Cold Acclimation Favors Metabolic Stability in Drosophila suzukii

Abstract

The invasive fruit fly pest, Drosophila suzukii, is a chill susceptible species, yet it is capable of overwintering in rather cold climates, such as North America and North Europe, probably thanks to a high cold tolerance plasticity. Little is known about the mechanisms underlying cold tolerance acquisition in D. suzukii. In this study, we compared the effect of different forms of cold acclimation (at juvenile or at adult stage) on subsequent cold tolerance. Combining developmental and adult cold acclimation resulted in a particularly high expression of cold tolerance. As found in other species, we expected that cold-acclimated flies would accumulate cryoprotectants and would be able to maintain metabolic homeostasis following cold stress. We used quantitative target GC-MS profiling to explore metabolic changes in four different phenotypes: control, cold acclimated during development or at adult stage or during both phases. We also performed a time-series GC-MS analysis to monitor metabolic homeostasis status during stress and recovery. The different thermal treatments resulted in highly distinct metabolic phenotypes. Flies submitted to both developmental and adult acclimation were characterized by accumulation of cryoprotectants (carbohydrates and amino acids), although concentrations changes remained of low magnitude. After cold shock, non-acclimated chill-susceptible phenotype displayed a symptomatic loss of metabolic homeostasis, correlated with erratic changes in the amino acids pool. On the other hand, the most cold-tolerant phenotype was able to maintain metabolic homeostasis after cold stress. These results indicate that cold tolerance acquisition of D. suzukii depends on physiological strategies similar to other drosophilids: moderate changes in cryoprotective substances and metabolic robustness. In addition, the results add to the body of evidence supporting that mechanisms underlying the different forms of acclimation are distinct.

Keywords: cold shock; cold tolerance; homeostasis; metabolites; metabotype; recovery; spotted wing drosophila.

FIGURE 1

Thermal treatments experienced by flies during development (25°C or developmental acclimation [DA] at 10°C), and at adult stage (25°C or adult acclimation [AA] at 10°C), leading to the four treatments groups, and sampling scheme used for the time-series metabolic analysis. Ctrl, control flies; DA, developmental acclimation; AA, adult acclimation; DA + AA, combined developmental and adult acclimation.

FIGURE 2

Drosophila suzukii cold survival according to thermal treatments. Flies have been subjected to an acute cold stress at -5°C for 100 min (A). Survival was assayed 4, 24, and 48 h after cold shock. Bars represents survival probability ± standard error of the mean (SEM). Phenotypes with the same letters are not significantly different, disregarding the temporal effect (p-value < 0.05; least-squares means comparisons); n = 100 flies per condition. D. suzukii critical thermal minimum (Ct_min) depending on thermal treatments (B). Bars represents mean Ct_min ± Standard Error of the Mean (SEM). Groups with the same letters are not significantly different (p-value < 0.05; Tukey HSD); n = minimum 60 flies per condition. Chill coma recovery time (CCRT) according to thermal treatments (C). Flies were submitted to 0°C for 12 h and then CCRT was recorded at 25°C. Each point corresponds to the recovery time of one fly. Recovery curves were analyzed using survival analyses. Groups with the same letters are not significantly different (p-value < 0.008; Gehan-Breslow-Wilcoxon tests); n = 40 flies per condition; Ctrl, control flies; DA, developmental acclimation; AA, adult acclimation; DA + AA, combined developmental and adult acclimation.

FIGURE 3

Concentrations of the different biochemical families after the different thermal treatments. Boxplot sharing a same letter are not significantly different (p-value < 0.05; Tukey test); n = approximately 80 flies per condition. Ctrl, control flies; DA, developmental acclimation; AA, adult acclimation; DA + AA, combined developmental and adult acclimation.

FIGURE 4

Principal component analyses (PC1 vs. PC2) on the 45 metabolite concentrations after the different thermal treatments; n = approximately 80 flies per condition (A). Correlation circle of the 45 metabolites after acclimation (B). Metabolites highlighted in red or fuchsia correspond to the five metabolites contributing the most positively to PC1 and PC2, respectively; Metabolites highlighted in blue or green correspond to the five metabolites contributing the most negatively to PC1 and PC2, respectively. Ctrl, control flies; DA, developmental acclimation; AA, adult acclimation; DA + AA, combined developmental and adult acclimation.

FIGURE 5

Concentration of the different metabolite categories during the recovery from a cold stress at -5°C for 100 min (before, 0, 4, 8, and 12 h after the cold stress); n = approximately 80 flies per condition per time point. Ctrl, control flies; DA, developmental acclimation; AA, adult acclimation; DA + AA, combined developmental and adult acclimation.

FIGURE 6

Principal component analyses (PC1 vs. PC2) on the 45 metabolite concentrations during the recovery from an acute cold stress at -5°C for 100 min (before, 0, 4, 8, and 12 h after the cold stress); n = approximately 80 flies per condition per time point (A). Projection of the centroid scores of the PCA on PC1 according to recovery time (before, 0, 4, 8, and 12 h after the cold stress) (B). Correlation values of the different concentrations of metabolites in relation to the principal components PC1 (C) and PC2 (D) in the PCA. Correlations are ranked on the Y-axis according to their values. Light and dark gray bars, respectively, correspond to metabolites negatively or positively correlated to PC-1 or -2. Ctrl: Control flies; DA: developmental acclimation; AA: adult acclimation; DA + AA: combined developmental and adult acclimation.