Department of Ecology and Genetics, University of Oulu, Oulu, Finland.
Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland.
J Biol Rhythms. 2021 Jun;36(3):226-238. doi: 10.1177/0748730421997265. Epub 2021 Mar 22.
Insect species with a wide distribution offer a great opportunity to trace latitudinal variation in the photoperiodic regulation of traits important in reproduction and stress tolerances. We measured this variation in the photoperiodic time-measuring system underlying reproductive diapause in , using a Nanda-Hamner (NH) protocol. None of the study strains showed diel rhythmicity in female diapause proportions under a constant day length (12 h) and varying night lengths in photoperiods ranging from 16 to 84 h at 16°C. In the northernmost strains (above 55°N), nearly all females entered diapause under all photoperiods and about half of them even in continuous darkness, while the females of the southern strains showed high diapause proportions only in the circadian 24 h photoperiod. Significant correlation between the strains' mean diapause proportions in ≥ 24 h photoperiods and critical day length (CDL; half of the females enter diapause) suggests at least partial causal connection between the traits. Interestingly, females of the northern strains entered diapause even in ≤ 24 h photoperiods, where the night length was shorter than their critical night length (24 h - CDL), but where the females experienced a higher number of Light:Dark cycles than in 24 h photoperiods. NH experiments, performed on the control and selection lines in our previous selection experiment, and completed here, gave similar results and confirmed that selection for shorter, southern-type CDL decreases female diapausing rate in non-circadian photoperiods. Overall, our study shows that females measure night length quantitatively, that the photoperiodic counter may play a prominent but slightly different role in extra short and extra long photoperiods and that northern strains show high stability against perturbations in the photoperiod length and in the presence of LD cycles. These features are best explained by the quantitative versions of the damped external coincidence model.
分布广泛的昆虫物种为追踪重要繁殖和应激容忍特征的光周期调节的纬度变化提供了极好的机会。我们使用 Nanda-Hamner (NH) 方案测量了 生殖滞育下光周期计时系统中的这种变化。在 16°C 时，在所研究的菌株中，没有一个菌株在 16 到 84 小时的光周期范围内，在恒定的 12 小时光照长度和变化的夜间长度下表现出雌性滞育比例的昼夜节律性。在最北部的菌株（北纬 55°以上）中，几乎所有的雌性在所有光周期下都进入滞育，其中一半甚至在连续黑暗中，而南部菌株的雌性只有在昼夜 24 小时光周期下才表现出高滞育比例。在 ≥ 24 小时光周期中，菌株平均滞育比例与临界日长（CDL；一半雌性进入滞育）之间存在显著相关性，这表明这些特征之间至少存在部分因果关系。有趣的是，即使在 ≤ 24 小时的光周期中，北部菌株的雌性也进入滞育，此时夜间长度短于其临界夜间长度（24 小时-CDL），但在这些光周期中，雌性经历的光照：黑暗循环数比 24 小时光周期多。我们之前的选择实验中以及这里完成的 NH 实验，对控制和选择系进行了实验，结果相似，证实了选择较短的、南方型 CDL 会降低非昼夜光周期中雌性的滞育率。总的来说，我们的研究表明， 雌性定量测量夜间长度，光周期计数器在极短和极长的光周期中可能发挥突出但略有不同的作用，并且北部菌株对光周期长度的干扰和 LD 循环的存在表现出高度的稳定性。这些特征最好用阻尼外部巧合模型的定量版本来解释。
