Oxygen changes drive non-uniform scaling inDrosophila melanogasterembryogenesis

In Drosophila embryogenesis, increasing either oxygen concentration or temperature accelerates development. Having previously investigated temperature’s impact on embryogenesis, we characterized developmental response to oxygen levels using time-lapse imaging. Changing oxygen concentrations greatly impact survival, with developmental rate changes that are dwarfed by those induced by temperature. While extreme temperatures increase early embryo mortality, mild hypoxia increases arrest and death during mid-embryogenesis and mild hyperoxia increases survival over normoxia. Though not independent, the reactions to temperature and oxygen are fundamentally different, with developmental time being inversely proportional to oxygen concentration but logarithmically related to temperature. Most notably, while development scales uniformly with temperature, oxygen changes drive developmental heterochrony. Morphological processes change with oxygen concentration at different rates. Gut formation is more severely slowed by decreases in oxygen, while head involution and syncytial development are less impacted than the rest of development. These data reveal that uniform scaling, seen with changes in temperature, is not the default result of adjusting developmental rate.