Resistance to oxidative stress induced by paraquat correlates well with both decreased and increased lifespan in Drosophila melanogaster

There is increasing support for the notion that genetic variation for lifespan, both within and between species, is correlated with variation in the efficiency of the free radical scavenging system and the ability to withstand oxidative stress. In Drosophila, resistance to dietary paraquat, a free radical generator, is often used as a measure of resistance to oxidative stress and is reported to give firm positive correlations with longevity. Recently it has been suggested that an increase in antioxidative defences in Drosophila only has a beneficial effect in relatively short-lived stocks. This implies that mechanisms of lifespan determination can be different in lines with different genetic constitution. Here we test if variation in resistance to dietary paraquat co-segregates with variation in lifespan in two sets of Drosophila melanogaster lines that were selected for decreased and increased virgin lifespan respectively. Flies of the short-lived lines show decreased resistance to paraquat compared to the control lines, indicating low resistance against oxidative stress. On the other hand, both males and females of the long-lived lines show, despite increased feeding rates on paraquat-supplemented food, no decreased survival compared to control lines. This shows that flies of the long-lived lines have increased paraquat resistance, but that this is masked by increased feeding rate, resulting in increased exposure to paraquat. This suggests that resistance to paraquat is a correlated response to selection on virgin lifespan over the entire genetic range