Data from: Maintaining genetic diversity and population panmixia through dispersal and not gene flow in a holocyclic heteroecious aphid species

Heteroecious holocyclic aphids exhibit both sexual and asexual reproduction and alternate among primary and secondary hosts. Most of these aphids can feed on several related hosts, and invasions to new habitats may limit the number of suitable hosts. For example, the aphid specialist Aphis glycines survives only on the primary host buckthorn (Rhamnus spp.) and the secondary host soybean (Glycine max) in North America where it is invasive. Owing to this specialization and sparse primary host distribution, host colonization events could be localized and involve founder effects, impacting genetic diversity, population structure and adaptation. We characterized changes in the genetic diversity and structure across time among A. glycines populations. Populations were sampled from secondary hosts twice in the same geographical location: once after secondary colonization (early season), and again immediately before primary host colonization (late season). We tested for evidence of founder effects and genetic isolation in early season populations, and whether or not late-season dispersal restored genetic diversity and reduced fragmentation. A total of 24 single-nucleotide polymorphisms and 6 microsatellites were used for population genetic statistics. We found significantly lower levels of genotypic diversity and more genetic isolation among early season collections, indicating secondary host colonization occurred locally and involved founder effects. Pairwise FST decreased from 0.046 to 0.017 in early and late collections, respectively, and while genetic relatedness significantly decreased with geographical distance in early season collections, no spatial structure was observed in late-season collections. Thus, late-season dispersal counteracts the secondary host colonization through homogenization and increases genetic diversity before primary host colonization.

转主全周期蚜虫（Heteroecious holocyclic aphids）兼具有性生殖与无性生殖，并会在初生寄主与次生寄主之间交替完成生活史。此类蚜虫多数可取食多种近缘寄主，而入侵至新栖息地时，其适宜寄主的范围可能会受到限制。例如，专食性蚜虫大豆蚜（Aphis glycines）在其入侵的北美地区，仅能以鼠李属植物（Rhamnus spp.）作为初生寄主，以大豆（Glycine max）作为次生寄主。由于这种寄主专化性以及初生寄主分布较为稀疏，寄主定殖事件可能具有局域性，并伴随奠基者效应，进而对遗传多样性、种群结构与适应性产生影响。本研究对大豆蚜种群随时间推移的遗传多样性与种群结构变化进行了表征。研究在同一地理区域内的次生寄主上进行了两次采样：一次为次生寄主定殖后（生长季早期），另一次为初生寄主定殖前即刻（生长季晚期）。我们针对早期种群的奠基者效应与遗传隔离证据进行了检验，并探究了生长季晚期的扩散是否能够恢复遗传多样性并降低种群片段化程度。本研究共采用24个单核苷酸多态性位点与6个微卫星标记开展种群遗传学统计分析。结果显示，生长季早期的采样样本中，基因型多样性显著更低，且遗传隔离程度更高，这表明次生寄主定殖具有局域性且伴随奠基者效应。两两遗传分化系数（FST）值从早期采样的0.046下降至晚期采样的0.017；同时，生长季早期样本的遗传相关性随地理距离增加显著降低，而晚期采样样本中未观察到空间结构。综上，生长季晚期的扩散通过遗传均质化抵消了次生寄主定殖带来的影响，并在初生寄主定殖前提升了种群的遗传多样性。