Abstract
Prey reconfigure their physiology to avoid costs of prolonged predator pressure. However, these changes might not occur under periodic predation risk, with repeating acute phases. To test the effect of predation risk continuity on changes in prey physiology, we exposed amphipods: Dikerogammarus villosus and Gammarus jazdzewskii to periodic and constant predation cue. After one week, we measured: cellular defence systems: total antioxidant status (TAS), heat shock proteins (Hsp70); intracellular damage marker: lipid peroxidation (TBARS); condition index: glycogen concentration. Predator presence reduced TAS level in G. jazdzewskii independent of its continuity and in D. villosus after periodic exposure. Amphipods showed downregulation of Hsp70 when exposed to periodic (D. villosus) or constant (G. jazdzewskii) predation risk. Exposure to predators reduced TBARS level in D. villosus (irrespective of the continuity) and G. jazdzewskii (periodic exposure). Glycogen concentration in both species was not affected by predator presence. Thus, the continuity of the predator cue shaped prey physiology reconfiguration, optimizing costs of physiological adjustments under challenging conditions. Nevertheless, the lack of negative consequences of the prolonged exposure to the predator cue, whether constant or periodic, shows that amphipods can thrive under chronic predation risk, which is a constant part of the wild environment.
Highlights
In natural ecosystems, predator pressure is variable and unpredictable
Gammarids originated from two locations: individuals of D. villosus were caught using trap substrata in the nearshore zone of the Włocławek Reservoir while individuals of G. jazdzewskii were captured in the River Zielona Struga with a hand net
D. villosus exposed to the periodic predation risk demonstrated lower TAS compared to the control individuals (Fig. 1A)
Summary
In natural ecosystems, predator pressure is variable and unpredictable. in the aquatic environment, low concentration of predator kairomones is constantly present and defence reactions depend on the increase in the concentration of the chemical signal. Some studies demonstrated that most of the cost of the defence reaction, exhibited as the oxidative stress, was suffered during the initial exposure to the predation signal, while the subsequent prolonged and constant stimulation resulted in the reduction in oxidative damage despite the sustained increased metabolic rate[22]. We hypothesized that the continuity of the predation risk is a key factor responsible for prey physiology reconfiguration resulting in the reduction of costs related to oxidative damage. To test this hypothesis, we checked whether total consequences of exposure to periodic predation risk (with the acute response phases repeated each time and separated by safe periods) could exceed those resulting from the constant predation risk (when prey can decrease their acute responses to overlapping exposure events). To obtain a wide picture of changes in prey condition, we measured a range of physiological parameters informing of: (1) antioxidant defence potential (TAS: total antioxidant status), (2) intra-cellular damage as indicated by the level of lipid peroxidation (measured as the concentration of thiobarbituric acid reactive substances, TBARS), (3) concentration of a crucial but energetically costly part of the cellular defence system: heat shock proteins (Hsp70) and (4) concentration of the main energy storage material (glycogen)
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