Claghorn Gerald C, Thompson Zoe, Kay Jarren C, Ordonez Genesis, Hampton Thomas G, Garland Theodore
Physiol Biochem Zool. 2017 Sep/Oct;90(5):533-545. doi: 10.1086/692909.
Postural and kinematic aspects of running may have evolved to support high runner (HR) mice to run approximately threefold farther than control mice. Mice from four replicate HR lines selectively bred for high levels of voluntary wheel running show many differences in locomotor behavior and morphology as compared with four nonselected control (C) lines. We hypothesized that HR mice would show stride alterations that have coadapted with locomotor behavior, morphology, and physiology. More specifically, we predicted that HR mice would have stride characteristics that differed from those of C mice in ways that parallel some of the adaptations seen in highly cursorial animals. For example, we predicted that limbs of HR mice would swing closer to the parasagittal plane, resulting in a two-dimensional measurement of narrowed stance width. We also expected that some differences between HR and C mice might be amplified by 6 d of wheel access, as is used to select breeders each generation. We used the DigiGait Imaging System (Mouse Specifics) to capture high-speed videos in ventral view as mice ran on a motorized treadmill across a range of speeds and then to automatically calculate several aspects of strides. Young adults of both sexes were tested both before and after 6 d of wheel access. Stride length, stride frequency, stance width, stance time, brake time, propel time, swing time, duty factor, and paw contact area were analyzed using a nested analysis of covariance, with body mass as a covariate. As expected, body mass and treadmill speed affected nearly every analyzed metric. Six days of wheel access also affected nearly every measure, indicating pervasive training effects, in both HR and C mice. As predicted, stance width was significantly narrower in HR than C mice. Paw contact area and duty factor were significantly greater in minimuscle individuals (subset of HR mice with 50%-reduced hind limb muscle mass) than in normal-muscled HR or C mice. We conclude that stride characteristics of house mice are adaptable in response to both selective breeding and changes in daily locomotor behavior (activity levels) that occur during as few as 6 d. These results have important implications for understanding the evolution and coadaptation of locomotor behavior and performance.
跑步的姿势和运动学方面可能已经进化，以支持高跑步量（HR）小鼠比对照小鼠多跑大约三倍的距离。从四个重复的HR品系中选择性培育出的高水平自主轮转跑步小鼠，与四个未选择的对照（C）品系相比，在运动行为和形态上表现出许多差异。我们假设HR小鼠会表现出与运动行为、形态和生理共同适应的步幅改变。更具体地说，我们预测HR小鼠的步幅特征将与C小鼠不同，其方式类似于在高度奔跑型动物中看到的一些适应性变化。例如，我们预测HR小鼠的四肢会更靠近矢状旁平面摆动，从而导致站立宽度的二维测量值变窄。我们还预期，HR和C小鼠之间的一些差异可能会因6天的轮转运动而放大，就像每代用于选择繁殖小鼠的方式一样。我们使用DigiGait成像系统（Mouse Specifics）在小鼠以一系列速度在电动跑步机上奔跑时，从腹侧视图捕获高速视频，然后自动计算步幅的几个方面。在6天的轮转运动前后，对年轻的成年雌雄小鼠都进行了测试。使用协方差嵌套分析，以体重作为协变量，分析步长、步频、站立宽度、站立时间、制动时间、推进时间、摆动时间、负荷因子和爪接触面积。正如预期的那样，体重和跑步机速度几乎影响了每个分析指标。6天的轮转运动也几乎影响了每一项测量，表明在HR和C小鼠中都存在普遍的训练效果。正如预测的那样，HR小鼠的站立宽度明显比C小鼠窄。最小肌肉个体（HR小鼠的一个子集，后肢肌肉质量减少50%）的爪接触面积和负荷因子明显大于正常肌肉的HR或C小鼠。我们得出结论，家鼠的步幅特征能够适应选择性育种以及在短短6天内发生的日常运动行为（活动水平）变化。这些结果对于理解运动行为和性能的进化及共同适应具有重要意义。
