Dietary live yeast alters metabolic profiles, protein biosynthesis and thermal stress tolerance of Drosophila melanogaster

International audienceThe impact of nutritional factors on insect's life-history traits such as reproduction and lifespan has been excessively examined; however, nutritional determinant of insect's thermal tolerance has not received a lot of attention. Dietary live yeast represents a prominent source of proteins and amino acids for laboratory-reared drosophilids. In this study, Drosophila melanogaster adults were fed on diets supplemented or not with live yeast. We hypothesized that manipulating nutritional conditions through live yeast supplementation would translate into altered physiology and stress tolerance. We verified how live yeast supplementation affected body mass characteristics, total lipids and proteins, metabolic profiles and cold tolerance (acute and chronic stress). Females fed with live yeast had increased body mass and contained more lipids and proteins. Using GC/MS profiling, we found distinct metabolic fingerprints according to nutritional conditions. Metabolite pathway enrichment analysis corroborated that live yeast supplementation was associated with amino acid and protein biosyntheses. The cold assays revealed that the presence of dietary live yeast greatly promoted cold tolerance. Hence, this study conclusively demonstrates a significant interaction between nutritional conditions and thermal tolerance

Description des limites thermiques basales de Drosophila suzukii

editorial reviewe

Cold acclimation triggers major transcriptional changes in Drosophila suzukii

editorial reviewedInsect life is directly depending on environment temperature. Low temperatures can alter cellular homeostasis resulting in chill damages and in most extreme cases, lethality. To counteract these deleterious effects, insects can use acclimation-related physiological adjustments. The spotted wing drosophila (SWD) Drosophila suzukii is an invasive pest of red berries. SWD is known to be chill susceptible, succumbing to cold exposures way above 0 °C. Yet, it overwinters in harsh European winter conditions, which might be partly due to its highly plastic cold tolerance. However, little is known about underlying mechanisms of cold acclimation in SWD. Here, we promoted SWD cold tolerance through increasing acclimation periods (i.e. from 2 h to 9 days) and selected the most extreme phenotype to characterize transcriptional changes by RNAseq. Significative changes were noticed in SWD cold tolerance after acclimation: the longest the acclimation period, the highest the cold tolerance. Flies acclimated for 9 days were selected for sequencing. RNAseq revealed up to 2200 significantly differentially expressed genes (1200 up- and 1000 down-regulated) compared to non-acclimated flies. Functional annotations on the up-regulated set revealed many enriched GO-terms among which transport of ions across membranes and signaling were highly represented. We also noticed upregulations of several genes involved in thermal stress resistance, like heat shock proteins and Starvin. Involvements of a cluster of genes related to ion transport in cold-hardy flies is sensible, considering that loss of ion homeostasis is the major mechanism responsible for chill-injuries. Functional annotations on the down-regulated set revealed many GO-terms related to oogenesis. This likely reflects reduced reproductive process of acclimated females. Data were validated with rt-qPCR on selected genes. Overall, these results participate to our understanding of SWD low temperature biology, a knowledge of importance for better prediction of SWD population dynamics in temperate areas

Metabolic and Proteomic Profiling of Diapause in the Aphid Parasitoid Praon volucre

Background: Diapause, a condition of developmental arrest and metabolic depression exhibited by a wide range of animals is accompanied by complex physiological and biochemical changes that generally enhance environmental stress tolerance and synchronize reproduction. Even though some aspects of diapause have been well characterized, very little is known about the full range of molecular and biochemical modifications underlying diapause in non-model organisms. Methodology/Principal Findings: In this study we focused on the parasitic wasp, Praon volucre that exhibits a pupal diapause in response to environmental signals. System-wide metabolic changes occurring during diapause were investigated using GC-MS metabolic fingerprinting. Moreover, proteomic changes were studied in diapausing versus nondiapausing phenotypes using a combination of two-dimensional differential gel electrophoresis (2D-DIGE) and mass spectrometry. We found a reduction of Krebs cycle intermediates which most likely resulted from the metabolic depression. Glycolysis was galvanized, probably to favor polyols biosynthesis. Diapausing parasitoids accumulated high levels of cryoprotective polyols, especially sorbitol. A large set of proteins were modulated during diapause and these were involved in various functions such as remodeling of cytoskeleton and cuticle, stress tolerance, protein turnover, lipid metabolism and various metabolic enzymes. Conclusions/Significance: The results presented here provide some first clues about the molecular and biochemical events that characterize the diapause syndrome in aphid parasitoids. These data are useful for probing potential commonality of parasitoids diapause with other taxa and they will help creating a general understanding of diapause underpinnings and a background for future interpretations

