Seasonal change in glycogen and inositol/sorbitol contents of the house spider, Achaearanea tepidariorum (Araneae: Theridiidae)

Metabolite Profiling of the Social Spider Stegodyphus dumicola Along a Climate Gradient

Animals experience climatic variation in their natural habitats, which may lead to variation in phenotypic responses among populations through local adaptation or phenotypic plasticity. In ectotherm arthropods, the expression of thermoprotective metabolites such as free amino acids, sugars, and polyols, in response to temperature stress, may facilitate temperature tolerance by regulating cellular homeostasis. If populations experience differences in temperatures, individuals may exhibit population-specific metabolite profiles through differential accumulation of metabolites that facilitate thermal tolerance. Such thermoprotective metabolites may originate from the animals themselves or from their associated microbiome, and hence microbial symbionts may contribute to shape the thermal niche of their host. The social spider Stegodyphus dumicola has extremely low genetic diversity, yet it occupies a relatively broad temperature range occurring across multiple climate zones in Southern Africa. We investigated whether the metabolome, including thermoprotective metabolites, differs between populations, and whether population genetic structure or the spider microbiome may explain potential differences. To address these questions, we assessed metabolite profiles, phylogenetic relationships, and microbiomes in three natural populations along a temperature gradient. The spider microbiomes in three genetically distinct populations of S. dumicola showed no significant population-specific pattern, and none of its dominating genera (Borrelia, Diplorickettsia, and Mycoplasma) are known to facilitate thermal tolerance in hosts. These results do not support a role of the microbiome in shaping the thermal niche of S. dumicola. Metabolite profiles of the three spider populations were significantly different. The variation was driven by multiple metabolites that can be linked to temperature stress (e.g., lactate, succinate, or xanthine) and thermal tolerance (e.g., polyols, trehalose, or glycerol): these metabolites had higher relative abundance in spiders from the hottest geographic region. These distinct metabolite profiles are consistent with a potential role of the metabolome in temperature response.

Hydration Dynamics in Solutions of Cyclic Polyhydroxyl Osmolytes

Simple sugars are remarkably effective at preserving protein and enzymatic structures against thermal and hydrostatic stress. Here, we investigate the hydrodynamic and biopreservative properties of three small cyclic molecules: glucose, myo-inositol, and methyl-α-d-glucopyranoside using circular dichroism spectroscopy and isothermal calorimetry. Using ultrafast fluorescence frequency upconversion spectroscopy, we measure the dynamical retardation of hydration dynamics in cosolute solutions. We find that all three molecules are effective modifiers of hydration dynamics in solution and all are also effective at protecting model protein systems against thermal denaturation. Methyl-α-d-glucopyranoside is found to be the most effective dynamic reducer displaying an approximately 30% increase in solvation relaxation time as compared to water in a cosolute free solution. myo-Inositol and glucose both exhibit a smaller reduction in dynamics with similar magnitudes of concentration dependence. Using these cosolute models, we demonstrate that the thermal enhancement of protein structure does not correlate strongly with either the dynamical reduction of the bulk solution nor with the number of hydrogen bonds a cosolute makes with the solvent. Furthermore, solutions of glucose at twice the concentration of trehalose are shown to have similar magnitudes of dynamical impact. This implies that regulation of hydration dynamics is not a distinguishing characteristic of successful osmolytes. This work highlights the need for further studies and computational analysis to understand the phenomena of preferential exclusion and the contribution of hydration dynamics to protein structural stability.

Genome wide gene-expression analysis of facultative reproductive diapause in the two-spotted spider mite Tetranychus urticae

BACKGROUND

Diapause or developmental arrest, is one of the major adaptations that allows mites and insects to survive unfavorable conditions. Diapause evokes a number of physiological, morphological and molecular modifications. In general, diapause is characterized by a suppression of the metabolism, change in behavior, increased stress tolerance and often by the synthesis of cryoprotectants. At the molecular level, diapause is less studied but characterized by a complex and regulated change in gene-expression. The spider mite Tetranychus urticae is a serious polyphagous pest that exhibits a reproductive facultative diapause, which allows it to survive winter conditions. Diapausing mites turn deeply orange in color, stop feeding and do not lay eggs.

