Abstract
Abstract Esox lucius L. (northern pike) inhabits river, lake, and brackish water ecosystems of the temperate region in North America and Eurasia. In many areas of its native range, the species is confronted with human‐induced disturbances that can affect local and regional genetic diversity. Conservation of genetic diversity constitutes an important policy objective. Therefore, we investigated how the genetic population structure and patterns suggestive of hybridisation among subpopulations from different catchments vary with the type of ecosystem (river vs. lake) and the integrity of the ecosystem assessed using ecological status assessments of the European Water Framework Directive and indices of the wetland quality (in rivers) and trophic state (in lakes). In total, 1,384 pike samples from the North, Baltic, and Black Sea drainages in Germany were analysed. We differentiated between metapopulations from each hydrogeographic region using genotypes from 15 microsatellites and mitochondrial cyt b sequences. Individual populations showed signs of genetic admixture ranging from almost zero to complete replacement by foreign genotypes originating from different catchments. Hierarchical general linear modelling revealed a significantly positive association of the degree of genetic hybridisation with decreasing ecological status. An eroded population substructure indicative of hybridisation was also significantly elevated in rivers relative to lakes and in heavily modified water bodies. Results were consistent when using ecological status assessments by the Water Framework Directive and an alternative environmental quality index based on the health of wetlands in rivers and trophic state in lakes. We speculate that macrophyte loss through loss of wetlands or in response to eutrophication fostered genetic mixing among different subpopulations, which were brought into secondary contact either due to stocking or due to natural dispersal from foreign catchments. Our findings suggest that anthropogenic alteration of freshwater ecosystems may influence the genetic structures present in a freshwater top piscivore at both local and regional scales.
Highlights
Animal and plant populations are evolving in human-d ominated landscapes (Christie & Knowles, 2015; Ortego et al, 2015; Sexton et al, 2013; Smith & Bernatchez, 2008)
We investigated how the genetic population structure and patterns suggestive of hybridisation among subpopulations from different catchments vary with the type of ecosystem and the integrity of the ecosystem assessed using ecological status assessments of the European Water Framework Directive and indices of the wetland quality and trophic state
The objective of the present study was to explore whether the ecological status of the inland water bodies in Germany would be associated with the genetic structure of contemporary pike populations, with respect to potential genetic admixture among populations of E. lucius of different hydrogeographic regions
Summary
Animal and plant populations are evolving in human-d ominated landscapes (Christie & Knowles, 2015; Ortego et al, 2015; Sexton et al, 2013; Smith & Bernatchez, 2008). Stocking and facilitated natural migration through human-made artificial connections among different river basins have substantially increased the speed of human-assisted secondary contact among subpopulations of fish relative to natural factors alone and thereby can shape contemporary genetic structures through rapid evolution (Lin et al, 2020; van Poorten et al, 2011). (Heath et al, 2010) All of these examples support the idea that the outcome of secondary contact between different populations or lineages is influenced by local ecological conditions, but as yet little is known about how local environmental conditions determine population structure of intensively exploited species at large geographical scales
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