Metabolomic and ecdysteroid variations in Anopheles gambiae s.l. mosquitoes exposed to the stressful conditions of the dry season in Burkina Faso, West Africa

This study explored the metabolic adjustments prompted by a switch between the rainy and dry season conditions in the African malaria mosquitoes Anopheles gambiae (M and S molecular forms) and Anopheles arabiensis. Mosquitoes were reared in contrasted experimental conditions reflecting environmental variation in Burkina Faso. Thirty-five metabolites (including sugars, polyols, and amino acids) were monitored in newly emerged males and females, and their ecdysteroid titers were determined. Metabolomic signatures were remarkably similar across species, when specimens of same age and sex were reared under identical experimental conditions. In males and females, amino acids (including glycine, leucine, phenylanine, serine, threonine, and valine) were accumulated in 1-h-old mosquitoes, then decreased 24 h after emergence, probably reflecting adult maturation and the amino acid-consuming process of cuticle sclerotisation. In turn, elevated amounts of alanine and proline in 24-h-old mosquitoes may assist the development of flight ability. Lower concentration of tricarboxylic acid cycle intermediates and isoleucine characterized older females reared under dry season conditions, suggesting metabolic and reproduction depression. In all cases, ecdysteroid concentration was much higher in males than in females, with significant seasonal variation in males. This might reflect a unique role of these hormones in shaping reproductive strategies and population demography in the An. gambiae s.l. species complex, further contributing to local adaptation in a highly fluctuating environment.

Low environmentally relevant levels of bioactive xenobiotics and associated degradation products cause cryptic perturbations of metabolism and molecular stress responses in Arabidopsis thaliana

Anthropic changes and chemical pollution confront wild plant communities with xenobiotic combinations of bioactive molecules, degradation products, and adjuvants that constitute chemical challenges potentially affecting plant growth and fitness. Such complex challenges involving residual contamination and mixtures of pollutants are difficult to assess. The model plant Arabidopsis thaliana was confronted by combinations consisting of the herbicide glyphosate, the fungicide tebuconazole, the glyphosate degradation product aminomethylphosphonic acid (AMPA), and the atrazine degradation product hydroxyatrazine, which had been detected and quantified in soils of field margins in an agriculturally intensive region. Integrative analysis of physiological, metabolic, and gene expression responses was carried out in dose-response experiments and in comparative experiments of varying pesticide combinations. Field margin contamination levels had significant effects on plant growth and metabolism despite low levels of individual components and the presence of pesticide degradation products. Biochemical and molecular analysis demonstrated that these less toxic degradation products, AMPA and hydroxyatrazine, by themselves elicited significant plant responses, thus indicating underlying mechanisms of perception and transduction into metabolic and gene expression changes. These mechanisms may explain observed interactions, whether positive or negative, between the effects of pesticide products (AMPA and hydroxyatrazine) and the effects of bioactive xenobiotics (glyphosate and tebuconazole). Finally, the metabolic and molecular perturbations induced by low levels of xenobiotics and associated degradation products were shown to affect processes (carbon balance, hormone balance, antioxidant defence, and detoxification) that are likely to determine environmental stress sensitivity.

Deciphering the metabolic changes associated with diapause syndrome and cold acclimation in the two-spotted spider mite Tetranychus urticae

Diapause is a common feature in several arthropod species that are subject to unfavorable growing seasons. The range of environmental cues that trigger the onset and termination of diapause, in addition to associated hormonal, biochemical, and molecular changes, have been studied extensively in recent years; however, such information is only available for a few insect species. Diapause and cold hardening usually occur together in overwintering arthropods, and can be characterized by recording changes to the wealth of molecules present in the tissue, hemolymph, or whole body of organisms. Recent technological advances, such as high throughput screening and quantification of metabolites via chromatographic analyses, are able to identify such molecules. In the present work, we examined the survival ability of diapausing and non-diapausing females of the two-spotted spider mite, Tetranychus urticae, in the presence (0 or 5°C) or absence of cold acclimation. Furthermore, we examined the metabolic fingerprints of these specimens via gas chromatography-mass spectrophotometry (GC-MS). Partial Least Square Discriminant Analysis (PLS-DA) of metabolites revealed that major metabolic variations were related to diapause, indicating in a clear cut-off between diapausing and non-diapausing females, regardless of acclimation state. Signs of metabolic depression were evident in diapausing females, with most amino acids and TCA cycle intermediates being significantly reduced. Out of the 40 accurately quantified metabolites, seven metabolites remained elevated or were accumulated in diapausing mites, i.e. cadaverine, gluconolactone, glucose, inositol, maltose, mannitol and sorbitol. The capacity to accumulate winter polyols during cold-acclimation was restricted to diapausing females. We conclude that the induction of increased cold hardiness in this species is associated with the diapause syndrome, rather than being a direct effect of low temperature. Our results provide novel information about biochemical events related to the cold hardening process in the two-spotted spider mite.

