Morphological and molecular characterization of the ciliate parasite Tetrahymena rostrata infecting the renal organ of the dusky slug (Arion fuscus)

Abstract

The histophagous ciliate Tetrahymena rostrata (Kahl, 1926) is a facultative parasite of the renal organ of land snails and slugs. The possibility of transovum transmission and the lack of heteroparental sex make T. rostrata an interesting model for studying host specificity and distribution patterns in pathogenic ciliates. We recorded mass Tetrahymena infection in the dusky slug ( Arion fuscus (O.F. Müller, 1774)) collected in Slovakia, Central Europe. Based on the mitochondrial 16S rRNA gene and barcoding cytochrome c oxidase subunit I (COI) sequences, Slovak isolates belong to the TRO-1 subgroup. Strains of T. rostrata, however, do not cluster according to the relatedness of their gastropod hosts, i.e., various phylogenetically unrelated snails and slugs are parasitized by members of both T. rostrata subclades (TRO-1 and TRAUS). Invasion of adult gastropods through the integumentary pouch might be thus a more important transmission way than the transovum route. Geographic distances of T. rostrata isolates are not correlated with divergences in COI sequences. The absence of a clear relationship between genetic and geographic distances might have been, however, also caused by the human-mediated transmission of invasive gastropods.