Sewage treatment plant associated genetic differentiation in the blue mussel from the Baltic Sea and Swedish west coast.

Josefine Larsson,Mats Grahn,Mikael Lönn,Justyna Świeżak,Emma E Lind,Katarzyna Smolarz

doi:10.7717/peerj.2628

Josefine Larsson, Mats Grahn + Show 4 more

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https://doi.org/10.7717/peerj.2628

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Abstract

Human-derived environmental pollutants and nutrients that reach the aquatic environment through sewage effluents, agricultural and industrial processes are constantly contributing to environmental changes that serve as drivers for adaptive responses and evolutionary changes in many taxa. In this study, we examined how two types of point sources of aquatic environmental pollution, harbors and sewage treatment plants, affect gene diversity and genetic differentiation in the blue mussel in the Baltic Sea area and off the Swedish west coast (Skagerrak). Reference sites (REF) were geographically paired with sites from sewage treatments plant (STP) and harbors (HAR) with a nested sampling scheme, and genetic differentiation was evaluated using a high-resolution marker amplified fragment length polymorphism (AFLP). This study showed that genetic composition in the Baltic Sea blue mussel was associated with exposure to sewage treatment plant effluents. In addition, mussel populations from harbors were genetically divergent, in contrast to the sewage treatment plant populations, suggesting that there is an effect of pollution from harbors but that the direction is divergent and site specific, while the pollution effect from sewage treatment plants on the genetic composition of blue mussel populations acts in the same direction in the investigated sites.

Highlights

Human activities are constantly contributing to environmental changes that serve as drivers for evolutionary responses in many taxa
By using a combination of a nested sampling scheme, with a high-resolution marker (AFLP), we examined if pollution from sewage treatment plants and harbors could (i) affect the gene diversity at polluted sites, (ii) cause genetic differentiation between polluted sites and reference sites, and (iii) cause differentiation that is consistent in direction in sites within pollution types or if the direction of differentiation is divergent between individual polluted sites
sewage treatments plant (STP) and HAR sites were paired with a reference site (REF) that was not influenced by sewage effluents or harbor associated pollutants

Summary

Introduction

Human activities are constantly contributing to environmental changes that serve as drivers for evolutionary responses in many taxa (see review by Palumbi, 2001 and Smith & Bernatchez, 2008). Natural populations are expected to experience changes in genetic diversity and genetic differentiation through genetic drift, gene flow and selection, and it is evident that anthropogenic activities can have impact on these processes (Smith & Bernatchez, 2008; Banks et al, 2013). Anthropogenic environmental pollutants in the aquatic environment originate from, for example, sewage effluents, agriculture and. Pollutants can affect organisms on an individual level by affecting their behavior and/or physiology, and on a population level and a multigenerational level trough natural selection (Chevin, Lande & Mace, 2010; Banks et al, 2013; Whitehead, 2014). In populations with strong gene flow (panmixia or near panmixia) and random larval dispersal across habitats, heritable trans-generational local adaptation is hindered, but footprints of spatially varying single-generation selection across habitats can still be detected (e.g., in the European eel (Anguilla anguilla) and American eel (Anguilla rostrata) (Gagnaire et al, 2012; Ulrik et al, 2014; Laporte et al, 2016)

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