Genetic and environmental canalization are not associated among altitudinally varying populations of Drosophila melanogaster

Abstract

Organisms are exposed to environmental and mutational effects influencing both mean and variance of phenotypes. Potentially deleterious effects arising from this variation can be reduced by the evolution of buffering (canalizing) mechanisms, ultimately reducing phenotypic variability. As such, there has been interest regarding the plausible conditions that enable canalizing mechanisms to evolve. Under some models, the circumstances under which genetic canalization evolves is limited, despite apparent empirical evidence for it. It has been argued that canalizing mechanisms for mutational effects may evolve as a correlated response to environmental canalization (the congruence model). Yet, empirical evidence has not consistently supported the prediction of a correlation between genetic and environmental canalization. In a recent study, a population of Drosophila melanogaster adapted to high altitude showed evidence of genetic decanalization relative to those from low-altitudes. Using strains derived from these populations, we tested if they also varied for environmental canalization, rearing them at different temperatures. Using wing morphology, we quantified size, shape, cell (trichome) density and frequencies of mutational defects. We observed the expected differences in wing size and shape, cell density and mutational defects between the high- and low-altitude populations. However, we observed little evidence for a relationship between a number of measures of environmental canalization with population or with visible defect frequency. Our results do not support the predicted association between genetic and environmental canalization.