Data from: Integrating gastrocnemius force–length properties, in vivo activation and operating lengths reveals how Anolis deal with ecological challenges

A central question in biology is how animals successfully behave under complex natural conditions. Although changes in locomotor behaviour, motor control and force production in relation to incline are commonly examined, a wide range of other factors, including a range of perch diameters, pervades arboreal habitats. Moving on different substrate diameters requires considerable alteration of body and limb posture, probably causing significant shifts in the lengths of the muscle–tendon units powering locomotion. Thus, how substrate shape impacts in vivo muscle function remains an important but neglected question in ecophysiology. Here, we used high-speed videography, electromyography, in situ contractile experiments and morphology to examine gastrocnemius muscle function during arboreal locomotion in the Cuban knight anole, Anolis equestris. The gastrocnemius contributes more to the propulsive effort on broad surfaces than on narrow surfaces. Surprisingly, substrate inclination affected the relationship between the maximum potential force and fibre recruitment; the trade-off that was present between these variables on horizontal surfaces became a positive relationship on inclined surfaces. Finally, the biarticular nature of the gastrocnemius allows it to generate force isometrically, regardless of substrate diameter and incline, despite the fact that the tendons are incapable of stretching during cyclical locomotion. Our results emphasize the importance of considering ecology and muscle function together, and the necessity of examining both mechanical and physiological properties of muscles to understand how animals move in their environment.生物学的核心议题之一，是动物如何在复杂的自然环境中成功完成行为活动。尽管学界常针对坡度变化探究运动行为、运动控制与力产出的改变，但树栖生境中广泛存在诸多其他因素，其中便涵盖了不同直径的栖木。在不同直径的基质上移动时，动物的躯体与肢体姿态需要大幅调整，这大概率会显著改变驱动运动的肌肉-肌腱单元（muscle–tendon units）的长度。因此，基质形态如何影响活体肌肉功能，仍是生态生理学（ecophysiology）中一个重要却被忽视的研究问题。本研究借助高速摄像（high-speed videography）、肌电图（electromyography）、原位收缩实验（in situ contractile experiments）与形态学分析手段，对古巴骑士安乐蜥（Anolis equestris）在树栖运动过程中的腓肠肌（gastrocnemius）功能进行了考察。相较于狭窄基质，腓肠肌在宽阔基质上对推进力的贡献更为显著。令人意外的是，基质坡度会改变最大潜在力与肌纤维募集之间的关联：在水平基质上二者呈现权衡关系，而在倾斜基质上二者则呈现正相关关系。最后，腓肠肌的双关节属性使其能够产生等长收缩力，无论栖息基质的直径与坡度如何，即便肌腱在周期性运动过程中无法被拉伸。本研究结果强调，需将生态学与肌肉功能结合起来考量，同时也指明，要理解动物如何在其自然环境中运动，必须同时探究肌肉的力学与生理特性。