Department of Botany, Faculty of Science, Charles University, 128 00 Prague, Czech Republic.
Department of Natural History, University Museum, University of Bergen, 5020 Bergen, Norway.
Proc Natl Acad Sci U S A. 2022 May 31;119(22):e2112737119. doi: 10.1073/pnas.2112737119. Epub 2022 May 26.
Tropical alpine floras are renowned for high endemism, spectacular giant rosette plants testifying to convergent adaptation to harsh climates with nightly frosts, and recruitment dominated by long-distance dispersal from remote areas. In contrast to the larger, more recent (late Miocene onward) and contiguous expanses of tropical alpine habitat in South America, the tropical alpine flora in Africa is extremely fragmented across small patches on distant mountains of variable age (Oligocene onward). How this has affected the colonization and diversification history of the highly endemic but species-poor afroalpine flora is not well known. Here we infer phylogenetic relationships of ∼20% of its species using novel genome skimming data and published matrices and infer a timeframe for species origins in the afroalpine region using fossil-calibrated molecular clocks. Although some of the mountains are old, and although stem node ages may substantially predate colonization, most lineages appear to have colonized the afroalpine during the last 5 or 10 My. The accumulation of species increased exponentially toward the present. Taken together with recent reports of extremely low intrapopulation genetic diversity and recent intermountain population divergence, this points to a young, unsaturated, and dynamic island scenario. Habitat disturbance caused by the Pleistocene climate oscillations likely induced cycles of colonization, speciation, extinction, and recolonization. This study contributes to our understanding of differences in the histories of recruitment on different tropical sky islands and on oceanic islands, providing insight into the general processes shaping their remarkable floras.
热带高山植物以高特有性而闻名，壮观的巨型玫瑰状植物证明了它们对夜间结霜等恶劣气候的趋同适应，并且以远距离扩散从偏远地区为主导进行繁殖。与南美洲更大、更新（中新世以来）和连续的热带高山生境相比，非洲的热带高山植物区系在不同年龄（渐新世以来）的遥远山脉上极其分散，呈小块状。这种情况如何影响高度特有但物种贫乏的非洲高山植物区系的殖民和多样化历史，目前还不太清楚。在这里，我们使用新的基因组扫描数据和已发表的矩阵来推断其约 20%物种的系统发育关系，并使用化石校准的分子钟推断非洲高山地区物种起源的时间框架。尽管一些山脉很古老，并且尽管茎节点年龄可能大大早于殖民化，但大多数谱系似乎在过去 5 或 10 万年中殖民了非洲高山地区。物种的积累呈指数增长到现在。与最近报道的极低的种群内遗传多样性和最近的山脉间种群分化相结合，这表明了一个年轻、不饱和和动态的岛屿情景。更新世气候振荡引起的栖息地干扰可能引发了周期性的殖民、物种形成、灭绝和再殖民。这项研究有助于我们了解不同热带天空岛屿和海洋岛屿上的招募历史差异，为了解塑造它们显著植物区系的一般过程提供了线索。
