Conceptual framework of the eco-physiological phases of insect diapause development justified by transcriptomic profiling

Characterization of pre-diapause phase in the northern Drosophila species D. ezoana

Drosophila ezoana is a virilis group Drosophila species inhabiting northern latitudes. The flies enter adult reproductive diapause to survive winter upon exposure to short photoperiod conditions (short-day) over several consecutive days. Insect pre-diapause phase - the duration between the beginning of exposure to short days and expression of diapause is thought to be comprised of two distinct phases - (a) photoperiodic time measurement that detects short-days, followed by (b) physiological events leading to the expression of diapause phenotype. A short-day dependent segment of the pre-diapause phase thus approximates the process of photoperiodic time measurement. Continuous darkness has been found to be a neutral condition with respect to diapause regulation in many insect species. The effect of variable number of short-days followed by continuous darkness on diapause incidence thus allows identification of short-day dependent segment of pre-diapause phase thereby mapping the process of photo-periodic time measurement. Although, few weeks of exposure to short-days in adult stage is known to be sufficient for the expression of diapause in D. ezoana, the number of short days required for the completion of photo-periodic time measurement has never been systematically analysed. Our experiments show that continuous darkness is a neutral condition for diapause regulation also in D. ezoana. We utilized the neutral nature of continuous darkness to map the process of photoperiodic time measurement in the D. ezoana strain 124OJ8 which showed that integration of short-day photic cues over the first 10 days of pre-diapause phase is essential for diapause induction.

Lipid composition differs in diapause and nondiapause states of spotted stem borer, Chilo partellus

Spotted stem borer, Chilo partellus, undergoes larval diapause (hibernation and aestivation), and depends on the food reserve accumulated during feeding stage for its survival. Lipids are the primary source of energy during diapause, and essential for different cellular, biochemical and physiological functions. However, there is no information on lipid and lipophilic compound contents during different stages of hibernation, aestivation and nondiapause in C. partellus. Thus, we compared the concentration and composition of lipids in pre-diapause, diapause and post-diapause stages of hibernation and aestivation with nondiapause stages of C. partellus. The studies revealed significant differences in total lipids and various lipophilic compounds during different stages of diapause as compared to nondiapause C. partellus. The total lipids were significantly lower during diapause stage of aestivation and hibernation as compared to nondiapause larvae. Further, the linoleic acid, Methyl 3-methoxytetradecanoate, and l-(+)-Ascorbic acid 2,6-dihexadecanoate were significantly lower, and oleic and palmitoleic acids greater during pre-diapause and diapause stages of hibernation and aestivation as compared to nondiapause larvae. The cholesterol content was significantly greater during pre-diapause stage of hibernation, and diapause and post-diapause stages of aestivation as compared to nondiapause stages. The unsaturation ratio was significantly higher in the pre-diapause and diapause stages and lower in post-diapause stage of aestivation than the hibernation and nondiapause states. This study provides insights on differential lipid profiles during different phases of diapause, which could be useful for further understanding biochemical and physiological cross-talk, and develop target-specific technologies for the management of C. partellus.

Insulin Signaling Pathway Mediates FoxO-Pepck Axis Regulation of Glucose Homeostasis in Drosophila suzukii

The agricultural pest Drosophila suzukii exhibits a strong preference for feeding on fresh fruits, demonstrating high adaptability to sugary environments. Meanwhile, high sugar levels stimulate insulin secretion, thereby regulating the steady state of sugar metabolism. Understanding the mechanisms related to sugar metabolism in D. suzukii is crucial due to its adaptation to these specific environmental conditions. The insulin signaling pathway is an evolutionarily conserved phosphorylation cascade with significant roles in development and metabolism. We observed that the activation of the insulin signaling pathway inhibited FoxO activity and downregulated the expression of Pepck, thereby activating glycolysis and reducing glucose levels. By contrast, inhibiting insulin signaling increased the FoxO activity and upregulated the expression of Pepck, which activated gluconeogenesis and led to increased glucose levels. Our findings demonstrated the crucial role of the insulin signaling pathway in mediating glucose metabolism through the FoxO-Pepck axis, which supports the ecological adaptation of D. suzukii to high-sugar niches, thereby providing insights into its metabolic control and suggesting potential strategies for pest management. Elucidating these molecular processes is important for understanding metabolic regulation and ecological specialization in D. suzukii.

Population Density-Dependent Developmental Regulation in Migratory Locust

Insect development is intricately governed by hormonal signaling pathways, yet the pivotal upstream regulator that potentiates hormone activation remains largely elusive. The migratory locust, Locusta migratoria, exhibits population density-dependent phenotypic plasticity, encompassing traits such as flight capability, body coloration, and behavior. In this study, we elucidated a negative correlation between population density and ontogenetic development during the nymphal stage of locusts. We found that the level of density influences the developmental trajectory by modulating transcript abundance within the ecdysone signaling pathway, with knockdown of the prothoracicotropic hormone (PTTH) resulting in developmental delay. Transcriptomic analysis of locust brains across solitary and gregarious phases revealed significant differential expression of genes involved in various pathways, including protein synthesis, energy metabolism, hormonal regulation, and immunity. Notably, knockdown experiments targeting two energy regulators, adipokinetic hormone (AKH) and insulin-like polypeptide 1 (ilp1), failed to elicit changes in the developmental process in solitary locusts. However, knockdown of immunoglobulin (IG) significantly shortened the developmental time in higher-density populations. Collectively, our findings underscore the regulatory role of population density in determining developmental duration and suggest that an immune-related gene contributes to the observed differences in developmental patterns.

Variation in Thermal Sensitivity of Diapause Development among Individuals and over Time Predicts Life History Timing in a Univoltine Insect

AbstractPhysiological time is important for understanding the development and seasonal timing of ectothermic animals but has largely been applied to developmental processes that occur during spring and summer, such as morphogenesis. There is a substantial knowledge gap in the relationship between temperature and development during winter, a season that is increasingly impacted by climate change. Most temperate insects overwinter in diapause, a developmental process with little obvious morphological change. We used principles from the physiological time literature to measure and model the thermal sensitivity of diapause development rate in the apple maggot fly Rhagoletis pomonella, a univoltine fly whose diapause duration varies substantially within and among populations. We show that diapause duration can be predicted by modeling a relationship between temperature and development rate that is shifted toward lower temperatures compared with typical models of morphogenic, nondiapause development. However, incorporating interindividual variation and ontogenetic variation in the temperature-to-development rate relationship was critical for accurately predicting fly emergence, as diapause development proceeded more quickly at high temperatures later in diapause. We conclude that the conceptual framework may be flexibly applied to other insects and discuss possible mechanisms of diapause timers and implications for phenology with warming winters.

Sublethal acetamiprid affects reproduction, development and disrupts gene expression in Binodoxys communis

At present, understanding of neonicotinoid toxicity in arthropods remains limited. We here evaluated the lethal and sublethal effects of acetamiprid in F0 and F1 generations of Binodoxys communis using a range of sublethal concentrations. The 10% lethal concentration (LC10) and half lethal concentration (LC25) of ACE had negative effects on the B. communis survival rate, adult longevity, parasitism rate, and emergence rate, and significantly prolonged the duration of the developmental cycle. ACE also had intergenerational effects, with some biological indices affected in the F1 generation after pesticide exposure. Transcriptomic analysis demonstrated that differentially expressed genes were enriched in specific pathways including the amino acid metabolism, carbohydrate metabolism, energy metabolism, exogenous metabolism, signal transduction, and glutathione metabolism pathways. These results indicated strong contact toxicity of ACE to B. communis, which may inhibit their biological control capacity. These results improve our understanding of the toxicological mechanisms of parasitic natural enemies in response to insecticide exposure.

A time course analysis through diapause reveals dynamic temporal patterns of microRNAs associated with endocrine regulation in the butterfly Pieris napi

Organisms inhabiting highly seasonal environments must cope with a wide range of environmentally induced challenges. Many seasonal challenges require extensive physiological modification to survive. In winter, to survive extreme cold and limited resources, insects commonly enter diapause, which is an endogenously derived dormant state associated with minimized cellular processes and low energetic expenditure. Due to the high degree of complexity involved in diapause, substantial cellular regulation is required, of which our understanding primarily derives from the transcriptome via messenger RNA expression dynamics. Here we aim to advance our understanding of diapause by investigating microRNA (miRNA) expression in diapausing and direct developing pupae of the butterfly Pieris napi. We identified coordinated patterns of miRNA expression throughout diapause in both head and abdomen tissues of pupae, and via miRNA target identification, found several expression patterns to be enriched for relevant diapause-related physiological processes. We also identified two candidate miRNAs, miR-14-5p and miR-2a-3p, that are likely involved in diapause progression through their activity in the ecdysone pathway, a critical regulator of diapause termination. miR-14-5p targets phantom, a gene in the ecdysone synthesis pathway, and is upregulated early in diapause. miR-2a-3p has been found to be expressed in response to ecdysone, and is upregulated during diapause termination. Together, the expression patterns of these two miRNAs match our current understanding of the timing of hormonal regulation of diapause in P. napi and provide interesting candidates to further explore the mechanistic role of microRNAs in diapause regulation.

