Development of respiratory function in the American locustSchistocerca americanaI. Across-instar effects

Abstract

SUMMARYWe tested the hypothesis that oxygen delivery from the atmosphere to the tissues becomes more difficult as grasshoppers increase in body size throughout development due to increases in tracheal length. If this is true,then older, larger grasshoppers should have smaller safety margins [higher critical oxygen partial pressures (PO2s)] for oxygen delivery than younger, smaller grasshoppers. We exposed grasshoppers of first, third and fifth instars and adults to decreasing levels of atmospheric O2 and measured their ventilatory responses. Contrary to our prediction, we found that larger grasshoppers had critical PO2s eight times lower than juveniles due in part to their threefold lower mass-specific metabolic rates and their ability to quadruple convective gas exchange. Adults more than doubled abdominal pumping frequency and increased tidal volume by 25% as PO2 decreased fourfold, whereas the youngest juveniles showed no such responses. This study indicates that juveniles may be more susceptible to hypoxia in natural situations, such as exposure to high altitude or restricted burrows. Also, larger size is not necessarily correlated with a smaller safety margin for oxygen delivery in insects.

Body size effects on the oxygen-sensitivity of dragonfly flight

“…8). These results suggest that large and small flying dragonflies have similar safety margins for oxygen delivery, which is similar to what has been observed with resting (Greenlee and Harrison, 2004;Greenlee et al, 2007) and hopping grasshoppers (Kirkton et al, 2005), resting beetles (Lease et al, 2012) and feeding caterpillars (Greenlee and Harrison, 2005). The finding that oxygen sensitivity is independent of size during flight is particularly important because the oxygen demand of insects is highest during flight.…”

“…Direct tests of whether the physiological and behavioral functions of larger insects are more sensitive to declining oxygen levels have been negative for resting grasshoppers (Greenlee and Harrison, 2004;Greenlee et al, 2007), hopping grasshoppers (Kirkton et al, 2005), resting beetles (Lease et al, 2012) and feeding caterpillars (Greenlee and Harrison, 2005). However, these prior tests for an increase in oxygen sensitivity with body size can be criticized on the basis that they did not examine insects during high rates of aerobic metabolism when the oxygen delivery system is operating near its maximal capacity.…”

The evolutionary consequences of oxygenic photosynthesis: a body size perspective

“…Critical oxygen level does not scale with size across species of grasshoppers (Greenlee et al 2007) or during development in grasshoppers and caterpillars Harrison 2004, 2005). In fact, the metabolic safety margin increases with size in the grasshopper Schistocerca americana (Greenlee and Harrison 2004). Decrease in endurance during aerobic exercise with size in grasshoppers appears to reflect an increase in mass-specific metabolic rate with size rather than a decrease in the absolute capacity of the organism to supply its muscles with oxygen (Kirkton et al 2005).…”

Oxygen safety margins set thermal limits in an insect model system

“…While such changes are indeed likely to affect organisms through a number of potential cellular mechanisms (reviewed in Harrison and Haddad, 2011), their impacts could differ depending on species-specific critical oxygen levels before metabolism is depressed (critical oxygen partial pressure, P crit ), and the maximum delivery ability of a specific gas exchange system (respiratory conductance), which can vary substantially both within and among species (e.g. Greenlee and Harrison, 2004;Lease et al, 2006;Klok et al, 2010). The effects of oxygen supply have been investigated during ontogeny in the context of limitations on body size (e.g.…”