RESULTS

We investigated essential physiological processes in diapausing mites by studying genome-wide expression changes, using a custom built microarray. Analysis of this dataset showed that a remarkable number, 11% of the total number of predicted T. urticae genes, were differentially expressed. Gene Ontology analysis revealed that many metabolic pathways were affected in diapausing females. Genes related to digestion and detoxification, cryoprotection, carotenoid synthesis and the organization of the cytoskeleton were profoundly influenced by the state of diapause. Furthermore, we identified and analyzed an unique class of putative antifreeze proteins that were highly upregulated in diapausing females. We also further confirmed the involvement of horizontally transferred carotenoid synthesis genes in diapause and different color morphs of T. urticae.

CONCLUSIONS

This study offers the first in-depth analysis of genome-wide gene-expression patterns related to diapause in a member of the Chelicerata, and further adds to our understanding of the overall strategies of diapause in arthropods.

Myo-inositol as a main metabolite in overwintering flies: seasonal metabolomic profiles and cold stress tolerance in a northern drosophilid fly

Coping with seasonal changes in temperature is an important factor underlying the ability of insects to survive over the harsh winter conditions in the northern temperate zone, and only a few drosophilids have been able to colonize sub-polar habitats. Information on their winter physiology is needed as it may shed light on the adaptive mechanisms of overwintering when compared with abundant data on the thermal physiology of more southern species, such as Drosophila melanogaster. Here we report the first seasonal metabolite analysis in a Drosophila species. We traced changes in the cold tolerance and metabolomic profiles in adult Drosophila montana flies that were exposed to thermoperiods and photoperiods similar to changes in environmental conditions of their natural habitat in northern Finland. The cold tolerance of diapausing flies increased noticeably towards the onset of winter; their chill coma recovery times showed a seasonal minimum between late autumn and early spring, whereas their survival after cold exposure remained high until late spring. The flies had already moderately accumulated glucose, trehalose and proline in autumn, but the single largest change occurred in myo-inositol concentrations. This increased up to 400-fold during the winter and peaked at 147 nmol mg(-1) fresh mass, which is among the largest reported accumulations of this compound in insects.

Seasonal change of the thermal response in relation to myo-inositol metabolism in adults of Aulacophora nigripennis (Coleoptera Chrysomelidae)

The thermal response of Aulacophora nigripennis adults in relation to myo-inositol metabolism changed seasonally. Myo-inositol accumulation was stimulated at 15 and 5 degrees C in October (autumn), but only 5 degrees C was effective for the accumulation in December (early winter). In February (mid winter), myo-inositol degradation was prominent at both temperatures. Myo-inositol metabolism of this beetle thus gradually shifts from synthesis to degradation as the season progresses. This may be related to the progress of diapause development and may contribute to the seasonal profile of the myo-inositol pool in a natural population. Post-diapause adults in March (spring) and June (early summer) regained the ability for myo-inositol accumulation at 5 degrees C. Thus, there are at least two types of myo-inositol accumulation in this beetle; one is under the control of diapause and the other responds directly to environmental conditions independently of diapause.

Adult diapause and cold hardiness in Aulacophora nigripennis (Coleoptera: Chrysomelidae)

We investigated the control of diapause termination and seasonal changes of cold hardiness and polyol content in Aulacophora nigripennis. Adults were ready to start post-diapause development upon transfer to high temperature by late February irrespective of photoperiod. Photoperiod probably functions to maintain diapause before winter because adults resume reproductive development at a long photoperiod in autumn. Adults showed a decreased supercooling point (SCP), increased chill tolerance and high myo-inositol content during winter. Chill tolerance at 0 degrees C appears to be a more suitable indicator of their cold hardiness than SCP because they die at 0 degrees C without freezing and they normally have no chance of being exposed to low subzero temperatures close to their SCP. The temporal pattern for changes in chill tolerance was synchronized with that for fluctuations in myo-inositol content, indicating a possible causal relationship between the two phenomena.

Evolutionary Relationship between Diapause and Cold Hardiness in the House Spider, Achaearanea tepidariorum (Araneae: Theridiidae)

The relationship between diapause and cold hardiness of the house spider, Achaearanea tepidariorum, differed geographically. In a cool-temperate population, enhanced chilling tolerance and supercooling ability were observed in diapause individuals, whereas a subtropical population showed only chilling tolerance. Because this spider is considered to be of tropical origin, it would follow that the ancestral diapause of this spider was equipped with chilling tolerance, but not with an increased supercooling ability. It seems that the ability to lower the supercooling point evolved through natural selection in the course of expansion of this species to the northern climates. Copyright 1997 Elsevier Science Ltd. All rights reserved