Insects in fluctuating thermal environments.

All climate change scenarios predict an increase in both global temperature means and the magnitude of seasonal and diel temperature variation. The nonlinear relationship between temperature and biological processes means that fluctuating temperatures lead to physiological, life history, and ecological consequences for ectothermic insects that diverge from those predicted from constant temperatures. Fluctuating temperatures that remain within permissive temperature ranges generally improve performance. By contrast, those which extend to stressful temperatures may have either positive impacts, allowing repair of damage accrued during exposure to thermal extremes, or negative impacts from cumulative damage during successive exposures. We discuss the mechanisms underlying these differing effects. Fluctuating temperatures could be used to enhance or weaken insects in applied rearing programs, and any prediction of insect performance in the field-including models of climate change or population performance-must account for the effect of fluctuating temperatures

Exposition à des conditions desséchantes et tolérance croisée à des stress thermiques chez le petit ténébrion Alphitobius diaperinus

Le développement et la prolifération rapides des espèces exotiques dans de nouvelles régions peuvent être liés à leur importante plasticité phénotypique. Par ailleurs, les phénomènes de tolérance croisée, autrement dit les réponses mises en place afin de mieux tolérer un stress environnemental amélioreraient également la tolérance à un autre stress, pourrait contribuer au succès invasif de certains insectes exotiques. Par exemple, de bonnes capacités de résistance au froid ont été documentées chez plusieurs insectes d’origine tropicale, bien que ces espèces ne soient pas soumises à de basses températures dans leurs milieux naturels. Des observations similaires ont été signalées chez le petit ténébrion Alphitobius diaperinus (Coleoptera: Tenebrionidae), un coléoptère invasif d’origine tropicale, qui se développe dans les denrées stockées. Cette espèce présente un niveau élevé de tolérance à la dessiccation, et l’existence d’une tolérance croisée entre la tolérance à la dessiccation et au froid pourrait ainsi faciliter établissement et son expansion dans les milieux naturels des régions tempérées. Dans cette étude, nous avons examiné si les adultes d’A. diaperinus préalablement exposés à la dessiccation présentaient des capacités de survie accrues lorsqu’ils étaient réexposés cette condition de dessiccation (7 % d’humidité relative), ou bien à des températures basses (5°C), ou élevées (38°C). Nos résultats indiquent que la durée de la survie est similaire entre les insectes pré-exposés à la dessiccation et les témoins lorsque ceux-ci sont ensuite maintenus à 7 % HR ou 5°C. Cependant, nous avons constaté que les adultes d’A. diaperinus préalablement exposés à 7 % HR présentaient une durée de survie accrue au chaud (temps nécessaire pour obtenir une mortalité de 50 % de la population allongé de 4 jours). Dans une seconde expérience, nous avons inclus une période de récupération suite à l’exposition préalable à la dessiccation (7 % HR). Les insectes ont été maintenus à humidité modérée (50% HR) ou bien à forte humidité (100% HR) pendant 12h avant que leur survie à la dessiccation, la tolérance au froid et au chaud ne soient testées. Nous avons alors constaté que la réhydratation générait des réponses différentes en termes de tolérance croisée par rapport à la première expérience. En effet, la survie au froid (5°C) a dans ce cas été augmentée (temps nécessaire pour obtenir une mortalité de 50% de la population allongé de 3 jours), tandis qu’aucun effet n’a été obtenu sur la tolérance au chaud. Par ailleurs, nous n’avons trouvé aucun effet de l’exposition préalable à la dessiccation sur la capacité de survie ultérieure à cette condition expérimentale. En résumé, nous avons obtenu des preuves de tolérance croisée entre les conditions expérimentales desséchantes (7 % HR) et chaudes (38°C), et entre la dessiccation et les conditions froides (5°C). Ces effets sont hautement dépendants des conditions expérimentales, plus particulièrement de la mise en place d’une période de récupération avant l’exposition à un autre stress. Ces résultats suggèrent l’existence de mécanismes de tolérance croisée complexes.The ability of invasive species to rapidly expand into new regions may be related to their greater phenotypic plasticity. In addition, cross-tolerance, i.e. a response by which tolerance to one stress can enhance tolerance to another stress, may contribute to the invasive success of some alien insects. For instance, a certain level of cold hardiness has been documented in several tropical insects, although these species never experience cool or freezing temperatures in their natural environments. Similar observations were reported in the lesser mealworm Alphitobius diaperinus (Coleoptera: Tenebrionidae), an invasive beetle of tropical origin that thrives in stored products. This species shows a high basal desiccation tolerance, and cross-tolerance between desiccation and cold could have facilitated its successful establishment in temperate areas. In this study, we examined if dry pre-exposed beetles have increased ability to survive desiccation (7 % RH), cold (5°C), or heat stress (38°C). Survival duration remained similar between dry pre-exposed and control beetles that were subjected to desiccation or cold stress. However, we found that dry pre-exposed beetles had increased heat tolerance (Lt50 postponed by 4 days). In a second experiment, dry pre-exposed insects were allowed to recover either with water supply or with moderate humidity (50 % RH) before being assessed for desiccation, cold and heat tolerance. We found that rehydration changed cross-tolerance patterns: cold survival was promoted (Lt50 postponed by 3 days), while heat tolerance was not affected anymore. We found no effect of dry pre-exposure on the subsequent ability to survive dry condition. In summary, we found some evidence of cross-tolerance between desiccating and heat conditions, and between desiccating and cold conditions, but these effects depended on whether the beetles were allowed to recover or rehydrate before being exposed to another stress. These findings suggest complex and differential cross-tolerance mechanisms

