Pittendrigh C S, Takamura T
Hopkins Marine Station of Stanford University, Pacific Grove, California 93950.
J Biol Rhythms. 1989 Summer;4(2):217-35.
The circadian rhythm of eclosion activity and its pacemaker were analyzed in a series of latitudinal races of Drosophila auraria ranging from 34.2 degrees to 42.9 degrees N in Japan. The phase of the rhythm (psi EL) to the daily photoperiod (PP) changes as daylength is increased, and the slope of psi EL (PP) changes with latitude. Is is sufficiently greater in the north to cause a phase reversal of northern and southern races on long versus short photoperiods. This reversal is found in assays of the pacemaker's phase (psi PL) as well as that of the rhythm (psi EL). Assay of the pacemaker shows that its period (tau) is longer in northern than in southern races, and that the amplitude of its phase response curve (PRC) is lower in the north. The period of the rhythm in all latitudinal races is longer than 24 hr in short photoperiods (LD 1:23), but is probably less than 24 hr (as an aftereffect of photoperiod) in longer days such as LD 14:10. The observed north-south differences in the phase relation of both pacemaker and rhythm to the light cycle are explained by the latitudinal clines in pacemaker properties and a postulated aftereffect of photoperiod on tau. It is suggested that the latitudinal cline in PRC amplitude has functional significance in conserving the amplitude of the pacemaker's signal to the rest of the system it times. Computer simulation shows that without such a reduction in the perceived light intensity, pacemaker amplitude will be lowered by the increase in duration of the daily light at higher latitudes.
对日本北纬34.2度至42.9度范围内的一系列极光果蝇纬度种群的羽化活动昼夜节律及其起搏器进行了分析。随着日长增加，节律相位（psi EL）相对于每日光周期（PP）发生变化，且psi EL（PP）的斜率随纬度而改变。在北方，这种变化足够大，以至于在长光周期与短光周期条件下，北方和南方种群的相位发生反转。这种反转在起搏器相位（psi PL）以及节律相位（psi EL）的测定中均有发现。对起搏器的测定表明，其周期（tau）在北方种群中比南方种群更长，且其相位响应曲线（PRC）的振幅在北方更低。在短光周期（LD 1:23）下，所有纬度种群的节律周期均长于24小时，但在较长光周期如LD 14:10下，可能短于24小时（作为光周期的后效应）。观察到的起搏器和节律与光周期的相位关系在南北之间的差异，可通过起搏器特性的纬度梯度变化以及光周期对tau的假定后效应来解释。有人认为，PRC振幅的纬度梯度变化在保持起搏器向其定时的系统其他部分发送信号的振幅方面具有功能意义。计算机模拟表明，如果没有这种感知光强度的降低，在高纬度地区，起搏器的振幅会因每日光照时长的增加而降低。
