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.

寄生生物是地球上多样性最为丰富的生命类群之一，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使得我们可以原位采集其遗传结构及其形成机制的相关数据。本研究以一种寄生植物为对象，探讨交配、扩散与定殖在其宿主宗形成（host race formation）过程中的作用。我们以索诺兰沙漠（Sonoran Desert）中两种豆科寄主树种——格雷格相思树（Senegalia greggii）与维氏牧豆树（Prosopis velutina）上的媒介传播型沙漠槲寄生（Phoradendron californicum）为研究材料，利用微卫星（microsatellites）标记开展种群遗传学分析。研究结果与宿主宗形成的理论预期一致：我们在同域分布的种群中检测到了显著的寄主关联遗传结构，地理位点带来的遗传变异极小，且仅存在微弱的距离隔离（isolation by distance）效应。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——研究发现单个槲寄生的初始开花日期与其遗传祖先成分显著相关。本研究通过遗传检测发现了具有中间祖先血统的杂交个体。我们还检测到了一类个体，其大概率是寄主物种间扩散后近期成功定殖的产物，这类个体的出现频率与宿主宗间的杂交个体相近。据此推测，宿主宗之间的基因流障碍可能在交配阶段较扩散阶段更为显著。此外，我们还发现，在更为稀有且孤立的寄主树种S. greggii上生长的槲寄生，其近交（inbreeding）系数与寄主内个体的亲缘关系度（relatedness）更高。本研究覆盖了多个空间尺度，旨在解析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演化与物种形成研究具有重要启示意义。