Biology Department, Adelphi University, Garden City, NY 11530, USA.
Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, CA 95060, USA.
Integr Comp Biol. 2020 Jul 1;60(1):180-189. doi: 10.1093/icb/icaa016.
Fishes overcome a variety of challenges in order to invade the terrestrial environment. Terrestrial invasions by fish occur over a variety of environmental contexts. In order to advance their bodies on land, fishes capable of terrestrial excursions tend to use one of three different types of locomotor modes: axial-based, appendage-based, or axial-appendage-based. Elongate species with reduced appendages, such as the American eel, Anguilla rostrata, rely on axial based locomotion in water and on land. When eels move from water to land as part of their complex life cycle, they inevitably encounter a variety of substrates and must traverse variable degrees of incline. The aim of this study was to determine the effect of substrate and incline on the terrestrial locomotion of the American eel. In order to do this, eels were filmed from a dorsal view on three substrates and four inclines: sand, loose pebbles, and fixed (glued) pebbles at 0°, 5°, 10°, and 15°. We digitized 20 evenly spaced points along the body to examine the following characteristics of locomotion: velocity, distance ratio (DR), and wave parameters such as wave amplitude, frequency, and length and assessed whether substrate, incline, or body position affected these parameters. DR, our metric of movement efficiency, was highest on the flat sand condition and lowest on 15° pebble conditions. Efficiency also varied across the body. Velocity followed a similar pattern being highest on sand at 0° and lowest at the steepest inclines. Wave amplitude generally increased toward the tail but was similar across substrates and inclines. Wave frequency was relatively consistent across the body on both pebble substrates, but on sand, frequency was higher toward the head but decreased toward the tail. Wavelengths on sand were the longest at 0° near the head and shorter wavelengths were observed on steeper inclines. Both pebble substrates elicited lower wavelengths that were more similar across the body. Overall, A. rostrata were more effective in navigating compliant substrates but struggled at steeper inclines. Our findings provide insight into locomotor challenges that American eels may encounter as they move from and between bodies of water.
鱼类为了入侵陆地环境克服了各种各样的挑战。鱼类在各种环境背景下向陆地入侵。为了在陆地上推进身体，能够进行陆地探险的鱼类往往使用三种不同类型的运动模式之一：轴基、附肢基或轴-附肢基。像美洲鳗这样身体细长、附肢减少的物种，在水中和陆地上都依赖于轴基运动。当鳗鱼作为其复杂生命周期的一部分从水中移动到陆地时，它们不可避免地会遇到各种基质，并且必须穿越不同程度的坡度。本研究旨在确定基质和坡度对美洲鳗的陆地运动的影响。为此，我们从背侧拍摄了鳗鱼在三种基质和四种坡度（沙、松散卵石和固定（胶合）卵石，坡度分别为 0°、5°、10°和 15°）上的运动。我们沿着身体数字化了 20 个均匀间隔的点，以检查运动的以下特征：速度、距离比（DR）和波参数，如波幅、频率、长度，并评估基质、坡度或身体位置是否影响这些参数。DR 是我们衡量运动效率的指标，在平坦的沙质条件下最高，在 15°卵石条件下最低。效率也在身体上有所不同。速度在 0°沙质条件下最高，在最陡峭的坡度条件下最低，遵循类似的模式。波幅通常在尾部增加，但在基质和坡度上相似。在两种卵石基质上，波频在整个身体上相对一致，但在沙质基质上，波频在头部较高，但在尾部较低。在头部附近的 0°沙质条件下，波长最长，在较陡的坡度上观察到较短的波长。两种卵石基质都产生了更相似的较低波长。总的来说，A. rostrata 在适应基质上的导航更有效，但在较陡的坡度上挣扎。我们的发现为美洲鳗在从水体和水体之间移动时可能遇到的运动挑战提供了一些见解。
