Data from: One step ahead: a parasitoid disperses farther and forms a wider geographic population than its fig wasp host

The structure of populations across landscapes influences the dynamics of their interactions with other species. Understanding the geographic structure of populations can thus shed light on the potential for interacting species to coevolve. Host – parasitoid interactions are widespread in nature, and also represent a significant force in the evolution of plant – insect interactions. However, there have been few comparisons of population structure between an insect host and its parasitoid. We used microsatellite markers to analyse the population genetic structure of Pleistodontes imperialis sp. 1, a fig-pollinating wasp of Port Jackson fig (Ficus rubiginosa), and its main parasitoid, Sycoscapter sp. A, in eastern Australia. Besides exploring this host – parasitoid system, our study also constitutes, to our knowledge, the first study of population structure in a non-pollinating fig wasp species. We collected matched samples of pollinators and parasitoids at several sites in two regions separated by up to 2000 km. We found that pollinators occupying the two regions represent distinct populations, but, in contrast, parasitoids formed a single population across the wide geographic range sampled. We observed genetic isolation by distance for each species, but found consistently lower FST and RST values between sites for parasitoids compared with pollinators. Previous studies have indicated that pollinators of monoecious figs can disperse over very long distances, and we provide the first genetic evidence that their parasitoids may disperse as far, if not farther. The contrasting geographic population structures of host and parasitoid highlight the potential for geographic mosaics in this important symbiotic system.

景观中种群的结构会影响其与其他物种的相互作用动态。因此，解析种群的地理结构，有助于揭示互作物种协同演化的潜在可能。寄主-寄生蜂互作在自然界中广泛存在，同时也是驱动植物-昆虫互作演化的重要力量。然而，目前针对昆虫寄主与其寄生蜂之间的种群结构对比研究仍较为匮乏。
我们借助微卫星标记（microsatellite markers），分析了澳大利亚东部地区的两种物种的群体遗传结构：其一为波特杰克逊榕（Ficus rubiginosa）的传粉榕小蜂Pleistodontes imperialis sp. 1，其二为其主要寄生蜂Sycoscapter sp. A。本研究不仅解析了这一寄主-寄生蜂系统，据我们所知，同时也是首次针对非传粉榕小蜂物种的种群结构开展的研究。
我们在两个相隔最远达2000公里的区域内的多个采样点，收集了匹配的传粉者与寄生蜂样本。研究结果显示，分布于两个区域的传粉榕小蜂构成了两个独立的种群；与之形成鲜明对比的是，寄生蜂在整个大范围采样区域内仅形成单一的种群。
我们在两个物种中均观测到了距离隔离效应，但相较于传粉榕小蜂，寄生蜂各采样点间的FST与RST值始终更低。已有研究表明，雌雄同株榕的传粉榕小蜂可实现长距离扩散，而我们的研究首次提供了遗传学证据，证明其寄生蜂即便未实现更远距离的扩散，至少也能达到相当的扩散范围。
寄主与寄生蜂之间截然不同的地理种群结构，凸显了这一重要共生系统中地理镶嵌格局的潜在可能。