Physiological responses of cold acclimation in Drosophila suzukii

editorial reviewedThe spotted wing drosophila (SWD) Drosophila suzukii is an invasive pest. To control this pest, information about its cold tolerance is required. Several studies have focused on SWD overwintering strategies and reported increased cold tolerance of winter morph (WM) compared to summer morph (SM). However, underlying mechanisms of this difference are not yet known. Our first goal was to study the impact of WM-inducing conditions on SWD cold tolerance and their metabolites composition. We expected to find an accumulation of cryoprotectant metabolites in cold hardy WM flies. Flies were reared at 25°C to induce SM, or at 10°C to induce WM. Cold tolerance was assayed by measuring survival after a stress at -5°C/1h40, minimal critical temperature and chill coma recovery. All metrics confirmed that WM-inducing conditions deeply promoted cold tolerance. SM and WM metabotypes were compared using target and quantitative GC/MS profiling. WM were characterized by an accumulation of several carbohydrates and amino acids, but quantitative changes were rather small (max 6 fold-change). Because robustness in metabolic networks is supposed to be a key element of cold tolerance, we assessed whether different levels of cold acclimation would favor metabolic stability. We generated four different phenotypes: development at 10°C to generate WM that were next acclimated as adults for 7 days at 10 or 25°C (WM10 or WM25) and development at 25°C to generate SM that were next acclimated as adults for 7 days at 10 or 25°C (SM10 or SM25). Using the same measures of cold tolerance, we found that cold tolerance ranked as follow: WM10>SM10>WM25>SM25. Stability of metabolic homeostasis was assessed in these four phenotypic groups using time-series GC/MS profiling. We monitored profiles before, right after, 4h, 8h or 12h after an acute cold shock. During recovery, both WM25 and SM25 metabotypes strongly deviated from origin, and did not return to initial state. This alteration was correlated with uncontrolled augmentation of the total amount of amino acids, which is symptomatic of cold injuries. WM10 presented the strongest temporal stability of metabolic profiles, suggesting a capacity to maintain homeostasis in this cold hardy phenotype. Finally, SM10 presented an intermediate response (as for cold tolerance). Data suggest that the proximal acclimation treatment (ie. at adult stage) is more critical in promoting cold tolerance that acclimation during development. Data corroborate that cold hardiness is associated to metabolic stability during stress and recovery. These results give new information to understand SWD cold tolerance

