Choudhury Anindo, Nadler Steven A
1 Division of Natural Science, St. Norbert College, 100 Grant Street, DePere, Wisconsin 54115.
2 Department of Entomology and Nematology, One Shields Avenue, University of California-Davis, Davis, California 95616-8668.
J Parasitol. 2018 Oct;104(5):496-504. doi: 10.1645/17-195. Epub 2018 Jul 6.
Nematodes are common in the parasite communities of North American freshwater fishes, and the majority of them belong to 1 conventional order, Spirurida Chitwood, 1933. Within the Spirurida, the superfamilies Habronematoidea Chitwood and Wehr, 1932 and Thelazioidea Sobolev, 1949 have undergone considerable diversification. The dominant families of these 2 superfamilies, Cystidicolidae Skrjabin 1946 and Rhabdochonidae Railliet, 1916, respectively, are particularly common, widely distributed, and diverse, especially in North America, yet their phylogenetic relationships remain largely unexplored. In this study, we use near complete sequences of the 18S rRNA genes ( SSU rDNA) from species in 6 genera ( Capillospirura Skrjabin, 1924, Cystidicola Fischer, 1798, Salmonema Moravec, Santos and Brasil-Sato, 2008, Rhabdochona Railliet, 1916, Spinitectus Fourment, 1883, and a putative new cystidicolid in mooneyes, Hiodontidae), along with a species of Hedruris Nitzsch, 1812 from newts as a surrogate for the fish parasite Hedruris tiara VanCleave and Mueller, 1932, to explore their phylogenetic relationships. These sequences, together with available sequences from a range of other nematodes, including fish nematodes in other groups (Camallanoidea and 'Seuratoidea'), were analyzed using Bayesian inference and maximum likelihood. The results from both analyses indicate, for the first time, support for the close relationships of the sturgeon parasite Capillospirura with Ascarophis van Beneden, 1871 and Cystidicola; the relationship of the cystidicolid from Hiodontidae with Salmonema of salmonid fishes; the monophyly of the 2 dominant spiruridan genera of fishes, Rhabdochona and Spinitectus; and for previous relationships among Nearctic Spinitectus spp. The results also indicate a closer relationship of Rhabdochona and Spinitectus than is suggested by their conventional classification and reject the monophyly of Habronematoidea, Thelazioidea, and Cystidicolidae. Hedruridae appears to be an early branching lineage of spirurins. Finally, the pattern of association between the fish parasites in this study and their hosts indicates, with few exceptions, ecologically driven diversification events involving host shifting not related to the phylogenetic relationships of their hosts.
线虫在北美淡水鱼的寄生虫群落中很常见，其中大多数属于1个传统目，即1933年的旋尾目（Spirurida Chitwood）。在旋尾目中，1932年的吸吮线虫超科（Habronematoidea Chitwood and Wehr）和1949年的颚口线虫超科（Thelazioidea Sobolev）经历了相当程度的多样化。这两个超科的优势科，分别是1946年的囊宫科（Cystidicolidae Skrjabin）和1916年的棒线虫科（Rhabdochonidae Railliet），特别常见、分布广泛且种类多样，尤其是在北美，但它们的系统发育关系在很大程度上仍未得到探索。在本研究中，我们使用了6个属（1924年的毛细旋尾线虫属（Capillospirura Skrjabin）、1798年的囊宫线虫属（Cystidicola Fischer）、2008年的鲑生线虫属（Salmonema Moravec, Santos and Brasil-Sato）、1916年的棒线虫属（Rhabdochona Railliet）、1883年的旋尾线虫属（Spinitectus Fourment）以及大眼鱼科中一种假定的新囊宫科线虫）物种的18S核糖体RNA基因（SSU rDNA）的近乎完整序列，以及1812年来自蝾螈的赫德鲁线虫属（Hedruris Nitzsch）的一个物种作为鱼类寄生虫1932年的皇冠赫德鲁线虫（Hedruris tiara VanCleave and Mueller）的替代物，来探索它们的系统发育关系。这些序列与一系列其他线虫的可用序列一起，包括其他类群（驼形线虫超科和“瑟拉托线虫超科”）的鱼类线虫，使用贝叶斯推断和最大似然法进行了分析。两种分析的结果首次表明支持鲟鱼寄生虫毛细旋尾线虫与1871年的蛔虫属（Ascarophis van Beneden）和囊宫线虫属的密切关系；大眼鱼科囊宫科线虫与鲑科鱼类的鲑生线虫属的关系；鱼类两个优势旋尾目属棒线虫属和旋尾线虫属的单系性；以及近北极旋尾线虫属物种之间以前的关系。结果还表明棒线虫属和旋尾线虫属之间的关系比它们传统分类所显示的更密切，并拒绝吸吮线虫超科、颚口线虫超科和囊宫科的单系性。赫德鲁科似乎是旋尾线虫的一个早期分支谱系。最后，本研究中鱼类寄生虫与其宿主之间的关联模式表明，除了少数例外，涉及宿主转移的生态驱动的多样化事件与它们宿主的系统发育关系无关。
