Identification of Candidate Genes Involved in the Survival of Drosophila in Extreme O2 Environments

The origin and evolution of life forms depended by and large on O2 availability over thousands of years. The mechanism of the adaptation process under strong selection pressure, however, is subject to some debate. For instance, it could be mediated by extant mutations or cryptic genetic variation that yield a fitness advantage in the new environment, or by mutations that arise de novo. For sexually reproducing organisms, multiple favored variants can also be acquired on a single haplotype via recombination to alleviate the effect of clonal interference and accelerate adaptation. It is however difficult to directly observe evolution in action. In the current study, we have identified the genomic intervals under selection in the high and low O2‐adapted Drosophila melanogaster. The adapted Drosophila melanogaster constitutes flies that could complete its life cycle in 90% and 4% O2 environments respectively, which otherwise is lethal for the naive flies. We used UAS‐RNAi x daGal4 system to functionally validate the role of specific genes of the top selected genomic interval. The top interval selected under high O2 environment consisted of 32 genes that includes four non‐protein‐coding genes. RNAi lines were available for 15 genes (15/28) that were evenly scattered across this interval. The high O2 tolerance assay indicate >98% eclosion rate in the adapted flies. Four genes i.e., CG15472, Klf15, CG2861 and CG42594, depicts a relatively higher number of pupation compared to the controls (12±0.6 to 14±2.5 versus <7 pupae counts per vial. The average pupae eclosed was higher for two of the genes, CG15472 and CG42594, although these numbers were significantly lower than the adapted flies. The percentage eclosion rate was significantly higher for CG15472 ‐(91.4 ±16.7%), which is close to the 98% eclosion seen in the adapted flies. Similarly, we have identified intervals under selection in the low O2 adapted flies. Remarkably, there was higher proportion of genes from the Notch signaling pathway in these selected intervals. Our results so far indicate that CG15472 from the top selected interval is one of the important gene playing critical role in the successful adaptation of flies to high O2 environment. Similarly, the Notch signaling pathway has an important role in the successful adaptation of flies to extremely low O2.