Genetic limits to evolutionary change
Genetic variation is assumed to be ubiquitous in natural populations of organisms, and quantitative traits typically have intermediate levels of heritable variation. This variation is thought to be maintained by a balance between mutation and stabilizing selection. Yet there have been a number of instances reported in the literature where genetic variance in traits is low enough to limit evolutionary change. This lack of variation provides an explanation for the ecological limits of species. Here we describe experiments designed to dissect a genetic limit in two rainforest insect species in an attempt to understand why genetic variance might be limited and how this limit might be overcome. We test the hypotheses that limits might be overcome by increasing developmental variation and by allowing populations to undergo bottlenecks to increase epistatic genetic variance. We emphasize that closely related species can differ markedly in the genetic architecture underlying selected traits despite conservation of the genome.