Sigwart Julia D, Lindberg David R
Marine Laboratory, Queen's University Belfast, BT22 1PF, Northern Ireland, UK; and Department of Integrative Biology, Museum of Paleontology and Center for Computational Biology, University of California, Berkeley, CA, 94720, USA
Marine Laboratory, Queen's University Belfast, BT22 1PF, Northern Ireland, UK; and Department of Integrative Biology, Museum of Paleontology and Center for Computational Biology, University of California, Berkeley, CA, 94720, USA.
Syst Biol. 2015 May;64(3):384-95. doi: 10.1093/sysbio/syu105. Epub 2014 Dec 2.
Mollusks are the most morphologically disparate living animal phylum, they have diversified into all habitats, and have a deep fossil record. Monophyly and identity of their eight living classes is undisputed, but relationships between these groups and patterns of their early radiation have remained elusive. Arguments about traditional morphological phylogeny focus on a small number of topological concepts but often without regard to proximity of the individual classes. In contrast, molecular studies have proposed a number of radically different, inherently contradictory, and controversial sister relationships. Here, we assembled a data set of 42 unique published trees describing molluscan interrelationships. We used these data to ask several questions about the state of resolution of molluscan phylogeny compared with a null model of the variation possible in random trees constructed from a monophyletic assemblage of eight terminals. Although 27 different unique trees have been proposed from morphological inference, the majority of these are not statistically different from each other. Within the available molecular topologies, only four studies to date have included the deep sea class Monoplacophora; but 36.4% of all trees are not significantly different. We also present supertrees derived from two data partitions and three methods, including all available molecular molluscan phylogenies, which will form the basis for future hypothesis testing. The supertrees presented here were not constructed to provide yet another hypothesis of molluscan relationships, but rather to algorithmically evaluate the relationships present in the disparate published topologies. Based on the totality of available evidence, certain patterns of relatedness among constituent taxa become clear. The internodal distance is consistently short between a few taxon pairs, particularly supporting the relatedness of Monoplacophora and the chitons, Polyplacophora. Other taxon pairs are rarely or never found in close proximity, such as the vermiform Caudofoveata and Bivalvia. Our results have specific utility for guiding constructive research planning to better test relationships in Mollusca as well as other problematic groups. Taxa with consistently proximate relationships should be the focus of a combined approach in a concerted assessment of potential genetic and anatomical homology, whereas unequivocally distant taxa will make the most constructive choices for exemplar selection in higher level phylogenomic analyses.
软体动物是现存形态差异最大的动物门类，它们已经分化到了所有栖息地，并且拥有深厚的化石记录。其八个现存纲的单系性和分类地位是无可争议的，但这些类群之间的关系以及它们早期辐射的模式仍然难以捉摸。关于传统形态系统发育的争论集中在少数拓扑概念上，但往往没有考虑各个纲之间的亲缘关系。相比之下，分子研究提出了一些截然不同、本质上相互矛盾且有争议的姐妹关系。在这里，我们汇集了一个数据集，其中包含42个描述软体动物相互关系的已发表独特树。我们使用这些数据提出了几个问题，以探讨与由八个终端的单系组合构建的随机树中可能的变异零模型相比，软体动物系统发育的解析状态。尽管从形态推断中已经提出了27种不同的独特树，但其中大多数在统计学上彼此并无差异。在现有的分子拓扑结构中，迄今为止只有四项研究纳入了深海的单板纲；但所有树中有36.4%并无显著差异。我们还展示了源自两个数据分区和三种方法的超树，包括所有现有的分子软体动物系统发育树，这将为未来的假设检验奠定基础。这里展示的超树并非为了提供另一种关于软体动物关系的假设，而是为了通过算法评估不同已发表拓扑结构中存在的关系。基于现有证据的总体情况，组成类群之间的某些亲缘关系模式变得清晰起来。少数分类单元对之间的节点间距离始终较短，尤其支持单板纲和石鳖纲（多板纲）之间的亲缘关系。其他分类单元对很少或从未被发现彼此接近，例如蠕虫状的尾腔纲和双壳纲。我们的结果对于指导建设性的研究规划具有特定作用，以便更好地检验软体动物以及其他有问题类群中的关系。具有始终接近关系的分类单元应该成为在协同评估潜在遗传和解剖同源性时采用综合方法的重点，而明确遥远的分类单元将成为在更高层次的系统基因组分析中进行范例选择的最具建设性的选择。
