Environmental and evolutionary consequences of altered atmospheric oxygen in Drosophila melanogaster

Abstract

Experimental evolution was used to independently evolve 12 replicate populations of Drosophila melanogaster for 34+ generations in one of three treatment environments of varying PO2: hypoxia (5.0-10.1 kPa), normoxia (21.3 kPa), and hyperoxia (40.5 kPa). Several traits related to whole animal performance and metabolism were monitored during experimental evolution and several common garden assays were performed at various stages to directly compare evolved and acclimatory differences between treatments. Results clearly demonstrate the evolution of increased anoxia tolerance in hypoxia-evolved populations, suggesting adaptation to this environment. This was correlated with an increase in citrate synthase activity compared to normoxic (control) populations, suggesting an increase in mitochondrial density in these populations. In contrast, no direct evidence of increased performance of the hyperoxia-evolved populations was detected, although an evolutionary cost was observed as a substantial decline in anoxia tolerance. Changes in performance did not result in an increase in any of the fitness components measured, including productivity and longevity, suggesting that these assays failed to capture the components of fitness relevant to adaptation.