Temporal flexibility in activity rhythms of a diurnal rodent, the ice rat (<i>Otomys sloggetti</i>)

Diurnality in rodents is relatively rare and occurs primarily in areas with low nighttime temperatures such as at high altitudes and desert areas. However, many factors can influence temporal activity rhythms of animals, both in the field and the laboratory. The temporal activity patterns of the diurnal ice rat were investigated in the laboratory with, and without, access to running wheels, and in constant conditions with running wheels. Ice rats appeared to be fundamentally diurnal but used their running wheels during the night. In constant conditions, general activity remained predominantly diurnal while wheel running was either nocturnal or diurnal. In some animals, entrainment of the wheel running rhythm was evident, as demonstrated by free-running periods that were different from 24 h. In other animals, the wheel running activity abruptly switched from nocturnal to subjective day as soon as the animals entered DD, and reverted back to nocturnal once returned to LD, suggesting the rhythms were masked by light. Wheel running rhythms appears to be less robust and more affected by light compared to general activity rhythms. In view of present and future environmental changes, the existence of more unstable activity rhythms that can readily switch between temporal niches might be crucial for the survival of the species.啮齿类动物的昼行性（diurnality）相对罕见，主要分布于夜间气温较低的区域，如高海拔地带与荒漠地区。然而，无论是野外还是实验室环境，诸多因素均可影响动物的时间活动节律（temporal activity rhythms）。本研究在实验室中设置了可接触跑轮（running wheels）、不可接触跑轮两种条件，以及带有跑轮的恒定环境条件，对昼行性冰鼠的时间活动模式进行了探究。冰鼠本质上表现为昼行性，但会在夜间使用跑轮。在恒定环境条件下，冰鼠的整体活动仍以昼行性为主，但其跑轮活动可呈现夜行性或昼行性两种状态。部分个体的跑轮活动节律呈现出明显的节律同步化（entrainment）现象，其自由运转周期（free-running periods）与24小时存在显著差异。另有部分个体的跑轮活动会在进入持续黑暗（DD，constant darkness）条件后，骤然从夜行性切换至主观昼期；而当重返光照-黑暗循环（LD，light-dark cycle）条件时，又会恢复为夜行性，这表明跑轮节律受到光照的掩蔽效应。相较于整体活动节律，跑轮活动节律的稳定性更弱，且更易受光照影响。鉴于当前及未来的环境变化，具备可在时间生态位（temporal niches）间快速切换的不稳定活动节律，或许对该物种的生存至关重要。