A test of the Chitty hypothesis: inheritance of life-history traits in meadow voles Microtus pennsylvanicus

Abstract

The Chitty hypothesis proposes that the demographic changes occurring in microtine cycles are mediated by natural selection operating on the genetic composition of the population. Implicit is the assumption that a suite of life-history traits is simultaneously undergoing selection and that these traits are strongly heritable. This was tested 1) by determining whether the year-to-year differences in phenotypes in fluctuating meadow vole populations in the field are maintained in samples of young animals raised in the laboratory, and 2) whether the variation seen in the field has a heritable basis as determined by half-sib analysis. In the field, young from the year when population size was increasing grew more rapidly than those from the peak year; in the laboratory, the opposite occurred. Ages at sexual maturity showed similar differences. Heritability analysis was performed on body weight, growth rate, and age and weight at sexual maturity. Virtually all these traits showed significant dam effects, but small or nonexistant sire effects. Thus, most of the variation was nongenetic in origin; maternal and other environmental effects were of overriding importance. The heritabilities of these traits in nature are thus usually lower than necessary for natural selection to operate in the time frames characteristic of microtine cycles. -from Authors