Data from: Contrasting genetic responses to population fragmentation in a coevolving fig and fig wasp across a mainland-island archipelago

Interacting species of pollinator–host systems, especially the obligate ones, are sensitive to habitat fragmentation, due to the nature of mutual dependence. Comparative studies of genetic structure can provide insights into how habitat fragmentation contributes to patterns of genetic divergence among populations of the interacting species. In this study, we used microsatellites to analyse genetic variation in Chinese populations of a typical mutualistic system – Ficus pumila and its obligate pollinator Wiebesia sp. 1 – in a naturally fragmented landscape. The plants and wasps showed discordant patterns of genetic variation and geographical divergence. There was no significant positive relationship in genetic diversity between the two species. Significant isolation-by-distance (IBD) patterns occurred across the populations of F. pumila and Wiebesia sp. 1 as whole, and IBD also occurred among island populations of the wasps, but not the plants. However, there was no significant positive relationship in genetic differentiation between them. The pollinator populations had significantly lower genetic variation in small habitat patches than in larger patches, and three island pollinator populations showed evidence of a recent bottleneck event. No effects of patch size or genetic bottlenecks were evident in the plant populations. Collectively, the results indicate that, in more fragmented habitats, the pollinators, but not the plants, have experienced reduced genetic variation. The contrasting patterns have multiple potential causes, including differences in longevity and hence number of generations experiencing fragmentation; different dispersal patterns, with the host's genes dispersed as seeds as well as a result of pollen dispersal via the pollinator; asymmetrical responses to fluctuations in partner populations; and co-existence of a rare second pollinating wasp on some islands. These results indicate that strongly interdependent species may respond in markedly different ways to habitat fragmentation.

传粉者-宿主互作系统中的交互物种，尤其是专性互作类群，因二者相互依存的特性，对栖息地破碎化高度敏感。遗传结构比较研究可揭示栖息地破碎化如何塑造互作物种种群间的遗传分化格局。本研究以自然破碎化景观中的典型互作系统——薜荔（Ficus pumila）及其专性传粉者榕小蜂（Wiebesia sp. 1）——为研究对象，利用微卫星标记分析其中国种群的遗传变异。研究发现，宿主植物与传粉者的遗传变异及地理分化格局存在显著差异；二者的遗传多样性间未呈现显著正相关关系。薜荔与榕小蜂（Wiebesia sp. 1）的整体种群均呈现显著的距离隔离效应（Isolation-by-Distance, IBD）格局；且榕小蜂的岛屿种群间存在IBD格局，但薜荔种群间并未出现该现象。然而二者的遗传分化程度间并未呈现显著正相关关系。传粉者种群在小型生境斑块中的遗传变异水平显著低于大型斑块，且3个岛屿上的传粉者种群均显示出近期经历遗传瓶颈的证据；而薜荔种群则未表现出与生境斑块大小或遗传瓶颈相关的显著效应。综合来看，研究结果表明：在破碎化程度更高的生境中，传粉者种群的遗传变异水平出现下降，而宿主植物种群并无此现象。上述迥异的格局存在多种潜在成因，包括寿命差异导致的破碎化影响世代数不同；扩散模式差异——宿主植物的基因可通过种子传播，也可借助传粉者的花粉传播实现扩散；对伙伴种群波动的不对称响应；以及部分岛屿上共存的稀有第二种传粉榕小蜂。本研究结果表明：高度依存的互作物种对栖息地破碎化的响应可能存在显著差异。