Oxygen supply limits the chronic heat tolerance of locusts during the first instar only

Abstract

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.

An increase in management actions has compensated for past climate change effects on desert locust gregarization in western Africa

“…For desert locusts, temperature increases can have positive effects on gregarization in the areas that were at the lower temperature range to start with, but in extremely hot and arid deserts these further temperature increases could also impede population development [ 62 ]. Indeed, temperatures exceeding their temperature tolerance limits can trigger heat stress for which their chances of survival depend strongly on shade availability, hydration state, and also oxygen supply during the first instar [ 63 , 64 ]. However, increased precipitation can reduce these risks, as shown for some species of grasshoppers, by counterbalancing the impact of warming on egg development for example [ 65 ].…”

Submergence tolerance in immature stages of the stalk‐eyed fly Sphyracephala detrahens (Diptera: Diopsidae)

“…Oxygen consumption and accumulation of metabolic end‐products associated with activity can affect survival (El‐Kady et al, 1999; Hoback & Stanley, 2001). Increased respiratory performance associated with development can increase hypoxic tolerance (Youngblood et al, 2020). Alternatively, submergence in water may induce mortality during moulting (Jones & Kunz, 1996).…”

Climate change expected to improve digestive rate and trigger range expansion in outbreaking locusts

“…Because most ectotherms permit their daily temperature to vary over a range (Angilletta et al, 2019; Berk & Heath, 1975; Hertz et al, 1993), we assumed that locusts only sought shade if the modeled body temperature exceeded an upper set point of 40.9°C (i.e., the upper 68th percentile of field‐active body temperatures), at which point locusts retreated to 90% shade to avoid heat stress. This upper set point approximated the body temperature (42°C) that reduced the long‐term survival of S. cancellata in the laboratory (Youngblood et al, 2020). At night, we assigned locusts the body temperature in 90% shade, because locusts tend to roost under trees (Chappell & Whitman, 1990).…”