APPENDIX_Macaronesia_mosses_distribs.xlsx

Endemism, a hallmark of island biodiversity, reaches its lowest levels among bryophytes compared with other land plants. Whether this pattern reflects low diversification rates, and why, or loss of endemicity due to extinctions or subsequent continental (back) colonisation, is examined here through a review and meta-analysis of available evidence in the Macaronesian flora. A significant genetic differentiation (Gst) was consistently found between Macaronesian and continental populations, ruling-out the hypothesis that intense migrations necessarily hamper differentiation. A significant phylogeographical signal in the data (Nst&gt;Gst) was further found in more than 1/3 of the species investigated, involving that mutation rates are higher than dispersal rates and evidencing incipient speciation. The significantly higher average <i>N</i>_<em>ST</em> between extra-European regions and Macaronesia compared to Europe and Macaronesia suggests, however, that incipient speciation is more likely to occur between distant (Macaronesian vs extra-European populations) than closer (Macaronesian vs European) populations. In line with this, ancestral area estimations in Macaronesian endemic bryophyte species reveal that at least 50% of them have an extra-European origin, in contrast with the almost exclusively (&gt;90%) European/Mediterranean origin of Macaronesian endemic spermatophytes. Allopatric speciation via long-distance dispersal and subsequent divergence of a single endemic species prevails in island bryophytes, wherein sympatric radiations virtually never occur. Such a speciation mode does not trigger high rates of endemism, in contrast to radiations in Macaronesian spermatophytes, which contribute to 56% of the total number of endemics. Several mechanisms may explain the failure of island bryophytes to diversify <i>in situ</i>, including the fact that oceanic islands are too small or insufficiently isolated from each other or from continents to promote sympatric speciation, the lack of key innovations, and phylogenetic niche conservatism for stable habitats not prone to trigger radiations. By comparisons with spermatophytes, continental (back-)colonisation further largely prevails in bryophytes and, unlike in many instances in angiosperms, is not followed by <i>in situ</i> speciation on the mainland. The consequent loss of the endemic status of species that did speciate on islands, but subsequently enlarged their range, further accounts for the low rates of endemism among island bryophyte floras and invalidates the use of endemism rates as a proxy of speciation rates in the group.

特有性（Endemism）作为岛屿生物多样性（island biodiversity）的标志性特征，在苔藓植物（bryophytes）中的水平显著低于其他陆生植物类群。本研究通过对马卡罗尼西亚植物区系（Macaronesian flora）现有证据的综述与元分析（meta-analysis），探讨了该格局是否源于较低的多样化速率（diversification rates）及其背后成因，或是由灭绝事件（extinctions）或后续大陆反向定殖（continental (back) colonisation）导致的特有性丧失。
研究始终发现马卡罗尼西亚种群与大陆种群间存在显著的遗传分化（genetic differentiation，Gst），这一结果排除了“强烈的基因流必然阻碍分化”的假说。进一步分析显示，超三分之一的研究物种的数据中呈现显著的系统地理信号（phylogeographical signal，Nst>Gst），这表明突变速率高于扩散速率，同时印证了初期物种形成（incipient speciation）的存在。
不过，欧洲以外区域与马卡罗尼西亚种群间的平均Nst显著高于欧洲与马卡罗尼西亚种群间的平均Nst，这暗示初期物种形成在亲缘关系更远的种群（马卡罗尼西亚与欧洲以外种群）间比亲缘关系较近的种群（马卡罗尼西亚与欧洲种群）间更易发生。
与此结论一致，对马卡罗尼西亚特有苔藓植物的祖先分布区重建结果显示，其中至少50%的类群起源于欧洲以外区域；而马卡罗尼西亚特有种子植物（spermatophytes）的起源则几乎全部（>90%）为欧洲/地中海区域。
岛屿苔藓植物的物种形成模式以通过长距离扩散（long-distance dispersal）实现的异域物种形成（allopatric speciation）及后续单个特有类群的分化为主，几乎从未出现同域辐射（sympatric radiations）。与马卡罗尼西亚种子植物的辐射演化不同，这种物种形成模式并未催生较高的特有性水平——后者贡献了马卡罗尼西亚地区56%的特有物种总数。
有多种机制可解释岛屿苔藓植物难以发生原位（in situ）多样化的原因：包括大洋岛屿面积过小、岛屿间或岛屿与大陆间的隔离程度不足，无法推动同域物种形成；缺乏关键创新性状；以及针对稳定生境的系统发育生态位保守性，难以触发辐射演化。
与种子植物相比，大陆反向定殖在苔藓植物中更为普遍；且与被子植物（angiosperms）中的多数情况不同，这类定殖并未伴随陆地区域的原位物种形成。那些曾在岛屿上完成物种形成、后续却扩张了分布范围的类群，其特有身份随之丧失，这进一步解释了岛屿苔藓植物区系特有性水平较低的成因，同时也表明特有性速率无法作为该类群物种形成速率的替代指标。