Comparative mitochondrial genomics among Spirometra (Cestoda: Diphyllobothriidae) and the molecular phylogeny of related tapeworms.

The larva of Spirometra erinaceieuropaei can parasitize humans, causing a serious parasitic zoonosis known as sparganosis. Although it is medically important, our knowledge about the phylogenetic position of S. erinaceieuropaei and its evolutionary history is fragmentary. In this study, complete mitochondrial (mt) genomes of 4 geographically distinct isolates of S. erinaceieuropaei spargana collected from 4 frog hosts (Hylarana guentheri, Rana nigromaculata, R. rugulosa, R. temporaria) were characterized using an Illumina sequencing platform. In addition, all available mt genomes of Cestoda in GenBank were included to reconstruct the phylogeny and to explore the evolutionary history of these tapeworms. The genome features of S. erinaceieuropaei contained 12 protein-coding genes (PCGs), 22 transfer RNA genes, 2 ribosomal RNA genes and 2 non-coding regions. Nucleotide sequences of mtDNA from different frog hosts were similar. Three genes, cox1, cytb and nad4, had high levels of nucleotide diversity. Phylogenetic analyses supported the sibling relationship between Bothriocephalidae and Diphyllobothriidae. Molecular dating analysis indicated that the divergence between Diphyllobothrium and Diplogonoporus started in the late Miocene. The mt genomes of S. erinaceieuropaei will serve as a useful dataset for studying the genetics and systematics of the species of Spirometra genus in particular and diphyllobothriid tapeworms in general.