Kumar Vinod, Wingfield John C, Dawson Alistair, Ramenofsky Marilyn, Rani Sangeeta, Bartell Paul
Department of Science and Technology, University of Delhi, Delhi 110 007, India.
Physiol Biochem Zool. 2010 Sep-Oct;83(5):827-35. doi: 10.1086/652243.
Timekeeping is important at two levels: to time changes in physiology and behavior within each day and within each year. For the former, birds have a system of at least three independent circadian clocks present in the retina of the eyes, the pineal gland, and the hypothalamus. This differs from the situation in mammals in which the input, pacemaker, and output are localized in different structures. Each bird clock interacts with at least one other clock, and together, they appear to form a centralized clock system that keeps daily time. These clocks have a powerful endogenous component, and the daily light-dark cycle entrains them to 24 h. The timing and duration of life history stages that make up annual cycle of an individual must also be controlled by some form of timekeeping. However, evidence for the existence of an equivalent endogenous circannual clock is less clear. Environmental cues, particularly photoperiod, appear to have a more direct role than simply entraining the clock to calendar time. For example, the timing of migration is probably greatly influenced by photoperiod, but its manifestation each day, as Zugunruhe, appears to be under circadian control. Migration involves marked changes in physiology to cope with the energetic demands. There is still much that we do not know about how organisms' timekeeping systems respond to their natural environment, particularly how salient signals from the environment are perceived and then transduced into appropriately timed biological functions. However, given that changes in environmental input affects the clock, increasing human disturbance of the environment is likely to adversely affect these systems.
一是记录每天内以及每年内生理和行为的变化。对于前者，鸟类有一个至少由三个独立的昼夜节律时钟组成的系统，分别存在于眼睛的视网膜、松果体和下丘脑。这与哺乳动物的情况不同，在哺乳动物中，输入、起搏器和输出位于不同的结构中。每只鸟的时钟至少与另一个时钟相互作用，它们共同似乎形成了一个记录每日时间的中央时钟系统。这些时钟有强大的内源性成分，每日的明暗周期将它们调整为24小时。构成个体年度周期的生命史阶段的时间安排和持续时间也必须由某种形式的计时来控制。然而，存在等效的内源性年周期时钟的证据不太明确。环境线索，特别是光周期，似乎比仅仅将时钟调整到日历时间具有更直接的作用。例如，迁徙的时间可能受光周期的极大影响，但其每天作为迁徙不安的表现似乎受昼夜节律控制。迁徙涉及生理上的显著变化以应对能量需求。关于生物体的计时系统如何响应其自然环境，特别是环境中的显著信号如何被感知然后转化为适时的生物功能，我们仍有很多未知之处。然而，鉴于环境输入的变化会影响时钟，人类对环境干扰的增加很可能对这些系统产生不利影响。
