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）兼具有性与无性繁殖能力，且会在初生寄主与次生寄主之间交替完成生活周期。这类蚜虫多数可取食多种近缘寄主，而其入侵新栖息地后，适宜寄主的数量可能会受到限制。例如，专食性蚜虫大豆蚜（Aphis glycines）在其入侵的北美地区，仅能以初生寄主鼠李属植物（Rhamnus spp.）和次生寄主大豆（Glycine max）为食。鉴于这种寄主专化性以及初生寄主分布稀疏的特点，蚜虫的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。本研究针对大豆蚜种群的遗传多样性与种群结构随时间的变化展开了表征分析。研究人员在同一地理区域的次生寄主上开展了两次采样：一次为次生寄主定殖后（早季），另一次为初生寄主定殖前即刻（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种群遗传多样性、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）位点与6个微卫星标记（microsatellites）进行种群遗传学统计分析。结果显示，早季采样样本的基因型多样性显著更低，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。早季与晚季采样样本的成对遗传分化系数（FST）分别从0.046降至0.017；早季采样样本中，遗传相关性随地理距离增加显著降低，但晚季采样样本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。