Sessa Emily B, Juslén Aino, Väre Henry, Chambers Sally M
Department of Biology, University of Florida, Gainesville, Florida 32611 USA
Genetics Institute, University of Florida, Gainesville, Florida 32611 USA.
Am J Bot. 2017 Mar;104(3):477-486. doi: 10.3732/ajb.1600392. Epub 2017 Mar 21.
Our goal was to infer the phylogenetic relationships and historical biogeography of the genus with a focus on taxa in sub-Saharan Africa and neighboring islands. In general, little is known about the relationships between African fern species and their congeners in other geographic regions, and our aim was to determine whether the sub-Saharan African species of are monophyletic and evolved within Africa or arrived there via repeated dispersals into Africa from other regions.
We obtained sequence data for five chloroplast markers from 214 species of and 18 outgroups. We performed phylogenetic and molecular dating analyses using a Bayesian relaxed clock method in BEAST with fossil and secondary calibration points and estimated ancestral ranges for the genus globally by comparing multiple models in BioGeoBEARS.
We found that 22 of 27 accessions of sub-Saharan African belong to a large clade of 31 accessions that also includes taxa from Indian and Atlantic Ocean islands. Additional accessions of taxa from our regions of interest have Asian, Hawaiian, European, or North American species as their closest relatives.
The majority of sub-Saharan African species are descended from a shared common ancestor that dispersed to Africa from Asia approximately 10 Ma. There have been subsequent dispersal events from the African mainland to islands in the Atlantic and Indian Oceans, including Madagascar. Several additional species are estimated to have descended from ancestors that reached Africa via separate events over the last roughly 20 million years.
我们的目标是推断该属的系统发育关系和历史生物地理学，重点关注撒哈拉以南非洲及邻近岛屿的分类群。总体而言，对于非洲蕨类植物物种与其在其他地理区域的同属物种之间的关系知之甚少，我们的目的是确定撒哈拉以南非洲的该属物种是否为单系类群，是在非洲进化而来还是通过从其他区域反复扩散到非洲而到达那里。
我们从该属的214个物种和18个外类群中获取了五个叶绿体标记的序列数据。我们在BEAST中使用贝叶斯松弛时钟方法进行系统发育和分子年代分析，并设置了化石和二级校准点，通过在BioGeoBEARS中比较多个模型来估计该属在全球范围内的祖先分布范围。
我们发现，撒哈拉以南非洲该属的27个样本中有22个属于一个包含31个样本的大分支，其中还包括来自印度洋和大西洋岛屿的分类群。我们感兴趣区域的其他分类群样本的最近亲缘种为亚洲、夏威夷、欧洲或北美洲的物种。
撒哈拉以南非洲该属的大多数物种都起源于一个共同的祖先，该祖先大约在1000万年前从亚洲扩散到非洲。随后发生了从非洲大陆到包括马达加斯加在内的大西洋和印度洋岛屿的扩散事件。估计还有几个物种起源于在过去大约2000万年中通过不同事件到达非洲的祖先。
