Data from: Long distance dispersal and genetic structure of natural populations: an assessment of the inverse isolation hypothesis in peat mosses

It is well accepted that the shape of the dispersal kernel, especially its tail, has a substantial effect on the genetic structure of species. Theory predicts that dispersal by fat-tailed kernels reshuffles genetic material and thus preserves genetic diversity during colonization. Moreover, if efficient long distance dispersal is coupled with random colonization, an inverse isolation effect is predicted to develop in which increasing genetic diversity per colonizer is expected with increasing distance from a genetically variable source. By contrast, increasing isolation leads to decreasing genetic diversity when dispersal is via thin-tailed kernels. Here we use a well-established model group for dispersal biology (peat mosses: genus Sphagnum) with a fat-tailed dispersal kernel, and the natural laboratory of the Stockholm archipelago to study the validity of the inverse isolation hypothesis in spore-dispersed plants in island colonization. Population genetic structure of three species (S. fallax, S. fimbriatum and S. palustre) with contrasting life histories and ploidy levels were investigated on a set of islands using microsatellites. Our data show (φ’st, AMOVA, IBD) that dispersal of the two most abundant species can be well approximated by a random colonization model. We find that genetic diversity per colonizer on islands increases with distance from the mainland for S. fallax and S. fimbriatum. By contrast, S. palustre deviates from this pattern, owing to its restricted distribution in the region affecting its source pool strength. Therefore, the inverse isolation effect appears to hold in natural populations of peat mosses and, likely, in other organisms with small diaspores.

学界普遍认为，扩散核（dispersal kernel）的形态，尤其是其尾部特征，对物种种群的遗传结构具有显著影响。理论预测，采用肥尾扩散核的扩散方式会重新组合遗传物质，因此在定殖过程中维持遗传多样性。此外，若高效的长距离扩散与随机定殖相结合，理论上会产生反向隔离效应（inverse isolation effect）：即随着与遗传变异源的距离增加，每个定殖个体的遗传多样性也会提升。与之相反，若扩散采用瘦尾扩散核，则隔离程度越高，遗传多样性越低。本研究以肥尾扩散核型的泥炭藓属（*Sphagnum*）——扩散生物学领域公认的模式类群——以及斯德哥尔摩群岛这一天然实验场为研究对象，旨在验证孢子传播植物在岛屿定殖过程中的反向隔离效应假说的合理性。本研究利用微卫星标记（microsatellites），对一组岛屿上的3种泥炭藓——镰叶泥炭藓（*S. fallax*）、纤枝泥炭藓（*S. fimbriatum*）和沼泽泥炭藓（*S. palustre*）——开展了种群遗传结构分析，这3个物种的生活史与倍性水平均存在显著差异。研究数据显示（φ’st、分子方差分析（AMOVA）、隔离距离（IBD））：两种优势泥炭藓的扩散过程可通过随机定殖模型进行良好拟合。我们发现，镰叶泥炭藓与纤枝泥炭藓的岛屿定殖个体的遗传多样性，均随其与大陆的距离增加而升高。与之相反，沼泽泥炭藓的模式与此不符，这是由于该区域内其分布范围受限，进而影响了其源种群库强度（source pool strength）。综上，反向隔离效应在泥炭藓的自然种群中成立，且大概率也适用于其他具有小型传播体（diaspore）的生物类群。