| Abstract: | The nature of the interaction among deleterious mutations is important to models in many areas of evolutionary biology. In addition, interactions between genetic and environmental factors may affect the predictions of such models. Individuals of unknown genotypes of Arabidopsis thaliana, ecotype Marburg, were exposed to five levels of chemical (EMS) mutagenesis and three levels of Pseudomonas syringae infection. Survival, growth and flowering characteristics of each individual were measured. The logarithm of fitness is expected to be a linear function of mutation number if mutations act independently. Furthermore, the expected number of mutations should be approximately a linear function of time of exposure to mutagen. Therefore, nonlinear effects of mutagen exposure on the logarithm of fitness characters would suggest epistasis between mutations. Similarly, if pathogen infection and mutation act independently of each other, their effects should be additive on a log scale. Statistical interactions between these factors would suggest they do not act independently; particularly, if highly mutated individuals suffer more when infected than do less mutated individuals, this suggests that pathogens and mutations act synergistically. Pseudomonas-infected individuals were shown to have an increased probability of flowering under conditions of short day length, but to ultimately produce fewer flowers than uninfected individuals. This suggests a plastic response to stress and, despite that response, an ultimately deleterious effect of infection on fitness. Leaf rosette growth was negatively and linearly related to the expected number of mutations, and the effects of mutation on different life-cycle stages appeared to be uncorrelated. No significant interactions between pathogen and mutation main effects were found. These results suggest that mutations act multiplicatively with each other and with pathogen infection in determining individual fitness. |
