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（parasite）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，则使得研究者可以原位采集其遗传结构及其形成机制的相关数据。本研究针对一种寄生植物，探讨了交配、扩散与定植过程在其寄主宗形成（host race formation）中发挥的作用。本研究以索诺兰沙漠（Sonoran Desert）中两种豆科寄主树种——格雷格相思（Senegalia greggii）与维氏牧豆树（Prosopis velutina）——上的媒介传播型沙漠槲寄生（Phoradendron californicum）为研究对象，利用微卫星（microsatellite）标记开展种群遗传学研究。研究结果与寄主宗形成假说一致：我们在同域分布（sympatry）的种群中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源（genetic ancestry）存在相关性。通过遗传检测，我们发现了具有中间型祖源的杂交个体。研究还检测到一类大概率源于跨寄主物种扩散后近期成功定植的个体，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要强于扩散阶段。我们同时发现，在更为稀有且孤立的寄主树种格雷格相思（S. greggii）上，槲寄生的近交系数与寄主内个体亲缘关系值均更高。本研究覆盖了多个空间尺度，旨在阐明媒介与寄主的双重交互如何影响寄生植物的种群结构，其研究结果对寄生生物的毒力进化与物种形成研究具有参考意义。