Herbarium, Research & Conservation Branch, Singapore Botanic Gardens, National Parks Board, 1 Cluny Road, 259569 Singapore; Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK.
Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK.
Mol Phylogenet Evol. 2020 May;146:106752. doi: 10.1016/j.ympev.2020.106752. Epub 2020 Feb 3.
The legume subfamily Detarioideae is exceptionally diverse in tropical Africa and Madagascar, compared to South America or Asia, a trend contrary to that shown by most other pantropical plant groups. We aim to elucidate the process of diversification giving rise to these high diversity levels by focussing our investigations on the Daniellia clade, which is present in both Africa and Madagascar. The Daniellia clade is an early-diverging lineage of subfamily Detarioideae (Leguminosae; pea family) and consists of three genera: Daniellia, Brandzeia and Neoapaloxylon. The species belonging to this group exhibit a wide range of habitat types. The Madagascar endemics Brandzeia (1 species) and Neoapaloxylon (3 species) occupy dry woodlands and arid succulent habitats respectively. Daniellia alsteeniana and D. oliveri are found in savannahs while the remaining eight species within Daniellia all occupy rainforest habitats. Phylogenetic analyses were generated from a dense, multi-individual species level sampling of the clade. Divergence time estimates were carried out using a molecular clock method to investigate biogeographical patterns and shifts in habitat types within the Daniellia clade, and conservation assessments were conducted to determine the levels of extinction risks these species are facing. We estimate that the Daniellia clade first emerged during the Early Eocene from an ancestor present in the rainforests of North Africa at that time, reflecting an ancestral habitat preference. There was a first major split over the course of the Eocene, giving rise to both African rainforest and Madagascan savannah lineages. With the emergence of a drier climate and vegetation type in Africa during the Eocene, it is likely that a dry-climate adapted lineage from the Daniellia clade ancestor could have dispersed through suitable savannah or woodland regions to reach Madagascar, subsequently giving rise to the savannah-adapted ancestor of Brandzeia and Neoapaloxylon in the Early Miocene. The African rainforest lineage gave rise to the genus Daniellia, which is postulated to have first diversified in the Middle Miocene, while savannah species of Daniellia emerged independently during the Pliocene, coinciding with the global rise of C4-dominated grasslands. More than half of the species in the Daniellia clade are near threatened or threatened, which highlights the need to understand the threats of anthropogenic pressures and climate change these species are facing to prioritise their conservation.
豆科菜豆亚科在热带非洲和马达加斯加的多样性非常丰富，与南美洲或亚洲形成鲜明对比，这与大多数其他泛热带植物群的趋势相反。我们的目标是通过聚焦于非洲和马达加斯加都存在的 Daniellia 进化枝，阐明导致这些高多样性水平的多样化过程。Daniellia 进化枝是豆科（豌豆科；豆科）菜豆亚科的一个早期分支，由三个属组成：Daniellia、Brandzeia 和 Neoapaloxylon。属于该组的物种表现出广泛的栖息地类型。马达加斯加特有种 Brandzeia（1 种）和 Neoapaloxylon（3 种）分别占据干旱林地和干旱肉质栖息地。Daniellia alsteeniana 和 D. oliveri 见于热带稀树草原，而 Daniellia 属的其余 8 种则全部占据雨林栖息地。通过对该进化枝的密集、多个体种水平采样进行了系统发育分析。使用分子钟方法进行了分歧时间估计，以研究 Daniellia 进化枝内的生物地理模式和栖息地类型的变化，并进行了保护评估，以确定这些物种面临的灭绝风险水平。我们估计，Daniellia 进化枝最早出现在早始新世，起源于当时北非的雨林中的一个祖先，反映了一个祖先的栖息地偏好。在始新世期间发生了第一次主要分裂，产生了非洲雨林和马达加斯加热带稀树草原两个谱系。随着始新世期间非洲气候和植被类型变得更加干燥，Daniellia 进化枝祖先的一种适应干旱气候的谱系可能已经通过适宜的热带稀树草原或林地传播到马达加斯加，随后在中新世产生了 Brandzeia 和 Neoapaloxylon 的适应热带稀树草原的祖先。非洲雨林谱系产生了 Daniellia 属，该属被推测首先在中新世多样化，而 Daniellia 的热带稀树草原物种在更新世独立出现，与全球 C4 主导的草原的兴起相一致。Daniellia 进化枝中有一半以上的物种处于近危或受威胁状态，这突出表明需要了解这些物种面临的人为压力和气候变化的威胁，以便确定其保护的优先次序。