Temperature has an overriding role compared to photoperiod in regulating the seasonal timing of winter moth egg hatching

To accurately predict species' phenology under climate change, we need to gain a detailed mechanistic understanding of how different environmental cues interact to produce the seasonal timing response. In the winter moth (Operophtera brumata), seasonal timing of egg hatching is strongly affected by ambient temperature and has been under strong climate change-induced selection over the past 25 years. However, it is unclear whether photoperiod received at the egg stage also influences timing of egg hatching. Here, we investigated the relative contribution of photoperiod and temperature in regulating winter moth egg development using two split-brood experiments. We experimentally shifted the photoperiod eggs received by 2-4 weeks compared to the actual calendar date and measured the timing of egg hatching, both at a constant temperature and in combination with two naturally changing temperature treatments - mimicking a cold and a warm year. We found an eight-fold larger effect of temperature compared to photoperiod on egg development time. Moreover, the very small photoperiod effects we found were outweighed by both between- and within-clutch variation in egg development time. Thus, we conclude that photoperiod received at the egg stage does likely not play a substantial role in regulating the seasonal timing of egg hatching in the winter moth. These insights into the regulatory mechanism of seasonal timing could have important implications for predicting insect climate change adaptation, as we might expect different targets of selection depending on the relative contribution of different environmental cues.

ArHsp90 is important in stress tolerance and embryo development of the brine shrimp, Artemia franciscana

Females of the extremophile crustacean, Artemia franciscana, either release motile nauplii via the ovoviviparous pathway or encysted embryos (cysts) via the oviparous pathway. Cysts contain an abundant amount of the ATP-independent small heat shock protein that contributes to stress tolerance and embryo development, however, little is known of the role of ATP-dependent molecular chaperone, heat shock protein 90 (Hsp90) in the two processes. In this study, a hsp90 was cloned from A. franciscana. Characteristic domains of ArHsp90 were simulated from the deduced amino acid sequence, and 3D structures of ArHsp90 and Hsp90s of organisms from different groups were aligned. RNA interference was then employed to characterize ArHsp90 in A. franciscana nauplii and cysts. The partial knockdown of ArHsp90 slowed the development of nauplius-destined, but not cyst-destined embryos. ArHsp90 knockdown also reduced the survival and stress tolerance of nauplii newly released from A. franciscana females. Although the reduction of ArHsp90 had no effect on the development of diapause-destined embryos, the resulting cysts displayed reduced tolerance to desiccation and low temperature, two stresses normally encountered by A. franciscana in its natural environment. The results reveal that Hsp90 contributes to the development, growth, and stress tolerance of A. franciscana, an organism of practical importance as a feed source in aquaculture.

Genetic constraints in genes exhibiting splicing plasticity in facultative diapause

Phenotypic plasticity is produced and maintained by processes regulating the transcriptome. While differential gene expression is among the most important of these processes, relatively little is known about other sources of transcriptional variation. Previous work suggests that alternative splicing plays an extensive and functionally unique role in transcriptional plasticity, though plastically spliced genes may be more constrained than the remainder of expressed genes. In this study, we explore the relationship between expression and splicing plasticity, along with the genetic diversity in those genes, in an ecologically consequential polyphenism: facultative diapause. Using 96 samples spread over two tissues and 10 timepoints, we compare the extent of differential splicing and expression between diapausing and direct developing pupae of the butterfly Pieris napi. Splicing differs strongly between diapausing and direct developing trajectories but alters a smaller and functionally unique set of genes compared to differential expression. We further test the hypothesis that among these expressed loci, plastically spliced genes are likely to experience the strongest purifying selection to maintain seasonally plastic phenotypes. Genes with unique transcriptional changes through diapause consistently had the lowest nucleotide diversity, and this effect was consistently stronger among genes that were differentially spliced compared to those with just differential expression through diapause. Further, the strength of negative selection was higher in the population expressing diapause every generation. Our results suggest that maintenance of the molecular mechanisms involved in diapause progression, including post-transcriptional modifications, are highly conserved and likely to experience genetic constraints, especially in northern populations of P. napi.

Diapause-induced shift in the content of major carbohydrates in Chilo partellus (Swinhoe)

Although several aspects like diapause determining factors, population structure, reproductive physiology, and genetics of diapause have been investigated, there is no clarity on carbohydrate energetics during larval diapause in Chilo partellus (Swinhoe). Present studies revealed significant variation between the nondiapausing and diapausing C. partellus for total carbohydrates, glycogen, sorbitol, and trehalose contents in different body parts, life stages, and for body parts × life stages interaction. Total carbohydrate content started declining, while sorbitol and trehalose increased in all the body parts as the C. partellus larvae progressed from prediapausing to diapausing state. However, glycogen content spiked in all the body parts at prediapausing stage, which then declined during diapause. Among the body parts, total carbohydrate content was significantly greater in the hemolymph as compared to other body parts of both larvae and pupae of C. partellus. Glycogen content was significantly greater in the larval fat bodies and pupal hemolymph as compared to their other body parts. In diapausing larvae, sorbitol and trehalose were greater in the integument than in other body parts. Furthermore, there was spike in trehalose and decrease in sorbitol in all the body parts of pupae from diapausing than those from nondiapausing larvae. These findings suggest that the diapause alterate and/or fluctuate major carbohydrates in different body parts of both larvae and pupae of C. partellus. This information will be helpful in better understanding the diapause energetics and overwintering metabolic cryoprotection in insects.

E93 gene in the swimming crab, Portunus trituberculatus: Responsiveness to 20-hydroxyecdysone and methyl farnesoate and role on regulating ecdysteroid synthesis

Ecdysone-induced protein 93 (E93) is a metamorphic determinant involved in crosstalk between 20-hydroxyecdysone (20E) and juvenile hormone (JH) during the insect molting process. The present study identified the E93 gene from the swimming crab, P. trituberculatus, and found it was widely distributed in adult tissues. PtE93 mRNA levels in Y-organ and epidermis fluctuated during the molt cycle, suggesting its involvement in juvenile molting. In vitro and in vivo treatments with 20E led to an induction of PtE93 expression in Y-organ and epidermis, while we found the opposite effect for methyl farnesoate (MF) treatments, a crustacean equivalent of insect JH. We also observed that two genes for ecdysteroid biosynthesis, Spook (Spo) and Shadow (Sad), were suppressed by 20E and induced by MF, showing a negative correlation between PtE93 and ecdysteroid biosynthesis. PtE93 RNA interference (RNAi) induced Spo and Sad expression levels, elevated ecdysteroid content in culture medium, and relieved the 20E inhibitory effect on ecdysteroid synthesis, indicating an inhibitory role of PtE93 on ecdysteroid synthesis. Overall, our results suggest that E93 may be involved in the crosstalk between 20E and MF during crustacean molting, and its presence in Y-organ is closely related to ecdysteroid synthesis.

Transcriptome-based analysis reveals a crucial role of the 20E/HR3 pathway in the diapause of Pieris rapae

Pieris rapae is among the most damaging pests globally, and diapause makes it highly resistant to environmental stresses, playing a crucial role in the survival and reproduction of P. rapae while exacerbating the challenges of pest management and control. However, the mechanisms of its diapause regulation remain poorly understood. This research used RNA sequencing to profile the transcriptomes of three diapause phases (induction and preparation, initiation, maintenance) and synchronous nondiapause phases in P. rapae. During each comparison phase, 759, 1045, and 4721 genes were found to be differentially expressed. Among these, seven clock genes and seven pivotal hormone synthesis and metabolism genes were identified as having differential expression patterns in diapause type and nondiapause type. The weighted gene co-expression network analysis (WGCNA) revealed the red and blue modules as pivotal for diapause initiation, while the grey module was identified to be crucial to diapause maintenance. Meanwhile, the hub genes HDAC11, METLL16D, Dyw-like, GST, and so on, were identified within these hub modules. Moreover, an ecdysone downstream nuclear receptor gene, HR3, was found to be a shared transcription factor across all three phases. RNA interference of HR3 resulted in delayed pupal development, indicating its involvement in regulating pupal dipause in P. rapae. The further hormone assays revealed that the 20-hydroxyecdysone (20E) titer in diapause type pupae was lower than that in nondiapause type pupae, which exhibited a similar trend to HR3. When 20E was injected into diapause pupae, the HR3 expression levels were improved, and the pupal diapause were broken. These results indicate that the 20E/HR3 pathway is a critical pathway for the diapause regulation of P. rapae, and perturbing this pathway by ecdysone treatment or RNAi would result in the disruption of diapause. These findings provide initial insights into the molecular mechanisms of P. rapae diapause and suggest the potential use of ecdysone analogs and HR3 RNAi pesticides, which specifically target to diapause, as a means of pest control in P. rapae.

A transcriptomic examination of encased rotifer embryos reveals the developmental trajectory leading to long-term dormancy; are they "animal seeds"?

