Data from: Genetic patterns of Magnolia in the Lesser Antilles: Stepwise colonisation leading to highly inbred island 'populations'

Aim: Test for genetic signatures of island biogeographic patterns, using a slowly evolving, recent colonist with a low dispersal capability in an island chain without linear chronosequence; evaluate the multiple-endemic status of the species; and quantify genetic diversity of extant island populations. Location: The Lesser Antilles (Caribbean). Taxon: Magnolia dodecapetala (Magnoliaceae). Methods: Genetic diversity was characterised using Sanger sequencing of 21 individuals amplified for 11 DNA markers, plus microsatellite data of 195 individuals genotyped with 19 simple sequence repeat (SSR) markers. Sanger sequencing data were used to construct a Bayesian phylogenetic hypothesis, while SSR markers were used to run approximate Bayesian computation (ABC) demographic analyses and calculate population statistics. Results: Both types of molecular data support stepwise colonization, decoupled from known island ages. The ABC analyses support a north to south migration while the Sanger sequencing data indicates a mixture of island progression rule and stepping stone dispersal. The SSR data show strong genetic structuring per island and significant inbreeding in all populations except in Saint Lucia. The lowest genetic diversity is found in the population from Saint Vincent. A high amount of genetic linkage occurs in a subpopulation from Dominica. Main conclusions: Biogeographic patterns for the complex geological setting of the Lesser Antilles are uncovered using a slowly evolving study species. All genetic data support treating each island as distinct Management Units for conservation and call for a re-evaluation of the species limits. Inbreeding threatens the survival of island populations and the populations of Saint Vincent and Dominica represent conservation priorities.

研究目的：检验岛屿生物地理格局（island biogeographic patterns）的遗传特征，在无线性时间序列（linear chronosequence）的岛链中，选取演化缓慢、近期拓殖且扩散能力较低的类群；评估该物种的多岛特有分布地位，并量化现存岛屿种群的遗传多样性。
研究区域：加勒比海小安的列斯群岛（Lesser Antilles）。
研究类群：十二瓣木兰（Magnolia dodecapetala，木兰科Magnoliaceae）。
研究方法：通过对21个个体的11个DNA标记位点进行Sanger测序（Sanger sequencing），结合195个个体经19个简单序列重复（simple sequence repeat, SSR）标记分型的微卫星数据，表征种群遗传多样性。其中，Sanger测序数据用于构建贝叶斯系统发育假说，而SSR标记则用于开展近似贝叶斯计算（approximate Bayesian computation, ABC）种群人口学分析，并计算种群统计指标。
研究结果：两类分子数据均支持与已知岛屿形成年龄解耦的逐步定植模式。近似贝叶斯计算分析支持自北向南的迁移路径，而Sanger测序数据则显示岛屿进展法则（island progression rule）与踏脚石扩散（stepping stone dispersal）的混合扩散模式。SSR数据显示，除圣卢西亚种群外，其余所有种群均存在显著的岛屿间遗传结构与近交现象。圣文森特种群的遗传多样性最低，多米尼加的一个亚种群存在较高水平的遗传连锁。
主要结论：本研究通过选取演化缓慢的研究类群，揭示了小安的列斯群岛复杂地质背景下的生物地理格局。所有遗传数据均支持将每个岛屿作为独立的保护管理单元（Management Units），并呼吁重新评估该物种的分类界限。近交现象威胁着岛屿种群的存续，其中圣文森特与多米尼加的种群为优先保护对象。