Microsatellites for northern pike (Esox lucius) populations in Germany

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 hybridization 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 (WFD) and indices of
the wetland quality (in rivers) and trophic state (in lakes). 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 modeling revealed a significantly positive association of
the degree of genetic hybridization with decreasing ecological status. An
eroded population substructure indicative of hybridization 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 WFD 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.