PDF(Pubmed)
Abstract：
The southern coast of Africa is one of the few places in the world where water temperatures are predicted to cool in the future. This endemism-rich coastline is home to two sister species of kelps of the genus Ecklonia maxima and Ecklonia radiata, each associated with specific thermal niches, and occuring primarily on opposite sides of the southern tip of Africa. Historical distribution records indicate that E. maxima has recently shifted its distribution ~ 70 km eastward, to sites where only E. radiata was previously reported. The contact of sister species with contrasting thermal affinities and the occurrence of mixed morphologies raised the hypothesis that hybridization might be occurring in this contact zone. Here we describe the genetic structure of the genus Ecklonia along the southern coast of Africa and investigate potential hybridization and cryptic diversity using a combination of nuclear microsatellites and mitochondrial markers. We found that both species have geographically discrete genetic clusters, consistent with expected phylogeographic breaks along this coastline. In addition, depth-isolated populations were found to harbor unique genetic diversity, including a third Ecklonia lineage. Mito-nuclear discordance and high genetic divergence in the contact zones suggest multiple hybridization events between Ecklonia species. Discordance between morphological and molecular identification suggests the potential influence of abiotic factors leading to convergent phenotypes in the contact zones. Our results highlight an example of cryptic diversity and hybridization driven by contact between two closely related keystone species with contrasting thermal affinities.
摘要：
非洲南部海岸是世界上少数几个预测未来水温会变冷的地方之一。这种特有性丰富的海岸线是两种姐妹海带的家园，它们是埃克洛尼亚属和埃克洛尼亚属的海带，每个都与特定的热生态位相关，主要发生在非洲南端的两侧。历史分布记录表明，E.maxima最近已将其分布向东移动约70公里，以前只报道了辐射大肠杆菌的地点。姐妹物种与热亲和力形成鲜明对比的接触以及混合形态的出现提出了这样的假设，即在该接触区可能发生杂交。在这里，我们描述了非洲南部沿海Ecklonia属的遗传结构，并使用核微卫星和线粒体标记的组合研究了潜在的杂交和隐秘的多样性。我们发现这两个物种都有地理上离散的遗传簇，与沿该海岸线的预期系统地理中断一致。此外,发现深度隔离的种群具有独特的遗传多样性，包括第三个埃克洛尼亚血统。线粒体核不一致和接触区的高度遗传差异表明Ecklonia物种之间发生了多次杂交事件。形态学和分子鉴定之间的不一致表明，非生物因素的潜在影响导致接触区中表型趋同。我们的结果突出了一个秘密多样性和杂交的例子，该例子是由两个密切相关的基石物种之间的接触驱动的，具有相反的热亲和力。
