Vaanholt Lobke M, De Jong Berber, Garland Theodore, Daan Serge, Visser G Henk
University of Groningen, Department of Behavioural Biology, Kerklaan 30, 9751 NN, Haren, The Netherlands.
J Exp Biol. 2007 Jun;210(Pt 11):2013-24. doi: 10.1242/jeb.001974.
Free-living animals must forage for food and hence may face energetic constraints imposed by their natural environmental conditions (e.g. ambient temperature, food availability). Simulating the variation in such constraints, we have experimentally manipulated the rate of work (wheel running) mice must do to obtain their food, and studied the ensuing behavioural and physiological responses. This was done with a line of mice selectively bred for high spontaneous wheel running and a randomly bred control line that vary in the amount of baseline wheel-running activity. We first determined the maximum workload for each individual. The maximum workload animals could engage in was around 23 km d(-1) in both control and activity-selected mice, and was not associated with baseline wheel-running activity. We then kept mice at 90% of their individual maximum and measured several physiological and behavioural traits. At this high workload, mice increased wheel-running activity from an average of 10 to 20 km d(-1), and decreased food intake and body mass by approximately 20%. Mass-specific resting metabolic rate strongly decreased from 1.43 to 0.98 kJ g(-1) d(-1), whereas daily energy expenditure slightly increased from 2.09 to 2.25 kJ g(-1) d(-1). Costs of running decreased from 2.3 to 1.6 kJ km(-1) between baseline and workload conditions. At high workloads, animals were in a negative energy balance, resulting in a sharp reduction in fat mass as well as a slight decrease in dry lean mass. In addition, corticosterone levels increased, and body temperature was extremely low in some animals at high workloads. When challenged to work for food, mice thus show significant physiological and behavioural adjustments.
自由生活的动物必须觅食，因此可能面临自然环境条件（如环境温度、食物可获得性）所施加的能量限制。为了模拟这种限制的变化，我们通过实验操纵了小鼠获取食物所需进行的工作量（轮转奔跑），并研究了随之产生的行为和生理反应。实验使用了一组经过选择性培育以实现高自发轮转奔跑的小鼠和一组随机繁殖的对照小鼠，它们在基线轮转奔跑活动量上有所不同。我们首先确定了每只小鼠的最大工作量。对照小鼠和经过活动选择的小鼠能够承受的最大工作量均约为每天23公里，且与基线轮转奔跑活动无关。然后，我们将小鼠的工作量维持在其个体最大工作量的90%，并测量了多个生理和行为特征。在这种高工作量下，小鼠的轮转奔跑活动从平均每天10公里增加到20公里，食物摄入量和体重下降了约20%。单位体重的静息代谢率从1.43千焦/克/天大幅降至0.98千焦/克/天，而每日能量消耗则从2.09千焦/克/天略有增加至2.25千焦/克/天。在基线和工作量条件之间，奔跑成本从2.3千焦/公里降至1.6千焦/公里。在高工作量下，动物处于负能量平衡状态，导致脂肪量急剧减少，干瘦体重也略有下降。此外，皮质酮水平升高，在高工作量下，一些动物的体温极低。因此，当面临为获取食物而工作的挑战时，小鼠会表现出显著的生理和行为调整。
