Detection and molecular characteristics of Pyelosomum cochlear (Digenea: Pronocephalidae) in the urinary bladder of the green sea turtle (Chelonia mydas) in the Northwest Pacific Ocean

Abstract

The genus Pyelosomum consists of parasitic flukes occurring primarily in marine turtles; Pyelosomum cochlear Looss 1899 is the only species of this genus that parasitizes the urinary bladder. In this study, we detected flukes in the urinary bladders of 20 of 88 green sea turtles (Chelonia mydas) harvested in the Ogasawara Islands, in the Northwest Pacific Ocean. We identified the flukes as P. cochlear based on detailed morphological observations and comparisons of morphometric measurements of the species reported previously. Nucleotide sequences of nuclear ribosomal 18S and 28S regions and the mitochondrial cytochrome c oxidase subunit 1 (COI) region were determined for the flukes. The 18S and 28S phylogenetic trees revealed that the species of the superfamily Pronocephaloidea, including P. cochlear, constituted a single clade, but the species of the family Pronocephalidae did not constitute a single taxon. These findings suggest that Pronocephalidae is a paraphyletic group. The COI sequences of P. cochlear exhibited high genetic diversity, suggesting that they would be useful markers to understand the genetic structure of the parasite and its evolutionary relationship with the host turtle populations. This is the first study to provide the nucleotide sequences of Pyelosomum species; these data will be available for further molecular studies of this genus and its related taxa.

Keywords: Chelonia mydas; Ogasawara Islands; Phylogeny; Pronocephaloidea; Pyelosomum cochlear.