Drosophila melanogaster sperm turn more oxidative in the female.

Males and females of many species store sperm for extended periods. During storage, sperm are predicted to undergo cellular and functional changes, especially towards glycolytic energy metabolism because oxygen radicals derived from oxidative phosphorylation can affect sperm motility and fertilisation ability. However, not all species can use both major energy metabolism pathways. Here we examine the fruit fly Drosophila melanogaster and ask whether sperm metabolism can be fuelled by both glycolysis and oxidative phosphorylation, and to what extent metabolism changes during storage. Inhibiting glycolysis in vitro leads to a more oxidative state of sperm, inhibition of oxidative phosphorylation increased the glycolytic component assessed by multi-photon autofluorescence lifetime imaging (FLIM) of NAD(P)H. We further examined sperm in male and female sperm storage organs using FLIM of NAD(P)H and FAD. In intact storage organs, we find that, unexpectedly, i) sperm were more oxidative in females than males, and ii) oxidative phosphorylation increased with storage duration in females. Our observation that the relative contribution of both major energy metabolic pathways in Drosophila melanogaster sperm differs in males and females and over storage time has important evolutionary implications.