Adaptations of insects to hypoxia: Morphological, metabolic and behavioural responses

Insects rely on oxygen for oxidative metabolism, which is crucial for ATP production and overall metabolic functions. Hypoxia, defined as inadequate oxygen supply, poses significant challenges to insect survival, reproductive success, and flight performance. This review categorizes hypoxia into environmental and functional types and examines its physiological and ecological impacts on insects inhabiting hypoxic environments, such as aquatic systems, flood-prone soils, and high altitudes. Critical adaptations include alterations in tracheal morphology, metabolic shifts from aerobic to anaerobic pathways, and specific behavioural responses aimed at enhancing oxygen uptake. Notably, signalling pathways like Nitric Oxide Synthase (NOS) and Hypoxia-Inducible Factor (HIF) are activated under low-oxygen conditions, promoting necessary physiological changes. The review highlights how hypoxia leads to decreased survivability, reduced fecundity, extended developmental times, and altered flight activity. Moreover, it discusses the variation in sensitivity to hypoxia among terrestrial and aquatic insects. Understanding these adaptations provides insight into the resilience of insects in fluctuating oxygen environments and underscores the evolutionary significance of hypoxia tolerance in ecological contexts.