Biomechanics of Segmented Axial Musculature in Salamanders and Fishes

超过一半的脊椎动物是鱼类，然而它们肌肉的三维几何形状和游泳行为之间的基本关系却知之甚少。鱼的身体肌肉被组织成短段的肌肉纤维，由腱状的胶原蛋白片分开（在“片状”鱼片中，这些片段就是薄片）。在每个节段内，肌肉纤维以复杂的轨迹运行，节段本身折叠成圆锥形。这些肌肉复杂的3D结构使得人们很难理解它们在游泳中的功能。本研究的总体目标是了解两种模型系统中节段肌肉组织的功能：水生蝾螈（Siren lacertina）的成虫和斑马鱼（Danio rerio）的幼虫。选择这些模型物种是因为它们使用分段的身体肌肉来游泳，但它们肌肉段的三维几何形状比成年鱼更简单。跨学科的方法来解决这个问题，包括数学建模，三维数字成像与激光扫描共聚焦显微镜，和测量肌肉收缩（肌肉劳损）在游泳与声脉冲为基础的技术，声压测量。本研究的三个具体目的是：(1)建立蛇舌草肌纤维应变、纵向应变和三维节段变形关系的数学模型；(2)利用声压测量法测量剑鱼游泳过程中肌纤维应变、纵向应变和三维节段变形，对模型进行验证和完善；(3)使用共聚焦显微镜测量斑马鱼幼虫的节段肌肉的三维结构，并应用我们的3D模型来深入了解斑马鱼幼虫肌肉节段的结构与功能之间的关系（斑马鱼幼虫将在它们第一次开始自由游动时进行研究-在它们孵出卵后一两天）。这项研究的结果将产生对肌肉纤维角度、肌肉节段形状和结缔组织结构对游泳力学的影响的综合理解。在未来，这些结果将应用于鱼类物种的巨大多样性，以了解鱼类肌肉骨骼系统的进化。

More than half of all vertebrate animals are fish, yet the fundamental relationship between the 3-dimensional (3D) geometry of their muscles and swimming behavior is poorly understood. The body muscles of fish are organized into short segments of muscle fibers, separated by sheets of tendon-like collagen (in "flaky" fish fillets, the segments are the flakes). Within each segment, muscle fibers run in complex trajectories and the segments themselves are folded into cone-like shapes. The complex, 3D structure of these muscles has made it difficult to understand how they function in swimming. The general objective of this study is to understand the function of segmented musculature in two model systems: adults of an aquatic salamander, Siren lacertina, and larvae of zebrafish, Danio rerio. These model species were chosen because they use segmented body muscles for swimming, but the 3D geometry of their muscle segments is simpler than in adult fishes. Interdisciplinary approaches to this problem will be used including mathematical modeling, 3D digital imaging with laser scanning confocal microscopy, and measurement of muscle contraction (muscle strain) during swimming with a sound-pulse based technique, sonomicrometry. The three specific aims of this study are: (1) to develop a mathematical model of the relationship between muscle fiber strain, longitudinal strain, and 3D segment deformation in S. lacertina; (2) to test and refine the model by measuring muscle fiber strain, longitudinal strain, and 3D segment deformation with sonomicrometry during swimming in S. lacertina; and (3) to use confocal microscopy to measure the 3D architecture of segmented musculature in zebrafish larvae, and apply our 3D model to gain insight into the relationship between structure and function of larval zebrafish muscle segments (larval zebrafish will be studied when they first begin to swim freely - a day or two after they hatch out of their eggs). The results of this study will yield an integrated understanding of the effects of muscle fiber angle, muscle segment shape, and connective tissue architecture on the mechanics of swimming. In the future, these results will be applied to the vast diversity of fish species, in order to understand the evolution of the musculoskeletal system in fishes.