HETEROZYGOSITY, AGGRESSION, AND POPULATION FLUCTUATIONS IN MEADOW VOLES (MICROTUS-PENNSYLVANICUS)

We tested whether variation in heterozygosity could produce cyclic cha nges in population size in meadow voles (Microtus pennsylvanicus). For this to occur, three conditions must be met: (1) populations are more outbred (Heterozygotic) at high than low population density, (2) hete rozygotic voles are more aggressive than relatively inbred individuals , and (3) heterozygotic voles have lower reproductive fitness, though being superior at defending resources. We found no evidence that heter ozygosity varied with population size or that reproductive success var ied with heterozygosity. However, the former test was indirect and rel atively weak. We directly measured aggression and heterozygosity of in dividual voles. Aggression was significantly related to heterozygosity : higher heterozygosity correlated with more aggression in males and l ess aggression in females. The proportion of variance in aggression th at could be explained by heterozygosity was small. These results sugge st that changes in population size of meadow voles could not be driven by systematic changes in heterozygosity with population size.