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.

异寄主全周期蚜虫（Heteroecious holocyclic aphids）兼具有性与无性生殖，且会在初生寄主与次生寄主间交替转换。多数此类蚜虫可取食多种近缘寄主，而入侵新栖息地可能会缩减其适宜寄主的范围。例如，专性蚜虫物种大豆蚜（Aphis glycines）在其入侵的北美地区，仅能以初生寄主鼠李属（Rhamnus spp.）植物与次生寄主大豆（Glycine max）为寄主存活。鉴于这种寄主专化性与初生寄主分布的稀疏性，寄主定殖事件可能具有局域性，并伴随奠基者效应（founder effects），进而影响种群的遗传多样性、种群结构与适应性。本研究对大豆蚜种群的遗传多样性与种群结构随时间的变化进行了表征分析。研究团队在同一地理区域的次生寄主上进行了两次采样：一次为次生定殖后（早季），另一次为初生寄主定殖前的晚季。本研究旨在检验早季种群是否存在奠基者效应与遗传隔离，并探究晚季扩散是否能够恢复遗传多样性并缓解种群片段化。本研究共采用24个单核苷酸多态性（single-nucleotide polymorphisms, SNPs）位点与6个微卫星（microsatellites）标记开展种群遗传学统计分析。研究结果显示，早季采样种群的基因型多样性显著更低，且遗传隔离程度更高，表明次生寄主定殖具有局域性且伴随奠基者效应。两两种群间的FST值分别从早季采样的0.046下降至晚季采样的0.017；同时，早季采样种群的遗传相关性随地理距离增加显著降低，而晚季采样种群未观测到空间遗传结构。综上，晚季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。