Abstract
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.
Highlights
Anthropogenic factors can have a major impact on the contemporary distribution of intraspecific genetic diversity
The same loci had relatively high frequencies of null alleles estimated in FreeNA (6.9% and 7.9%, respectively, Additional file 1: Table S1), despite no apparent evidence of null alleles, allele dropout or scoring errors due to stuttering in results assessed by MICRO-CHECKER
To avoid potential bias caused by these loci, population-level genetic variability was analysed using a reduced dataset of 9 loci
Summary
Anthropogenic 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 current interspecific and intraspecific diversity of the European biota has been substantially shaped by cycles of expansion and contraction of species ranges Similar periodic range expansions and contractions due to climatic fluctuations occurred over much shorter timespans within the Holocene [5]. Such dynamics frequently generated temporarily isolated populations in local refugia. When contemporary ranges were recolonized from multiple refugia, distinct genetic lineages sometimes met in contact zones and hybridized (e.g. [7, 8]), thereby increasing genetic diversity in these secondary contact zones
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