Abstract
We previously demonstrated that, while changes in temperature produce dramaticshifts in the time elapsed during Drosophila melanogaster embryogenesis, therelative timing of events within embryogenesis does not change. However, it wasunclear if this uniform scaling is an intrinsic property of developing embryos, orif it is specific to thermal fluctuations. To investigate this, here we characterizethe embryonic response to changes in oxygen concentration, which also impactdevelopmental rate, using time-lapse imaging, and find it fundamentally differentfrom the temperature response. Most notably, changes in oxygen levels drivedevelopmental heterochrony, with the timing of several morphological processesshowing distinct scaling behaviors. Gut formation is severely slowed by decreasesin oxygen, while head involution and syncytial development are less impactedthan the rest of development, and the order of several developmental landmarksis inverted at different oxygen levels. These data reveal that the uniform scalingseen with changes in temperature is not a trivial consequence of adjusting developmentalrate. The developmental rate changes produced by changing oxygenconcentrations dwarf those induced by temperature, and greatly impact survival.While extreme temperatures increase early embryo mortality, mild hypoxia increasesarrest and death during mid-embryogenesis and mild hyperoxia increasessurvival over normoxia.
Highlights
After discovering that the time elapsed during different morphological stages of Drosophila embryogenesis scale uniformly as temperature changes the overall time of embryogenesis[1], several colleagues questioned whether the result was surprising, suggesting instead that it was a natural and trivial consequence of physical and chemical laws
Oxygen concentration controls developmental rate We used automated time-lapse imaging in an airtight box with oxygen concentration control (±1%) and precise temperature control (±0.1°C) to track development using previously described methods[1]
We investigated embryos raised at constant oxygen concentrations (29%, 25%, 21%, 17%, 14%, and 10% O2) and kept at three different temperatures (17.5°C, 22.5°C, and 27.5°C), giving a total of eighteen specific conditions with over 800 embryos
Summary
After discovering that the time elapsed during different morphological stages of Drosophila embryogenesis scale uniformly as temperature changes the overall time of embryogenesis[1], several colleagues questioned whether the result was surprising, suggesting instead that it was a natural and trivial consequence of physical and chemical laws. To explore this possibility, and to provide orthogonal insight into the mechanisms of the control of developmental timing, we sought to manipulate developmental rate in a temperature-independent manner.
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