Data from: Adaptive differences in circadian clock gene expression patterns and photoperiodic diapause induction in Nasonia vitripennis

Day length (photoperiod) and temperature oscillate daily and seasonally and are important cues for season-dependent behaviour. Larval diapause of the parasitoid Nasonia vitripennis is maternally induced following a certain number of days (switch point) of a given critical photoperiod (CPP). Both the switch point and CPP follow a latitudinal cline in European N. vitripennis populations,. We previously showed that allelic frequencies of the clock gene period correlate with this diapause induction cline. Here, we report that circadian expression of four clock genes, period (per), cryptochrome-2 (cry-2), clock (clk) and cycle (cyc), oscillates as a function of photoperiod and latitude of origin in wasps from populations from the extremes of the cline. Expression amplitudes are lower in northern wasps, indicating a weaker, more plastic, clock. Northern wasps also have a later onset of activity and longer free running rhythms in constant conditions. Per RNAi caused speeding up of the circadian clock, changed the expression of other clock genes and delayed diapause in both southern and northern wasps. These results point towards adaptive latitudinal clock-gene expression differences and to a key role of per in the timing of photoperiodic diapause induction of N. vitripennis.

昼夜时长（光周期，photoperiod）与温度呈每日及季节性周期性波动，是调控季节依赖性行为的关键环境线索。寄生性蜂类丽蝇蛹集金小蜂（Nasonia vitripennis）的幼虫滞育，需由母代在暴露于特定临界光周期（critical photoperiod, CPP）达一定天数（转换点，switch point）后方可诱导产生。欧洲该物种的自然种群中，转换点与临界光周期均呈现纬度渐变群（latitudinal cline）分布特征。我们此前的研究证实，时钟基因（clock gene）period的等位基因频率与该滞育诱导的纬度渐变群显著相关。本研究以纬度渐变群两端的种群黄蜂为样本，发现4种时钟基因——周期基因（period，简称per）、隐花色素2（cryptochrome-2，简称cry-2）、时钟基因（clock，简称clk）及循环基因（cycle，简称cyc）——的昼夜表达模式随光周期及种群原产地纬度呈现周期性波动。北部种群黄蜂的基因表达振幅更低，提示其生物钟节律更弱且可塑性更强。此外，北部种群黄蜂在恒定环境条件下，活动启动时点更晚，自由运行节律（free running rhythm）周期也更长。对per基因实施RNA干扰（RNAi）后，南北种群黄蜂的生物钟均出现节律加速现象，其余时钟基因的表达模式亦发生改变，且滞育诱导进程均出现延迟。本研究结果表明，时钟基因的表达存在适应性的纬度梯度差异，且period基因在丽蝇蛹集金小蜂的光周期依赖性滞育诱导时序中发挥关键调控作用。