Genetic variation of Sparicotyle chrysophrii (Monogenea: Microcotylidae) from the gilthead sea bream Sparus aurata (Teleostei: Sparidae) in the Mediterranean Sea

The gill monogenean Sparicotyle chrysophrii (Van Beneden & Hesse, 1863) Mamaev, 1984 is a specific and common parasite of wild and cultured gilthead sea bream Sparus aurata Linnaeus, 1758, able to cause disease and mortality in aquaculture systems. Few molecular studies have been carried out on this monogenean, and its population structure and genetic diversity are barely known. This study provides the first contribution to the population genetic variation of S. chrysophrii , based on two molecular markers - the structural ribosomal RNA (rRNA) for the large subunit (28S) and the cytochrome c oxidase subunit I (COI) gene. Samples were collected from the gills of farmed and wild S. aurata from Italy and the Spanish Mediterranean. The analysis included previously published sequences. The 28S rDNA analysis was consistent with previous studies of specimens isolated from S. aurata and confirmed the presence of only one species on the gills of this host in the Mediterranean Sea. The COI sequences analysis suggested that the samples isolated in a previous study from a different host species, wild Boops boops (Linnaeus, 1758) in the Adriatic Sea, may represent a new undescribed sister species of S. chrysophrii . The low nucleotide diversity of S. chrysophrii isolated only from S. aurata versus the high haplotype diversity revealed small differences between haplotypes. The haplotypes shared between wild and farmed hosts from Spain provided the first molecular evidence of the possible transfer of S. chrysophrii between wild and farmed populations of S. aurata . The mtDNA COI analysis did not show a clear genetic structure, probably the result of several factors including coevolution, wild and farmed host interactions, and host population structure in space and time.