Data from: Tracing the origin of the early wet-season Anopheles coluzzii in the Sahel

In arid environments the source of the malaria mosquito populations that re-establish soon after first rains remains a puzzle and alternative explanations have been proposed. Using genetic data, we evaluated whether the early Rainy Season (RS) population of Anopheles coluzzii is descended from the preceding late-RS generation at the same locality, consistent with dry season (DS) dormancy (aestivation), or from migrants from distant locations. Distinct predictions derived from these two hypotheses were assessed, based on variation in 738 SNPs in eleven A. coluzzii samples, including seven samples spanning two years in a Sahelian village. As predicted by the ‘local origin under aestivation hypothesis’, temporal samples from the late RS and those collected after the first rain of the following RS were clustered together, whilst larger genetic distances were found among samples spanning the RS. Likewise, multi-locus genotype composition of samples from the end of the RS were similar across samples until the following RS, unlike samples that spanned the RS. Consistent with reproductive arrest during the DS, no genetic drift was detected between samples taken over that period, despite encompassing extreme population minima, whereas it was detected between samples spanning the RS. Accordingly, the variance in allele frequency increased with time over the RS, but not over the DS. However, not all the results agreed with aestivation. Large genetic distances separated samples taken a year apart, and during the first year, within-sample genetic diversity declined and increased back during the late RS, suggesting a bottleneck followed by migration. The decline of genetic diversity followed a mass distribution of insecticide treated nets was accompanied by a reduced mosquito density and a rise in the mutation conferring resistance to pyrethroids, indicating a bottleneck due to insecticidal selection. Overall, our results support aestivation in A. coluzzii during the DS that is accompanied by long distance migration in the late-RS.在干旱环境中，首次降雨后迅速重建的疟蚊种群的来源始终是一个未解之谜，学界已提出多种替代解释。本研究利用遗传数据，评估了科兹按蚊（Anopheles coluzzii）的雨季（Rainy Season, RS）早期种群究竟源自同一地点前一季的雨季晚期种群（符合旱季（Dry Season, DS）滞育（夏蛰，aestivation）假说），还是来自远方种群的迁入。基于11份科兹按蚊样本中738个单核苷酸多态性（Single Nucleotide Polymorphisms, SNPs）的变异情况，我们对这两种假说的独特预测进行了验证；其中7份样本采集自萨赫勒地区某村庄，覆盖两年的采样周期。正如“滞育下的本地起源假说”所预测的那样，雨季晚期的时序样本与次年首次降雨后采集的样本聚为一类，而跨越整个雨季的样本之间则呈现出更大的遗传距离。同样，雨季末期样本的多位点基因型组成在次年雨季到来前始终保持相似，而跨越整个雨季的样本则无此特征。与旱季生殖停滞的特征相符，尽管采样期间种群经历了极端的数量低谷，但该时段内的样本之间未检测到遗传漂变；而跨越雨季的样本之间则检测到了遗传漂变。因此，等位基因频率的方差随雨季时长增加而升高，但旱季时段并无此变化。然而，并非所有结果都支持夏蛰滞育假说。间隔一年采集的样本之间存在较大遗传距离；在第一年的采样中，样本内遗传多样性先下降后在雨季晚期回升，这提示种群经历了瓶颈效应后又发生了迁入。在大规模分发经杀虫剂处理的蚊帐后，遗传多样性出现下降，同时蚊群密度降低、拟除虫菊酯类杀虫剂抗性突变的频率升高，这表明杀虫选择压力导致了种群瓶颈效应。综上，本研究结果支持科兹按蚊在旱季存在滞育，且雨季晚期会发生长距离种群迁入。