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.

媒介传播植物病害的流行病学特征极大地受媒介生物的扩散能力与寄主植物范围的影响。媒介寄主范围的扩宽可提升病害传播潜力，而寄主专化性则会催生特定的病害循环。因此，媒介寄主转移的过程及其对应的流行病学效应，隶属于同域进化（sympatric evolution）与预适应种群迁入（immigration of preadapted populations）的研究框架。本研究针对分布北限区域内，葡萄茎枯植原体（stolbur phytoplasma）的媒介暗纹长翅蜡蝉（Hyalesthes obsoletus）从田旋花（field bindweed）转移至荨麻（stinging nettle）的寄主转移事件，分析其究竟通过同域进化形成，还是由预适应种群迁入所导致。对荨麻的利用已引发由荨麻专化型植原体菌株引起的葡萄黑果病（bois noir）暴发。对分布北限区域与祖先分布区域种群的微卫星（microsatellite）数据分析，为北限区域的同域寄主宗进化提供了强有力的证据：在同域分布位点中，与寄主植物相关的种群间存在显著分化（0.054 < FHT < 0.098），且该分化在5年间保持稳定。尽管基因流呈现不对称性——从旧寄主种群流向新预测寄主宗种群，且后者的遗传多样性显著降低，但北限区域同域分布的寄主宗种群间的遗传相似度，高于这些种群与祖先分布区域内同域种群间的遗传相似度；而在祖先分布区域中，并未发现遗传寄主宗的存在证据。虽然在北限区域的田旋花种群中检测到了迁入事件，但该事件无法解释寄主宗的分化，却暗示植物非专化媒介可能携带了荨麻专化型植原体菌株。北限区域寄主宗的进化，催生了基于媒介的特异性葡萄黑果病循环。