Non‐Consumptive Effects of Cannibalism Elicit a Metabolic Response in Dragonfly Larvae

Predator-prey interactions typically involve changes in metabolic rates associated with hunting, foraging, and activation/maintenance of defense mechanisms. Similar response can result from non-consumptive effects mediated by chemical cues, such as alarm cues (indicating predation), diet cues (signaling food resources), and kairomones (indicating predator or prey availability). While the impact of interspecific chemical communication on energy expenditure is well-studied, the role of conspecific chemical cues is less understood. This study examines non-consumptive effects of cannibalism on metabolic rates in dragonfly larvae (<i>Sympetrum sanguineum</i>). During the respiratory experiment, larvae were exposed to low and high concentrations of conspecific kairomones and kairomones with cues from injured conspecifics to simulate different population densities and conspecific interactions. Our results showed that high concentrations of kairomones and cues from injured conspecifics significantly increased larval respiration rates in comparison with controls and low concentrations. This suggests that in an environment with constant exposure to each other's cues, larvae face ongoing readiness costs, impacting their individual fitness and population dynamics.