Genetic tools have been extremely useful to study the colonization history and dynamics of invasive species and infer source populations. In addition, understanding the distribution of genetic diversity of non-indigenous species is important to understand factors contributing to invasive success. Here, we used genetic markers to study the invasion history of the quagga mussel Dreissena rostriformis (Deshayes 1838). The invasion of North American and European watercourses by the quagga mussel is of major concern since this dreissenid mussel has widespread ecological and economic impacts in invaded regions. Through the use of mitochondrial (COI) and nuclear (microsatellites) markers and based on a large sampling, including both native and invasive ranges, we characterized the recent invasion of Western Europe by D. rostriformis. Scenario testing Bayesian analysis (approximate Bayesian computation methods) suggests that Western Europe was most probably invaded from the Pontic region via the southern corridor (Danube River, the Main-Danube Canal and the Main and Rhine rivers). Furthermore, pairwise F ST values suggest a second invasion to Western Europe from North America via trans-Atlantic shipping. The high genetic diversity and low differentiation among D. rostriformis populations suggest high propagule pressure and frequent exchanges between the Pontic region, Eastern North America and Western Europe. Our study concludes that multiple introductions and high propagule pressure have shaped the genetic composition of populations in Western Europe. The results provide valuable information for future management plans in order to control the spread of highly invasive aquatic species.
The insular limestone karsts of northern Vietnam harbor a very rich biodiversity. Many taxa are strongly associated with these environments, and individual species communities can differ considerably among karst areas. The exact processes that have shaped the biotic composition of these habitats, however, remain largely unknown. In this study, the role of two major processes for the assembly of snail communities on limestone karsts was investigated, interspecific competition and filtering of taxa due to geographical factors. Communities of operculate land snails of the genus Cyclophorus were studied using the dry and fluid‐preserved specimen collections of the Natural History Museum, London. Phylogenetic distances (based on a Bayesian analysis using DNA sequence data) and shell characters (based on 200 semilandmarks) were used as proxies for ecological similarity and were analyzed to reveal patterns of overdispersion (indicating competition) or clustering (indicating filtering) in observed communities compared to random communities. Among the seven studied karst areas, a total of 15 Cyclophorus lineages were found. Unique communities were present in each area. The analyses revealed phylogenetic overdispersion in six and morphological overdispersion in four of seven karst areas. The pattern of frequent phylogenetic overdispersion indicated that competition among lineages is the major process shaping the Cyclophorus communities studied. The Coastal Area, which was phylogenetically overdispersed, showed a clear morphological clustering, which could have been caused by similar ecological adaptations among taxa in this environment. Only the community in the Cuc Phuong Area showed a pattern of phylogenetic clustering, which was partly caused by an absence of a certain, phylogenetically very distinct group in this region. Filtering due to geographical factors could have been involved here. This study shows how museum collections can be used to examine community assembly and contributes to the understanding of the processes that have shaped karst communities in Vietnam.
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