Hebei Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology, Hebei Collaborative Innovation Center for Eco-Environment, College of Life Sciences, Hebei Normal University, Shijiazhuang, 050024, Hebei Province, People's Republic of China.
Hebei Research Center of the Basic Discipline Cell Biology, Ministry of Education Key Laboratory of Molecular and Cellular Biology, Shijiazhuang, 050024, Hebei Province, People's Republic of China.
Parasit Vectors. 2023 Aug 10;16(1):275. doi: 10.1186/s13071-023-05889-9.
The family Toxocaridae is a group of zooparasitic nematodes of veterinary, medical and economic significance. However, the evolutionary relationship of Porrocaecum and Toxocara, both genera currently classified in Toxocaridae, and the monophyly of the Toxocaridae remain under debate. Moreover, the validity of the subgenus Laymanicaecum in the genus Porrocaecum is open to question. Due to the scarcity of an available genetic database, molecular identification of Porrocaecum nematodes is still in its infancy.
A number of Porrocaecum nematodes collected from the Eurasian marsh harrier Circus aeruginosus (Linnaeus) (Falconiformes: Accipitridae) in the Czech Republic were identified using integrated morphological methods (light and scanning electron microscopy) and molecular techniques (sequencing and analyzing the nuclear 18S, 28S and ITS regions). The complete mitochondrial genomes of the collected nematode specimens and of Porrocaecum (Laymanicaecum) reticulatum (Linstow, 1899) were sequenced and annotated for the first time. Phylogenetic analyses of ascaridoid nematodes based on the amino acid sequences of 12 protein-coding genes of mitochondrial genomes were performed using maximum likelihood and Bayesian inference.
A new species of Porrocaecum, named P. moraveci n. sp., is described based on the morphological and genetic evidence. The mitogenomes of P. moraveci n. sp. and P. reticulatum both contain 36 genes and are 14,517 and 14,210 bp in length, respectively. Comparative mitogenomics revealed that P. moraveci n. sp. represents the first known species with three non-coding regions and that P. reticulatum has the lowest overall A + T content in the mitogenomes of ascaridoid nematodes tested to date. Phylogenetic analyses showed the representatives of Toxocara clustered together with species of the family Ascarididae rather than with Porrocaecum and that P. moraveci n. sp. is a sister to P. reticulatum.
The characterization of the complete mitochondrial genomes of P. moraveci n. sp. and P. reticulatum is reported for the first time. Mitogenomic phylogeny analyses indicated that the family Toxocaridae is non-monophyletic and that the genera Porrocaecum and Toxocara do not have an affinity. The validity of the subgenus Laymanicaecum in Porrocaecum was also rejected. Our results suggest that: (i) Toxocaridae should be degraded to a subfamily of the Ascarididae that includes only the genus Toxocara; and (ii) the subfamily Porrocaecinae should be resurrected to include only the genus Porrocaecum. The present study enriches the database of ascaridoid mitogenomes and provides a new insight into the systematics of the superfamily Ascaridoidea.
蛔目是一类具有兽医、医学和经济重要性的动物寄生线虫。然而，目前分类在蛔科中的旋尾目属和弓首蛔虫属的进化关系以及蛔科的单系性仍存在争议。此外，旋尾目属中的亚属赖马蛔虫属的有效性也存在疑问。由于可用遗传数据库的匮乏，旋尾目线虫的分子鉴定仍处于起步阶段。
从捷克共和国欧亚沼泽雕（林奈）（隼形目：鹰科）中收集了一些旋尾目线虫，使用综合形态学方法（光镜和扫描电子显微镜）和分子技术（测序和分析核 18S、28S 和 ITS 区）对其进行了鉴定。首次对收集的线虫标本和旋尾目属（赖马蛔虫属）网状旋尾线虫（林斯托，1899）的完整线粒体基因组进行了测序和注释。使用最大似然法和贝叶斯推断，基于线粒体基因组 12 个蛋白编码基因的氨基酸序列，对棘头虫目线虫进行了系统发育分析。
基于形态学和遗传证据，描述了旋尾目属的一个新种，命名为莫拉维采旋尾线虫。莫拉维采旋尾线虫和网状旋尾线虫的线粒体基因组均包含 36 个基因，长度分别为 14517 和 14210 bp。比较线粒体基因组学表明，莫拉维采旋尾线虫代表了第一个已知具有三个非编码区的物种，而网状旋尾线虫在迄今为止测试的棘头虫目线虫的线粒体基因组中具有最低的总体 A+T 含量。系统发育分析表明，弓首蛔虫属的代表与棘头虫科的物种聚在一起，而不是与旋尾目属的物种聚在一起，而且莫拉维采旋尾线虫是网状旋尾线虫的姐妹种。
首次报道了莫拉维采旋尾线虫和网状旋尾线虫完整线粒体基因组的特征。线粒体基因组系统发育分析表明，蛔科并非单系，旋尾目属和弓首蛔虫属之间没有亲缘关系。旋尾目属中的亚属赖马蛔虫属也被否定。我们的研究结果表明：（i）蛔科应降级为棘头虫科的一个亚科，仅包括弓首蛔虫属；（ii）旋尾目亚科应恢复，仅包括旋尾目属。本研究丰富了棘头虫目线粒体基因组数据库，为超目棘头虫目系统发育提供了新的见解。