BACKGROUND

Organisms from many distinct evolutionary lineages acquired the capacity to enter a dormant state in response to environmental conditions incompatible with maintaining normal life activities. Most studied organisms exhibit seasonal or annual episodes of dormancy, but numerous less studied organisms enter long-term dormancy, lasting decades or even centuries. Intriguingly, many planktonic animals produce encased embryos known as resting eggs or cysts that, like plant seeds, may remain dormant for decades. Herein, we studied a rotifer Brachionus plicatilis as a model planktonic species that forms encased dormant embryos via sexual reproduction and non-dormant embryos via asexual reproduction and raised the following questions: Which genes are expressed at which time points during embryogenesis? How do temporal transcript abundance profiles differ between the two types of embryos? When does the cell cycle arrest? How do dormant embryos manage energy?

RESULTS

As the molecular developmental kinetics of encased embryos remain unknown, we employed single embryo RNA sequencing (CEL-seq) of samples collected during dormant and non-dormant embryogenesis. We identified comprehensive and temporal transcript abundance patterns of genes and their associated enriched functional pathways. Striking differences were uncovered between dormant and non-dormant embryos. In early development, the cell cycle-associated pathways were enriched in both embryo types but terminated with fewer nuclei in dormant embryos. As development progressed, the gene transcript abundance profiles became increasingly divergent between dormant and non-dormant embryos. Organogenesis was suspended in dormant embryos, concomitant with low transcript abundance of homeobox genes, and was replaced with an ATP-poor preparatory phase characterized by very high transcript abundance of genes encoding for hallmark dormancy proteins (e.g., LEA proteins, sHSP, and anti-ROS proteins, also found in plant seeds) and proteins involved in dormancy exit. Surprisingly, this period appeared analogous to the late maturation phase of plant seeds.

CONCLUSIONS

The study highlights novel divergent temporal transcript abundance patterns between dormant and non-dormant embryos. Remarkably, several convergent functional solutions appear during the development of resting eggs and plant seeds, suggesting a similar preparatory phase for long-term dormancy. This study accentuated the broad novel molecular features of long-term dormancy in encased animal embryos that behave like "animal seeds".

Diapause survival requires a temperature-sensitive preparatory period

Diapause is a form of internally-controlled dormancy that allows insects to avoid stressful conditions and periods of low food availability. Eastern spruce budworm (Choristoneura fumiferana Clemens), like many cold-adapted insects, enter diapause well in advance of winter conditions, thus exposing them to elevated temperatures during fall that can deplete energy stores and impact post-diapause survival. We explored the impact of fall conditions on C. fumiferana by manipulating the length of the fall period and exposure temperatures during the diapause initiation phase of second instar larvae in a factorial design. We exposed second instar larvae to four fall temperatures (10, 15, 20, and 25°C) and five exposure times (1, 2, 4, 6, and 10 weeks) prior to standardized diapause conditions. We measured metabolites (glycogen, glycerol, and protein) prior to and during diapause for a subset of individuals. We also measured post-diapause survival by quantifying emergence following diapause conditions for a subset of individuals. We found that long, warm fall conditions depleted glycogen content and lowered post-diapause survival. We also found that short, cool conditions impacted post-diapause survival, although glycogen content remained high. Our results showed that fall conditions have substantial fitness consequences to overwintering insects. Optimal fall conditions struck a balance between exposure time and temperature. Our findings point to a potentially adaptive reason for early diapause onset: that an undescribed, but temperature-sensitive process is occurring in C. fumiferana larvae during the diapause initiation period that is essential for overwintering survival and successful post-diapause emergence.

OXPHOS capacity is diminished and the phosphorylation system inhibited during diapause in an extremophile, embryos of Artemia franciscana

Diapause exhibited by embryos of Artemia franciscana is accompanied by severe arrest of respiration. A large fraction of this depression is attributable to downregulation of trehalose catabolism that ultimately restricts fuel to mitochondria. This study now extends knowledge on the mechanism by revealing metabolic depression is heightened by inhibitions within mitochondria. Compared with that in embryo lysates during post-diapause, oxidative phosphorylation (OXPHOS) capacity P is depressed during diapause when either NADH-linked substrates (pyruvate and malate) for electron transfer (electron transfer capacity, E) through respiratory Complex I or the Complex II substrate succinate are used. When pyruvate, malate and succinate were combined, respiratory inhibition by the phosphorylation system in diapause lysates was discovered as judged by P/E flux control ratios (two-way ANOVA; F1,24=38.78; P<0.0001). Inhibition was eliminated as the diapause extract was diluted (significant interaction term; F2,24=9.866; P=0.0007), consistent with the presence of a diffusible inhibitor. One candidate is long-chain acyl-CoA esters known to inhibit the adenine nucleotide translocator. Addition of oleoyl-CoA to post-diapause lysates markedly decreased the P/E ratio to 0.40±0.07 (mean±s.d.; P=0.002) compared with 0.79±0.11 without oleoyl-CoA. Oleoyl-CoA inhibits the phosphorylation system and may be responsible for the depressed P/E in lysates from diapause embryos. With isolated mitochondria, depression of P/E by oleoyl-CoA was fully reversed by addition of l-carnitine (control versus recovery with l-carnitine, P=0.338), which facilitates oleoyl-CoA transport into the matrix and elimination by β-oxidation. In conclusion, severe metabolic arrest during diapause promoted by restricting glycolytic carbon to mitochondria is reinforced by depression of OXPHOS capacity and the phosphorylation system.

The gut microbiome mediates adaptation to scarce food in Coleoptera

Beetles are ubiquitous cave invertebrates worldwide that adapted to scarce subterranean resources when they colonized caves. Here, we investigated the potential role of gut microbiota in the adaptation of beetles to caves from different climatic regions of the Carpathians. The beetles' microbiota was host-specific, reflecting phylogenetic and nutritional adaptation. The microbial community structure further resolved conspecific beetles by caves suggesting microbiota-host coevolution and influences by local environmental factors. The detritivore species hosted a variety of bacteria known to decompose and ferment organic matter, suggesting turnover and host cooperative digestion of the sedimentary microbiota and allochthonous-derived nutrients. The cave Carabidae, with strong mandibula, adapted to predation and scavenging of animal and plant remains, had distinct microbiota dominated by symbiotic lineages Spiroplasma or Wolbachia. All beetles had relatively high levels of fermentative Carnobacterium and Vagococcus involved in lipid accumulation and a reduction of metabolic activity, and both features characterize adaptation to caves.

Snow flies self-amputate freezing limbs to sustain behavior at sub-zero temperatures

Temperature profoundly impacts all living creatures. In spite of the thermodynamic constraints on biology, some animals have evolved to live and move in extremely cold environments. Here, we investigate behavioral mechanisms of cold tolerance in the snow fly (Chionea spp.), a flightless crane fly that is active throughout the winter in boreal and alpine environments of the northern hemisphere. Using thermal imaging, we show that adult snow flies maintain the ability to walk down to an average body temperature of -7°C. At this supercooling limit, ice crystallization occurs within the snow fly's hemolymph and rapidly spreads throughout the body, resulting in death. However, we discovered that snow flies frequently survive freezing by rapidly amputating legs before ice crystallization can spread to their vital organs. Self-amputation of freezing limbs is a last-ditch tactic to prolong survival in frigid conditions that few animals can endure. Understanding the extreme physiology and behavior of snow insects holds particular significance at this moment when their alpine habitats are rapidly changing due to anthropogenic climate change. VIDEO ABSTRACT.

Mortality caused by extracellular freezing is associated with fragmentation of nuclear DNA in larval haemocytes of two drosophilid flies

The great complexity of extracellular freezing stress, involving mechanical, osmotic, dehydration and chemical perturbations of the cellular milieu, hampers progress in understanding the nature of freezing injury and the mechanisms to cope with it in naturally freeze-tolerant insects. Here, we show that nuclear DNA fragmentation begins to occur in larval haemocytes of two fly species, Chymomyza costata and Drosophila melanogaster, before or at the same time as the sub-zero temperature is reached that causes irreparable freezing injury and mortality in freeze-sensitive larval phenotypes. However, when larvae of the freeze-tolerant phenotype (diapausing-cold acclimated-hyperprolinemic) of C. costata were subjected to severe freezing stress in liquid nitrogen, no DNA damage was observed. Artificially increasing the proline concentration in freeze-sensitive larvae of both species by feeding them a proline-enriched diet resulted in a decrease in the proportion of nuclei with fragmented DNA during freezing stress. Our results suggest that proline accumulated in diapausing C. costata larvae during cold acclimation may contribute to the protection of nuclear DNA against fragmentation associated with freezing stress.

