Abiotic stress does not magnify the deleterious effects of spontaneous mutations

Abstract

Although the effects of deleterious alleles often are predicted to be greater in stressful environments, there is no theoretical basis for this prediction and the empirical evidence is mixed. Here we characterized the effects of three types of abiotic stress (thermal, oxidative and hyperosmotic) on two sets of nematode (Caenorhabditis elegans) mutation accumulation (MA) lines that differ by threefold in fitness. We compared the survival and egg-to-adult viability between environments (benign and stressful) and between fitness categories (high-fitness MA, low-fitness MA). If the environment and mutation load have synergistic effects on trait means, then the difference between the high and low-fitness MA lines should be larger in stressful environments. Although the stress treatments consistently decreased survival and/or viability, we did not detect significant interactions between fitness categories and environment types. In contrast, we did find consistent evidence for synergistic effects on (micro) environmental variation. The lack of signal in trait means likely reflects the very low starting fitness of some low-fitness MA lines, the potential for cross-stress responses and the context dependence of mutational effects. In addition, the large increases in the environmental variance in the stressful environments may have masked small changes in trait means. These results do not provide evidence for synergism between mutation and stress.

Fitness decline under osmotic stress inCaenorhabditis eleganspopulations subjected to spontaneous mutation accumulation at varying population sizes

“…Alternatively, harsh environmental conditions may unmask the cumulative fitness effects of a load of cryptic mutations with slightly deleterious fitness coefficients that were undetected under benign assay conditions (Baer ; Andrew et al. ). However, this load of slightly deleterious mutations ( s < 0.…”

“…First, the osmotic stress may more sensitively reveal the effects of mutations with large selection coefficients that are expected to be eradicated by purifying selection in large population sizes. Alternatively, harsh environmental conditions may unmask the cumulative fitness effects of a load of cryptic mutations with slightly deleterious fitness coefficients that were undetected under benign assay conditions (Baer 2008;Andrew et al 2015). However, this load of slightly deleterious mutations (s < 0.…”

Effects of mutation and selection on plasticity of a promoter activity in Saccharomyces cerevisiae

“…By comparing trait variation among lines in which nonlethal mutations have accumulated in the near absence of selection, these studies estimate the mutational variance (V m ), which is the phenotypic variance added to a population each generation by new mutations. The V m was found to differ among environments (indicating GxE interactions) for some traits (29)(30)(31)(32) but not others (33,34), demonstrating that the propensity of new mutations to alter plasticity differs depending on the trait and environments considered. Because mutation accumulation Significance From seasonal variation in the color of butterfly wings to trees bending toward the light, organisms often change in response to their environment.…”

Environmental stress does not increase the mean strength of selection

“…Kraemer et al ., ; Martinossi‐Allibert et al ., ) or reduced (e.g. Kishony & Leibler, ; Andrew et al ., ) under stress. Selective regimes can differ in a diversity of ways across environments without changing in average selection strength.…”