School of Biological Sciences, The University of Western Australia, Perth, WA 6009, Australia; Aquatic Zoology & Molecular Systematics Unit, Western Australian Museum, Welshpool, WA 6106, Australia.
Department of Invertebrate Zoology & Geology, California Academy of Sciences, San Francisco, CA 94118, USA.
Mol Phylogenet Evol. 2018 Jul;124:27-36. doi: 10.1016/j.ympev.2018.02.008. Epub 2018 Feb 21.
Chromodoris is a genus of colourful nudibranchs that feed on sponges and is found across the Indo-Pacific. While this was once the most diverse chromodorid genus, recent work has shown that the genus should be restricted to a monophyletic lineage that contains only 22 species, all of which exhibit black pigmentation and planar spawning behaviour. Earlier phylogenies of this group are poorly resolved and thus additional work is needed to clarify species boundaries within Chromodoris. This study presents a maximum-likelihood phylogeny based on mitochondrial loci (COI, 16S) for 345 Chromodoris specimens, including data from 323 new specimens and 22 from GenBank, from across the Indo-Pacific. Species hypotheses and phylogenetic analysis uncovered 39 taxa in total containing 18 undescribed species, with only five of 39 taxa showing stable colour patterns and distinct morphotypes. This study also presents the first evidence for regional mimicry in this genus, with C. colemani and C. joshi displaying geographically-based variation in colour patterns which appear to match locally abundant congenerics, highlighting the flexibility of these colour patterns in Chromodoris nudibranchs. The current phylogeny contains short branch lengths, polytomies and poor support at interior nodes, which is indicative of a recent radiation. As such, future work will employ a transcriptome-based exon capture approach for resolving the phylogeny of this group. In all, this study included 21 of the 22 described species in the Chromodoris sensu stricto group with broad sampling coverage from across the Indo-Pacific, constituting the most comprehensive sampling of this group to date. This work highlights several cases of undocumented diversity, ultimately expanding our knowledge of species boundaries in this group, while also demonstrating the limitations of colour patterns for species identification in this genus.
双色海牛是一类以海绵为食的色彩鲜艳的裸鳃类动物，分布于印度-太平洋地区。虽然这曾经是最具多样性的双色海牛属，但最近的研究表明，该属应仅限于一个单系谱系，其中只包含 22 个物种，所有这些物种都表现出黑色色素沉着和平板产卵行为。该类群的早期系统发育关系分辨率较差，因此需要进一步的工作来澄清双色海牛属内的物种界限。本研究基于线粒体基因座（COI、16S）为 345 个双色海牛标本构建了最大似然系统发育树，包括来自印度-太平洋地区的 323 个新标本和 22 个来自 GenBank 的数据。物种假说和系统发育分析总共发现了 39 个分类群，其中包含 18 个未描述的物种，只有 39 个分类群中的 5 个表现出稳定的颜色模式和明显的形态型。本研究还首次为该属的区域性模拟提供了证据，C. colemani 和 C. joshi 表现出基于地理的颜色模式变化，这些变化似乎与当地丰富的近缘种相匹配，突出了这些双色海牛裸鳃类动物颜色模式的灵活性。当前的系统发育树包含短分支长度、多系群和内部节点的支持度差，这表明最近发生了辐射。因此，未来的工作将采用基于转录组的外显子捕获方法来解决该组的系统发育关系。总的来说，本研究包括了 22 个描述的双色海牛属物种中的 21 个，以及来自印度-太平洋地区的广泛采样，是迄今为止对该组最全面的采样。这项工作突出了一些未记录的多样性案例，最终扩大了我们对该组物种界限的认识，同时也表明了颜色模式在该属物种鉴定中的局限性。
