Heat-induced hormesis in longevity as correlated response to thermal-stress selection in Drosophila buzzatii

Hormesis in longevity is a widespread phenomenon across the animal kingdom. It takes place when longevity is improved as an indirect effect of mild stress. We explored some possible evolutionary trajectories of hormesis in longevity in artificially selected lines of Drosophila buzzatii. The lines were bi-directionally selected for either knockdown resistance to heat stress (K−, K+) or chill-coma recovery (CCR−, CCR+, with the + and – signs indicating selection for decreased and increased tolerance, respectively). All K and CCR lines successfully diverged due to thermal-stress selection. The heat-inducible hormesis in longevity was substantial in both K− and CCR− females, whereas no hormesis was apparent for females in CCR+, K+ and control lines. Among-line differences in longevity of non-heat-treated females disappeared after a heat-hardening treatment. Hormesis effects on the demographic senescence rate were sex-specific and consistently higher in the shorter-lived than in the longer-lived lines. Hormesis is an adaptive response, as its magnitude can evolutionary increase with stress-sensitivity.