An experimental evolution study confirms that discontinuous gas exchange does not contribute to body water conservation in locusts

Abstract

The adaptive nature of discontinuous gas exchange (DGE) in insects is contentious. The classic 'hygric hypothesis', which posits that DGE serves to reduce respiratory water loss (RWL), is still the best supported. We thus focused on the hygric hypothesis in this first-ever experimental evolution study of any of the competing adaptive hypotheses. We compared populations of the migratory locust (Locusta migratoria) that underwent 10 consecutive generations of selection for desiccation resistance with control populations. Selected locusts survived 36% longer under desiccation stress but DGE prevalence did not differ between these and control populations (approx. 75%). Evolved changes in DGE properties in the selected locusts included longer cycle and interburst durations. However, in contrast with predictions of the hygric hypothesis, these changes were not associated with reduced RWL rates. Other responses observed in the selected locusts were higher body water content when hydrated and lower total evaporative water loss rates. Hence, our data suggest that DGE cycle properties in selected locusts are a consequence of an evolved increased ability to store water, and thus an improved capacity to buffer accumulated CO 2 , rather than an adaptive response to desiccation. We conclude that DGE is unlikely to be an evolutionary response to dehydration challenge in locusts.

Body size, metabolic rate and diapause in the oriental hornet (Vespa orientalis), in two extreme climatic regions

“…DGC in hornets was recorded only during reduced activity (rest) times. This respiratory pattern is known from many invertebrates and vertebrates during periods of metabolic rate reduction, and several adaptive explanations have been suggested for this ventilation pattern (Chown et al, 2006; Hetz & Bradley, 2005; Levin et al, 2015; Lighton, 1991; Talal et al, 2016). An early explanation for the adaptive role of DGC indicated a possible mechanism to minimize the water loss of an insect (Levy & Schneiderman, 1958), but to date, there is much controversy relating to the origin of this gas exchange pattern (Lighton, 2007; Matthews, 2018).…”

Metabolic rate scaling, ventilation patterns and respiratory water loss in red wood ants: activity drives ventilation changes, metabolic rate drives water loss

“…The metabolic rate of insects is correlated with the pattern of ventilation Bradley, 2009, 2010;Gibbs and Johnson, 2004). There are three principal ventilation patterns observed in insects; continuous, discontinuous and cyclic (Chown and Nicolson, 2004), though the adaptive value of these patterns remains unclear (Chown et al, 2006;Gudowska et al, 2015;Marais et al, 2005;Schimpf et al, 2012;Talal et al, 2016). To date, most studies have focused on discontinuous gas exchange cycles (DGC) (Buck and Kesiter, 1955;Chown et al, 2006;Lighton, 1994;Quinlan and Gibbs, 2006), though the majority of insects do not use DGC (Marais et al, 2005).…”