Cohen Rotem, Smale Laura, Kronfeld-Schor Noga
Department of Zoology, Tel Aviv University, Tel Aviv, Israel.
Chronobiol Int. 2009 Apr;26(3):430-46. doi: 10.1080/07420520902820939.
Most animals can be categorized as nocturnal, diurnal, or crepuscular. However, rhythms can be quite plastic in some species and vary from one individual to another within a species. In the golden spiny mouse (Acomys russatus), a variety of rhythm patterns have been seen, and these patterns can change considerably as animals are transferred from the field into the laboratory. We previously suggested that these animals may have a circadian time-keeping system that is fundamentally nocturnal and that diurnal patterns seen in their natural habitat reflect mechanisms operating outside of the basic circadian time-keeping system (i.e., masking). In the current study, we further characterized plasticity evident in the daily rhythms of golden spiny mice by measuring effects of lighting conditions and access to a running wheel on rhythms in general activity (GA) and body temperature (Tb). Before the wheel was introduced, most animals were active mainly during the night, though there was considerable inter-individual variability and patterns were quite plastic. The introduction of the wheel caused an increase in the level of nighttime activity and Tb in most individuals. The periods of the rhythms in constant darkness (DD) were very similar, and even slightly longer in this study (24.1+/-0.2 h) than in an earlier one in which animals had not been provided with running wheels. We found no correlation between the distance animals ran in their wheels and the period of their rhythms in DD. Re-entrainment after phase delays of the LD cycle occurred more rapidly in the presence than absence of the running wheel. The characteristics of the rhythms of golden spiny mice seen in this study may be the product of natural selection favoring plasticity of the circadian system, perhaps reflecting what can happen during an evolutionary transition as animals move from a nocturnal to a diurnal niche.
大多数动物可分为夜行性、昼行性或晨昏性。然而，某些物种的节律具有相当大的可塑性，且同一物种内个体之间也存在差异。在金刺鼠（Acomys russatus）中，已观察到多种节律模式，并且随着动物从野外转移到实验室，这些模式会发生显著变化。我们之前曾提出，这些动物可能具有一个基本为夜行性的昼夜节律计时系统，而在其自然栖息地观察到的昼行性模式反映了在基本昼夜节律计时系统之外起作用的机制（即掩盖效应）。在本研究中，我们通过测量光照条件和使用跑步轮对总体活动（GA）和体温（Tb）节律的影响，进一步刻画了金刺鼠日常节律中明显的可塑性。在引入跑步轮之前，大多数动物主要在夜间活动，尽管个体间存在相当大的差异，且模式具有很大可塑性。跑步轮的引入使大多数个体的夜间活动水平和体温升高。在持续黑暗（DD）条件下，节律周期非常相似，甚至在本研究中（24.1±0.2小时）比早期未提供跑步轮时的研究稍长。我们发现动物在跑步轮上跑的距离与它们在DD条件下的节律周期之间没有相关性。在存在跑步轮的情况下，与不存在跑步轮相比，光暗周期（LD）相位延迟后的重新同步发生得更快。本研究中观察到的金刺鼠节律特征可能是自然选择有利于昼夜节律系统可塑性的产物，也许反映了动物从夜行性生态位向昼行性生态位进化转变过程中可能发生的情况。
