Genetic diversity in the <i>Diplosoma listerianum</i> complex (Ascidiacea: Didemnidae) from the Western Atlantic

(Received 19 January 2021; revised 27 September 2021; accepted 27 September 2021) <i>Diplosoma listerianum</i> has been re-described with more than 40 currently invalid names, but recent data suggests that some of those names may be valid. At least four distinct clades were recently revealed by molecular analysis using mitochondrial DNA (mtDNA). Yet, very few samples were analyzed from the western Atlantic, of which none were from the extensive Brazilian coast. Here, we analyze genetic diversity in <i>D. listerianum</i> in light of morphological data. We sequenced 55 samples from Brazil, Panama, Mexico, and the United States and analyzed them together with published data, to test whether local populations are part of widespread, known, clades or are native species hidden within this complex. Phylogenetic analysis found eight clades, three of which were different from the ones recovered before. Former clade A was split into two larger clades: clade A1 occurs in the western Atlantic, on the Pacific side of Panama and in South Africa; clade A2 occurs worldwide, with representatives found on every continent. Species delimitation analyses (ABGD, bPTP and GMYC) found 16 MOTUs, which suggests that those large clades are very diverse and may comprise more than one species. Diversity was greatest in Panama (6 clades) and Mexico (3 clades). Larval morphological characters were examined and described here. However, for only a few of the sequenced samples could fully grown larvae be obtained and phenotypic variation was large. Thus, larval morphology could not be used to diagnose molecular clades. <i>Diplosoma listerianum</i> remains a species complex, with evidence of ongoing speciation, and high genetic diversity, especially in the tropical western Atlantic. Fast-growing colonies, rapid life cycles, and amenability to cultivation in the laboratory indicate that this species can be a model for studies in speciation.

(2021年1月19日收稿；2021年9月27日修回；2021年9月27日录用) 利斯尔双海鞘（*Diplosoma listerianum*）曾被重新描述，并关联了40余个当前已无效的学名，但近期研究数据表明其中部分学名可能仍有效。近期基于线粒体DNA（mtDNA）的分子分析已揭示至少4个独立演化支。然而，针对西大西洋的分析样本极少，且未包含巴西广阔沿岸海域的样品。本研究结合形态学数据，对利斯尔双海鞘的遗传多样性展开分析。我们对采集自巴西、巴拿马、墨西哥及美国的55份样品进行了测序，并结合已发表数据开展联合分析，以验证当地种群是否隶属于已被广泛报道的已知演化支，或是隐藏在该物种复合群中的本土物种。系统发育分析共鉴定出8个演化支，其中3个为此前未被报道的新支系。原演化支A被拆分为两个更大的支系：演化支A1分布于西大西洋、巴拿马太平洋沿岸及南非海域；演化支A2则为广布类群，在各大陆均有分布记录。物种界定分析（ABGD、bPTP及GMYC）共识别出16个分子操作分类单元（Molecular Operational Taxonomic Unit, MOTU），表明上述大型演化支具有极高的多样性，可能包含多个隐存物种。遗传多样性最为丰富的区域为巴拿马（涵盖6个演化支）与墨西哥（涵盖3个演化支）。本研究对该物种的幼体形态特征进行了观察与描述，但仅从少量测序样品中成功获取到完全发育的幼体，且表型变异幅度较大。因此，幼体形态特征无法用于区分分子演化支。利斯尔双海鞘仍属于物种复合群，存在持续物种形成的证据，且具有极高的遗传多样性，尤其在热带西大西洋海域。该物种具有生长迅速的群体、短暂的生活周期以及易于实验室培养的特性，使其可作为物种形成研究的模式生物。

搜集汇总

背景与挑战

背景概述

该数据集聚焦于西大西洋的Diplosoma listerianum复合体的遗传多样性研究，通过对55个样本的分子和形态学分析，揭示了八个遗传分支（包括三个新分支）和潜在的多个隐藏物种，表明该物种具有高遗传多样性和持续物种形成过程。研究强调了热带西大西洋地区（如巴拿马和墨西哥）的多样性最高，并指出该物种可作为物种形成研究的模型。