Herbarium and Library of African Botany, C.P. 265, Université Libre de Bruxelles, Campus de la Plaine, Boulevard du Triomphe 1050, Brussels, Belgium; Plant Ecology and Biogeochemistry, C.P. 244, Université Libre de Bruxelles, Campus de la Plaine, Boulevard du Triomphe, 1050, Brussels, Belgium.
Cullman Program for Molecular Systematics, New York Botanical Garden, Bronx, NY 10458-5126, USA; PhD Program in Biology, Graduate Center, City University of New York, 365 5th Ave., New York, NY 10016, USA.
Mol Phylogenet Evol. 2021 Jun;159:107105. doi: 10.1016/j.ympev.2021.107105. Epub 2021 Feb 16.
Angraecoid orchids present a remarkable diversity of chromosome numbers, which makes them a highly suitable system for exploring the impact of karyotypic changes on cladogenesis, diversification and morphological differentiation. We compiled an annotated cytotaxonomic checklist for 126 species of Angraecinae, which was utilised to reconstruct chromosomal evolution using a newly-produced, near-comprehensive phylogenetic tree that includes 245 angraecoid taxa. In tandem with this improved phylogenetic framework, using combined Bayesian, maximum likelihood and parsimony approaches on ITS-1 and five plastid markers, we propose a new cladistic nomenclature for the angraecoids, and we estimate a new timeframe for angraecoid radiation based on a secondary calibration, and calculate diversification rates using a Bayesian approach. Coincident divergence dates between clades with identical geographical distributions in the angraecoids and the pantropical orchid genus Bulbophyllum suggest that the same events may have intervened in the dispersal of these two epiphytic groups between Asia, continental Africa, Madagascar and the Neotropics. The major angraecoid lineages probably began to differentiate in the Middle Miocene, and most genera and species emerged respectively around the Late Miocene-Pliocene boundary and the Pleistocene. Ancestral state reconstruction using maximum likelihood estimation revealed an eventful karyotypic history dominated by descending dysploidy. Karyotypic shifts seem to have paralleled cladogenesis in continental tropical Africa, where approximately 90% of the species have descended from at least one inferred transition from n = 17-18 to n = 25 during the Middle Miocene Climatic Transition, followed by some clade-specific descending and ascending dysploidy from the Late Miocene to the Pleistocene. Conversely, detected polyploidy is restricted to a few species lineages mostly originating during the Pleistocene. No increases in net diversification could be related to chromosome number changes, and the apparent net diversification was found to be highest in Madagascar, where karyotypic stasis predominates. Finally, shifts in chromosome number appear to have paralleled the evolution of rostellum structure, leaflessness, and conspicuous changes in floral colour.
杓兰族植物呈现出显著的染色体数目多样性，这使得它们成为探索核型变化对进化分支、多样化和形态分化影响的高度合适系统。我们编制了一份 126 种杓兰亚族的注释细胞分类清单，该清单用于利用新产生的、近乎全面的系统发育树重建染色体进化，该系统发育树包括 245 种杓兰类植物。与这个改进的系统发育框架相结合，我们使用 ITS-1 和五个质体标记的联合贝叶斯、最大似然和简约法，提出了一个新的杓兰类分类命名法，并根据二次校准估计了杓兰类辐射的新时间框架，并使用贝叶斯方法计算了多样化率。在杓兰类和泛热带兰属 Bulbophyllum 中具有相同地理分布的分支之间的趋同分化日期表明，相同的事件可能介入了这两个附生类群在亚洲、非洲大陆、马达加斯加和新热带地区之间的扩散。主要的杓兰类谱系可能在中新世开始分化，大多数属和种分别出现在晚中新世-上新世边界和更新世。使用最大似然估计的祖先状态重建揭示了一个以下降非整倍性为主的丰富核型历史。核型变化似乎与非洲大陆热带地区的进化分支平行，在那里，大约 90%的物种来自至少一次从中新世气候转型期的 n=17-18 到 n=25 的推断转变，随后在晚中新世到更新世期间发生了一些特定分支的下降和上升非整倍性。相反，检测到的多倍体仅限于少数物种谱系，这些谱系主要起源于更新世。净多样化的增加似乎与染色体数目的变化无关，并且在马达加斯加发现的净多样化最高，那里的核型稳定占主导地位。最后，染色体数目的变化似乎与蕊喙结构、无叶性和花的颜色的显著变化的进化平行。
