Meeting Abstract
The hygric hypothesis for the evolution of the discontinuous gas exchange (DGE) pattern in insects posits that DGE serves primarily to reduce respiratory water loss. In this study we directly tested predictions of the hygric hypothesis by using, for the first time, an experimental evolution approach. We compared populations of the migratory locust (Locusta migratoria) that underwent ten consecutive generations of selection for desiccation-resistance, with corresponding control populations. Response to selection was reflected in a 36% longer survival time of the experimental populations compared to controls, at 30° C, with no access to fresh food (8.3±0.4d and 6.1±0.3d, respectively). In contrast with one prediction of the hygric hypothesis, DGE prevalence did not differ between selected and control populations (circa. 75% in both groups). We recorded significantly lower evaporative water loss rates (EWL) and higher body water content in the hydrated selected populations. Selected locusts exhibited significantly longer DGE cycles than controls (longer interburst but not burst durations). However, in contrast with predictions of the hygric hypothesis, these evolved changes in DGE properties were not associated with reduced rates of respiratory water loss in the selected locusts. Hence, our data suggest that longer cycle and interburst durations are a consequence of an evolved increased ability to store water, and thus buffer accumulated CO2, rather than an adaptive response to desiccation stress. We conclude that the DGE pattern is unlikely to be an evolutionary response to dehydration challenge in locusts.
