Veronika Bartáková

Modelling the invasion history of Sinanodonta woodiana in Europe: Tracking the routes of a sedentary aquatic invader with mobile parasitic larvae

Understanding the invasive potential of species outside their native range is one of the most pressing questions in applied evolutionary and ecological research. Admixture of genotypes of invasive species from multiple sources has been implicated in successful invasions, by generating novel genetic combinations that facilitate rapid adaptation to new environments. Alternatively, adaptive evolution on standing genetic variation, exposed by phenotypic plasticity and selected by genetic accommodation, can facilitate invasion success. We investigated the population genetic structure of an Asian freshwater mussel with a parasitic dispersal stage, Sinanodonta woodiana, which has been present in Europe since 1979 but which has expanded rapidly in the last decade. Data from a mitochondrial marker and nuclear microsatellites have suggested that all European populations of S. woodiana originate from the River Yangtze basin in China. Only a single haplotype was detected in Europe, in contrast to substantial mitochondrial diversity in native Asian populations. Analysis of microsatellite markers indicated intensive gene flow and confirmed a lower genetic diversity of European populations compared to those from the Yangtze basin, though that difference was not large. Using an Approximate Bayesian Modelling approach, we identified two areas as the probable source of the spread of S. woodiana in Europe, which matched historical records for its establishment. Their populations originated from a single colonization event. Our data do not support alternative explanations for the rapid recent spread of S. woodiana; recent arrival of a novel (cold‐tolerant) genotype or continuous propagule pressure. Instead, in situ adaptation, facilitated by repeated admixture, appears to drive the ongoing expansion of S. woodiana. We discuss management consequences of our results.

Fine-scale genetic structure of the European bitterling at the intersection of three major European watersheds

BackgroundAnthropogenic factors can have a major impact on the contemporary distribution of intraspecific genetic diversity. Many freshwater fishes have finely structured and locally adapted populations, but their natural genetic structure can be affected by river engineering schemes across river basins, fish transfers in aquaculture industry and conservation management. The European bitterling (Rhodeus amarus) is a small fish that is a brood parasite of freshwater mussels and is widespread across continental Europe. Its range recently expanded, following sharp declines in the 1970s and 1980s. We investigated its genetic variability and spatial structure at the centre of its distribution at the boundary of three watersheds, testing the role of natural and anthropogenic factors in its genetic structure.ResultsSequences of mitochondrial cytochrome B (CYTB) revealed that bitterling colonised central Europe from two Ponto-Caspian refugia, which partly defines its contemporary genetic structure. Twelve polymorphic microsatellite loci revealed pronounced interpopulation differentiation, with significant small-scale differentiation within the same river basins. At a large scale, populations from the Baltic Sea watershed (middle Oder and Vistula basins) were distinct from those from the Black Sea watershed (Danube basin), while populations from rivers of the North Sea watershed (Rhine, Elbe) originated from the admixture of both original sources. Notable exceptions demonstrated the potential role of human translocations across watersheds, with the upper River Oder (Baltic watershed) inhabited by fish from the Danube basin (Black Sea watershed) and a population in the southern part of the River Elbe (North Sea watershed) basin possessing a signal of admixture from the Danube basin.ConclusionsHydrography and physical barriers to dispersal are only partly reflected in the genetic structure of the European bitterling at the intersection of three major watersheds in central Europe. Drainage boundaries have been obscured by human-mediated translocations, likely related to common carp, Cyprinus carpio, cultivation and game-fish management. Despite these translocations, populations of bitterling are significantly structured by genetic drift, possibly reinforced by its low dispersal ability. Overall, the impact of anthropogenic factors on the genetic structure of the bitterling populations in central Europe is limited.

No effect of recent sympatry with invasive zebra mussel on the oviposition decisions and reproductive success of the bitterling fish, a brood parasite of unionid mussels

The presence of non-native species can affect coevolved relationships. However, rapid reciprocal changes in coevolutionary associations provide the potential to quickly respond to a new situation. We studied a system where bitterling fish (Rhodeus amarus) parasitize unionid mussels by laying their eggs onto their gills. This association is affected by the infestation of unionid shells by the non-native zebra mussel (Dreissena polymorpha). In a series of experiments under experimental, semi-natural and natural conditions, we compared the behavioural response to zebra mussel infestation of unionid shells, its effect on oviposition decisions and their population consequences between bitterling populations naïve to zebra mussels and those recently sympatric with zebra mussels. We found no effect of recent sympatry on bitterling preoviposition behaviour and oviposition decisions and only a weak effect on their reproductive success. Bitterling from both populations inspected infested and non-infested mussels at the same rate but preferred to oviposit into non-infested unionid hosts. However, neither bitterling population completely avoided oviposition into infested unionids and three ovipositions into zebra mussels were observed. Overall, there was a clear negative relationship between the number of zebra mussels on unionid host shells and the number of juvenile bitterling emerging from the mussels. Our study demonstrated a lack of rapid evolutionary response to adaptively modulate oviposition choice after recent zebra mussel invasion.