Uncovering neutral and adaptive genomic differentiation among European perch with brackish water and freshwater origin in the western Baltic Sea region

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Environmental variation across the range of wild species can lead to local adaptations. The Baltic Sea was formed when the Fenno-Scandian ice sheet retreated around 12 thousand years ago, creating a new brackish water habitat colonised by both marine and freshwater fish species. The European perch (Perca fluviatilis) is a predatory freshwater fish with a large geographical distribution across Eurasia, where it inhabits a wide range of environmental niches. In the Baltic Sea region it has even developed a specialised brackish water perch variant that can tolerate environmental salinity levels, which are lethal to freshwater perch. However, very little is known about the underlying mechanisms facilitating the colonisation and adaptation of perch to the Baltic Sea. Here, we use Genotyping-By-Sequencing data from six freshwater and six brackish water localities to disclose the evolutionary relationship between freshwater and brackish water perch. Our results show that the brackish water perch occurs in multiple distinct genetic clusters. We find that gene flow between brackish water perch with full access to the sea likely led to lower levels of differentiation and higher diversity than in freshwater perch. Selection analyses suggest that genomic adaptation played a role in the colonisation of the Baltic Sea and that the top three regions under selection harbour salinity tolerance genes. We complete by discussing the implications of our findings for management of brackish water perch in the western Baltic sea.

TidsskriftFisheries Research
Antal sider11
StatusUdgivet - 2023

Bibliografisk note

Funding Information:
The authors would like to thank Lasse Vinner, Pernille S. Olsen and Tina B. Brand at Globe Institute for help during laboratory work and professor Kim Præbel for valuable input. E.A.F.C. was supported by the Carlsberg Foundation (grant number CF19–0400 ). M.T.O. was supported via the BONUS BALTHEALTH project, BONUS (Art. 185 ), funded jointly by the EU, Innovation Fund Denmark (grants 6180–00001B and 6180–00002B ), Forschungszentrum Jülich GmbH, German Federal Ministry of Education and Research (grant FKZ 03F0767A ), Academy of Finland (grant 311966 ) and Swedish Foundation for Strategic Environmental Research (MISTRA). P.R.M. and H.C. were supported by Aage V. Jensens nature Foundation (Grant number 100307 ). Last, but not least, the authors would like to thank two anonymous reviewers for their constructive feedback and valuable input.

Publisher Copyright:
© 2023 The Authors

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