Evidence for evolutionary constraints in Drosophila metal biology

Mutations in single Drosophila melanogaster genes can alter total body metal accumulation. We therefore asked whether evolutionary constraints maintain biologically abundant metal ions (iron, copper, manganese and zinc) to similar concentrations in different species of Drosophilidae, or whether metal homeostasis is a highly adaptable trait as shown previously for triglyceride and glycogen storage. To avoid dietary influences, only species able to grow and reproduce on a standard laboratory medium were selected for analysis. Flame atomic absorption spectrometry was used to determine metal content in 5-days-old adult flies. Overall, the data suggest that the metallome of the nine species tested is well conserved. Meaningful average values for the Drosophilidae family are presented. Few statistically significant differences were noted for copper, manganese and zinc between species. In contrast, Drosophila erecta and Drosophila virilis showed a 50% increase above average and a 30% decrease below average in iron concentrations, respectively. The changes in total body iron content correlated with altered iron storage in intestinal ferritin stores of these species. Hence, the variability in iron content could be accounted for by a corresponding adaptation in iron storage regulation. We suggest that the relative expression of the multitude of metalloenzymes and other metal-binding proteins remains overall similar between species and likely determines relative metal abundances in the organism. The availability of a complete and annotated genome sequence of different Drosophila species presents opportunities to study the evolution of metal homeostasis in closely related organisms that have evolved separately for millions or dozens of million years.