OXYGEN-SENSITIVE FLIGHT METABOLISM IN THE DRAGONFLY ERYTHEMIS-SIMPLICICOLLIS

Insect flight metabolism is completely aerobic, and insect resting met abolism is quite insensitive to atmospheric oxygen level, suggesting a large safety margin in the capacity of the tracheal system to deliver oxygen during flight. We tested the sensitivity of flight initiation and metabolism to atmospheric oxygen level in the libellulid dragonfly Erythemis (Mesothemis) simplicicollis using flow-through respirometri c measurements of the rate of CO2. emission ((V) over dot(CO2)). Fligh t initiations were unimpaired in atmospheric oxygen levels as low as 1 0 %, However, flight metabolic rate was affected by ambient oxygen lev el. Flight (V) over dot(CO2) decreased in hypoxic mixtures (30 kPa or 10 kPa oxygen) and increased in hyperoxic atmospheres (30 kPa or 50 kP a oxygen), suggesting that ambient oxygen level influences flight musc le oxygen partial pressure (P-O2) and the vigour of flight, These are the first data to show oxygen-limitation of flight metabolism in a fre e-flying insect. A low safety margin for oxygen delivery during dragon fly flight is consistent with a previous hypothesis that atmospheric h yperoxia facilitated gigantism in Paleozoic protodonates. However, all ometric studies of tracheal morphology, and mechanisms and capacity of gas exchange in extant insects are necessary in order to test the hyp othesis that the oxygen-sensitivity of aerobic metabolism increases wi th body size in insects.