Time Constraints Modulate the Effects of Predator Cues and a Metal Across Life Stages in a Damselfly

Animals are increasingly exposed to multiple co-occurring stressors. Environmental factors such as seasonal time constraints (TC), predation risk, and pollutants strongly influence fitness-related traits in aquatic organisms. Yet, the interactive effects of such stressors, especially across life stages, remain unclear. We examined immediate and delayed effects of predator cue exposure during the post-overwintering egg stage and the larval stage, both subjected to early- or late-season photoperiods, and how these factors interacted with subsequent larval exposure to predator cues and copper in the damselfly Lestes sponsa. Copper was used due to its known effects as a pesticide on aquatic invertebrates. We measured immediate effects of egg predator cue on egg hatching (development time), carry-over effects on larval survival and growth rate, and behavioural (activity, resting, freezing, feeding) and physiological (oxidative damage, cellular energy allocation) traits after larval exposure to metal and predator cues. Several pairwise stressor interactions occurred, but none were modified by a third stressor. Predator cues during the egg stage delayed hatching under strong TC and led to sex-specific carry-over effects: males had reduced growth under strong TC. Copper increased oxidative damage only under weak TC, suggesting that strong TC can induce a hormetic antioxidant response. Short-term copper exposure did not affect survival, behaviour, or net energy budget. However, predator exposure during the egg stage modified energy allocation, increasing it under weak TC and reducing it under strong TC, indicating context-dependent trade-offs. Behavioural responses were shaped by predator cues and TC; fast-growing larvae under strong TC increased activity and feeding, while predator-exposed individuals reduced these behaviours. These findings show how environmental stressors interact across life stages and traits, shaping plastic, sex-specific responses. By integrating natural and anthropogenic stressors with life-history timing, our study advances understanding of how ecological and evolutionary processes shape stress responses.