GENETIC CHANGES AT THE TRANSFERRIN LOCUS IN THE RED-BACKED VOLE (CLETHRIONOMYS GAPPERI).

Abstract

Genetic changes at the transferrin locus in Clethrionomys gapperi were intermittently monitored in a subarctic population from 1966 to 1978. Over this 13-year period, only minor fluctuations in gene frequency were observed. Gene frequency of Tf/sup J/ increased over winter during declines from high nonbreeding density in autumn. This phenomenon may have been responsible for a general negative correlation between the frequency of Tf/sup J/ and population density. Outside of winter, no frequency changes were detected within trappable age-classes of voles from relatively discrete seasonal generations. Excess of Tf/sup M/J/ heterozygotes occurred in three of four samples of young voles that matured in the year of their birth. A similar heterozygote excess occurred in one of six samples of overwintered voles taken in a year characterized by a high rate of population growth. These results suggest that selection may occur during ecologically different conditions of high density or population growth. A heterozygote advantage in early-season cohorts may account for the maintenance of transferrin polymorphism. This hypothesis requires further data on the breeding structure and early life history of voles.