Temporal Dynamics of Microgeographic Structure of Genetic Variation in Microtus californicus

Abstract

Demographic and genetic changes were documented in a 20-month study of a population of the California vole, Microtus californicus. Dramatic changes in density, typical of microtine rodents, were observed. During the time that population density declined rapidly, rare alleles were lost at three of the loci, PGD, GPI, and GOT-1, and the less-common allele decreased in frequency at the fourth locus, LAP. The genetic structure of the population was dynamic. During phases of the population cycle in which the density was low, genetic differentiation (as measured by Wright's F_ST) was relatively high for areas separated by only 50–200 m (F̄_ST ≃0.04). The level of genetic differentiation among areas decreased when the population size increased. These changes in genetic differentiation are consistent with predictions based on theoretical models of population structure in which effective population size and migration are the critical variables.