Sorbonne Université, Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN/IPSL), CNRS UMR, Paris, France.
Université Libre de Bruxelles, Faculté des Sciences, Service Evolution Biologique et Ecologie, Bruxelles, Belgium.
Ann Bot. 2020 Jun 19;126(1):73-83. doi: 10.1093/aob/mcaa049.
Afromontane forests host a unique biodiversity distributed in isolated high-elevation habitats within a matrix of rain forests or savannahs, yet they share a remarkable flora that raises questions about past connectivity between currently isolated forests. Here, we focused on the Podocarpus latifolius-P. milanjianus complex (Podocarpaceae), the most widely distributed conifers throughout sub-Saharan African highlands, to infer its demographic history from genetic data.
We sequenced the whole plastid genome, mitochondrial DNA regions and nuclear ribosomal DNA of 88 samples from Cameroon to Angola in western Central Africa and from Kenya to the Cape region in eastern and southern Africa to reconstruct time-calibrated phylogenies and perform demographic inferences.
We show that P. latifolius and P. milanjianus form a single species, whose lineages diverged during the Pleistocene, mostly between approx, 200 000 and 300 000 years BP, after which they underwent a wide range expansion leading to their current distributions. Confronting phylogenomic and palaeoecological data, we argue that the species originated in East Africa and reached the highlands of the Atlantic side of Africa through two probable latitudinal migration corridors: a northern one towards the Cameroon volcanic line, and a southern one towards Angola. Although the species is now rare in large parts of its range, no demographic decline was detected, probably because it occurred too recently to have left a genetic signature in our DNA sequences.
Despite the ancient and highly fluctuating history of podocarps in Africa revealed by palaeobotanical records, the extended distribution of current P. latifolius/milanjianus lineages is shown to result from a more recent history, mostly during the mid-late Pleistocene, when Afromontane forests were once far more widespread and continuous.
高山森林拥有独特的生物多样性，分布在雨林或热带稀树草原基质中的孤立高海拔生境中，但它们拥有显著的植物群，这引发了关于当前孤立森林之间过去连通性的问题。在这里，我们专注于罗汉松属（Podocarpus）的宽叶罗汉松-米叶罗汉松复合体（罗汉松科），这是整个撒哈拉以南非洲高海拔地区分布最广的针叶树，从遗传数据推断其种群历史。
我们对来自喀麦隆到安哥拉的西中非和从肯尼亚到南非海角地区的 88 个样本进行了全质体基因组、线粒体 DNA 区和核核糖体 DNA 的测序，以重建时间校准的系统发育树并进行种群推断。
我们表明，宽叶罗汉松和米叶罗汉松形成了一个单一的物种，其谱系在更新世分化，主要在约 20 万至 30 万年前，之后它们经历了广泛的扩张，导致了它们目前的分布。对比系统基因组学和古生态学数据，我们认为该物种起源于东非，并通过两个可能的南北向迁移走廊到达大西洋侧非洲的高地：一个向北朝向喀麦隆火山线，另一个向南朝向安哥拉。尽管古植物学记录揭示了非洲罗汉松属植物的古老和高度波动的历史，但目前宽叶罗汉松/米叶罗汉松谱系的广泛分布被证明是最近的历史结果，主要发生在更新世中期至晚期，当时高山森林曾经更加广泛和连续。
尽管古植物学记录揭示了非洲罗汉松属植物的古老和高度波动的历史，但目前宽叶罗汉松/米叶罗汉松谱系的广泛分布被证明是最近的历史结果，主要发生在更新世中期至晚期，当时高山森林曾经更加广泛和连续。
