Press release_RSBL-2019-0182_R2.odt from A global metabarcoding analysis expands molecular diversity of Platyhelminthes and reveals novel early-branching clades

Understanding biological diversity is crucial for ecological and evolutionary studies. Even though a great part of animal diversity has already been documented, both morphological surveys and metabarcoding analyses have previously shown that some animal groups, such as Platyhelminthes, may harbour hidden diversity. To better understand the molecular diversity of Platyhelminthes, one of the most diverse and biomedically important animal phyla, we here combined data from six marine and two freshwater metabarcoding expeditions that cover a broad variety of aquatic habitats and analysed the data by phylogenetic placement. Our results show that a great part of the hidden diversity is located in early-branching clades such as Catenulida and Macrostomorpha, as well as in late-diverging clades such as Proseriata and Rhabdocoela. We also report the first freshwater record of Gnosonesimida, a group previously thought to be exclusively marine. Finally, we identified two putative novel freshwater platyhelminth clades that branch between well-defined orders of the phylum. Thus, our analyses of several environmental datasets confirm that a large part of the diversity of Platyhelminthes remains undiscovered, point to groups with more potential novel species and identify freshwater environments as potential reservoirs for novel species of flatworms.

解析生物多样性对于生态学与进化生物学研究至关重要。尽管多数动物类群的多样性已被文献记录，但此前的形态学调查与宏条形码（metabarcoding）分析均证实，部分动物类群——如扁形动物门（Platyhelminthes）——存在大量隐存多样性。作为物种多样性极为丰富且在生物医学领域具有重要价值的动物门之一，扁形动物门的分子多样性亟待深入解析。为此，本研究整合了覆盖多样水生生境的6项海洋宏条形码科考与2项淡水宏条形码科考数据，并通过系统发育定位（phylogenetic placement）分析对数据进行了处理。研究结果显示，大量隐存多样性分布于早期分化的演化支，如链涡虫目（Catenulida）与大口目（Macrostomorpha），以及晚期分化的演化支，如原卵黄目（Proseriata）与杆吻目（Rhabdocoela）。此外，本研究首次报道了此前被认为仅为海洋类群的Gnosonesimida的淡水分布记录。最后，本研究在该门的明确目级类群之间，鉴定出两个疑似新的淡水扁形动物演化支。综上，本研究对多份环境数据集的分析证实，扁形动物门仍有大量多样性尚未被发现，指出了存在更多新物种潜力的类群，并明确淡水生境可作为扁形动物新物种的潜在储库。