Doktorsvörn 2. okt. Population genetic structure in gadoid fish with focus on Atlantic cod

Föstudagur, October 2, 2015 – 14:00

Population genetic structure in gadoid fish with focus on Atlantic cod Gadus morhua – Phd. defence Guðni M. Eiríksson

On Friday the 2nd of October Guðni Magnús Eiríksson will defend his Ph.D. thesis in Biology. The thesis is titled: Population genetic structure in gadoid fish with focus on Atlantic cod Gadus morhua.

Opponents are dr. Dorte Bekkevold, Senior reseach scientist, Technical University of Denmark, and dr. William Stewart Grant, research coordinator at Commercial Fisheries Division, Alaska Department of Fish and Game.

The supervisor is dr. Einar Árnason, Professor at the Faculty of Life and Environmental Sciences at the University of Iceland. The doctoral committee also includes dr. Jarle Mork, Professor at the NTNU Department of Biology, Trondheim, Norway, and dr. Kristinn Pétur Magnússon, Professor at the Faculty of Natural Resource Sciences at the University of Akureyri.

The ceremony will be chaired by dr. Eva Benediktsdóttir, Associate Professor and the Head of the Faculty of Life and Environmental Sciences at the University of Iceland.


In the present study genetic variation and population genetic structure in spawning Atlantic cod, Gadus morhua, around Iceland was examined. Earlier research on population genetic structure in cod has not been conclusive and the use of different molecular methods have shown different patterns. It is important to determine why different methods show different patterns in order to describe the population genetic structure in cod. In the present study both microsatellite DNA variation and mitochondrial DNA sequence variation were estimated. Both methods have commonly been used in population genetic studies in cod.

Findings of microsatellite DNA variation analysis showed a genetic difference between cod from the waters south and north of Iceland. However, analysis of the observed difference suggest that it can be explained by natural selection affecting genetic variation at a single microsatellite loci (Gmo34). When disregarding this locus from the analysis no genetic difference was observed. A small but significant genetic difference was found among Atlantic cod sampled at different depths off the south coast of Iceland, indicating that different populations of Atlantic cod may be found at different depths. Analysis of mtDNA sequence variation showed no overall genetic difference among different geographic areas around Iceland. Analysis of temporal mtDNA sequence variation showed rapid changes in allele frequencies, particularly in cod from NE-Iceland, suggesting that the mtDNA sequence variation can be useful for detecting recent population divergence. Thus, the findings of the present study do not suggest that cod around Iceland is geographically divided into distinct historical populations as has been suggested in some earlier studies. On the contrary the findings suggest high levels of gene flow in Atlantic cod around Iceland.

Genetic variation and population genetic structure across the North Atlantic ocean was also examined in saithe Pollachius virens, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus using mtDNA sequence variation at the cytochrome c oxidase subunit I locus. The results showed limited trans-Atlantic genetic structure for all the species indicating high levels of gene flow or insufficient time for genetic differentiation to have become established. The observed genetic sequence variation for saithe and haddock suggest sex-biased migration pattern. The results indicate that females may be more philopatric and males more migratory. Such behaviour has rarely been described for marine fish and is worth further research.

The observed mitochondrial sequence variation for all the studied species indicate sudden population expansion, reflected in high number of singletons and a shallow genealogy. However, the estimated timing of expansion varies among the examined species, suggesting that the biological, historical or analytical factors resulting in the observed pattern may differ among the species.