The haemoglobin polymorphism of whiting (Merlangius merlangus L.) in the northeast Atlantic
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- Institutt for biologi 
The HbI* polymorphism in cod (Gadus morhua L.) has been thoroughly investigated during 50 years. It has two common alleles, and several studies have indicated that allele frequencies are influenced by environmental factors, and form clines on both sides of the Atlantic. The whiting (Merlangius merlangus L.) is a close gadoid relative of cod with very similar biology, ecology and geographical distribution. The whiting haemoglobin shows a similar polymorphism to that in cod, with two common alleles. Some studies have assumed that the same alleles are observed in whiting and cod. If that is the case, one might expect the whiting allele frequencies to display similar latitudinal clines as that in cod. Initial IFPAG analysis in this study revealed an only partial identity of whiting and cod HbI* alleles; they shared one common allele, the cod HbI1 allele of Sick (1961), which decreases in frequency from south to north. Altogether 198 blood samples from whiting in Lofoten and Trondheim were collected and genotyped using IFPAG. Together with reported whiting HbI* frequencies from more southern regions (Kattegat, North Sea and northern coast of Scotland) found in the literature, an adequate coverage of the east Atlantic was obtained. The HbI1 allele frequencies in altogether 992 whiting from 16 locations formed a statistically very significant south-north cline. Furthermore, a regression of HbI1 allele frequency on mean SST (Sea Surface Temperature) was very significant. The results support a temperature-driven selection model in both whiting and cod.