P1.205 Wednesday, Jan. 4 Atmospheric oxygen availability limits thermotolerance at upper lethal temperatures: an examination of environmental oxygen limitation in insects MCCUE, Marshall D; St. Mary's University email@example.com
Thermotolerance is an important factor in shaping the biogeographic distribution of animals and potentially a species’ ability to cope with climate change. The current paradigm is that the primary mechanism restricting survival at high temperatures, particularly in endotherms, is the physiological hysteresis between oxygen supply and oxygen demand. Despite broad support for this thesis, it rests on little direct empirical support, particularly among terrestrial animals. The classic test of resource limitation is to examine performance of an organism under normal conditions and under conditions where the potentially limiting resource is increased and decreased. Oxygen delivery, and possibly thermotolerance, in insects is thought to be limited by the diffusion of oxygen throughout the tracheal system. Therefore, I exposed several species of insects to ambient temperatures just above their thermal lethal limit and recorded lethal exposure times under several ambient oxygen concentrations (i.e. normoxia 21%, hypoxia 0,10%, and hyperoxia 35,95%) to investigate how ambient oxygen availability affects thermotolerance. I also tested specific predictions about how such effects were related to body size and developmental stage. Survival curves were compared using Kaplan-Meyer log rank analyses. The results suggest that insects generally exhibited increased thermotolerance at 35% oxygen and decreased thermotolerance at 10% oxygen, although some species showed no significant effects. Performance was decreased in all cases under anoxia, yet results were mixed at 95% oxygen. Insects have existed over the past 350 million years during which the oxygen availability of Earth’s atmosphere is thought to have fluctuated from 10% to 35%; it will be important to consider how oxygen availability may have influenced the physiological performance and biogeography of ancient insects.