Metabolic fingerprinting of the responses to salinity in the invasive ground beetle Merizodus soledadinus at the Kerguelen Islands

Salinity is an abiotic factor that may impact survival and fitness of terrestrial insects in coastal environments. Meanwhile, some terrestrial arthropods can survive in hypersaline environments, and counterbalance osmotic stress by intra- and extracellular buildups of organic osmolytes. The ground beetle Merizodus soledadinus originates from South America and it is distributed in forests and riparian zones, where salinity levels are considerably low. This species has been introduced at the Kerguelen Islands a century ago, where it colonized coastal areas (tide drift lines), and must thus withstand salinity variations due to tide, spray, and organic matter deposited therein. In the present study, we addressed the physiological plasticity of M. soledadinus to saline conditions, by monitoring body water content and survival in adults experimentally subjected to different salinities. We also investigated possible metabolic adjustments involved at three contrasted salinity levels (0‰, 35‰, 70‰) at 4 and 8°C. We hypothesized that this invasive ground beetle can withstand a broad range of salinity conditions thanks to the plastic accumulation of compatible solutes. The study revealed a progressive drop in body water content in individuals exposed to 35‰ and 70‰, as opposed to the controls. Metabolic fingerprints showed compatible solute (erythritol, alanine, glycine and proline) accumulation at medium and high salinity conditions (35‰ and 70‰). We concluded that the osmo-induced accumulation of amino acids and polyols was likely to modulate the ground beetles' body water balance on medium saline substrates, thus enhancing their survival ability.

Does cold tolerance plasticity correlate with the thermal environment and metabolic profiles of a parasitoid wasp?

Tolerance of ectotherm species to cold stress is highly plastic according to thermal conditions experienced prior to cold stress. In this study, we investigated how cold tolerance varies with developmental temperature (at 17, 25 and 30°C) and whether developmental temperature induces different metabolic profiles. Experiments were conducted on the two populations of the parasitoid wasp, Venturia canescens, undergoing contrasting thermal regimes in their respective preferential habitat (thermally variable vs. buffered). We predicted the following: i) development at low temperatures improves the cold tolerance of parasitoid wasps, ii) the shape of the cold tolerance reaction norm differs between the two populations, and iii) these phenotypic variations are correlated with their metabolic profiles. Our results showed that habitat origin and developmental acclimation interact to determine cold tolerance and metabolic profiles of the parasitoid wasps. Cold tolerance was promoted when developmental temperatures declined and population originating from variable habitat presented a higher cold tolerance. Cold tolerance increases through the accumulation of metabolites with an assumed cryoprotective function and the depression of metabolites involved in energy metabolism. Our data provide an original example of how intraspecific cold acclimation variations correlate with metabolic response to developmental temperature.

Habitat phenotyping of two sub-Antarctic flies by metabolic fingerprinting: evidence for a species outside its home?

Metabolic fingerprinting can elucidate rearrangements of metabolic networks in organisms exposed to various environmental conditions. Maintenance of organismal performance occurs by alterations in metabolic fluxes and pathways, resulting in habitat-specific metabolic signatures. Several insects of sub-Antarctic Islands, including the wingless flies Anatalanta aptera and Calycopteryx moseleyi, are exposed to saline organic matter accumulated along littoral margins. However, C. moseleyi has long been considered restricted to a habitat of lower salinity, the Kerguelen cabbage. High C. moseleyi densities identified in saline decaying seaweeds are intriguing, and may involve osmoregulatory adjustments including accumulation of osmoprotectants. In the present work, we examined quantitative metabotypes (metabolic phenotypes) among wild C. moseleyi individuals from seaweeds versus non-saline Kerguelen cabbages. They were compared to metabotypes from wild A. aptera, a common fly on seaweed. Statistical procedures designed to magnify between-class differences failed to clearly separate C. moseleyi metabotypes from cabbage and seaweed, despite contrasted morphotypes, diets, and salinities. A. aptera exhibited higher glycerol, inositol, trehalose, and other osmoprotectants concentrations that may enhance its performance under saline environments. Seaweed may represent a secondary niche in C. moseleyi, promoted by the marked reduction in Kerguelen cabbage frequency subsequent to climate change, and herbivorous pressures caused by rabbit invasion.