Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK.
Ann Bot. 2013 Jul;112(1):151-60. doi: 10.1093/aob/mct106. Epub 2013 May 30.
Paleoclimatic data indicate that an abrupt climate change occurred at the Eocene-Oligocene (E-O) boundary affecting the distribution of tropical forests on Earth. The same period has seen the emergence of South-East (SE) Asia, caused by the collision of the Eurasian and Australian plates. How the combination of these climatic and geomorphological factors affected the spatio-temporal history of angiosperms is little known. This topic is investigated by using the worldwide sapindaceous clade as a case study.
Analyses of divergence time inference, diversification and biogeography (constrained by paleogeography) are applied to a combined plastid and nuclear DNA sequence data set. Biogeographical and diversification analyses are performed over a set of trees to take phylogenetic and dating uncertainty into account. Results are analysed in the context of past climatic fluctuations.
An increase in the number of dispersal events at the E-O boundary is recorded, which intensified during the Miocene. This pattern is associated with a higher rate in the emergence of new genera. These results are discussed in light of the geomorphological importance of SE Asia, which acted as a tropical bridge allowing multiple contacts between areas and additional speciation across landmasses derived from Laurasia and Gondwana.
This study demonstrates the importance of the combined effect of geomorphological (the emergence of most islands in SE Asia approx. 30 million years ago) and climatic (the dramatic E-O climate change that shifted the tropical belt and reduced sea levels) factors in shaping species distribution within the sapindaceous clade.
古气候数据表明，始新世-渐新世（E-O）边界发生了一次突然的气候变化，影响了地球上热带森林的分布。同一时期，由于欧亚板块和澳大利亚板块的碰撞，东南亚（SE）出现了。这些气候和地貌因素的结合如何影响被子植物的时空历史鲜为人知。本研究以全球无患子族为研究案例，对此进行了探讨。
采用叶绿体和核 DNA 联合序列数据集，进行了分歧时间推断、多样化和生物地理学（受古地理约束）分析。对一组树进行了生物地理学和多样化分析，以考虑系统发育和年代测定的不确定性。结果在过去气候波动的背景下进行了分析。
记录到 E-O 边界处的扩散事件数量增加，在中新世期间加剧。这种模式与新属出现的更高速度有关。这些结果与东南亚地貌的重要性有关，东南亚作为热带桥梁，允许多个地区之间的多次接触，并在从劳亚古陆和冈瓦纳古陆衍生的陆地上增加了物种形成。
本研究表明，地貌因素（东南亚大部分岛屿约 3000 万年前的出现）和气候因素（剧烈的 E-O 气候变化，改变了热带带和降低海平面）的综合效应在塑造无患子族内物种分布方面具有重要意义。
