Methuselah life history in a variety of conditions, implications for the use of mutants in longevity research

The laboratory has yielded many long-lived mutants of several model-organisms in the past few years. Many of the resulting claims for extended longevity have been nuanced or shown to be restricted to specific conditions, including environments and genetic backgrounds. Here, we test whether the long-lived mutant fruit fly methuselah (mth1) displays its apparent superiority in longevity and stress resistance in different environments, at different ages and in correlated traits. The results demonstrate that stress resistance at different times in life is not consistently higher in the mutant relative to its progenitor strain (w1118). Furthermore, the mth1 genotype only leads to an increase in longevity in an environment where reproduction is not stimulated. Also, virgin and mated life span were compared and showed that mating negatively affects life span, especially in the mth1 individuals. This reduced the life span enhancing effect of the mutation to zero. This apparent environment and mating dependent trade-off between longevity and reproduction supports the disposable soma theory of ageing. We conclude that these data can only provide limited information on natural variation. The data show the need to uncover the full complexity of variation in such traits in natural environments.