Adaptation to Low Salinity Promotes Genomic Divergence in Atlantic Cod (Gadus morhua L.).
Bottom Line: Our results show that discrete regions within the Atlantic cod genome are subject to directional selection and associated with adaptation to the local environmental conditions in the Baltic- and the North Sea, indicating divergence hitchhiking and the presence of genomic islands of divergence.We report a suite of outlier single nucleotide polymorphisms within or closely located to genes associated with osmoregulation, as well as genes known to play important roles in the hydration and development of oocytes.Hence, our data suggest that adaptive responses to the environmental conditions in the Baltic Sea may contribute to a strong and effective reproductive barrier, and that Baltic cod can be viewed as an example of ongoing speciation.
Affiliation: Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, Norway.Show MeSH
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Mentions: LD was evaluated among all 8,809 SNPs, independent of LG localization to detect both inter- and intrachromosomal LD. As expected, we find SNPs with high r 2 values (>0.75) within all LGs (supplementary table S3, Supplementary Material online). The distributions of the intrachromosomal r 2 values among the different LGs show that SNPs with high r 2 values often reside within the same scaffolds and hence are physically close. However, for LG2, 7 and 12, an extensive number of SNPs with high LD (fig. 3) covers multiple scaffolds including 15 and 5 scaffolds in two close but separated blocks in LG2, 14 scaffolds in LG7, and 31 scaffolds in LG12 (supplementary table S3, Supplementary Material online). The LD pattern (fig. 3) also shows less distinct blocks of elevated r 2 values in LG4, 10, and 17. Interestingly, relatively high levels of r 2 values (>0.3) also occur between SNPs on different LGs, particularly between LG1 and 2 and between LG2 and 4 (supplementary table S3, Supplementary Material online).Fig. 3.—
Affiliation: Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, Norway.