Data from: Sympatric diversification vs. immigration: deciphering host-plant specialization in a polyphagous insect, the stolbur phytoplasma vector Hyalesthes obsoletus (Cixiidae)

The epidemiology of vector transmitted plant diseases is highly influenced by dispersal and the host-plant range of the vector. Widening the vector's host range may increase transmission potential, whereas specialization may induce specific disease cycles. The process leading to a vector's host shift and its epidemiological outcome is therefore embedded in the frameworks of sympatric evolution vs. immigration of preadapted populations. In this study, we analyse whether a host shift of the stolbur phytoplasma vector, Hyalesthes obsoletus from field bindweed to stinging nettle in its northern distribution range evolved sympatrically or by immigration. The exploitation of stinging nettle has led to outbreaks of the grapevine disease bois noir caused by a stinging nettle-specific phytoplasma strain. Microsatellite data from populations from northern and ancestral ranges provide strong evidence for sympatric host-race evolution in the northern range: Host-plant associated populations were significantly differentiated among syntopic sites (0.054 < FHT < 0.098) and constant over 5 years. While gene flow was asymmetric from the old into the predicted new host race, which had significantly reduced genetic diversity, the genetic identity between syntopic host-race populations in the northern range was higher than between these populations and syntopic populations in ancestral ranges, where there was no evidence for genetic host races. Although immigration was detected in the northern field bindweed population, it cannot explain host-race diversification but suggests the introduction of a stinging nettle-specific phytoplasma strain by plant-unspecific vectors. The evolution of host races in the northern range has led to specific vector-based bois noir disease cycles.

媒介传播植物病害（vector-transmitted plant diseases）的流行病学特征，极易受媒介的扩散能力与宿主植物范围的影响。扩大宿主范围或可提升病害传播潜力，而宿主特化则可能催生特定的病害循环。因此，介导媒介发生宿主转移（host shift）的过程及其流行病学结局，均隶属于同域进化（sympatric evolution）与预适应种群迁入（immigration of preadapted populations）两大理论框架。本研究针对北部分布区内传播草状丛植病植原体（stolbur phytoplasma）的钝喙淡脉叶蝉（Hyalesthes obsoletus）展开分析，明确其从田旋花（field bindweed）向荨麻（stinging nettle）的宿主转移，究竟是通过同域进化形成，还是由预适应种群迁入所致。对荨麻的利用，已催生由荨麻特异性植原体菌株引发的葡萄黑果病（bois noir）暴发事件。取自北部分布区与祖先分布区种群的微卫星（microsatellite）数据，为北部分布区内宿主宗（host race）的同域进化提供了强有力证据：在同域栖息位点（syntopic sites）上，与宿主植物相关的种群间存在显著遗传分化（0.054 < FHT < 0.098），且该分化状态在5年的监测周期内保持稳定。尽管基因流（gene flow）呈不对称态势——从旧宿主宗流向遗传多样性显著降低的新宿主宗，但北部分布区内同域栖息的宿主宗种群间的遗传相似度，高于这些种群与祖先分布区内同域栖息种群的遗传相似度；而在祖先分布区内，未发现遗传宿主宗存在的相关证据。尽管在北部田旋花种群中检测到了迁入现象，但该现象无法解释宿主宗的分化，却提示存在通过植物非特异性媒介传播的荨麻特异性植原体菌株的引入事件。北部分布区内宿主宗的进化，已催生以媒介为核心的特异性葡萄黑果病循环。