Mutational contributions to genetic variance-covariance matrices: An experimental approach using induced mutations in Arabidopsis thaliana

Genetic potential for evolutionary change and covariational constraints are typically summarized as the genetic variance-covariance matrix G, and ther e is currently debate over the extent to which G remains effectively consta nt during the course of adaptive evolution. However, G provides only a temp orally restricted view of constraints that ignores possible biases in how n ew mutations affect multivariate phenotypes. We used chemical mutagenesis t o study the effect of mutations as summarized by the mutational covariance matrix, M, in Arabidopsis thaliana. By introducing mutations into three iso genic strains of A. thaliana, we were able to quantify M directly as the ge netic variance-covariance matrix of mutagenized lines. Induced mutations ge nerally did not alter the means of the six morphology and life-history trai ts we measured, but they did affect the levels of available genetic variati on and the covariances among traits. However, these effects were not consis tent among the three isogenic lines; that is, there were significant differ ences among the lines in both the number of mutations produced by ethyl-met hane-sulfonate treatment and the M matrices they induced. The evolutionary implications of the dependence of M on the number of mutations, the particu lar genetic background, and the mutagenic sampling of loci in the genome ar e discussed in light of commonly applied models of multivariate evolution a nd the potential for the genetic architecture itself to change in ways that facilitate the coordinated evolution of complex phenotypes.