Warming and photoperiod differentially mediate native and invasive alien predator effects on damselfly fitness traits

Invasive alien (IA) predators can disrupt predator-prey interactions and alter prey phenotypes. However, how their effects differ from those of native predators remains poorly understood. Additionally, it is unclear to what extent these impacts interact with environmental factors such as warming and photoperiod. To address these gaps, two complementary experiments were performed in the damselfly Ischnura elegans to test the effects of predator chemical cues (control, native noble crayfish, and IA spinycheek crayfish) in combination with (Experiment 1) temperature (ambient vs. warming) and short- and long-term predator cue exposure or (Experiment 2) photoperiod imposing different seasonal time constraints (early vs. late season). Effects on life-history (survival and growth rate), physiological (immune function measured as phenoloxidase (PO) activity and fat content), and behavioral (boldness and feeding rate) traits were subsequently quantified. In Experiment 1, responses to IA spinycheek crayfish cues differed from those induced by native noble crayfish cues across all trait types, with predator-specific responses strongly dependent on temperature. Following short-term exposure, predator-specific differences in boldness and PO activity were evident at ambient temperature but weakened under warming. Following long-term exposure, survival was lower under IA spinycheek than under native noble crayfish cues, whereas under warming, growth rate was lower following exposure to native noble crayfish cues than in the control, with the IA spinycheek treatment intermediate. In Experiment 2, the late photoperiod increased predator-specific differentiation in growth rate and boldness, primarily through stronger responses to native noble crayfish cues. The results broadly support the naïve prey hypothesis but show that responses to native and IA predators are not determined by predator novelty alone. Abiotic conditions, represented here by temperature and photoperiod, can modulate predator-specific plasticity, highlighting the importance of environmental context when predicting prey responses to biological invasions under climate change.