Characterization of the complete mitochondrial genome of Notocotylus sp. (Trematoda, Notocotylidae) and its phylogenetic implications

The parasite genus Notocotylus comprises at least 50 species colonizing mainly aquatic birds and to a lesser extent some mammals, particularly rodents. Here trematode specimens isolated from a wild black swan were characterized and identified to belong to the genus Notocotylus via morphological and molecular analyses. Phylogenetic position of the isolate among other trematodes was determined based on the ribosomal internal transcribed spacer (ITS) 1 and 2. The complete mitochondrial (mt) genome of the isolate was amplified, sequenced, assembled, analyzed, and annotated. The isolate has an AT-rich mt genome (14,317 bp in length) that comprises 12 protein-coding genes (PCGs), 22 transfer RNA genes, and two ribosomal RNA genes. The Notocotylus isolate identified in this study has relatively high mt genome sequence identity and identical gene content and arrangement to a known Notocotylidae species, Ogmocotyle sikae. The isolate formed a genetic clade with O. sikae in phylogenetic analysis of the concatenated PCG amino acid sequences. Compared to the ITS, the trematode mt genome appears more informative for resolving high-level phylogenies. To the best of our knowledge, this is the first study exploring the complete mt genome for the genus Notocotylus, and it offers a novel genomic resource that has important implications for trematode phylogenetics.