Data from: Population structure of a vector-borne plant parasite

Parasites are among the most diverse groups of life on Earth, yet complex natural histories often preclude studies of their speciation processes. The biology of parasitic plants facilitates in situ collection of data on both genetic structure and the mechanisms responsible for that structure. Here, we studied the role of mating, dispersal and establishment in host race formation of a parasitic plant. We investigated the population genetics of a vector-borne desert mistletoe (Phoradendron californicum) across two legume host tree species (Senegalia greggii and Prosopis velutina) in the Sonoran desert using microsatellites. Consistent with host race formation, we found strong host-associated genetic structure in sympatry, little genetic variation due to geographic site and weak isolation by distance. We hypothesize that genetic differentiation results from differences in the timing of mistletoe flowering by host species, as we found initial flowering date of individual mistletoes correlated with genetic ancestry. Hybrids with intermediate ancestry were detected genetically. Individuals likely resulting from recent, successful establishment events following dispersal between the host species were detected at frequencies similar to hybrids between host races. Therefore, barriers to gene flow between the host races may have been stronger at mating than at dispersal. We also found higher inbreeding and within-host individual relatedness values for mistletoes on the more rare and isolated host species (S. greggii). Our study spanned spatial scales to address how interactions with both vectors and hosts influence parasitic plant structure with implications for parasite virulence evolution and speciation.寄生生物是地球上物种多样性最高的生命类群之一，但其复杂的自然生活史往往阻碍了物种形成过程相关研究的开展。寄生植物的生物学特性使得研究者可原位获取其遗传结构及其形成机制的相关数据。本研究以一种寄生植物为对象，探讨了交配、扩散与定殖过程在其寄主宗形成（host race formation）中的作用。我们以索诺兰沙漠中的两种豆科寄主树种——相思树属Senegalia greggii与牧豆树属Prosopis velutina——上的媒介传播型沙漠槲寄生（Phoradendron californicum）为研究材料，利用微卫星标记（microsatellites）开展种群遗传学分析。研究结果与寄主宗形成假说相符：在同域分布（sympatry）的种群中，我们发现了显著的寄主关联遗传结构；地理位点对遗传变异的影响极小，且距离隔离（isolation by distance）效应微弱。我们推测，遗传分化源于不同寄主上槲寄生的开花时间差异——研究发现单株槲寄生的初始开花日期与其遗传祖先成分显著相关。通过遗传分析检测到了具有中间祖先成分的杂交个体。同时，研究还发现跨寄主物种扩散后近期成功定殖形成的个体，其出现频率与寄主宗间的杂交个体相近。由此推测，寄主宗之间的基因流障碍在交配阶段较扩散阶段更为显著。此外，在更为稀有且孤立的寄主物种S. greggii上，槲寄生的近交系数与寄主内个体间亲缘关系值均更高。本研究跨越不同空间尺度，探讨了媒介与寄主的双重交互作用如何塑造寄生植物的种群遗传结构，其研究结果对寄生生物的毒力进化与物种形成研究具有重要参考意义。