The effect of environmental stress on ageing in Cryptotermes secundus

Social insects seem to have overcome the almost universal trade-off between fecundity and longevity as queens can be highly fecund and at the same time reach lifespans of decades. By contrast, their non-reproducing workers are often short lived. One hypothesis to explain the long lifespan of queens is that they are better protected against stress than their workers. However, evidence is controversial and experimental studies are scarce. We aimed at manipulating environmental stress and ageing by exposing colonies of the less-socially complex termite Cryptotermes secundus to temperature regimes that differed in variance. In contrast to expectation, constant temperatures imposed more stress than variable temperatures. Survival of queens and workers as well as queens fecundity were partly reduced under constant conditions and both castes showed signs of ageing in the transcriptome signature under constant conditions. There was a clear oxidative stress defence signal under constant conditions which was, surprisingly, stronger for workers than queens. We discuss how our results relate to social complexity. We argue that workers which are totipotent to become reproductives, like in C. secundus, should invest more in anti-ageing mechanisms than sterile workers because the former can still reproduce and have not reached maturity yet.