Sex and genetic background influence Superoxide dismutase (cSOD) related phenotypic variation in Drosophila melanogaster

Mutations often have drastically different effects in different genetic backgrounds; understanding a gene's biological function then requires an understanding of its interaction with genetic diversity. The antioxidant enzyme cytosolic superoxide dismutase, cSOD, catalyzes the dismutation of the superoxide radical, a molecule that can induce oxidative stress if its concentration exceeds cellular control. Accordingly, Drosophila melanogaster lacking functional cSOD exhibit a suite of phenotypes including decreased longevity, hypersensitivity to oxidative stress, impaired locomotion, and reduced NADP(H) enzyme activity in males. To date, cSOD-null phenotypes have primarily been characterized using males carrying one allele, cSodⁿ¹⁰⁸red, in a single genetic background. We used analysis of variance, and the effect size partial eta squared, to partition the amount of variation attributable to cSOD activity, sex, and genetic background across a series of life history, locomotor, and biochemical phenotypes associated with the cSOD-null condition. Overall, the results demonstrate that the cSOD-null syndrome is largely consistent across sex and genetic background, but also significantly influenced by both. The sex-specific effects are particularly striking and our results support the idea that phenotypes cannot be considered fully defined if they are examined in limited genetic contexts.

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