Knutson Vanessa L, Gosliner Terrence M
California Academy of Sciences, Golden Gate Park, 55 Music Concourse Drive, San Francisco, CA 94118, USA.
California Academy of Sciences, Golden Gate Park, 55 Music Concourse Drive, San Francisco, CA 94118, USA.
Mol Phylogenet Evol. 2022 Jun;171:107470. doi: 10.1016/j.ympev.2022.107470. Epub 2022 Mar 28.
Nudibranchs are charismatic marine gastropods that lack a shell in the adult stage. While most nudibranchs feed on sessile animals such as sponges, bryozoans, and cnidarians, the nudibranch genus Gymnodoris Stimpson, 1855 evolved a more active and predatory lifestyle, including sea slug predation, cannibalism, and oddly enough, fish-fin parasitism. At the beginning of our work, no phylogenetic hypothesis existed for the genus, nor a clear picture of how Gymnodoris is related to other nudibranchs. Here we set out to reconstruct Gymnodoris phylogeny, investigate species diversity, and clarify the status of the genus name Analogium, which had been proposed for members of the genus with a linear gill filament arrangement. We present the first phylogenetic hypothesis for Gymnodoris, reconstructed by maximum likelihood and Bayesian inference using two mitochondrial and two nuclear loci, with gill filament arrangement plotted on the phylogeny. The backbone of the phylogeny remains unresolved with theseloci, however, we found that Gymnodoris comprises three main well-supported clades, which we refer to as the "subornata", "citrina" and "varied" clade, the latter two clades being comprised of several well-supported subclades. The sister group to Gymnodoris is a clade including the genera Vayssierea and Lecithophorus. Based on ABGD and PTP species delimitation methods, we conservatively estimate 65-70 species comprise our dataset. We further estimate that approximately 81% of the species we sampled are undescribed, and note that a linear gill filament arrangement has evolved multiple times within the genus. Gymnodoris is only monophyletic when the species with a linear gill arrangement are included. Therefore, at this time, we agree with the synonymy of Analogium striata with Gymnodoris striata by Rudman and Darvell (1990) and that the genus name Analogium is warranted as a junior synonym of Gymnodoris. Given the extensive undescribed diversity, and lack of resolution at some of the nodes in the phylogeny, patterns of diversification in diet are impossible to discern at this time and will require a large effort to both describe Gymnodoris species diversity and the diets of these candidate species.
裸鳃亚目动物是一类具有魅力的海洋腹足纲动物，成年后无外壳。虽然大多数裸鳃亚目动物以固着生物为食，如海绵、苔藓虫和刺胞动物，但裸鳃亚目动物裸鳃属（Gymnodoris）在1855年由斯廷普森命名，进化出了更为活跃的捕食性生活方式，包括捕食海蛞蝓、同类相食，以及奇怪的是，寄生在鱼鳍上。在我们的研究开始时，对于该属没有系统发育假说，也不清楚裸鳃属与其他裸鳃亚目动物的关系。在这里，我们着手重建裸鳃属的系统发育，调查物种多样性，并澄清曾被提议用于具有线性鳃丝排列的该属成员的属名“Analogium”的地位。我们提出了第一个关于裸鳃属的系统发育假说，通过使用两个线粒体和两个核基因座的最大似然法和贝叶斯推断进行重建，并将鳃丝排列绘制在系统发育树上。然而，这些基因座并未解决系统发育树的主干问题，我们发现裸鳃属包括三个主要的、得到有力支持的分支，我们将其称为“subornata”、“citrina”和“varied”分支，后两个分支由几个得到有力支持的亚分支组成。裸鳃属的姐妹群是一个包括Vayssierea属和Lecithophorus属的分支。基于ABGD和PTP物种界定方法，我们保守估计我们的数据集中有65 - 70个物种。我们进一步估计，我们采样的物种中约81%尚未被描述，并注意到线性鳃丝排列在该属内已经多次进化。只有当具有线性鳃排列的物种被包括在内时，裸鳃属才是单系的。因此，目前我们同意鲁德曼和达维尔（1990年）将条纹Analogium与条纹裸鳃属同义的观点，并且属名Analogium作为裸鳃属的次异名是合理的。鉴于广泛存在未被描述的多样性，以及系统发育中某些节点缺乏分辨率，目前无法辨别饮食的多样化模式，这将需要付出巨大努力来描述裸鳃属的物种多样性以及这些候选物种的饮食。
