Data from: History of the fragmentation of the African rain forest in the Dahomey Gap: insight from the demographic history of Terminalia superba

Paleo-environmental reconstructions show that the distribution of tropical African rain forests was affected by Quaternary climate changes. They suggest that the Dahomey Gap (DG) - the savanna corridor that currently separates Upper Guinean (UG, West Africa) and Lower Guinean (LG, western Central Africa) rain forest blocks – was forested during the African Humid Holocene period (from at least 9 ka till 4.5 ka), and possibly during other interglacial periods, while an open vegetation developed in the DG under drier conditions, notably during glacial maxima. Nowadays, relics of semi-deciduous forests containing UG and LG forest species are still present within the DG. We used one of these species, the pioneer tree Terminalia superba (Combretaceae), to study past forest fragmentation in the DG and its impact on infraspecific biodiversity. A Bayesian clustering analysis of 299 individuals genotyped at 14 nuclear microsatellites revealed five parapatric genetic clusters (UG, DG, and three in LG) with low to moderate genetic differentiation (Fst from 0.02 to 0.24). Approximate Bayesian Computation analyses inferred a demographic bottleneck around the penultimate glacial period in all populations. They also supported an origin of the DG population by admixture of UG and LG populations around 54 000 (27 600 - 161 000) years B.P., thus before the Last Glacial Maximum. These results contrast with those obtained on Distemonanthus benthamianus where the DG population seems to originate from the Humid Holocene period. We discuss these differences in light of the ecology of each species. Our results challenge the simplistic view linking population fragmentation/expansion with glacial/interglacial periods in African forest species.古环境重建研究表明，非洲热带雨林的分布曾受第四纪气候变化（Quaternary climate changes）影响。研究显示，当前分隔上几内亚（UG，西非）与下几内亚（LG，中非西部）雨林区块的稀树草原廊道——达荷美缺口（DG），在非洲湿润全新世（至少9千年前至4.5千年前）期间曾被森林覆盖，在其他间冰期或许亦是如此；而在气候更为干旱的时期，尤其是冰盛期，DG区域则发育着开放型植被。如今，DG区域内仍残存着包含UG与LG雨林物种的半落叶林。我们选取其中一种先锋树种——大翅榄仁（Terminalia superba，使君子科Combretaceae），用以研究DG区域过往的森林碎片化现象及其对种内生物多样性的影响。对299个个体的14个核微卫星（nuclear microsatellites）位点进行基因分型后开展的贝叶斯聚类分析（Bayesian clustering analysis）显示，共鉴定出5个具有低至中等遗传分化水平（Fst介于0.02至0.24之间）的邻域遗传簇，分别对应UG、DG以及LG区域的3个簇。近似贝叶斯计算（Approximate Bayesian Computation）分析推断，所有种群均在倒数第二次冰期前后经历了种群瓶颈（demographic bottleneck）事件。同时，该分析支持DG种群起源于约5.4万年前（2.76万至16.1万年前）的UG与LG种群的混合事件，这一时间早于末次冰盛期（Last Glacial Maximum）。这些结果与对Distemonanthus benthamianus的研究结果相悖，后者的DG种群似乎起源于非洲湿润全新世时期。我们结合两个物种的生态学特性对上述差异进行了探讨。本研究结果对“非洲雨林物种种群碎片化或扩张与冰期-间冰期周期简单绑定”的片面观点提出了质疑。