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Biological invasions are common among freshwater molluscs, with the North American planorbid gastropod Gyraulus parvus being reported from Europe (Germany) by the 1970s. It has since spread across Central and Western Europe, mostly living in artificial and highly modified habitats. However, considerable conchological and anatomical similarity exists between it and the native European G. laevis. Using four other European and one North American Gyraulus species as outgroups, separate phylogenetic analyses using mitochondrial and nuclear DNA sequences show that G. parvus and G. laevis are in fact part of the same species-level clade, with the former having nomenclatural priority. However, the structure within the mitochondrial tree suggests a North American origin of the invasive populations. It also makes it possible to track down the distribution of both races. Although native and non-native races in Europe tend to possess some differences in conchology and ecology, the degree of overlap makes it impossible to accurately distinguish between them without the DNA barcode data. Our results change the outlook on the conservation of the rare native race. While interspecific competition among snail species is rare, invasion on an intraspecific level may represent a serious threat for native populations.

Freshwater mollusc diversity has repeatedly been found to peak in lowland stagnant waters, which are highly exposed to human-made degradation and the spread of non-native species. Despite the increasing loss of these habitats, little is known about the main predictors of their mollusc diversity patterns. Therefore, we aimed to determine the environmental drivers of mollusc assemblage variation between and within sites by sampling 62 water bodies in the Dyje River floodplain (south-eastern Czechia). We measured 14 environmental variables, categorized as site-specific or plot-specific. Species richness and abundances were analysed by GLM and GEE; species compositional variance was assessed by NMDS and db-RDA ordinations. Mollusc species richness, ranging between 0 and 15 species per site, and abundance sharply decreased towards high trophy sites, with the chlorophyll-a concentration and water pH highly correlated with species counts. Species compositional variation was driven mainly by water trophy and the quality of organic detritus. Site heterogeneity turned out to significantly control local assemblages of molluscs, while the presence of individual species seemed to be filtered by site trophy and the shoreline length. Thus, to maintain high regional diversity of aquatic molluscs in lowland agricultural landscapes, the presence of low trophy sites seems to be essential.

The number of non-native species has dramatically increased over the last decades in many aquatic habitats of central Europe. Although the spreading of alien mollusc species can poses a serious threat to many native species, no attempt has been made to assemble and analyse an extensive dataset collected over a long time span. So far, eight non-native species of aquatic molluscs — five gastropods and three bivalves — have been recorded in the wild in the Czech Republic in central Europe. We assembled a dataset consisting of 1,783 sites with the presence of these non-native species recorded between 1891 and 2014. We aimed to explore the time course and spatial pattern of the invasions and to define some of the gross predictors of the occurrence of these species by categorizing their sites based on habitat type, elevation and distance from the nearest large river. We found that most of these species expressed affinities to non-natural standing waters and large rivers. The most invaded parts of the C...