Department of Biotechnology and Biosciences (BtBs), University of Milano-Bicocca, Milan, 20126, Italy.
Department of Earth and Environmental Science (DISAT), University of Milano-Bicocca, Milan, 20126, Italy.
Cladistics. 2024 Apr;40(2):107-134. doi: 10.1111/cla.12567. Epub 2023 Dec 19.
Capitate hydrozoans are a morphologically and ecologically diverse hydrozoan suborder, currently including about 200 species. Being grouped in two clades, Corynida and Zancleida, these hydrozoans still show a number of taxonomic uncertainties at the species, genus and family levels. Many Capitata species established symbiotic relationships with other benthic organisms, including bryozoans, other cnidarians, molluscs and poriferans, as well as with planktonic dinoflagellates for mixotrophic relationships and with bacteria for thiotrophic ectosymbioses. Our study aimed at providing an updated and comprehensive phylogeny reconstruction of the suborder, at modelling the evolution of selected morphological and ecological characters, and at testing evolutionary relationships between the symbiotic lifestyle and the other characters, by integrating taxonomic, ecological and evolutionary data. The phylogenetic hypotheses here presented shed light on the evolutionary relationships within Capitata, with most families and genera being recovered as monophyletic. The genus Zanclea and family Zancleidae, however, were divided into four divergent clades, requiring the establishment of the new genus Apatizanclea and the new combinations for species in Zanclea and Halocoryne genera. The ancestral state reconstructions revealed that symbiosis arose multiple times in the evolutionary history of the Capitata, and that homoplasy is a common phenomenon in the group. Correlations were found between the evolution of symbiosis and morphological characters, such as the perisarc. Overall, our results highlighted that the use of genetic data and a complete knowledge of the life cycles are strongly needed to disentangle taxonomic and systematic issues in capitate hydrozoans. Finally, the colonization of tropical habitat appears to have influenced the evolution of a symbiotic lifestyle, playing important roles in the evolution of the group.
头足类水螅是水螅亚目形态和生态多样性的一个亚目，目前包括约 200 种。这些水螅被分为两个分支，Corynida 和 Zancleida，在种、属和科水平上仍然存在许多分类学上的不确定性。许多头足类与其他底栖生物建立了共生关系，包括苔藓动物、其他刺胞动物、软体动物和多孔动物，以及与浮游甲藻的混合营养关系，以及与细菌的硫营养外共生关系。我们的研究旨在提供亚目最新和全面的系统发育重建，模拟选定形态和生态特征的进化，并通过整合分类学、生态学和进化数据来测试共生生活方式与其他特征之间的进化关系。这里提出的系统发育假说阐明了头足类内部的进化关系，大多数科和属都被重建为单系群。然而，Zanclea 属和 Zancleidae 科被分为四个不同的分支，需要建立新属 Apatizanclea 和 Zanclea 和 Halocoryne 属的新组合。祖先状态重建表明，共生在头足类的进化历史中多次出现，并且同形性是该组的常见现象。共生进化与形态特征之间存在相关性，例如周质。总体而言，我们的研究结果强调了在头足类水螅中使用遗传数据和完整的生命周期知识来解决分类和系统学问题的重要性。最后，热带生境的殖民化似乎影响了共生生活方式的进化，在该组的进化中发挥了重要作用。
