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

Abstract

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 (Sympetrum sanguineum). 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.

Keywords: cannibalism; chemical cues; dragonflies; oxygen consumption; population dynamics; respiration rate.

FIGURE 1

Experimental media preparation (A) D2: Kairomone from 2  S. sanguineum × L⁻¹, (B) D5: Kairomone from 5  S. sanguineum × L⁻¹, (C) D2 + IC: Similar to D2 but with additional cue from injured conspecifics. The arrows represent timelines of experimental media preparation. Glass vessels containing cannibals indicate low (A) and high (B) volumes, corresponding to low and high concentrations of kairomone cues, respectively. The numbers next to the vessels indicate replicates. (C) Contains an extra vessel labeled 2 h before experiment, marking the subsequent step necessary for D2 + IC medium preparation.

FIGURE 2

Respiratory rate (μmol O2 μg⁻¹ h⁻¹) of S. sanguineum exposed to different concentrations of kairomones (C, D2, D5) and cues from injured conspecific (D2 + IC); bars indicate standard deviation, *denotes treatments significantly different from the control treatment, C.