Naylor Emily R, Kawano Sandy M
Department of Biological Sciences, The George Washington University, Washington, D.C. 20052, U.S.A.
Integr Comp Biol. 2022 Jun 9. doi: 10.1093/icb/icac084.
Many ecological factors influence animal movement, including properties of the media that they move on or through. Animals moving in terrestrial environments encounter conditions that can be challenging for generating propulsion and maintaining stability, such as inclines and deformable substrates that can cause slipping and sinking. In response, tetrapods tend to adopt a more crouched posture and lower their center of mass on inclines and increase the surface area of contact on deformable substrates, such as sand. Many amphibious fishes encounter the same challenges when moving on land, but how these finned animals modulate their locomotion with respect to different environmental conditions and how these modifications compare with those seen within tetrapods is relatively understudied. Mudskippers (Gobiidae: Oxudercinae) are a particularly noteworthy group of amphibious fishes in this context given that they navigate a wide range of environmental conditions, from flat mud to inclined mangrove trees. They use a unique form of terrestrial locomotion called 'crutching', where their pectoral fins synchronously lift and vault the front half of the body forward before landing on their pelvic fins while the lower half of the body and tail are kept straight. However, recent work has shown that mudskippers modify some aspects of their locomotion when crutching on deformable surfaces, particularly those at an incline. For example, on inclined dry sand, mudskippers bent their bodies laterally and curled and extended their tails to potentially act as a secondary propulsor and/or anti-slip device. In order to gain a more comprehensive understanding of the functional diversity and context-dependency of mudskipper crutching, we compared their kinematics on different combinations of substrate types (solid, mud, dry sand) and inclines (0°, 10°, 20°). In addition to increasing lateral bending on deformable and inclined substrates, we found that mudskippers increased the relative contact time and contact area of their paired fins while becoming more crouched, responses comparable to those seen in tetrapods and other amphibious fishes. Mudskippers on these substrates also exhibited previously undocumented behaviors, such as extending and adpressing the distal portions of their pectoral fins more anteriorly, dorsoventrally bending their trunk, "belly-flopping" on sand, and "gripping" the mud substrate with their pectoral fin rays. Our study highlights potential compensatory mechanisms shared among vertebrates in terrestrial environments while also illustrating that locomotor flexibility and even novelty can emerge when animals are challenged with environmental variation.
许多生态因素会影响动物的运动，包括它们在其上或穿过的介质的特性。在陆地环境中移动的动物会遇到一些对产生推进力和保持稳定性具有挑战性的条件，例如可能导致滑倒和下沉的斜坡以及可变形的基质。作为回应，四足动物在斜坡上往往会采取更蹲伏的姿势并降低其重心，在诸如沙地等可变形基质上增加接触面积。许多两栖鱼类在陆地上移动时也会遇到同样的挑战，但这些有鳍动物如何根据不同的环境条件调节其运动，以及这些变化与四足动物的变化相比情况如何，相对而言研究较少。在这种情况下，弹涂鱼（虾虎鱼科：背眼虾虎鱼亚科）是一类特别值得注意的两栖鱼类，因为它们能在从平坦的泥地到倾斜的红树林等广泛的环境条件中活动。它们采用一种独特的陆地运动形式，称为“撑跳”，即它们的胸鳍同步抬起并将身体的前半部分向前跳跃，然后落在腹鳍上，而身体的下半部分和尾巴保持伸直。然而，最近的研究表明，弹涂鱼在可变形表面上撑跳时，尤其是在斜坡上时，会改变其运动的某些方面。例如，在倾斜的干沙地上，弹涂鱼会向侧面弯曲身体，卷曲并伸展尾巴，可能起到辅助推进器和/或防滑装置的作用。为了更全面地了解弹涂鱼撑跳的功能多样性和环境依赖性，我们比较了它们在不同类型的基质（固体、泥浆、干沙）和斜坡（0°、10°、20°）组合上的运动学。除了在可变形和倾斜的基质上增加侧向弯曲外，我们还发现弹涂鱼在变得更加蹲伏的同时，增加了其成对鳍的相对接触时间和接触面积，这些反应与四足动物和其他两栖鱼类的反应相当。在这些基质上的弹涂鱼还表现出以前未记录的行为，例如更向前地伸展和压紧胸鳍的远端部分，躯干进行背腹弯曲，在沙子上“ belly - flopping”，以及用胸鳍鳍条“抓住”泥浆基质。我们的研究突出了陆地环境中脊椎动物共有的潜在补偿机制，同时也表明当动物面临环境变化的挑战时，运动灵活性甚至新颖性可能会出现。
