A mitogenomic study of four at-risk maring fish species: Atlantic wolffish, spotted wolffish, northern wolffish, and Atlantic cod, with special emphasis on the waters off Newfoundland and Labrador

Lait, Linda Amy (2016) A mitogenomic study of four at-risk maring fish species: Atlantic wolffish, spotted wolffish, northern wolffish, and Atlantic cod, with special emphasis on the waters off Newfoundland and Labrador. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

High-resolution mitogenomics can answer questions as to how species survived the last glacial maximum, and can also address contemporary factors such as physical barriers, isolation, and gene flow. This study examines the population genomic structures of two genera of At-Risk marine fish species found across the North Atlantic Ocean, Atlantic cod (Gadus morhua) and wolffish (Anarhichas spp.). Despite their sympatric distribution, the two taxa exhibit very different life history characteristics, and have very different patterns of genetic variation and structure. Populations of Atlantic cod show high levels of genomic variation, with eight major clades found across most populations and trans-Atlantic differences. The Arctic lake population (Lake Qasigialiminiq) was significantly different from all other populations (ΦST = 0.15 to 0.34), and comprised two distinct and essentially monomorphic clades. The Baltic and Barents Sea populations showed high levels of diversity, extensive variation among samples, and significant pairwise differences with many Northwest Atlantic populations (ΦST = 0.03 to 0.18). Within Atlantic Canada there was no evidence of differentiation in Newfoundland waters or between trans-Laurentian populations (ΦST = 0.0 to 0.06). High diversity levels, the absence of European fish in the most recent clades, and the presence of basal lineages support a European origin to the postglacial expansion, with a second smaller refugium likely in North America. Atlantic wolffish (Anarhichas lupus) and the congeneric spotted and northern wolffish (A. minor and A. denticulatus) each comprised two or three haplogroups dating back to the Pleistocene glaciations (63 - 220 kya). The haplogroups were not structured geographically: in Atlantic wolffish the overall ΦST was 0.05 and pairwise values ranged from 0.0 to 0.24. A similar pattern of distinct but shallow groups was seen in spotted wolffish, while northern wolffish exhibited two deeper lineages. This suggests isolation in multiple glacial refugia – likely three nearby regions in European waters (Atlantic and spotted) or two more distant refugia (northern) – followed by secondary admixture during recolonisation of the Northwest Atlantic. The two taxa show very different patterns of variation and structure, with greater variation in Atlantic cod and greater structure in the sedentary wolffish species.

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