Divergence within and among Seaweed Siblings (Fucus vesiculosus and F. radicans) in the Baltic Sea.
Divergence within and among Seaweed Siblings (Fucus vesiculosus and F. radicans) in the Baltic Sea.
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DOI：
10.1371/journal.pone.0161266
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发表时间：
2016
期刊：
影响因子：
3.7
通讯作者：
Johannesson K
中科院分区：
文献类型：
--
作者：
Ardehed A;Johansson D;Sundqvist L;Schagerström E;Zagrodzka Z;Kovaltchouk NA;Bergström L;Kautsky L;Rafajlovic M;Pereyra RT;Johannesson K
密切相关的分类群为理解新物种的进化提供了重要的案例研究，但同时也可能挑战物种的鉴定和定义。在波罗的海，两种主要的和多年生的褐藻有着非常近的祖先。在8000年前，水袋墨角藻侵入了这片新近形成的冰川后海洋，此后不久，墨角藻从这一分支中分化出来，成为一种特有物种。在波罗的海，这两个物种都有性繁殖，但也通过无性分裂招募完全可育的新个体。早期的研究表明，在波斯尼亚海的北部和西部，以及爱沙尼亚的萨雷马岛周围，这两个分类群在形态和遗传学上存在局部差异，但地理模式似乎与F. radicans的单一起源相冲突。为了研究北部和爱沙尼亚分布之间的关系，我们利用9个微卫星位点分析了来自东波斯尼亚海、群岛海和芬兰湾种群的遗传变异。这些种群位于之前研究过的种群之间。然而，新种群并没有像简单的距离隔离模型所预期的那样，弥合西北波西尼亚海和爱沙尼亚之间截然不同的遗传差距，而是大大增加了总体遗传多样性，并显示出与先前分析的两个区域有很大的差异，显示出额外不同种群的迹象。与之前发现的在波黑海低盐度环境下无性繁殖增加的结果相比，我们发现芬兰湾一些生活在极低盐度环境中的种群有性繁殖水平很高。这项研究中产生的新数据支持了两个生殖隔离但非常密切相关的物种的早期结论。然而，新的结果也增加了物种内部相当大的遗传和形态复杂性。这使得物种在地理尺度上的分离更加困难，并表明需要更全面的方法来进一步解开波罗的海岩藻的有趣关系和历史。
Closely related taxa provide significant case studies for understanding evolution of new species but may simultaneously challenge species identification and definition. In the Baltic Sea, two dominant and perennial brown algae share a very recent ancestry. Fucus vesiculosus invaded this recently formed postglacial sea 8000 years ago and shortly thereafter Fucus radicans diverged from this lineage as an endemic species. In the Baltic Sea both species reproduce sexually but also recruit fully fertile new individuals by asexual fragmentation. Earlier studies have shown local differences in morphology and genetics between the two taxa in the northern and western Bothnian Sea, and around the island of Saaremaa in Estonia, but geographic patterns seem in conflict with a single origin of F. radicans. To investigate the relationship between northern and Estonian distributions, we analysed the genetic variation using 9 microsatellite loci in populations from eastern Bothnian Sea, Archipelago Sea and the Gulf of Finland. These populations are located in between earlier studied populations. However, instead of bridging the disparate genetic gap between N-W Bothnian Sea and Estonia, as expected from a simple isolation-by-distance model, the new populations substantially increased overall genetic diversity and showed to be strongly divergent from the two earlier analysed regions, showing signs of additional distinct populations. Contrasting earlier findings of increased asexual recruitment in low salinity in the Bothnian Sea, we found high levels of sexual reproduction in some of the Gulf of Finland populations that inhabit extremely low salinity. The new data generated in this study supports the earlier conclusion of two reproductively isolated but very closely related species. However, the new results also add considerable genetic and morphological complexity within species. This makes species separation at geographic scales more demanding and suggests a need for more comprehensive approaches to further disentangle the intriguing relationship and history of the Baltic Sea fucoids.