Transcriptomic evidence indicates that montane leaf beetles prioritize digestion and reproduction in a sex-specific manner during emergence from dormancy

During winter, many organisms conserve resources by entering dormancy, suppressing metabolism and biosynthesis. The transition out of winter dormancy to summer activity requires a quick reversal of this suppression, in order to exploit now-favorable environmental conditions. To date, mechanisms by which winter climate variation affects this transition remains unelucidated. Here we experimentally manipulated snow cover for naturally overwintering montane leaf beetles (Chrysomela aeneicollis), and profiled changes in gene expression during the transition out of dormancy in spring. Upon emergence, beetles up-regulate transcripts associated with digestion and nutrient acquisition and down regulate those associated with lipid metabolism, suggesting a shift away from utilizing stored lipid and towards digestion of carbohydrate-rich host plant tissue. Development of digestive capacity is followed by up-regulation of transcripts associated with reproduction; a transition that occurs earlier in females than males. Snow manipulation strongly affected the ground thermal regime and correspondingly gene expression profiles, with beetles showing a delayed up-regulation of reproduction in the dry compared to snowy plots. This suggests that winter conditions can alter the timing and prioritization of processes during emergence from dormancy, potentially magnifying the effects of declining snow cover in the Sierra's and other snowy mountains.

20-hydroxyecdysone Upregulates Ecdysone Receptor (ECR) Gene to Promote Pupation in the Honeybee, Apis mellifera Ligustica

A heterodimeric complex of two nuclear receptors, the ecdysone receptor (ECR) and ultraspiracle (USP), transduces 20-hydroxyecdysone (20E) signaling to modulate insect growth and development. Here, we aimed to determine the relationship between ECR and 20E during larval metamorphosis and also the specific roles of ECR during larval-adult transition in Apis mellifera. We found that ECR gene expression peaked in the 7-day-old larvae, then decreased gradually from the pupae stage. 20E slowly reduced food consumption and then induced starvation, resulting in small-sized adults. In addition, 20E induced ECR expression to regulate larval development time. Double-stranded RNAs (dsRNAs) were prepared using common dsECR as templates. After dsECR injection, larval transition to the pupal stage was delayed, and 80% of the larvae showed prolonged pupation beyond 18 h. Moreover, the mRNA levels of shd, sro, nvd, and spo, and ecdysteroid titers were significantly decreased in ECR RNAi larvae compared with those in GFP RNAi control larvae. ECR RNAi disrupted 20E signaling during larval metamorphosis. We performed rescuing experiments by injecting 20E in ECR RNAi larvae and found that the mRNA levels of ECR, USP, E75, E93, and Br-c were not restored. 20E induced apoptosis in the fat body during larval pupation, while RNAi knockdown of ECR genes reduced apoptosis. We concluded that 20E induced ECR to modulate 20E signaling to promote honeybee pupation. These results assist our understanding of the complicated molecular mechanisms of insect metamorphosis.

The gut microbiome mediates adaptation to scarce food in Coleoptera

Beetles are ubiquitous cave invertebrates worldwide that adapted to scarce subterranean resources when they colonized caves. Here, we investigated the potential role of gut microbiota in the adaptation of beetles to caves from different climatic regions of the Carpathians. The beetles' microbiota was host-specific, reflecting phylogenetic and nutritional adaptation. The microbial community structure further resolved conspecific beetles by caves suggesting microbiota-host coevolution and influences by local environmental factors. The detritivore species hosted a variety of bacteria known to decompose and ferment organic matter, suggesting turnover and host cooperative digestion of the sedimentary microbiota and allochthonous-derived nutrients. The cave Carabidae, with strong mandibulae adapted to predation and scavenging of animal and plant remains, had distinct microbiota dominated by symbiotic lineages Spiroplasma or Wolbachia . All beetles had relatively high levels of fermentative Carnobacterium and Vagococcus involved in lipid accumulation and a reduction of metabolic activity, and both features characterize adaptation to caves.

The fitness value of ecological information in a variable world

Information processing is increasingly recognized as a fundamental component of life in variable environments, including the evolved use of environmental cues, biomolecular networks, and social learning. Despite this, ecology lacks a quantitative framework for understanding how population, community, and ecosystem dynamics depend on information processing. Here, we review the rationale and evidence for 'fitness value of information' (FVOI), and synthesize theoretical work in ecology, information theory, and probability behind this general mathematical framework. The FVOI quantifies how species' per capita population growth rates can depend on the use of information in their environment. FVOI is a breakthrough approach to linking information processing and ecological and evolutionary outcomes in a changing environment, addressing longstanding questions about how information mediates the effects of environmental change and species interactions.

Molecular signatures of diapause in the Asian longhorned beetle: Gene expression

Most previous studies on gene expression during insect diapause do not address among-tissue variation in physiological processes. We measured transcriptomic changes during larval diapause in the Asian longhorned beetle, Anoplophora glabripennis (Coleoptera: Cerambycidae). We conducted RNA-seq on fat body, the supraesophageal ganglion, midgut, hindgut, and Malpighian tubules during pre-diapause, diapause maintenance, post-diapause quiescence, and post-diapause development. We observed a small, but consistent, proportion of genes within each gene expression profile that were shared among tissues, lending support for a core set of diapause-associated genes whose expression is tissue-independent. We evaluated the overarching hypotheses that diapause would be associated with cell cycle arrest, developmental arrest, and increased stress tolerance and found evidence of repressed TOR and insulin signaling, reduced cell cycle activity and increased capacity of stress response via heat shock protein expression and remodeling of the cytoskeleton. However, these processes varied among tissues, with the brain and fat body appearing to maintain higher levels of cellular activity during diapause than the midgut or Malpighian tubules. We also observed temperature-dependent changes in gene expression during diapause maintenance, particularly in genes related to the heat shock response and MAPK, insulin, and TOR signaling pathways. Additionally, we provide evidence for epigenetic reorganization during the diapause/post-diapause quiescence transition and expression of genes involved in post-translational modification, highlighting the need for investigations of the protein activity of these candidate genes and processes. We conclude that diapause development is coordinated via diverse tissue-specific gene expression profiles and that canonical diapause phenotypes vary among tissues.

Diapause-Linked Gene Expression Pattern and Related Candidate Duplicated Genes of the Mountain Butterfly Parnassius glacialis (Lepidoptera: Papilionidae) Revealed by Comprehensive Transcriptome Profiling

The mountain butterfly Parnassius glacialis is a representative species of the genus Parnassius, which probably originated in the high-altitude Qinhai-Tibet Plateau in the Miocene and later dispersed eastward into relatively low-altitude regions of central to eastern China. However, little is known about the molecular mechanisms underlying the long-term evolutionary adaptation to heterogeneous environmental conditions of this butterfly species. In this study, we obtained the high-throughput RNA-Seq data from twenty-four adult individuals in eight localities, covering nearly all known distributional areas in China, and firstly identified the diapause-linked gene expression pattern that is likely to correlate with local adaptation in adult P. glacialis populations. Secondly, we found a series of pathways responsible for hormone biosynthesis, energy metabolism and immune defense that also exhibited unique enrichment patterns in each group that are probably related to habitat-specific adaptability. Furthermore, we also identified a suite of duplicated genes (including two transposable elements) that are mostly co-expressed to promote the plastic responses to different environmental conditions. Together, these findings can help us to better understand this species' successful colonization to distinct geographic areas from the western to eastern areas of China, and also provide us with some insights into the evolution of diapause in mountain Parnassius butterfly species.

Fat enough for the winter? Does nutritional status affect diapause?

Many insects enter a dormant state termed diapause in anticipation of seasonal inhospitable conditions. Insects drastically reduce their feeding during diapause. Their reduced nutrient intake is paired with substantial nutrient costs: maintaining basal metabolism during diapause, repairing tissues damaged by adverse conditions, and resuming development after diapause. Many investigators have asked "Does nutrition affect diapause?" In this review, we survey the studies that have attempted to address this question. We propose the term nutritional status, a holistic view of nutrition that explicitly includes the perception, intake, and storage of the great breadth of nutrients. We examine the studies that have sought to test if nutrition affects diapause, trying to identify specific facets of nutritional status that affect diapause phenotypes. Curiously, low quality host plants during the diapause induction phase generally induce diapause, but food deprivation during the same phase generally averts diapause. Using the geometric framework of nutrition to identify specific dietary components that affect diapause may reconcile these contrasting findings. This framework can establish nutritionally permissive space, distinguishing nutrient changes that affect diapause from changes that induce other dormancies. Refeeding is another important experimental technique that distinguishes between diapause and quiescence, a non-diapause dormancy. We also find insufficient evidence for the hypothesis that nutrient stores regulate diapause length and suggest manipulations to investigate the role of nutrient stores in diapause termination. Finally, we propose mechanisms that could interface nutritional status with the diapause program, focusing on combined action of the nutritional axis between the gut, fat body, and brain.

