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Cryptic diversity in smooth-shelled mussels on Southern Ocean islands: connectivity, hybridisation and a marine invasion
Frontiers in Zoology ( IF 2.8 ) Pub Date : 2019-08-06 , DOI: 10.1186/s12983-019-0332-y
Małgorzata Zbawicka 1 , Jonathan P A Gardner 2 , Roman Wenne 1
Affiliation  

Large numbers of endemic species inhabit subantarctic continental coasts and islands that are characterised by highly variable environmental conditions. Southern hemisphere populations of taxa that are morphologically similar to northern counterparts have traditionally been considered to be extensions of such Northern hemisphere taxa, and may not exhibit differentiation amongst geographically isolated populations in the Southern Ocean. Smooth-shelled blue mussels of the genus Mytilus that exhibit an anti-tropical distribution are a model group to study phylogeography, speciation and hybridisation in the sea, and contribute to the theory and practice of marine biosecurity. We used a single nucleotide polymorphism (SNPs) panel that has the ability to accurately identify reference Northern and Southern hemisphere Mytilus taxa to test for evolutionary differentiation amongst native Southern Ocean island populations. Native mussels from the Falkland Islands and the Kerguelen Islands exhibited greatest affinity to native M. platensis d’Orbigny 1846 from the Atlantic coast of South America. The major Southern Ocean current flow from west to east is likely to explain the spreading of M. platensis to remote offshore islands, as adults via the process of rafting or perhaps directly as larvae. SNPs variation revealed that mussels from Tasmania were native and clearly differentiated from all other blue mussel groups in the Southern and Northern hemispheres. The native mussels M. planulatus from Tasmania and from mainland New Zealand (NZ), and tentatively M. aoteanus from the two NZ Southern Ocean offshore island groups (the Auckland Islands and Campbell Island), formed a distinct M. galloprovincialis–like Southern hemisphere group with closest affinity to Northern hemisphere M. galloprovincialis from the Mediterranean Sea. In all cases, the SNPs revealed evidence of hybridisation between two or more distinct taxa. The invasive Northern hemisphere M. galloprovincialis was identified only in Tasmania, amongst native mussels of a distinct Australian M. planulatus lineage. Overall, our results reveal that Southern hemisphere island mussels have mixed genome ancestry and are native, not introduced by human activities. The preservation of distinct evolutionary lineages of Southern hemisphere species needs to be an ongoing focus of conservation efforts, given that population sizes on some of the remote offshore oceanic islands will be small and may be more easily adversely affected by invasion and subsequent hybridisation and introgression than larger populations elsewhere.

中文翻译:

南大洋岛屿光滑壳贻贝的神秘多样性:连通性、杂交和海洋入侵

大量特有物种栖息在亚南极大陆海岸和岛屿,其特点是环境条件高度可变。在形态上与北部同类群相似的南半球类群种群传统上被认为是此类北半球类群的延伸,并且可能不会在南大洋地理上孤立的种群之间表现出差异。表现出反热带分布的贻贝属光滑壳蓝贻贝是研究海洋系统地理学、物种形成和杂交的模型组,并有助于海洋生物安全的理论和实践。我们使用了一个单核苷酸多态性 (SNP) 面板,该面板能够准确识别参考北半球和南半球 Mytilus 类群,以测试南大洋本土岛屿种群之间的进化分化。来自福克兰群岛和凯尔盖伦群岛的本地贻贝对来自南美洲大西洋沿岸的本地 M. platensis d'Orbigny 1846 表现出最大的亲和力。主要的南大洋洋流从西向东流动很可能解释了 M. platensis 作为成年人通过漂流过程或直接作为幼虫传播到偏远的近海岛屿。SNP 变异表明,来自塔斯马尼亚的贻贝是本地的,并且明显区别于南半球和北半球的所有其他蓝贻贝群。本地贻贝 M. 来自塔斯马尼亚岛和新西兰大陆 (NZ) 的 planulatus,以及来自新西兰南大洋两个近海岛屿群(奥克兰群岛和坎贝尔岛)的暂定 M. aoteanus,形成了一个独特的 M. galloprovincialis 类南半球群,与来自地中海的北半球 M. galloprovincialis。在所有情况下,SNP 揭示了两个或多个不同分类群之间杂交的证据。侵入性的北半球 M. galloprovincialis 仅在塔斯马尼亚州被发现,在独特的澳大利亚 M. planulatus 谱系的本地贻贝中。总体而言,我们的研究结果表明,南半球岛贻贝具有混合基因组血统,并且是原生的,不是由人类活动引入的。
更新日期:2020-04-22
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