Meeting Abstract
Predicting how organisms will respond to climate change requires a detailed understanding of how all life-stages respond to heat stress. Indeed, an animal’s heat tolerance changes during development, but the physiological mechanisms underlying these changes remain unknown. One proposed mechanism, known as oxygen limited thermal tolerance, occurs when metabolic demand during warming outstrips the energy supplied by aerobic respiration. Although this hypothesis has minimal support from studies of adult insects, early life-stages with less developed respiratory systems may be more susceptible to oxygen limitation. For example, as locusts develop, their capacity to deliver oxygen increases with each successive instar. Further, oxygen may become increasingly limited as locusts approach their next molt since the tracheal system does not grow during an instar. Here, we evaluated whether these ontogenetic shifts in oxygen delivery correspond with changes in heat tolerance in the South American locust (Schistocerca cancellata) and the American locust (Schistocerca americana). We measured changes in heat tolerance both within and among instars, as well as the effect of hypoxia on heat tolerance in each of these stages. Hypoxia decreased the survival of 1st-instar locusts at high temperatures, but did not do so for survival of any other instars. Within the 6th and final instar, heat tolerance decreased as animals progressed through the instar, but there was no effect of hypoxia on heat tolerance at any time during the 6th instar. These results suggest that oxygen limitation explains some of the ontogenetic variation in heat tolerance in locusts, but other variables can play a more important role depending on the life-stage.
