Genetic population structure of a top predatory fish (northern pike, Esox lucius) covaries with anthropogenic alteration of freshwater ecosystems

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.

Genetic diversity of the Southern Black Drum Pogonias courbina (Teleostei: Sciaenidae) from Río de la Plata and Atlantic Ocean coasts

“…According to Hauser & Ward (1998), if different stocks are identified, each of these populations could react independently to exploitation, representing different management units. Differences in habitat, migration, geographic segregation or human activities are considered as contributing factors for the genetic population structuring (Gonzalez & Zardoya 2007, Gao et al 2014, Eschbach et al 2021. Because P. courbina is a shared fishing resource in the Southwestern (SW) Atlantic Ocean (Machado et al 2020), it is very important to define whether it constitutes a single population or if this taxon is made up of different stocks in this region.…”

Drivers of neutral and adaptive differentiation in pike (Esox lucius) populations from contrasting environments

“…Previous population assignments of Baltic Sea pike have mainly been based on neutral microsatellite markers (Bekkevold et al, 2015; Eschbach et al, 2021; Möller et al, 2020; Nordahl et al, 2019; Wennerström et al, 2016). However, knowledge about how different evolutionary processes shape genetic structure and diversity requires that population genetic studies use molecular markers that capture variation also in coding regions (Andrews et al, 2016; Candy et al, 2015; Ford et al, 2015; Holderegger et al, 2006; Sunde et al, 2020a).…”