TM7 (Saccharibacteria) regulates the synthesis of linolelaidic acid and tricosanoic acid, and alters the key metabolites in diapause Clanis bilineata tsingtauica

Good exploitation and utilization of edible insects can effectively alleviate global food security crisis in years. The study on diapause larvae of Clanis bilineata tsingtauica (DLC) was conducted to explore how gut microbiota regulate the nutrients synthesis and metabolism of edible insects. The results showed that C. bilineata tsingtauica maintained a total and stable nutrition levels at early phase of diapause. The activity of instetinal enzymes in DLC fluctuated markedly with diapause time. Additionally, Proteobacteria and Firmicutes were the predominant taxa, and TM7 (Saccharibacteria) was the marker species of gut microbiota in DLC. Combined the gene function prediction analysis with Pearson correlation analysis, TM7 in DLC was mainly involved in the biosynthesis of diapause-induced differential fatty acids, i.e., linolelaidic acid (LA) and tricosanoic acid (TA), which was probably regulated by changing the activity of protease and trehalase, respectively. Moreover, according to the non-target metabolomics, TM7 might regulate the significant differential metabolites, i.e., D-glutamine, N-acetyl-d-glucosamine and trehalose, via the metabolism of amino acid and carbohydrate pathways. These results suggest that TM7 increased LA and decreased TA via the intestinal enzymes, and altered intestinal metabolites via the metabolism pathways, maybe a key mechanism for regulating the nutrients synthesis and metabolisms in DLC.

Molecular Mechanisms of Winter Survival

Winter provides many challenges for insects, including direct injury to tissues and energy drain due to low food availability. As a result, the geographic distribution of many species is tightly coupled to their ability to survive winter. In this review, we summarize molecular processes associated with winter survival, with a particular focus on coping with cold injury and energetic challenges. Anticipatory processes such as cold acclimation and diapause cause wholesale transcriptional reorganization that increases cold resistance and promotes cryoprotectant production and energy storage. Molecular responses to low temperature are also dynamic and include signaling events during and after a cold stressor to prevent and repair cold injury. In addition, we highlight mechanisms that are subject to selection as insects evolve to variable winter conditions. Based on current knowledge, despite common threads, molecular mechanisms of winter survival vary considerably across species, and taxonomic biases must be addressed to fully appreciate the mechanistic basis of winter survival across the insect phylogeny.

Physiological and life history changes associated with seasonal adaptation in the cactophilic Drosophila mojavensis

Many insects inhabiting temperate climates are faced with changing environmental conditions throughout the year. Depending on the species, these environmental fluctuations can be experienced within a single generation or across multiple generations. Strategies for dealing with these seasonal changes vary across populations. Drosophila mojavensis is a cactophilic Drosophila species endemic to the Sonoran Desert. The Sonoran Desert regularly reaches temperatures of 50°C in the summer months. As individuals of this population are rare to collect in the summer months, we simulated the cycling temperatures experienced by D. mojavensis in the Sonoran Desert from April to July (four generations) in a temperature- and light-controlled chamber, to understand the physiological and life history changes that allow this population to withstand these conditions. In contrast to our hypothesis of a summer aestivation, we found that D. mojavensis continue to reproduce during the summer months, albeit with lower viability, but the adult survivorship of the population is highly reduced during this period. As expected, stress resistance increased during the summer months in both the adult and the larval stages. This study examines several strategies for withstanding the Sonoran Desert summer conditions which may be informative in the study of other desert endemic species.

Time-Series Transcriptomic Analysis Reveals the Molecular Profiles of Diapause Termination Induced by Long Photoperiods and High Temperature in Chilo suppressalis

Survival and adaptation to seasonal changes are challenging for insects. Many temperate insects such as the rice stem borer (Chilo suppressalis) overcome the adverse situation by entering diapause, wherein development changes dynamically occur and metabolic activity is suppressed. The photoperiod and temperature act as major environmental stimuli of diapause. However, the physiological and molecular mechanisms that interpret the ecologically relevant environmental cues in ontogenetic development during diapause termination are poorly understood. Here, we used genome-wide high-throughput RNA-sequencing to examine the patterns of gene expression during diapause termination in C. suppressalis. Major shifts in biological processes and pathways including metabolism, environmental information transmission, and endocrine signalling were observed across diapause termination based on over-representation analysis, short time-series expression miner, and gene set enrichment analysis. Many new pathways were identified in diapause termination including circadian rhythm, MAPK signalling, Wnt signalling, and Ras signalling, together with previously reported pathways including ecdysteroid, juvenile hormone, and insulin/insulin-like signalling. Our results show that convergent biological processes and molecular pathways of diapause termination were shared across different insect species and provided a comprehensive roadmap to better understand diapause termination in C. suppressalis.

Rapid brain development and reduced neuromodulator titres correlate with host shifts in Rhagoletis pomonella

Host shifts are considered a key generator of insect biodiversity. For insects, adaptation to new host plants often requires changes in larval/pupal development and adult behavioural preference toward new hosts. Neurochemicals play key roles in both development and behaviour and therefore provide a potential source for such synchronization. Here, we correlated life-history timing, brain development and corresponding levels of 14 neurochemicals in Rhagoletis pomonella (Diptera: Tephritidae), a species undergoing ecological speciation through an ongoing host shift from hawthorn to apple fruit. These races exhibit differences in pupal diapause timing as well as adult behavioural preference with respect to their hosts. This difference in behavioural preference is coupled with differences in neurophysiological response to host volatiles. We found that apple race pupae exhibited adult brain morphogenesis three weeks faster after an identical simulated winter than the hawthorn race, which correlated with significantly lower titres of several neurochemicals. In some cases, particularly biogenic amines, differences in titres were reflected in the mature adult stage, when host preference is exhibited. In summary, life-history timing, neurochemical titre and brain development can be coupled in this speciating system, providing new hypotheses for the origins of new species through host shifts.

Insect cross-tolerance to freezing and drought stress: role of metabolic rearrangement

The accumulation of trehalose has been suggested as a mechanism underlying insect cross-tolerance to cold/freezing and drought. Here we show that exposing diapausing larvae of the drosophilid fly, Chymomyza costata to dry conditions significantly stimulates their freeze tolerance. It does not, however, improve their tolerance to desiccation, nor does it significantly affect trehalose concentrations. Next, we use metabolomics to compare the complex alterations to intermediary metabolism pathways in response to three environmental factors with different ecological meanings: environmental drought (an environmental stressor causing mortality), decreasing ambient temperatures (an acclimation stimulus for improvement of cold hardiness), and short days (an environmental signal inducing diapause). We show that all three factors trigger qualitatively similar metabolic rearrangement and a similar phenotypic outcome-improved larval freeze tolerance. The similarities in metabolic response include (but are not restricted to) the accumulation of typical compatible solutes and the accumulation of energy-rich molecules (phosphagens). Based on these results, we suggest that transition to metabolic suppression (a state in which chemical energy demand is relatively low but need for stabilization of macromolecules is high) represents a common axis of metabolic pathway reorganization towards accumulation of non-toxic cytoprotective compounds, which in turn stimulates larval freeze tolerance.

Enhanced Degradation of Juvenile Hormone Promotes Reproductive Diapause in the Predatory Ladybeetle Coccinella Septempunctata

Improved knowledge on the regulation of reproductive diapause in Coccinella septempunctata, an important predator of aphids, is crucial for improving shelf-life and mass production of the ladybeetles. In many insects, the absence of juvenile hormone (JH) is a central regulator of reproductive diapause. JH is principally degraded by JH esterase (JHE) and JH epoxide hydrolase (JHEH). Previous studies have shown that genes encoding these enzymes were upregulated in early diapause of C. septempunctata, but whether increased JH degradation contributes to the reduction of JH levels and facilitates reproductive diapause remains unknown. Here, we investigate the role of JH and JH degradation genes during reproductive diapause in C. septempunctata females. Applying methoprene, a JH analogue, to the diapause preparation females clearly elevated JH signaling and reversed diapause program, suggesting that a lower level of JH is critical for the induction of reproductive diapause in the ladybeetle. Full-length cDNA sequences of JHE and JHEH were cloned and characterized, and their deduced proteins contain all the conserved active domains and typical motifs as identified in other insects. The expressions of JHE and JHEH were both significantly increased in diapause preparation and remained at a high level for a period throughout diapause, and then decreased after the termination of diapause. Knocking down these JH degradation genes clearly increased the expression levels of JH-inducible genes Krüppel-homolog 1 (Kr-h1) and vitellogenin (Vg), indicating an elevated JH level. Simultaneously, silencing JH degradation genes distinctly reduced diapause-related features and promotes reproduction, indicated by accelerated ovary growth, yolk deposition, and suppressed lipid accumulation. These results indicate that the enhanced JH degradation plays a critical role in regulating reproductive diapause of C. septempunctata.

Identification of Intrinsically Disordered Proteins and Regions in a Non-Model Insect Species Ostrinia nubilalis (Hbn.)

Research in previous decades has shown that intrinsically disordered proteins (IDPs) and regions in proteins (IDRs) are as ubiquitous as highly ordered proteins. Despite this, research on IDPs and IDRs still has many gaps left to fill. Here, we present an approach that combines wet lab methods with bioinformatics tools to identify and analyze intrinsically disordered proteins in a non-model insect species that is cold-hardy. Due to their known resilience to the effects of extreme temperatures, these proteins likely play important roles in this insect's adaptive mechanisms to sub-zero temperatures. The approach involves IDP enrichment by sample heating and double-digestion of proteins, followed by peptide and protein identification. Next, proteins are bioinformatically analyzed for disorder content, presence of long disordered regions, amino acid composition, and processes they are involved in. Finally, IDP detection is validated with an in-house 2D PAGE. In total, 608 unique proteins were identified, with 39 being mostly disordered, 100 partially disordered, 95 nearly ordered, and 374 ordered. One-third contain at least one long disordered segment. Functional information was available for only 90 proteins with intrinsic disorders out of 312 characterized proteins. Around half of the 90 proteins are cytoskeletal elements or involved in translational processes.

