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，高度受媒介昆虫的扩散能力及其寄主范围调控。拓宽媒介的寄主范围或提升病害传播潜能，而专化性演化则可能催生专属的病害循环。因此，介导媒介昆虫寄主转换的过程及其流行病学效应，均被纳入同域进化（sympatric evolution）与预适应种群迁入（immigration of preadapted populations）两大研究框架。
本研究针对分布北限区域内，作为葡萄死顶植原体（stolbur phytoplasma）媒介的浅棕扁蜡蝉（Hyalesthes obsoletus），探究其寄主从田旋花（field bindweed）转换至荨麻（stinging nettle）的演化路径：该过程究竟是通过同域进化实现，还是依赖预适应种群的迁入完成。对荨麻的寄主利用，已引发由荨麻专化植原体株系导致的葡萄金黄化病（bois noir）暴发。
采自分布北限与祖先分布区的种群微卫星（microsatellite）数据，为北限区域的同域寄主宗演化提供了强有力证据：寄主植物关联种群在同域生境（syntopic sites）中呈现显著遗传分化（0.054 < FHT < 0.098），且该分化特征在5年周期内保持稳定。尽管基因流（gene flow）呈不对称性，从古老寄主宗流向遗传多样性（genetic diversity）显著降低的预测新寄主宗，但北限区域同域生境中寄主宗种群间的遗传相似度（genetic identity），高于这些种群与祖先分布区同域生境种群间的相似度——后者并未发现遗传寄主宗的存在。
虽在北限区域的田旋花种群中检测到迁入事件，但该事件无法解释寄主宗的分化，却暗示存在通过非寄主专化媒介传播的荨麻专化植原体株系。北限区域寄主宗的演化，已催生基于媒介昆虫的专属葡萄金黄化病循环。