Abstract
BackgroundRecent molecular studies have discovered substantial unrecognised diversity within the genus Diplostomum in fish populations in Europe and North America including three species complexes. However, data from the first intermediate host populations are virtually lacking. This study addresses the application of an integrative taxonomic approach to the cryptic species diversity of Diplostomum spp. in natural lymnaeid snail populations in Europe with a focus on the ‘D. mergi’ species complex.MethodsTotals of 1,909 Radix auricularia, 349 Radix peregra, 668 Stagnicola palustris and 245 Lymnaea stagnalis were sampled at five reservoirs of the Ruhr river system in Germany and screened for infections with Diplostomum spp. Cercariae were examined and identified alive, fixed and under scanning electron microscopy. Sequences from the barcode region of the cytochrome c oxidase subunit 1 (cox1) mitochondrial gene and from the internal transcribed spacer cluster (ITS1-5.8S-ITS2) of the rRNA gene were amplified for 51 and 13 isolates, respectively.ResultsDetailed morphological and molecular analyses provided evidence for three named species (Diplostomum spathaceum, D. pseudospathaceum and D. parviventosum), and a further four species-level lineages (‘D. mergi Lineages 2–4’ and ‘Diplostomum sp. Clade Q’ in the lymnaeid snail populations from the Ruhr river basin. The paper provides the first descriptions of molecularly identified cercariae of D. spathaceum and of the cercariae of D. parviventosum, three lineages of the ‘D. mergi’ species complex and of ‘Diplostomum sp. Clade Q’.ConclusionThe integration of molecular and morphological evidence for Diplostomum spp. achieved in this study will serve as a baseline for species identification of these important parasites of snail and fish populations and thus advance further studies on the distribution of Diplostomum spp. in Europe.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-0904-4) contains supplementary material, which is available to authorized users.
Highlights
Recent molecular studies have discovered substantial unrecognised diversity within the genus Diplostomum in fish populations in Europe and North America including three species complexes
This study addresses the application of an integrative taxonomic approach to the cryptic species diversity of Diplostomum spp. in natural lymnaeid snail populations in Europe with a focus on the ‘D. mergi’ species complex
Examination of 3,171 lymnaeid snails belonging to four species revealed a total of 78 infections with Diplostomum spp.: 35 in Radix auricularia, 27 in Lymnaea stagnalis and 16 in Stagnicola palustris; no infections were found in Radix peregra
Summary
Recent molecular studies have discovered substantial unrecognised diversity within the genus Diplostomum in fish populations in Europe and North America including three species complexes. The first studies addressing integration of morphological assessment and molecular prospecting for species diversity of the genus in Europe resulted in molecular elucidation of the life-cycles of Diplostomum spathaceum (Rudolphi, 1819) (type-species) and D. pseudospathaceum Niewiadomska, 1984 and provided evidence for a substantial unrecognised genetic and morphological diversity, i.e. 15 species-level lineages including three complexes of genetically distinct lineages [6,7,8,9]. Six of these originate from the snail and fish populations studied in the River Ruhr drainage in Germany. Most of these isolates, i.e. ‘D. mergi Lineage 3’, originate from fish and due to the low sampling effort only few isolates from their lymnaeid snail hosts are available: a single isolate for ‘D. mergi Lineage 1’ and three isolates for ‘D. mergi Lineage 2’, all from Radix auricularia (L.)
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