Royal Museum for Central Africa, Biology Department, Section Vertebrates, Tervuren, Belgium.
Université Libre de Bruxelles, Faculté des Sciences, Service Evolution Biologique et Ecologie, Bruxelles, Belgium.
Am J Bot. 2024 Jun;111(6):e16352. doi: 10.1002/ajb2.16352. Epub 2024 Jun 9.
Phylogenetic approaches can provide valuable insights on how and when a biome emerged and developed using its structuring species. In this context, Brachystegia Benth, a dominant genus of trees in miombo woodlands, appears as a key witness of the history of the largest woodland and savanna biome of Africa.
We reconstructed the evolutionary history of the genus using targeted-enrichment sequencing on 60 Brachystegia specimens for a nearly complete species sampling. Phylogenomic inferences used supermatrix (RAxML-NG) and summary-method (ASTRAL-III) approaches. Conflicts between species and gene trees were assessed, and the phylogeny was time-calibrated in BEAST. Introgression between species was explored using Phylonet.
The phylogenies were globally congruent regardless of the method used. Most of the species were recovered as monophyletic, unlike previous plastid phylogenetic reconstructions where lineages were shared among geographically close individuals independently of species identity. Still, most of the individual gene trees had low levels of phylogenetic information and, when informative, were mostly in conflict with the reconstructed species trees. These results suggest incomplete lineage sorting and/or reticulate evolution, which was supported by network analyses. The BEAST analysis supported a Pliocene origin for current Brachystegia lineages, with most of the diversification events dated to the Pliocene-Pleistocene.
These results suggest a recent origin of species of the miombo, congruently with their spatial expansion documented from plastid data. Brachystegia species appear to behave potentially as a syngameon, a group of interfertile but still relatively well-delineated species, an aspect that deserves further investigations.
系统发育方法可以提供有价值的见解，了解生物群落是如何以及何时形成和发展的，以及利用其结构物种。在这种情况下，Bra chystegia Benth 是 miombo 林地中占优势的树种属，它是非洲最大的林地和热带稀树草原生物群落历史的重要见证者。
我们使用针对 60 个 Brachystegia 标本进行靶向富集测序，对该属进行了进化历史重建，实现了近乎完整的物种采样。系统发育推断使用了超级矩阵（RAxML-NG）和汇总方法（ASTRAL-III）。评估了物种和基因树之间的冲突，并在 BEAST 中对系统发育进行了时间校准。使用 Phylonet 探索了物种间的基因渗入。
无论使用哪种方法，系统发育都是全球一致的。大多数物种都被恢复为单系，这与以前的质体系统发育重建不同，在以前的重建中，地理上接近的个体之间的谱系共享与物种身份无关。尽管如此，大多数个体基因树的系统发育信息量较低，而且在具有信息量时，主要与重建的物种树存在冲突。这些结果表明不完全谱系分选和/或网状进化，这得到了网络分析的支持。BEAST 分析支持 Brachystegia 现生谱系起源于上新世，大多数多样化事件的日期为上新世-更新世。
这些结果表明，miombo 的物种起源较近，与从质体数据记录的它们的空间扩张相一致。Brachystegia 物种似乎表现出潜在的合种行为，即一组可杂交但仍相对明确界定的物种，这一方面值得进一步研究。
