Population genetic variation of Calanus finmarchicus in Icelandic waters: preliminary evidence of genetic differences between Atlantic and Arctic populations

Large-scale circulation patterns in the North Atlantic may partition the ocean basin into three semi-distinct gyre systems: the Norwegian Sea, the northern North Atlantic, and the western North Atlantic. Zooplankton entrained in these gyres may be ecologically, reproductively, and (perhaps) genetically distinct owing to geographic isolation in different circulation systems and/or to isolation by distance. Previous studies have demonstrated that populations of the copepod Calanus finmarchicus in the eastern and western North Atlantic differ significantly in haplotype frequencies of the mitochondrial 16S rRNA. This study documents the results of our search for a more variable and easily assayed molecular population genetic character and provides preliminary evidence of population genetic structuring of C. finmarchicus across the boundary region between Atlantic and Arctic waters surrounding Iceland. The genetic traits used were DNA sequence variation and site-specific allele frequencies of a putative nuclear pseudogene of cytochrome oxidase I (COI), and non-coding (intron) and coding regions of the nuclear gene encoding phosphoglucose isomerase (PGI). All traits and both genes revealed significant population genetic differentiation among samples collected from the Northwest Atlantic, Norwegian Sea, North Sea, and Icelandic waters. All characters revealed significant differences among samples collected in Atlantic and Arctic waters surrounding Iceland. Molecular diversity of PGI and pseudo-COI may be useful in examining geographic partitioning of the C. finmarchicus populations on ecologically relevant time and space scales ranging from small-scale patches to ocean gyres.