Meeting Abstract
Prior studies, of insect taxa with a range of body sizes – four orders of magnitude – have now consistently demonstrated that insects have very uniform O2 safety margins. For quiescent insects these margins are quite low – 1 to 2.5 kPa PO2, independent of size. It’s argued this is due to the extensive array of tracheae penetrating insect tissues, evolved to optimise O2 delivery during maximal O2 demand. Additional studies indicated distinct scaling compensation in tracheal dimensions relative to body size. However, this tracheal hypermetry is insufficient by itself to effect optimal O2 delivery. Insects rely, quite significantly, on active ventilation for optimal tissue oxygenation when challenged with O2 demand vs O2 availability. The standard method of determining critical PO2 (CritPO2) is to reduce O2 during flow through respirometry to measure metabolic rates – assessed from CO2 release rates (VCO2). As PO2 is reduced VCO2 declines steadily, until a clear break in VCO2 occurs (CritPO2). However, ventilation increases notably from 7.5 to 3 kPa PO2, but due to reduced O2 availability to maintain metabolism this ventilatory increase is not reflected in the VCO2 patterns. Thus to investigate ventilation we also measured respiratory water vapour release rates (VH2O) as a proxy. As insects approach 7.5 kPa PO2 the drastic increase in ventilatory activity is clear from VH2O increases, and, conversely, closer to the CritPO2 ventilatory muscle activity decreases due to O2 starvation indicated by VH2O decreases. In this study, using scarabaeid beetle species ranging in size from 35 to <1 gram, we investigate whether insect body size has an effect on the onset and magnitude of ventilatory activity when challenged with O2 demand vs O2 availability. Supported by NSF IOS 1122157.
