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.虫媒植物病害（vector transmitted plant diseases）的流行学特征极大程度上受介体的扩散能力及其寄主植物范围调控。拓宽介体的寄主范围可能提升病害的传播潜能，而寄主专化则可能催生特定的病害循环模式。因此，介体寄主转换及其引发的流行学后果，其形成过程可纳入同域演化（sympatric evolution）与预适应种群迁入（immigration of preadapted populations）两大理论框架之中。本研究针对分布北界范围内的葡萄死顶植原体（stolbur phytoplasma）介体钝角叶蝉（Hyalesthes obsoletus）从田旋花（field bindweed）向刺荨麻（stinging nettle）的寄主转换事件，分析其演化究竟属于同域起源，还是由预适应种群迁入所导致。该介体对刺荨麻的寄主利用，已引发由刺荨麻专化型植原体菌株导致的葡萄黑果病（bois noir）暴发成灾。来自分布北界与祖先分布区种群的微卫星标记（microsatellite）数据，为北界范围内的同域寄主宗演化提供了坚实证据：与寄主植物相关联的种群在同生境共存位点间存在显著遗传分化（0.054 < FHT < 0.098），且该分化特征在5年监测周期中保持稳定。尽管基因流呈现不对称性：从祖先寄主种群流向预测的新寄主宗，且新寄主宗的遗传多样性显著降低，但分布北界内同生境共存的寄主宗种群间的遗传相似度，高于这些北界种群与祖先分布区同生境种群间的遗传相似度；而在祖先分布区中，并未发现遗传寄主宗存在的证据。尽管在北界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现象，却暗示了一种由非寄主专化型介体传播的刺荨麻专化型植原体菌株的引入过程。分布北界内寄主宗的演化，已催生了以介体为核心的特异性葡萄黑果病循环模式。