Genetic changes in an irradiated population of wild meadow voles (Microtus pennsylvanicus)

Abstract

Changes observed in the genetic structure of a wild population of meadow voles (Microtus pennsylvanicus) exposed to chronic gamma radiation are compared with those observed in a nearby unirradiated population. An average exposure of 14.6 ± 0.8 mGy/d of gamma radiation was administered from a 137Cs field irradiator to an otherwise unmanipulated population over 47 weeks. The demographic and genetic characteristics of the populations were estimated by livetrapping and by electrophoresis of the polymorphic plasma proteins encoded by transferrin and leucine aminopeptidase, respectively. Both the irradiated and control populations showed highly synchronous demographic changes: an autumn decline, very low density throughout the winter, a late spring increase, and late summer peak. Allele frequencies and F-statistics fluctuated dramatically throughout the low-density phase. Coincident with the acceleration of population growth, the genetic variables began to converge in the two populations. At the termination of the experiment, when population growth was slowing, the irradiated and control populations were genetically very similar. Sexual activity, longevity, and recruitment were each homogeneous among genotypes in both populations. The radiation treatment had no apparent effect on the genetic structure of the vole population. Gene flow at the beginning of an increase phase is suggested as a possible cause for convergence of the genetic attributes of the irradiated and unirradiated populations.