Harp Seals breed in only four areas of the North Atlantic and adjacent waters. In the western Atlantic, these are the Newfoundland / Labrador Ice Front (NL) and the southern Gulf of Saint Lawrence (GS). These two areas are separated by the Strait of Belle Isle at the tip of the Northern Peninsula of Newfoundland, as well as the freshwater outflow of the St. Lawrence River. Further East, breeding populations occur at Jan Mayen Island in the Greenland Sea (GS) east of Greenland, and in the White Sea (WS) east of the Kola Peninsula in Russia. Over-hunting of the Jan Mayen population in the early 20th century reduced its numbers to a small fraction of its former size. The extent to which gene flow connects the western and eastern pairs, and allows trans-Atlantic exchange, have been long-standing questions.

    An Analysis of Molecular Variance (AMOVA) is similar to a conventional Analysis of Variance (ANOVA), where the variance is DNA sequence variability. Harp Seals lend themselves well to AMOVA, because explicit a priori island models of gene flow, based on distances between populations, can be tested and compared. Model I shows that a significant fraction (Ø_SC = 0.0580, p < 0.05) of the variance occurs among all four populations taken separately, consistent with genetic isolation by distance. Model III, which combines the two western populations and leaves the two eastern populations separate, shows a fraction (Ø_CT = 0.0456, ns) among groups, and a fraction (Ø_SC = 0.0372, p < 0.05) among populations within groups.

    The notation of an AMOVA with haploid mtDNA data is different than for diploid allozyme of nucDNA markers. Ø_CT is equivalent to F_IS,  Ø_SC is equivalent to F_ST, and Ø_ST is equivalent to F_IT.

    HOMEWORK: Compare the results for Models II & IV with Model III. Explain the models in biological terms. Based on the AMOVA, which is (are) the best models of population structure? Why is Ø_ST identical across the different models?