Whitehead Natalie N, Kelly Scott A, Demes Jessica S, Schwartz Nicole E, Garland Theodore
Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, Riverside, CA 92521, USA.
Department of Zoology, Ohio Wesleyan University, Delaware, OH 43015, USA.
Behav Processes. 2023 Nov;213:104973. doi: 10.1016/j.beproc.2023.104973. Epub 2023 Nov 25.
Locomotor play is vigorous and seemingly purposeless behavior, commonly observed in young mammals. It can be costly in terms of energy expenditure, increased injury risk, and predator exposure. The main hypothesized benefit of locomotor play is enhancement of neuromuscular development, with effects persisting into adulthood. We hypothesized that levels of locomotor play would have evolved as a correlated response to artificial selection for increased voluntary exercise behavior. We studied mice from 4 replicate lines bred for voluntary wheel running (High Runner or HR) at 6-8 weeks of age and four non-selected Control (C) lines. Mice were weaned at 21 days of age and play behavior was observed for generations 20 (22-24 days old), 68 (22-23 days old), and 93 (15 days old). We quantified locomotor play as (1) rapid, horizontally directed jerk-run sequences and (2) vertical "bouncing." We used focal sampling to continuously record behavior in cages containing 4-6 individuals during the first 2-3 h of the dark cycle. Observations were significantly repeatable between observers and days. A two-way, mixed-model simultaneously tested effects of linetype (HR vs. C), sex, and their interaction. Contrary to our hypothesis, HR and C lines did not differ in any generation, nor did we find sex differences. However, differences among the replicate HR lines and among the replicate C lines were detected, and may be attributed to the effects of random genetic drift (and possibly founder effects). Thus, play behavior did evolve in this selection experiment, but not as a correlated response to selection for voluntary exercise.
运动性玩耍是一种剧烈且看似无目的的行为，常见于幼年哺乳动物。从能量消耗、受伤风险增加以及暴露于捕食者的角度来看，这种行为代价高昂。运动性玩耍的主要假定益处是促进神经肌肉发育，其影响会持续到成年期。我们推测，运动性玩耍的水平可能是作为对人工选择增加自愿运动行为的一种相关反应而进化的。我们研究了来自4个重复品系的小鼠，这些品系是为自愿在轮子上奔跑而培育的（高奔跑者或HR），年龄在6 - 8周，还有4个未经过选择的对照（C）品系。小鼠在21日龄断奶，对第20代（22 - 24日龄）、第68代（22 - 23日龄）和第93代（15日龄）的玩耍行为进行了观察。我们将运动性玩耍量化为：（1）快速、水平方向的急跑序列，以及（2）垂直“弹跳”。我们采用焦点取样法，在黑暗周期的前2 - 3小时内，连续记录置于装有4 - 6只个体笼子里的小鼠的行为。观察者之间以及不同日期的观察结果具有显著的可重复性。采用双向混合模型同时检验品系类型（HR与C）、性别及其交互作用的影响。与我们的假设相反，HR品系和C品系在任何一代中均无差异，我们也未发现性别差异。然而，在重复的HR品系之间以及重复的C品系之间检测到了差异，这可能归因于随机遗传漂变（以及可能的奠基者效应）。因此，在这个选择实验中玩耍行为确实发生了进化，但并非作为对自愿运动选择的相关反应。
