Trade-offs to flight capability in Gryllus firmus: the influence of whole-organism respiration rate on fitness

Journal

Wing dimorphism, where some macropterous long-winged (LW) individuals can fly whereas micropterous short-winged (SW) individuals cannot, is common in insects and believed to be maintained in part by trade-offs between flight capability and reproductive traits. In this paper we examine differences in whole-organism respiration rate between wing morphs of the sand cricket Gryllus firmus. We hypothesized that maintenance of the flight apparatus would result in elevated CO₂ respired because of the high metabolic cost of these tissues, which, in turn, constrain resources available for egg production in females. As the trade-off involves calling behaviour in males, we predicted no equivalent constraint on organ development in this sex. We found female macropters (particularly older crickets) had significantly higher residual respiration rates than micropters. In males, we found only marginal differences between wing morphs. In both sexes there was a highly significant effect of flight muscles status on residual respiration rate, individuals with functional muscles having higher respiration rates. Both female and male macropters had significantly smaller gonads than micropters. Whole-organism residual respiration rate was negatively correlated with fecundity: macropterous females with high respiration rates had smaller gonads compared with macropterous females with lower respiration rates.