Extreme heat directly limits an organism's survival and reproduction, but scientists cannot agree on what causes organisms to lose function or die during heating. According to the theory of oxygen-and capacity-limitation of thermal tolerance, heat stress occurs when a warming organism's demand for oxygen exceeds its supply, triggering a widespread drop in ATP concentration. This model predicts that an organism's heat tolerance should decrease under hypoxia, yet most terrestrial organisms tolerate the same amount of warming across a wide range of oxygen concentrations. This point is especially true for adult insects, who deliver oxygen through highly efficient respiratory systems. However, oxygen limitation at high temperatures may be more common during immature life stages, which have less developed respiratory systems. To test this hypothesis, we measured the effects of heat and hypoxia on the survival of locusts (Schistocerca cancellata) throughout development. We demonstrate that the heat tolerance of locusts depends on oxygen supply during the first instar but not during later instars.This finding provides further support for the idea that oxygen limitation of thermal tolerance depends on respiratory performance, especially during immature life stages.
13Extreme heat directly limits an organism's survival and reproduction, but scientists cannot agree 14 on what causes organisms to lose function or die during heating. According to the theory of 15 oxygen-and capacity-limitation of thermal tolerance, heat stress occurs when a warming 16 organism's demand for oxygen exceeds its supply, triggering a widespread drop in ATP 17 concentration. This model predicts that an organism's heat tolerance should decrease under 18hypoxia, yet most terrestrial organisms tolerate the same amount of warming across a wide range 19 of oxygen concentrations. This point is especially true for adult insects, who deliver oxygen 20 through highly efficient respiratory systems. However, oxygen limitation at high temperatures 21 may be more common during immature life stages, which have less developed respiratory 22 systems. To test this hypothesis, we measured the effects of heat and hypoxia on the survival of 23 locusts (Schistocerca cancellata) throughout development. We demonstrate that the heat 24 tolerance of locusts depends on oxygen supply during the first instar but not during later instars. 25This finding provides further support for the idea that oxygen limitation of thermal tolerance 26 depends on respiratory performance, especially during immature life stages. 27 28 230 , I., et al. (2014). Aerobic scope fails to 235 explain the detrimental effects on growth resulting from warming and elevated CO2 in 236 Atlantic halibut. J. Exp. Biol. 217,[711][712][713][714][715][716][717] Greenlee, K. J. and Harrison, J. F. (1998). Acid-base and respiratory responses to hypoxia in 238 the grasshopper Schistocerca americana.
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