POPULATION CYCLES AND GENE FREQUENCY FLUCTUATIONS IN FOXES OF THE GENUS VULPES, IN CANADA

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Abstract
Population densities of foxes of the genus Vulpes over most of Canada have shown a fairly regular 9 to 10 year cycle upon which has been superimposed a trend toward increase in numbers. These changes in density are investigated with reference to changes in frequency of the two genes that determine the presence of black rather than red pigment of the pelage. Of the 14 27-year series of gene frequency data, only two show any apparent correlation with the 9 to 10 year cycle in population density. These two, each with a negative correlation whose probability is less than.001, are for the "Alaskan black" gene in the North West Territories and for the "Canadian black" gene in Quebec. On the basis of these latter data the hypothesis is forwarded that there is some selective factor that may operate against these two "black" genes in an expanding population and may favor their increase in frequency when the population is decreasing in size. It is believed that this hypothesis is sufficient to explain the gradual decrease in gene frequency associated with the gradual increase in the size of the population. This hypothesis is utilized to explain the east–west gradient in gene frequency on the basis of negative selection from presumed eastern and western glacial refugia.

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