Exploring Cold Hardiness within a Butterfly Clade: Supercooling Ability and Polyol Profiles in European Satyrinae

The cold hardiness of overwintering stages affects the distribution of temperate and cold-zone insects. Studies on Erebia, a species-rich cold-zone butterfly genus, detected unexpected diversity of cold hardiness traits. We expanded our investigation to eight Satyrinae species of seven genera. We assessed Autumn and Winter supercooling points (SCPs) and concentrations of putatively cryoprotective sugars and polyols via gas chromatography–mass spectrometry. Aphantopus hyperantus and Hipparchia semele survived freezing of body fluids; Coenonympha arcania, C. gardetta, and Melanargia galathea died prior to freezing; Maniola jurtina, Chazara briseis, and Minois dryas displayed a mixed response. SCP varied from −22 to −9 °C among species. Total sugar and polyol concentrations (TSPC) varied sixfold (2 to 12 μg × mg−1) and eightfold including the Erebia spp. results. SCP and TSPC did not correlate. Alpine Erebia spp. contained high trehalose, threitol, and erythritol; C. briseis and C. gardetta contained high ribitol and trehalose; lowland species contained high saccharose, maltose, fructose, and sorbitol. SCP, TSPC, and glycerol concentrations were affected by phylogeny. Species of mountains or steppes tend to be freeze-avoidant, overwinter as young larvae, and contain high concentrations of trehalose, while those of mesic environments tend to be freeze-tolerant, overwinter as later instars, and rely on compounds such as maltose, saccharose, and fructose.

Metabolomics Reveals Changes in Metabolite Profiles among Pre-Diapause, Diapause and Post-Diapause Larvae of Sitodiplosis mosellana (Diptera: Cecidomyiidae)

Simple Summary

Diapause is a programmed developmental arrest coupled with an evident reduction in metabolic rate and a dramatic increase in stress tolerance. Sitodiplosis mosellana, a periodic but devastating wheat pest, spends the hot summer and cold winter as diapausing larvae. However, little is known about the metabolic changes underlying this obligatory diapause. The objective of this study was to identify significantly altered metabolites and pathways in diapausing S. mosellana at stages of pre-diapause, diapause, post-diapause quiescence and post-diapause development using gas chromatography/time-of-flight mass spectrometry and the orthogonal partial least squares discriminant analysis. Pairwise comparisons of the four groups showed that 54 metabolites significantly changed. Of which, 37 decreased in response to diapause, including four TCA cycle intermediates and most amino acids, whereas 12 increased. Three metabolites were significantly higher in the cold quiescence stage than in other stages. The elevated metabolites included the well-known cryoprotectants trehalose, glycerol, proline and alanine. In conclusion, the low metabolic rate and cold tolerance S. mosellana displayed during diapause may be closely correlated with its reduced TCA cycle activity or/and the increased biosynthesis of cryoprotectants. The results have contributed to our understanding of the biochemical mechanism underlying diapause and the related stress tolerance in this key pest.

Abstract

Sitodiplosis mosellana, a notorious pest of wheat worldwide, copes with temperature extremes during harsh summers and winters by entering obligatory diapause as larvae. However, the metabolic adaptive mechanism underlying this process is largely unknown. In this study, we performed a comparative metabolomics analysis on S. mosellana larvae at four programmed developmental stages, i.e., pre-diapause, diapause, low temperature quiescence and post-diapause development. In total, we identified 54 differential metabolites based on pairwise comparisons of the four groups. Of these metabolites, 37 decreased in response to diapause, including 4 TCA cycle intermediates (malic acid, citric acid, fumaric acid, α-ketoglutaric acid), 2 saturated fatty acids (palmitic acid, stearic acid) and most amino acids. In contrast, nine metabolites, including trehalose, glycerol, mannitol, proline, alanine, oleic acid and linoleic acid were significantly higher in both the diapause and quiescent stages than the other two stages. In addition to two of them (trehalose, proline), glutamine was also significantly highest in the cold quiescence stage. These elevated metabolites could function as cryoprotectants and/or energy reserves. These findings suggest that the reduced TCA cycle activity and elevated biosynthesis of functional metabolites are most likely responsible for maintaining low metabolic activity and cold tolerance during diapause, which is crucial for the survival and post-diapause development of this pest.

Timing of Diapause Initiation and Overwintering Conditions Alter Gene Expression Profiles in Megachile rotundata

Within the United States and Canada, the primary pollinator of alfalfa is the alfalfa leafcutting bee (ALCB), Megachile rotundata. Our previous findings showed that overwintering conditions impacted gene expression profile in ALCB prepupae that entered diapause early in the season. However, ALCB are a bivoltine species, which begs the question of whether bees entering diapause later in the season also show this trend. To better understand the effects of the timing of diapause initiation, we analyzed mRNA copy number of genes known to be involved in diapause regulation in early and late season diapausing ALCB that were overwintered in field conditions or using current agricultural management conditions. We hypothesized that overwintering conditions for late diapausing bees also affects gene expression profiles. Our results showed that expression profiles were altered by both overwintering condition and timing of diapause initiation, with bees that entered diapause earlier in the season showing different expression patterns than those that entered diapause later in the season. This trend was seen in expression of members of the cyclin family and several targets of the insulin signaling pathway, including forkhead box protein O (FOXO), which is known to be important for diapause regulation and stress responses. But, of the genes screened, the proto-oncogene, Myc, was the most impacted by the timing of diapause initiation. Under field conditions, there were significant differences in Myc expression between the early and late season samples in all months except for November and February. This same general trend in Myc expression was also seen in the laboratory-maintained bees with significant difference in expression in all months except for November, February, and May. These results support previous conclusions from our research showing that the molecular regulation of diapause development in ALCB is not a simple singular cascade of gene expression but a highly plastic response that varies between bees depending upon their environmental history.

Effects of Different Temperatures on the Development and Reproduction of Sitobion miscanthi From Six Different Regions in China

The increase in temperature caused by global warming has greatly impacted plant growth and pest population dynamics worldwide, especially for wheat aphids. In this study, Sitobion miscanthi individuals from six geographic populations located in different wheat-producing areas in China were compared with regard to their growth, development, survival, and reproductive under different temperature conditions (17, 22 and 27°C). A population life-table analysis and a correlation analysis between geographic factors and S. miscanthi longevity or fecundity were also performed. Temperature significantly affected the nymphal development duration (NDD), the adult longevity (ALY) and the fecundity (AFY) of the aphids, however, latitude can only affect the NDD and ALY. There is an obvious interaction between temperature and latitude on the NDD, ALY, and AFY. The NDD in the three northern populations was significantly shorter than that in the southern populations. The ALY in northern populations was significantly longer than that in southern populations at different temperatures. Except for Yinchuan population was no significantly different under different degrees, the ALY of other populations was significantly shortened at 27°C. The AFY of northern populations was significantly lower than that of southern populations at 22°C, while significantly higher at 27°C. With the increase of temperature, the fecundity of northern population gradually decreased from 17 to 22°C, while the southern population suddenly decreased at 27°C. The curves of survival rate (sxj) in southern populations were significantly shorter than that of northern population. Especially the populations in Suzhou and Wuhan, in which the survival rate decreased rapidly at 27°C. Age-specific survival rate (lx) of southern populations began to decline rapidly on 15 days of age at 27°C, while those of northern populations were not significantly affected until on 20 days of age. The highest peaks of age-stage fecundity (fxj), age-specific fecundity (mx), and age-specific net maternity (lxmx) were occurred in northern populations. In addition, there was a positive correlation between latitude and longevity under the three degrees, however, only at 27°C, there was a positive correlation between latitude and fecundity. Our result proved that the higher reproductive rate of southern population requires aphids to live at the suitable ambient temperature, and aphid populations in the north have a wider ecological amplitude. The results will be helpful for predicting the potential aphid outbreaks in China’s main wheat areas under suitable conditions.

