The Ponto-Caspian parasite Plagioporus cf. skrjabini reaches the River Rhine system in Central Europe: higher infestation in the native than in the introduced Danubian form of the gastropod Theodoxus fluviatilis

Abstract

The introduction of non-indigenous organisms in new areas in the context of host-parasite interactions is still poorly understood. This study aimed at a parasitological and histopathological comparison of two phylogenetically distinct forms of the freshwater snail Theodoxus fluviatilis in the River Rhine system: the native Northern-European form, which showed a decline for unknown reasons and is nowadays extinct in the River Rhine, and the non-indigenous Danubian form, which was introduced via the Main–Danube canal. We histopathologically examined populations of Northern-European T. fluviatilis from three smaller rivers of the Rhine system and of Danubian T. fluviatilis from the River Rhine, after confirming the phylogenetic background of the respective population genetically. Results showed differences in the prevalence of trematodes and histopathologic organic alterations between the two snail forms. Both were infected with an opecoelid trematode Plagioporus cf. skrjabini, whereby its prevalence was significantly higher in the Northern-European than in the Danubian form. The parasitic trematode is, to our knowledge, a new trematode species in the River Rhine system, presumably co-introduced through the invasion of its second intermediate and final hosts, i.e. Ponto-Caspian amphipods and gobies. Its impact on native populations of Northern-European T. fluviatilis needs to be subject of future studies.

Invading non-native populations replace native ones of the endangered freshwater snail Theodoxus fluviatilis in the river Rhine

“…Furthermore, T. fluviatilis individuals of haplotype F31 were less infested by the trematode Plagioparus cf. skrjabini (also an invader from the Caspian region) than individuals of the native haplotype (Rothmeier et al 2021). The presence of both non-native parasites and non-native hosts (or hosts of non-native haplotypes) outside their natural range may have an effect on native biodiversity.…”

“…The ML analysis for phylogenetical reconstruction revealed that individuals of the invading haplotype F31 belong to the Danubian group with haplotypes F38 (originally found in Ukraine; Bunje 2005) and MT563453 (recorded as a newly arriving haplotype in the northern part of the Upper Rhine in 2018; Rothmeier et al 2021) (Fig. 2).…”