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 oc ean basin into three semi-distinct gyre systems: the Norwegian Sea, the nor thern North Atlantic, and the western North Atlantic. Zooplankton entrained in these gyres may be ecologically, reproductively, and (perhaps) genetica lly distinct owing to geographic isolation in different circulation systems and/or to isolation by distance. Previous studies have demonstrated that p opulations of the copepod Calanus finmarchicus in the eastern and western N orth Atlantic differ significantly in haplotype frequencies of the mitochon drial 16S rRNA. This study documents the results of our search for a more v ariable and easily assayed molecular population genetic character and provi des preliminary evidence of population genetic structuring of C. finmarchic us across the boundary region between Atlantic and Arctic waters surroundin g Iceland. The genetic traits used were DNA sequence variation and site-spe cific allele frequencies of a putative nuclear pseudogene of cytochrome oxi dase I (COI), and non-coding (intron) and coding regions of the nuclear gen e encoding phosphoglucose isomerase (PGI). All traits and both genes reveal ed significant population genetic differentiation among samples collected f rom 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 r anging from small-scale patches to ocean gyres. (C) 2000 International Coun cil for the Exploration of the Sea.