Plasticity of insect body size in response to oxygen: integrating molecular and physiological mechanisms

• Hypoxia is a natural regulator of body size in insects.
• Oxygen restriction mediates phenotypic plasticity of body size in insects.
• A metabolic switch may support growth during oxygen restriction.

The hypoxia-induced reduction of body size in Drosophila and Manduca is ideal for understanding the mechanisms of body size plasticity. The mechanisms of size regulation are well-studied in these species, and the molecular mechanisms of oxygen sensing are also well-characterized. What is missing is the connection between oxygen sensing and the mechanisms that regulate body size in standard conditions. Oxygen functions both as a substrate for metabolism to produce energy and as a signaling molecule that activates specific cellular signaling networks. Hypoxia affects metabolism in a passive, generalized manner. Hypoxia also induces the activation of targeted signaling pathways, which may mediate the reduction in body size, or alternatively, compensate for the metabolic perturbations and attenuate the reduction in size. These alternative hypotheses await testing. Both perspectives — metabolism and information — are necessary to understand how oxygen affects body size.