Evol Ecol Res 2: 1009-1029 (2000)     Full PDF if your library subscribes.

Induced mutations: A novel tool to study phenotypic integration and evolutionary constraints in Arabidopsis thaliana

Mark D. Camara, Carrie A. Ancell and Massimo Pigliucci

Departments of Botany and of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA

Address all correspondence to Mark D. Camara, Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
e-mail: camara@lifesci.ucsb.edu


Adaptive phenotypic evolution is constrained by the availability of genetic variation and the patterns of phenotypic integration and genetic architecture among characters. Phenotypic and genotypic variance/covariance matrices provide a convenient quantitative summary of such patterns and are widely used in evolutionary studies. These matrices are, for mathematical tractability, assumed to remain constant or change only proportionally in the course of evolution. However, this assumption is tenuous over the medium and long term and cannot possibly hold at all taxonomic scales. One important source of genetic change is mutations, but low natural rates of mutation make them difficult to study at the population level. We used ethyl-methane-sulphonate to induce mutations in a flowering plant and assess their impact on the means and phenotypic variances of seven morphological and life-history traits as well as the covariances among these characters. We found that only one trait mean changed in response to mutagenesis, but that mutations generated new variance in all traits in a roughly dose-dependent fashion. Common principal components analyses of the matrices showed that the degree of divergence from a non-mutagenized control population is roughly dose-dependent. This overall divergence of covariance structure is the product of idiosyncratic mutation-induced changes in particular pairwise correlations among traits. One well-studied correlation between time to flowering and the number of rosette leaves at flowering persists in all mutagenic treatments. We discuss these findings and their implications for quantitative genetic models that assume constant variance/covariance matrices.

Keywords: Arabidopsis, canalization, genetic constraints, mutation, phenotypic covariance, pleiotropy.

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