Nonadaptive evolution of disease resistance in an annual legume

Abstract

Local populations of Amphicarpaea bracteata often contain genetically divergent lineages that differ strongly in disease resistance toward the specialist pathogen Synchytrium decipiens. In one population, lineages with disease resistance significantly decreased in frequency over a 2yr period, despite the continued presence of pathogens. Extensive self-pollination restricts the opportunity for recombination of alleles affecting separate traits, resulting in strong correlations between disease resistance and other ecologically important characters, including plant morphology, phenology, and patterns of reproductive allocation. Natural selection on these correlated characters may thus cause nonadaptive changes in disease resistance. Results imply that A. bracteata's mating system is a basic constraint interfering with its adaptation to pathogen attack. -from Author