| Summary: | Life history assays were performed on lines of <i>C. elegans</i> in which spontaneous mutations had been allowed to accumulate for 60 generations (Keightley and Caballero, 1997), using a range of harsh conditions. However, no significant degree of genotype by environment interaction was observed. Under some harsher experimental conditions, estimates of mutation rates increased, but the difference was not significant and these results do not lend support to the theory that differences in estimates of mutational parameters are due to variation in assay conditions. Even harsh conditions may not reveal the effects of all mutations that have accumulated and are deleterious in natural conditions, and the extent to which this may result in underestimation of the mutation rate has been unknown. I have measured the effects of EMS-induced mutations on a series of life history traits in <i>C. elegans</i>, in a situation where the number of mutational events induced has been calibrated from studies of suppressor-induced reversion mutations and forward mutations. None of the assays revealed the effects of more than ~ 10% of the deleterious mutations induced, indicating that standard mutation-accumulation experiments may have dramatically underestimated the rate at which mutations accumulate. Such mutations, although cryptic, may nonetheless be significant for evolutionary biology. Two of the lines were further analysed using an inbred-backcross approach, which provided confirmation that only a very small proportion of the induced mutations could be detected. The joint effects of induced mutations on longevity and productivity were also considered. Mortality curves were observed to flatten with age, and this was more notable among the EMS than control lines. One explanation for this was greater heterogeneity among the EMS lines, although other possible causes are discussed. Overall, bivariate analysis revealed strong, positive correlations between longevity and productivity traits, although one line showed a significant increase in longevity, and a correlated decline in early (but not total) productivity, as predicted by the optimality theory of ageing.
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