Extensive secondary contact among three glacial lineages of Arctic Char (Salvelinus alpinus) in Labrador and Newfoundland

Abstract

Aim The Pleistocene glaciation event prompted the allopatric divergence of multiple glacial lineages of Arctic char ( Salvelinus alpinus ), some of which have come into secondary contact upon their recolonization of the Holarctic. While three glacial lineages (Arctic, Atlantic, and Acadian) are known to have recolonized the western Atlantic, the degree of overlap of these three lineages is largely unknown. We sought to determine the distribution of these three glacial lineages in Labrador and Newfoundland at a fine spatial scale to assess their potential for introgression and their relative contribution to local fisheries. Location Labrador and Newfoundland, Canada. Methods We sequenced a portion of the D‐loop region in over 1,000 Arctic char ( S. alpinus ) samples from 67 locations across Labrador and Newfoundland. Results Within Labrador, the Arctic and Atlantic lineages were widespread. Two locations (one landlocked and one with access to the sea) also contained individuals of the Acadian lineage, constituting the first record of this lineage in Labrador. Atlantic and Acadian lineage individuals were found in both eastern and western Newfoundland. Multiple sampling locations in Labrador and Newfoundland contained fish of two or more different glacial lineages, implying their introgression. Glacial lineage did not appear to dictate contemporary genetic divergence between the pale and dark morph of char present in Gander Lake, Newfoundland. Both were predominately of the Atlantic lineage, suggesting the potential for their divergence in sympatry. Main conclusions Our study reveals Labrador and Newfoundland to be a unique junction of three glacial lineages which have likely hybridized extensively in this region.

The interaction of resource use and gene flow on the phenotypic divergence of benthic and pelagic morphs of Icelandic Arctic charr (Salvelinus alpinus)

“…However, we cannot completely exclude the possibility that divergence occurred during a period of allopatry followed by secondary contact as similar contemporary patterns of genetic variation may be generated by alternative divergence histories (Foote, 2018;Ravinet et al, 2017). Indeed, studies of Arctic charr, and other northern fishes, have shown that allopatric divergence followed by a secondary contact event is prevalent (Jacobs et al, 2020;Lehnert et al, 2019;Rougemont & Bernatchez, 2018;Rougeux et al, 2019;Salisbury et al, 2019). Although unlikely due to geography, it is also possible that populations of Arctic charr from lakes not included in this study could have contributed to morph formation.…”

Genomic data support management of anadromous Arctic Char fisheries in Nunavik by highlighting neutral and putatively adaptive genetic variation

“…In North America, Arctic Char comprises four known mitochondrial DNA (mtDNA) lineages associated with distinct glacial refugia (Brunner et al, 2001;Moore et al, 2015). The Arctic lineage is predominant in the south-eastern Arctic (Brunner et al, 2001;Moore et al, 2015), but populations across northern Labrador are admixed with the Atlantic lineage (Salisbury et al, 2019). Nunavik, situated in northern Québec (Canada), is one of the last regions in North America to have deglaciated following the last glacial maximum (LGM; Dalton et al, 2020;Dyke, 2004).…”

“…In North America, Arctic Char comprises four known mitochondrial DNA (mtDNA) lineages associated with distinct glacial refugia (Brunner et al, 2001 ; Moore et al, 2015 ). The Arctic lineage is predominant in the south‐eastern Arctic (Brunner et al, 2001 ; Moore et al, 2015 ), but populations across northern Labrador are admixed with the Atlantic lineage (Salisbury et al, 2019 ).…”

Investigating Diadromy in Fishes and Its Loss in an -Omics Era

“…In some species, resident populations are clearly genetically divergent from their diadromous counterparts (e.g., common galaxias; Delgado et al., 2019 ). In Arctic charr, sympatric anadromous and resident populations were until recently considered genetically indistinguishable, yet recent genomic data revealed genetically differentiated sympatric anadromous and resident populations in Labrador ( Salisbury et al, 2019 , 2020 ). Sockeye Salmon ( O. nerka ) on the other hand, exhibits examples of both genetically differentiated and non-differentiated sympatric resident and anadromous populations ( Nichols et al., 2016 ).…”