Cryoprotective Metabolites Are Sourced from Both External Diet and Internal Macromolecular Reserves during Metabolic Reprogramming for Freeze Tolerance in Drosophilid Fly, Chymomyza costata

Many cold-acclimated insects accumulate high concentrations of low molecular weight cryoprotectants (CPs) in order to tolerate low subzero temperatures or internal freezing. The sources from which carbon skeletons for CP biosynthesis are driven, and the metabolic reprogramming linked to cold acclimation, are not sufficiently understood. Here we aim to resolve the metabolism of putative CPs by mapping relative changes in concentration of 56 metabolites and expression of 95 relevant genes as larvae of the drosophilid fly, Chymomyza costata transition from a freeze sensitive to a freeze tolerant phenotype during gradual cold acclimation. We found that C. costata larvae may directly assimilate amino acids proline and glutamate from diet to acquire at least half of their large proline stocks (up to 55 µg per average 2 mg larva). Metabolic conversion of internal glutamine reserves that build up in early diapause may explain the second half of proline accumulation, while the metabolic conversion of ornithine and the degradation of larval collagens and other proteins might be two additional minor sources. Next, we confirm that glycogen reserves represent the major source of glucose units for trehalose synthesis and accumulation (up to 27 µg per larva), while the diet may serve as an additional source. Finally, we suggest that interconversions of phospholipids may release accumulated glycero-phosphocholine (GPC) and -ethanolamine (GPE). Choline is a source of accumulated methylamines: glycine-betaine and sarcosine. The sum of methylamines together with GPE and GPC represents approximately 2 µg per larva. In conclusion, we found that food ingestion may be an important source of carbon skeletons for direct assimilation of, and/or metabolic conversions to, CPs in a diapausing and cold-acclimated insect. So far, the cold-acclimation- linked accumulation of CPs in insects was considered to be sourced mainly from internal macromolecular reserves.

Life stage and the environment as effectors of transposable element activity in two bee species

Diapause is a complex physiological phenomenon that allows insects to weather stressful environmental conditions. The regulation of diapause is accordingly complex, including signaling pathways that involve both small RNA and mRNA and affect the cell cycle, stress resistance, and developmental timing. Transposable elements, mobile genetic elements that replicate within the genome, are also thought to be stress responsive and regulated by the small RNA pathway. Therefore, we asked what the relationship was between environmental stress, diapause status, and transposable element expression in two species of agriculturally important bees, Megachile rotundata and Osmia lignaria. We characterized the TE content of the genomes of both species, then evaluated the expression of TE families during temperature stress, general environmental stress, and diapause stage. We found that the genomic TE content of the two species was very different, and M. rotundata has a larger number of annotated TEs compared to O. lignaria. We also found that both diapause stage and temperature stress had large effects on TE expression. The fold change of TE famlies tended to be larger in those expressed during diapause, however there was only a small majority that were upregulated during diapause. This suggests that stress and diapause do not break down to a simple up-regulation or down-regulation of TEs, but rather that the TE family, the genomic position of its insertions, and the exact heterochromatin formation of the organism at any given environmental state or life stage may affect overall expression of TEs.

Extensive transcriptomic profiling of pupal diapause in a butterfly reveals a dynamic phenotype

Diapause is a common adaptation for overwintering in insects that is characterized by arrested development and increased tolerance to stress and cold. While the expression of specific candidate genes during diapause have been investigated, there is no general understanding of the dynamics of the transcriptional landscape as a whole during the extended diapause phenotype. Such a detailed temporal insight is important as diapause is a vital aspect of life cycle timing. Here, we performed a time-course experiment using RNA-Seq on the head and abdomen in the butterfly Pieris napi. In both body parts, comparing diapausing and nondiapausing siblings, differentially expressed genes are detected from the first day of pupal development and onwards, varying dramatically across these formative stages. During diapause there are strong gene expression dynamics present, revealing a preprogrammed transcriptional landscape that is active during the winter. Different biological processes appear to be active in the two body parts. Finally, adults emerging from either the direct or diapause pathways do not show large transcriptomic differences, suggesting the adult phenotype is strongly canalized.

Acclimations to Cold and Warm Conditions Differently Affect the Energy Metabolism of Diapausing Larvae of the European Corn Borer Ostrinia nubilalis (Hbn.)

The European corn borer Ostrinia nubilalis is a pest species, whose fifth instar larvae gradually develop cold hardiness during diapause. The physiological changes underlying diapause progression and cold hardiness development are still insufficiently understood in insects. Here, we follow a complex of changes related to energy metabolism during cold acclimation (5°C) of diapausing larvae and compare this to warm-acclimated (22°C) and non-diapause controls. Capillary electrophoresis of nucleotides and coenzymes has shown that in gradually cold-acclimated groups concentrations of ATP/ADP and, consequently, energy charge slowly decrease during diapause, while the concentration of AMP increases, especially in the first months of diapause. Also, the activity of cytochrome c oxidase (COX), as well as the concentrations of NAD+ and GMP, decline in cold-acclimated groups, until the latter part of diapause, when they recover. Relative expression of NADH dehydrogenase (nd1), coenzyme Q-cytochrome c reductase (uqcr), COX, ATP synthase (atp), ADP/ATP translocase (ant), and prohibitin 2 (phb2) is supressed in cold-acclimated larvae during the first months of diapause and gradually increases toward the termination of diapause. Contrary to this, NADP+ and UMP levels significantly increased in the first few months of diapause, after gradual cold acclimation, which is in connection with the biosynthesis of cryoprotective molecules, as well as regeneration of small antioxidants. Our findings evidence the existence of a cold-induced energy-saving program that facilitates long-term maintenance of larval diapause, as well as gradual development of cold hardiness. In contrast, warm acclimation induced faster depletion of ATP, ADP, UMP, NAD+, and NADP+, as well as higher activity of COX and generally higher expression of all energy-related genes in comparison to cold-acclimated larvae. Moreover, such unusually high metabolic activity, driven by high temperatures, lead to premature mortality in the warm-acclimated group after 2 months of diapause. Thus, our findings strongly support the importance of low temperature exposure in early diapause for gradual cold hardiness acquisition, successful maintenance of the resting state and return to active development. Moreover, they demonstrate potentially adverse effects of global climate changes and subsequent increase in winter temperatures on cold-adapted terrestrial organisms in temperate and subpolar regions.

Local thermal environment and warming influence supercooling and drive widespread shifts in the metabolome of diapausing Pieris rapae butterflies

Global climate change has the potential to negatively impact biological systems as organisms are exposed to novel temperature regimes. Increases in annual mean temperature have been accompanied by disproportionate rates of change in temperature across seasons, and winter is the season warming most rapidly. Yet, we know relatively little about how warming will alter the physiology of overwintering organisms. Here, we simulated future warming conditions by comparing diapausing Pieris rapae butterfly pupae collected from disparate thermal environments and by exposing P. rapae pupae to acute and chronic increases in temperature. First, we compared internal freezing temperatures (supercooling points) of diapausing pupae that were developed in common-garden conditions but whose parents were collected from northern Vermont, USA, or North Carolina, USA. Matching the warmer winter climate of North Carolina, North Carolina pupae had significantly higher supercooling points than Vermont pupae. Next, we measured the effects of acute and chronic warming exposure in Vermont pupae and found that warming induced higher supercooling points. We further characterized the effects of chronic warming by profiling the metabolomes of Vermont pupae via untargeted LC-MS metabolomics. Warming caused significant changes in abundance of hundreds of metabolites across the metabolome. Notably, there were warming-induced shifts in key biochemical pathways, such as pyruvate metabolism, fructose and mannose metabolism, and β-alanine metabolism, suggesting shifts in energy metabolism and cryoprotection. These results suggest that warming affects various aspects of overwintering physiology in P. rapae and may be detrimental depending on the frequency and variation of winter warming events. Further research is needed to ascertain the extent to which the effects of warming are felt among a broader set of populations of P. rapae, and among other species, in order to better predict how insects may respond to changes in winter thermal environments.

The life cycle of polyploid giant cancer cells and dormancy in cancer: Opportunities for novel therapeutic interventions

Recent data suggest that most genotoxic agents in cancer therapy can lead to shock of genome and increase in cell size, which leads whole genome duplication or multiplication, formation of polyploid giant cancer cells, activation of an early embryonic program, and dedifferentiation of somatic cells. This process is achieved via the giant cell life cycle, a recently proposed mechanism for malignant transformation of somatic cells. Increase in both cell size and ploidy allows cells to completely or partially restructures the genome and develop into a blastocyst-like structure, similar to that observed in blastomere-stage embryogenesis. Although blastocyst-like structures with reprogrammed genome can generate resistant or metastatic daughter cells or benign cells of different lineages, they also acquired ability to undergo embryonic diapause, a reversible state of suspended embryonic development in which cells enter dormancy for survival in response to environmental stress. Therapeutic agents can activate this evolutionarily conserved developmental program, and when cells awaken from embryonic diapause, this leads to recurrence or metastasis. Understanding of the key mechanisms that regulate the different stages of the giant cell life cycle offers new opportunities for therapeutic intervention.

