Properties of ethylmethane sulfonate-induced mutations affecting life-history traits in Caenorhabditis elegans and inferences about bivariate distributions of mutation effects

The homozygous effects of ethylmethane sulfonate (EMS)-induced mutations in Caenorhabditis elegans are compared across life-history traits. Mutagenesi s has a greater effect on early than late reproductive output, since EMS-in duced mutations tend to cause delayed reproduction. Mutagenesis changes the mean and variance of longevity much less than reproductive output traits. Mutations that increase total or early productivity are not detected, but t he net effect of mutations is to increase and decrease late productivity to approximately equal extents. Although most mutations decrease longevity, a mutant line with increased longevity was found. A flattening of mortality curves with age is noted, particularly in EMS lines. We infer that less tha n one-tenth of mutations that have fitness effects in natural conditions ar e detected in the laboratory, and such mutations have moderately large effe cts (similar to 20% of the mean). Mutational correlations for life-history traits are strong and positive. Correlations between early or late producti vity and longevity are of similar magnitude. We develop a maximum-likelihoo d procedure to infer bivariate distributions of mutation effects. We show t hat strong mutation-induced genetic correlations do not necessarily imply s trong directional correlations between mutational effects, since correlatio n is also generated by lines carrying different numbers of mutations.