Cell free Microcystis aeruginosa spent medium affects Daphnia magna survival and stress response.

Primary consumers in freshwater ecosystems, such as the zooplankton organism Daphnia magna, are highly affected by cyanobacteria, both as they may use it as a food source but also by cyanobacterial metabolites present in the water. Here, we investigate the impacts of cyanobacterial metabolites focussing on the environmental realistic scenario of the naturally released mixture without crushing cyanobacterial cells or their uptake as food. Therefore, D. magna were exposed to two concentrations of cell free cyanobacterial spent medium from Microcystis aeruginosa PCC 7806 to represent higher and lower ecologically-relevant concentrations of cyanobacterial metabolites. Including microcystin-LR, 11 metabolites have been detected of which 5 were quantified. Hypothesising concentration and time dependent negative impact, survival, gene expression marking digestion and metabolism, oxidative stress response, cell cycle and molting as well as activities of detoxification and antioxidant enzymes were followed for 7 days. D. magna suffered from oxidative stress as both catalase and glutathione S-transferase enzyme activities significantly decreased, suggesting enzyme exhaustibility after 3 and 7 days. Moreover, gene-expressions of the 4 stress markers (glutathione S-transferase, glutathione peroxidase, catalase and thioredoxin) were merely downregulated after 7 days of exposure. Energy allocation (expression of glyceraldehyde-3-phosphate dehydrogenase) was increased after 3 days but decreased as well after 7 days exposure. Cell cycle was impacted time dependently but differently by the two concentrations, along with an increasing downregulation of myosin heavy chain responsible for cell arrangement and muscular movements. Deregulation of nuclear hormone receptor genes indicate that D. magna hormonal steering including molting seemed impaired despite no detection of microviridin J in the extracts. As a consequence of all those responses and presumably of more than investigated molecular and physiological changes, D. magna survival was impaired over time, in a concentration dependent manner. Our results confirm that besides microcystin-LR, other secondary metabolites contribute to negative impact on D. magna survival and stress response

Cold Acclimation Favors Metabolic Stability in Drosophila suzukii

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

Functional Characterization of the Frost Gene in Drosophila melanogaster: Importance for Recovery from Chill Coma

BACKGROUND: Almost all animals, including insects, need to adapt to temperature fluctuations. The molecular basis of thermal adaptation is not well understood, although a number of candidate genes have been proposed. However, a functional link between candidate genes and thermal tolerance has rarely been established. The gene Frost (Fst) was first discovered when Drosophila flies were exposed to cold stress, but the biological function(s) of Fst has so far not been characterized. Because Fst is up-regulated after a cold stress, we tested whether it was essential for chill-coma recovery. METHODOLOGY/PRINCIPAL FINDINGS: A marked increase in Fst expression was detected (by RT-PCR) during recovery from cold stress, peaking at 42-fold after 2 h. The GAL4/UAS system was used to knock down expression of Fst and recovery ability was assessed in transgenic adults following 12 h of chill coma at 0 degrees C. The ability to recover from cold stress (short-, medium- and long-term) was significantly altered in the transgenic adults that had Fst silenced. These findings show that Fst plays an essential role in the recovery from chill coma in both males and females. CONCLUSIONS/SIGNIFICANCE: The Frost gene is essential for cold tolerance in Drosophila melanogaster and may play an important role in thermal adaptation