Molecular phylogenetics reveal multiple tertiary vicariance origins of the African rain forest trees
Molecular phylogenetics reveal multiple tertiary vicariance origins of the African rain forest trees
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DOI：
10.1186/1741-7007-6-54
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发表时间：
2008-12-16
期刊：
影响因子：
5.4
通讯作者：
Richardson, James E.
中科院分区：
文献类型：
--
作者：
Couvreur, Thomas L. P.;Chatrou, Lars W.;Richardson, James E.
热带雨林是地球上最具多样性的陆地生态系统。这种多样性是如何演变的，在很大程度上仍然无法解释。在非洲，雨林分布在两个地理上相互隔离的区域：几内亚-刚果中西部区域和东非沿海和山区区域。这些地区彼此之间有很强的植物区系亲缘关系，这表明它们以前通过始新世泛非洲雨林联系在一起。在这两个地区观察到的高水平的特有现象被假设是1）一个单一的分裂，然后是一个长期的隔离或2）自渐新世以来的多次分裂和重新连接的结果。为了验证这些假设，研究了热带雨林中特有类群的进化历史，限制了番荔枝科植物的非洲谱系。估计使用贝叶斯放松不相关的分子钟假设校准和系统发育的不确定性。结果：我们的研究结果提供了强有力的证据表明，东非特有的番荔枝科谱系有多个起源日期显着不同的时间跨越渐新世和中新世epochs。此外，这些连续的起源（C。3300万年、1600万年和800万年（Myr）与非洲已知的干旱化和地质活动时期相吻合，这些时期将使几内亚-刚果雨林与东非雨林相分离。所有东非类群被发现有多样化的更新世times.Conclusion：分子系统发育年代分析，这个大泛非洲的番荔枝科分支揭开了一个有趣的模式，多样化的雨林限制树木共同发生在西部/中部和东部非洲雨林。我们的研究结果表明，西部/中部和东部非洲雨林块之间的反复重新连接允许生物交换，而分手诱导物种通过vicariance，提高地方性的水平。这些结果提供了一个解释，今天的分布格局和起源的地方性非洲雨林树木。此外，鉴于所有研究的地方性东非属和物种的前更新世起源，这些结果也提供了重要的见解，在这些高度多样化，但受到威胁的生态系统设置保护的优先事项。
Background: Tropical rain forests are the most diverse terrestrial ecosystems on the planet. How this diversity evolved remains largely unexplained. In Africa, rain forests are situated in two geographically isolated regions: the West-Central Guineo-Congolian region and the coastal and montane regions of East Africa. These regions have strong floristic affinities with each other, suggesting a former connection via an Eocene pan-African rain forest. High levels of endemism observed in both regions have been hypothesized to be the result of either 1) a single break-up followed by a long isolation or 2) multiple fragmentation and reconnection since the Oligocene. To test these hypotheses the evolutionary history of endemic taxa within a rain forest restricted African lineage of the plant family Annonaceae was studied. Molecular phylogenies and divergence dates were estimated using a Bayesian relaxed uncorrelated molecular clock assumption accounting for both calibration and phylogenetic uncertainties.Results: Our results provide strong evidence that East African endemic lineages of Annonaceae have multiple origins dated to significantly different times spanning the Oligocene and Miocene epochs. Moreover, these successive origins (c. 33, 16 and 8 million years-Myr) coincide with known periods of aridification and geological activity in Africa that would have recurrently isolated the Guineo-Congolian rain forest from the East African one. All East African taxa were found to have diversified prior to Pleistocene times.Conclusion: Molecular phylogenetic dating analyses of this large pan-African clade of Annonaceae unravels an interesting pattern of diversification for rain forest restricted trees co-occurring in West/Central and East African rain forests. Our results suggest that repeated reconnections between the West/Central and East African rain forest blocks allowed for biotic exchange while the break-ups induced speciation via vicariance, enhancing the levels of endemicity. These results provide an explanation for present day distribution patterns and origins of endemicity for African rain forest trees. Moreover, given the pre-Pleistocene origins of all the studied endemic East African genera and species, these results also offer important insights for setting conservation priorities in these highly diversified but threatened ecosystems.