry (DPIV) and modifies it to study fish body and fin motion. This technique provides, for the first time, a means of experimentally quantifying water movement in the wake of freely swimming fishes, and calculating the magnitudes and directions of forces exerted on the water by fins and the body of freely-moving aquatic organisms. Progress on previous NSF grants has demonstrated the ability of DPIV to provide data critical to understanding mechanisms of aquatic locomotion in organisms, and has shown how using this new approach to measuring the motion of water leads to previously unexpected insights into the diversity of aquatic organisms. The general objectives of this research are to study the hydrodynamic function of fins in fishes, focusing on the dorsal and caudal fins in sunfish, trout, and sturgeon with the aim of testing several long-standing hypotheses in the literature regarding the mechanisms by which these fins generate force and allow fishes to maneuver and position themselves in the water. Of special interest is the hypothesis of "wake interception" : that fishes can enhance the force generated by their tail fin by having the tail intercept the hydrodynamic wake shed by the dorsal fin. If this hypothesis is corroborated, it will represent an important new general mechanism by which both organisms and man-made submersibles could increase their propulsive efficiency. This research project contributes to advanced training of undergraduates in new approaches and technologies for the study of animal biomechanics and evolution through individual student research projects in an advanced undergraduate course co-taught by the Principal Investigator (PI), the interdisciplinary training of biology graduate students in engineering approaches to the study of organismal function, and post-doctoral training for the next generation of academic faculty. The research proposed here will have increased breadth of impact through a broad new training program in biomechanics at Harvard University which integrates biomechanics graduate training in biology, chemistry, physics, and engineering. The PI is one of the faculty on this grant, and the research proposed will serve as projects for students undertaking mandatory rotations, thus introducing a wide diversity of chemistry, physics and engineering graduate students to concepts and approaches in organismic functional biology that they would not otherwise be exposed to.