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Abstract
Arctic freshwater ecosystems have been profoundly affected by climate change. Given that the Arctic charr (Salvelinus alpinus) is often the only fish species inhabiting these ecosystems, it represents a valuable model for studying the impacts of climate change on species life‐history diversity and adaptability. Using a genotyping‐by‐sequencing approach, we identified 5,976 neutral single nucleotide polymorphisms and found evidence for reduced gene flow between allopatric morphs from two high Arctic lakes, Linne'vatn (Anadromous, Normal, and Dwarf) and Ellasjøen (Littoral and Pelagic). Within each lake, the degree of genetic differentiation ranged from low (Pelagic vs. Littoral) to moderate (Anadromous and Normal vs. Dwarf). We identified 17 highly diagnostic, putatively adaptive SNPs that differentiated the allopatric morphs. Although we found no evidence for adaptive differences between morphs within Ellasjøen, we found evidence for moderate (Anadromous vs. Normal) to high genetic differentiation (Anadromous and Normal vs. Dwarf) among morphs within Linne'vatn based on two adaptive loci. As these freshwater ecosystems become more productive, the frequency of sympatric morphs in Ellasjøen will likely shift based on foraging opportunities, whereas the propensity to migrate may decrease in Linne'vatn, increasing the frequency of the Normal morph. The Dwarf charr was the most genetically distinct group. Identifying the biological basis for small body size should elucidate the potential for increased growth and subsequent interbreeding with sympatric morphs. Overall, neutral and adaptive genomic differentiation between allopatric and some sympatric morphs suggests that the response of Arctic charr to climate change will be variable across freshwater ecosystems.
Highlights
To investigate how Arctic charr may respond to climate change, we focus on morphs from two high latitude lakes, Linnevatn and Ellasjøen, in the Svalbard archipelago, a Norwegian territory in the Arctic Ocean
We found that landlocked Arctic charr in Ellasjøen had lower genetic diversity than those in Linnevatn
Isolated, allopatric populations of Arctic charr are likely to be ge‐ netically distinct, but genetic divergence among sympatric morphs varies, and response of populations and morphs to climate change probably needs to be considered on a case‐by‐case basis
Summary
Linnevatn (78°03′N, 13°50′E) is located on western Spitsbergen, the largest island in the Svalbard archipelago (Figure 1). It is the sec‐ ond largest lake on Svalbard with an area of 4.6 km and a maximum depth of 37 m, occurring ~10 m above sea level (Bøyum & Kjensmo, 1978). The lake is 21 m above sea level with an area of 0.73 km and a maximum depth of 43 m (Bertram & Lack, 1933; Klemetsen, Grotnes, Holthe, & Kirstoffersen, 1985). Lake Ellasjøen flows into the short River Fossåa, but the lake outlet is too steep to permit the migration of Arctic charr (Klemetsen et al, 1985). TA B L E 1 Arctic charr sampling information and summary statistics for filtered loci (8,075 SNPs) identified within each morph
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