No evidence of elevated germline mutation accumulation under oxidative stress in Caenorhabditis elegans

Abstract

Variation in rates of molecular evolution has been attributed to numerous, interrelated causes, including metabolic rate, body size, and generation time. Speculation concerning the influence of metabolic rate on rates of evolution often invokes the putative mutagenic effects of oxidative stress. To isolate the effects of oxidative stress on the germline from the effects of metabolic rate, generation time, and other factors, we allowed mutations to accumulate under relaxed selection for 125 generations in two strains of the nematode Caenorhabditis elegans, the canonical wild-type strain (N2) and a mutant strain with elevated steady-state oxidative stress (mev-1). Contrary to our expectation, the mutational decline in fitness did not differ between N2 and mev-1. This result suggests that the mutagenic effects of oxidative stress in C. elegans are minor relative to the effects of other types of mutations, such as errors during DNA replication. However, mev-1 MA lines did go extinct more frequently than wild-type lines; some possible explanations for the difference in extinction rate are discussed.

Figure 1

Frequency histogram of relative fitnesses (w) of the mev-1 and N2 MA lines. Data are presented as the proportion of mev-1 and N2 MA lines in each of 10 bins from 0.1 to 1.9 (mev-1 n = 60 lines, N2 n = 47 lines); w of the ancestral control in each strain is defined to equal 1. The proportion of lines above or below w = 1 does not differ between strains. Calculations for w are in Materials and Methods.