Table_1_Polyploidy on Islands: Its Emergence and Importance for Diversification.csv

Whole genome duplication or polyploidy is widespread among floras globally, but traditionally has been thought to have played a minor role in the evolution of island biodiversity, based on the low proportion of polyploid taxa present. We investigate five island systems (Juan Fernández, Galápagos, Canary Islands, Hawaiian Islands, and New Zealand) to test whether polyploidy (i) enhances or hinders diversification on islands and (ii) is an intrinsic feature of a lineage or an attribute that emerges in island environments. These island systems are diverse in their origins, geographic and latitudinal distributions, levels of plant species endemism (37% in the Galapagos to 88% in the Hawaiian Islands), and ploidy levels, and taken together are representative of islands more generally. We compiled data for vascular plants and summarized information for each genus on each island system, including the total number of species (native and endemic), generic endemicity, chromosome numbers, genome size, and ploidy levels. Dated phylogenies were used to infer lineage age, number of colonization events, and change in ploidy level relative to the non-island sister lineage. Using phylogenetic path analysis, we then tested how the diversification of endemic lineages varied with the direct and indirect effects of polyploidy (presence of polyploidy, time on island, polyploidization near colonization, colonizer pool size) and other lineage traits not associated with polyploidy (time on island, colonizer pool size, repeat colonization). Diploid and tetraploid were the most common ploidy levels across all islands, with the highest ploidy levels (>8x) recorded for the Canary Islands (12x) and New Zealand (20x). Overall, we found that endemic diversification of our focal island floras was shaped by polyploidy in many cases and certainly others still to be detected considering the lack of data in many lineages. Polyploid speciation on the islands was enhanced by a larger source of potential congeneric colonists and a change in ploidy level compared to overseas sister taxa.

全基因组复制（Whole Genome Duplication, WGD）或多倍体化（Polyploidy）在全球植物区系中广泛存在，但传统观点基于现存类群中多倍体类群占比较低的现象，认为其在岛屿生物多样性演化中仅发挥次要作用。本研究针对五个岛屿系统（胡安·费尔南德斯群岛、加拉帕戈斯群岛、加那利群岛、夏威夷群岛及新西兰）展开调查，旨在验证两个科学假说：其一，多倍体化会促进还是阻碍岛屿类群的物种分化；其二，多倍体化是演化支系的固有特征，还是仅在岛屿环境中才会显现的属性。这些岛屿系统在起源、地理与纬度分布、植物物种特有性水平（加拉帕戈斯群岛为37%，夏威夷群岛高达88%）以及倍性水平上均存在显著差异，整体可代表全球多数岛屿的特征。研究团队收集了维管植物（vascular plants）的相关数据，并针对每个岛屿系统中的各属整理了如下信息：物种总数（本土物种与特有物种）、属级特有性、染色体数目、基因组大小以及倍性水平。研究人员借助时间校准的系统发育树（dated phylogeny），推断了各演化支系的起源时间、殖民岛屿的事件次数，以及相较于非岛屿近缘支系的倍性水平变化情况。随后，通过系统发育路径分析（phylogenetic path analysis），本研究检验了多倍体化的直接与间接效应（包括多倍体化的存在与否、岛屿驻留时间、殖民前后的多倍体化事件、殖民源种群规模）以及与多倍体化无关的支系特征（岛屿驻留时间、殖民源种群规模、重复殖民事件）对特有支系分化水平的影响模式。二倍体与四倍体是所有岛屿中最常见的倍性类型，最高倍性（>8x）的记录见于加那利群岛（12x）与新西兰（20x）。总体而言，本研究聚焦的岛屿植物区系的特有类群分化在多数情况下受到多倍体化的调控；考虑到诸多支系仍缺乏相关数据，尚有更多关联有待后续发掘。相较于海外近缘类群，更大规模的同属殖民源种群以及倍性水平的变化，会促进岛屿上的多倍体物种形成。