Data from: Lack of genetic isolation by distance, similar genetic structuring but different demographic histories in a fig-pollinating wasp mutualism

Historical abiotic factors such as climatic oscillations and extreme climatic events as well as biotic factors have shaped the structuring of species’ genetic diversity. In obligate species-specific mutualisms, the biogeographic histories of the interacting species are tightly linked. This could be particularly true for nuclear genes in the Ficus-pollinating wasp mutualistic association as the insects disperse pollen from their natal tree. In this study we compare spatial genetic structure of plant and pollinator for the Ficus hirta-Valisia javana association throughout South-East China including Hainan Island, for both nuclear and cytoplasmic markers. We show that dispersal of the insect leads to plant and insect presenting similar signatures of lack of genetic isolation by distance for nuclear genes on the continent over a distance of 1000 km. But we also show that the demographic histories of plant and insect are strikingly different. This is in agreement with extreme climatic events leading to transient regional extinctions of the insects, associated with local survival of the plants. We also evidence genetic differentiation for both wasps and fig-tree between the continent and Hainan Island, although the Qiongzhou Strait is only on average 30 km wide suggesting that geographic isolation by itself has not been sufficient to generate this differentiation. Hence, our results suggest that in highly dispersive mutualistic systems, isolation by dispersal limitation across a geographic barrier could be supplemented by isolation by adaptation, and maybe by coevolution, allowing further genetic divergence. In such systems, species may frequently be composed of a single population.

诸如气候振荡与极端气候事件等历史非生物因子（abiotic factors），连同生物因子（biotic factors），共同塑造了物种种群遗传多样性（genetic diversity）的结构模式。在专性物种特异性互利共生（obligate species-specific mutualisms）关系中，互生物种的生物地理历史（biogeographic histories）紧密耦合。这一点在榕-传粉榕小蜂互利共生体系的核基因（nuclear genes）中体现得尤为显著，因为传粉昆虫会从其诞生的寄主树散播花粉。本研究针对分布于中国东南部（含海南岛）的粗叶榕（Ficus hirta）-爪哇瓦利榕小蜂（Valisia javana）互利共生体系，利用核基因（nuclear genes）与细胞质标记（cytoplasmic markers），对比分析了寄主植物与传粉昆虫的空间遗传结构。研究结果显示，在中国大陆范围内1000千米的空间尺度上，由于昆虫的扩散作用，植物与昆虫的核基因均未表现出距离隔离效应（genetic isolation by distance），二者的遗传模式高度相似。但同时我们也发现，寄主植物与传粉昆虫的种群历史动态（demographic histories）却存在显著差异。这一结果与极端气候事件导致昆虫发生暂时性区域性灭绝（regional extinctions）、而寄主植物得以在当地存活的假说相符。此外，我们还证实，尽管琼州海峡（Qiongzhou Strait）平均宽度仅约30千米，但中国大陆与海南岛之间的传粉榕小蜂与粗叶榕均存在遗传分化，这表明单纯的地理隔离并不足以产生此类遗传分化。因此，本研究结果表明，在高扩散能力的互利共生体系中，地理屏障带来的扩散限制（dispersal limitation）隔离可通过适应性隔离（isolation by adaptation）乃至协同进化（coevolution）得到补充，进而推动进一步的遗传分化。在这类体系中，物种通常可能仅由单一种群构成。