Invasion at the population level: a story of the freshwater snails Gyraulus parvus and G. laevis.
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.