Microgeographic differentiation in thermal and antipredator responses and their carry-over effects across life stages in a damselfly

Abstract

Global warming and invasive species, separately or combined, can impose a large impact on the condition of native species. However, we know relatively little about how these two factors, individually and in combination, shape phenotypes in ectotherms across life stages and how this can differ between populations. We investigated the non-consumptive predator effects (NCEs) imposed by native (perch) and invasive (signal crayfish) predators experienced only during the egg stage or during both the egg and larval stages in combination with warming on adult life history traits of the damselfly Ischnura elegans. To explore microgeographic differentiation, we compared two nearby populations differing in thermal conditions and predator history. In the absence of predator cues, warming positively affected damselfly survival, possibly because the warmer temperature was closer to the optimal temperature. In the presence of predator cues, warming decreased survival, indicating a synergistic effect of these two variables on survival. In one population, predator cues from perch led to increased survival, especially under the current temperature, likely because of predator stress acclimation phenomena. While warming decreased, predator cues increased larval development time with a proportionally stronger effect of signal crayfish cues experienced during the egg stage, indicating a negative carry-over effect from egg to larva. Warming and predator cues increased mass at emergence, with the predator effect driven mainly by exposure to signal crayfish cues during the egg stage, indicating a positive carry-over effect from egg to adult. Notably, warming and predator effects were not consistent across the two studied populations, suggesting a phenotypic signal of adaptation at a microgeographic scale to thermal conditions and predator history. We also observed pronounced shifts during ontogeny from synergistic (egg and early larval stage) toward additive (late larval stage up to emergence) effects between warming and predator stress. The results point out that population- and life-stage-specific responses in life-history traits to NCEs are needed to predict fitness consequences of exposure to native and invasive predators and warming in prey at a microgeographic scale.

Fig 1. Experimental design.

Ischnura elegans eggs were assigned to groups receiving no predator cues (control), native European perch cues (perch), or invasive alien signal crayfish cues (signal crayfish). At hatching, the egg control group continued as larval control group (CC). The egg perch cue group was divided into larval control (PC) and larval perch cue (PP) groups. The egg signal crayfish cue group was divided into larval control (SC) and larval signal crayfish cue (SS) groups.

Fig 2

Effects of predator cues and temperature (current and 4°C warming) on the egg development time in days (A) and degree-days (B) in I. elegans from two populations (Dąbski and Płaszowski). Error bars show 95% CI. Sample sizes per group are provided in (A). Abbreviations: C–control; P- perch cues; S- signal crayfish cues.

Fig 3

Effects of predator cues and temperature (current and 4°C warming) on larval survival after 14 days (A) and until emergence (B) in I. elegans from two populations (Dąbski and Płaszowski). Error bars show 95% CI. Abbreviations: CC—control (egg) and control (larva) group; PC—perch (egg) and control (larva) group; PP—perch (egg) and perch (larva) group; SC—signal crayfish (egg) and control (larva) group; SS—signal crayfish (egg) and signal crayfish (larva) group.

Fig 4

Effects of predator cues and temperature (current and warming) on the larval development time in days (A) and degree-days (B) in I. elegans from two populations (Dąbski and Płaszowski). Error bars show 95% CI. The sample size per group is provided in (A). Abbreviations as in Fig 3.

Fig 5. Effects of predator cues and temperature (current and warming) on the estimated mass at emergence in I. elegans from two populations (Dąbski and Płaszowski).

Error bars show 95% CI. Sample size per group is provided. Abbreviations as in Fig 3.