Radiation and Longevity Enhancement in Tribolium

Insects which have been exposed to ionizing radiation as young adults frequently exhibit greater mean longevity than do controls. This enhanced longevity has been observed in several genera of Diptera, in Lepidoptera, in Coleoptera, and in Orthoptera, among others, so the phenomenon is fairly ubiquitous. It is also very surprising: Any system exposed to ionizing radiation absorbs energy which is distributed among the system’s constituent atoms in essentially random fashion; thus, the system becomes more disordered, and we expect the consequences to be deleterious. Furthermore, even the recognized beneficial effects of ionizing radiation are secured by detrimental action on some component of the system, e.g., elimination of a tumor or of a parasite. Finally, although enhanced longevity of irradiated insects had first been reported some 40 years earlier (Davey 1919), the phenomenon was rediscovered in experiments stimulated by George Sacher’s observation of life shortening in irradiated rodents. This life-shortening effect took the form of a dose-dependent shift to the left of the Gompertz function (logarithm of age-specific mortality rate vs age), prompting suggestions that radiation either acted as an increment of age or served to accelerate the natural aging process(es). This, in turn, suggested that radiation damage and natural aging might share common molecular mechanisms, such as DNA damage or free radical interactions. In this context, longevity enhancement by radiation was particularly surprising.