Tissue-specific transcriptional patterns underlie seasonal phenotypes in honey bees (Apis mellifera)

Faced with adverse conditions, such as winter in temperate regions or hot and dry conditions in tropical regions, many insect species enter a state of diapause, a period of dormancy associated with a reduction or arrest of physical activity, development and reproduction. Changes in common physiological pathways underlie diapause phenotypes in different insect species. However, most transcriptomic studies of diapause have not simultaneously evaluated and compared expression patterns in different tissues. Honey bees (Apis mellifera) represent a unique model system to study the mechanisms underpinning diapause-related phenotypes. In winter, honey bees exhibit a classic diapause phenotype, with reduced metabolic activity, increased physiological nutritional resources and altered hormonal profiles. However, winter bees actively heat their colony by vibrating their wing muscles; thus, this tissue is not quiescent. Here, we evaluated the transcriptional profiles of flight muscle tissue and fat body tissue (involved in nutrient storage, metabolism and immune function) of winter bees. We also evaluated two behavioural phenotypes of summer bees: nurses, which exhibit high nutritional stores and low flight activity, and foragers, which exhibit low nutritional stores and high flight activity. We found winter bees and nurses have similar fat body transcriptional profiles, whereas winter bees and foragers have similar flight muscle transcriptional profiles. Additionally, differentially expressed genes were enriched in diapause-related gene ontology terms. Thus, honey bees exhibit tissue-specific transcriptional profiles associated with seasonal phenotypes, laying the groundwork for future studies evaluating the mechanisms, evolution and consequences of this tissue-specific regulation.

Influence of Microclimate Factors on Halyomorpha halys Dehydration

Simple Summary

The brown marmorated stink bug Halyomorpha halys has become a serious invasive species in Northern America and Europe, where it causes major damage to a wide range of crops. Understanding the ecology and behaviour of this pest is key to identifying the most effective strategies to contain its spread. Here we demonstrate that microclimate conditions affect H. halys water loss and that transpiration is influenced by feeding regime and sex. In the overwintering generation, transpiration does not seem influenced by population density and the first nutritional need of individuals exiting diapause is represented by hydration, likely due to water loss during the diapause. Our data suggest that hot and dry climates are not favourable for H. halys and may limit its geographical range. Similarly, microclimatic conditions within crops may have a significant impact on the distribution of H. halys and insect activity may be affected by crop management practices (e.g., pruning and irrigation).

Abstract

Understanding the interaction between insects and microclimate can be essential in order to plan informed and efficient treatments against agricultural pests. Microclimatic factors such as humidity and temperature can influence the population dynamics of the invasive agricultural pest Halyomorpha halys, the brown marmorated stink bug. The aim of this work was to evaluate the level of transpiration of H. halys in dry, normal and humid microclimates according to the sex, physiological conditions and developmental stage of individuals. Water loss during diapause and the effect of population density on insects’ transpiration were also assessed, as were the nutritional preferences of adults upon exiting diapause. Our data demonstrate that microclimatic conditions significantly influence the transpiration of this pest species. The effect of sex and feeding status on insects’ water loss is marked, while population density does not influence water loss in diapausing individuals. The first nutritional need of the overwintering generations is represented by hydration, likely due to the water loss during diapause.

Changes in metabolism and antioxidant systems during tropical diapause in the sunflower caterpillar Chlosyne lacinia (Lepidoptera: Nymphalidae)

Insect diapause shares many biochemical features with other states of metabolic depression, including the suppression of global metabolism, reorganization of metabolic pathways and improved stress resistance. However, little is known about the biochemical changes associated with the diapause phenotype in tropical insects. To investigate biochemical adaptations associated with tropical diapause, we measured the activities of metabolic and antioxidant enzymes, as well as glutathione levels, in the sunflower caterpillar Chlosyne lacinia at different times after initiation of diapause (<1, 20, 40, 60, and 120 days) and after arousal from diapause. Biochemical changes occurred early in diapausing animals, between the first 24 h and 20 days of diapause. Diapausing animals had reduced oxidative capacity associated with a decrease in the activities of peroxide-decomposing antioxidant enzymes. There was no sign of redox imbalance either during diapause or after recovery from diapause. Noteworthy, glutathione transferase and isocitrate dehydrogenase-NADP⁺ activities sharply increased in diapausing animals and stand out as diapause-associated proteins. The upregulation of these two enzymes ultimately indicate the occurrence of Preparation for Oxidative Stress in the tropical diapause of C. lacinia.

The amino acid and lipophilic profiles of Chilo partellus (Swinhoe) larvae fluctuate with diapause

The Chilo partellus (Crambidae: Lepidoptera) larvae undergoes both hibernation and estivation in India. Although, much has been done on reproductive physiological aspects, little is known about biochemical changes happening during hibernation and estivation in C. partellus. Thus, we mapped changes in amino acid and lipophilic profiles of C. partellus larvae while undergoing hibernation and estivation using high-performance liquid chromatography and gas chromatography mass spectroscopy. The studies revealed higher amounts of amino acids namely, serine, glycine, histidine, arginine, proline, tyrosine, and methionine in estivation, while lower in hibernation as compared with nondiapause larvae of C. partellus. Furthermore, the amounts of aspartic acid, glutamic acid, and alanine in hibernation, and threonine, valine, isoleucine, phenylalanine, and leucine in estivation were on par with nondiapause larvae. The lipophilic compounds namely, linoleic acid, stearic acid, eicosanoic acid, and n-pentadecanol were lower in hibernation than estivation and nondiapause larvae of C. partellus. Palmitoleic acid and methyl 3-methoxytetradecanoate contents were higher in hibernation than estivation and nondiapause, while myristic acid and lathosterol contents were higher in estivation than hibernation and nondiapause larvae of C. partellus. Cholesterol content was higher, while squalene and gamma-ergostenol were lower in hibernation and estivation as compared with nondiapause larvae of C. partellus. These findings suggest that certain amino acids may be constituents of heat-shock proteins and help C. partellus during estivation. However, the lipophilic compounds could be helpful in maintaining development during hibernation and estivation in C. partellus.

Optimal Conditions for Diapause Survival of Aprostocetus fukutai, an Egg Parasitoid for Biological Control of Anoplophora chinensis

Simple Summary

Diapause is a critical state of an insect’s life cycle when it undergoes arrestment of growth and/or reproduction to survive adverse environmental conditions and/or food shortage. Aprostocetus fukutai is a specialist egg parasitoid of the citrus longhorned beetle, Anoplophora chinensis, a high-risk invasive woodboring pest. The parasitoid overwinters as diapausing mature larva in the host egg and emerges in early summer in synchrony with the egg-laying of A. chinensis. Here, we determined the optimal conditions for diapause survival of this parasitoid. We showed that the parasitoid had a low (36.7%) diapause survival rate inside host eggs laid on potted plants due to desiccation or tree wound defense response under semi-natural conditions. Under laboratory rearing conditions, when parasitized host eggs were extracted from wood, the parasitoid did not survive at low humidity (44% RH). Survival rate increased with humidity, reaching the highest at 100% RH. Survival rate also increased with increasing chilling period temperature from 2 to 12.5 °C. Post-diapause developmental time decreased with increased humidity or temperature, but the reproductive fitness of the parasitoid was not significantly affected by the temperature regimes. Overall, high humidity (100% RH) and mild temperatures (12.5 °C) are the most suitable survival conditions for the diapausing parasitoid and thus should be used in laboratory rearing.

Abstract

Aprostocetus fukutai is a specialist egg parasitoid of the citrus longhorned beetle Anoplophora chinensis, a high-risk invasive pest of hardwood trees. The parasitoid overwinters as diapausing mature larvae within the host egg and emerges in early summer in synchrony with the egg-laying peak of A. chinensis. This study investigated the parasitoid’s diapause survival in parasitized host eggs that either remained in potted trees under semi-natural conditions in southern France or were removed from the wood and held at four different humidities (44, 75, 85–93 and 100% RH) at 11 °C or four different temperature regimes (2, 5, 10 and 12.5 °C) at 100% RH in the laboratory. The temperature regimes reflect overwintering temperatures across the parasitoid’s geographical distribution in its native range. Results show that the parasitoid resumed its development to the adult stage at normal rearing conditions (22 °C, 100% RH, 14L:10D) after 6- or 7-months cold chilling at both the semi-natural and laboratory conditions. It had a low survival rate (36.7%) on potted plants due to desiccation or tree wound defense response. No parasitoids survived at 44% RH, but survival rate increased with humidity, reaching the highest (93.7%) at 100% RH. Survival rate also increased from 21.0% at 2 °C to 82.8% at 12.5 °C. Post-diapause developmental time decreased with increased humidity or temperature. There was no difference in the lifetime fecundity of emerged females from 2 and 12.5 °C. These results suggest that 100% RH and 12.5 °C are the most suitable diapause conditions for laboratory rearing of this parasitoid.

Post-diapause transcriptomic restarts: insight from a high-latitude copepod

Background

Diapause is a seasonal dormancy that allows organisms to survive unfavorable conditions and optimizes the timing of reproduction and growth. Emergence from diapause reverses the state of arrested development and metabolic suppression returning the organism to an active state. The physiological mechanisms that regulate the transition from diapause to post-diapause are still unknown. In this study, this transition has been characterized for the sub-arctic calanoid copepod Neocalanus flemingeri, a key crustacean zooplankter that supports the highly productive North Pacific fisheries. Transcriptional profiling of females, determined over a two-week time series starting with diapausing females collected from > 400 m depth, characterized the molecular mechanisms that regulate the post-diapause trajectory.

Results

A complex set of transitions in relative gene expression defined the transcriptomic changes from diapause to post-diapause. Despite low temperatures (5–6 °C), the switch from a “diapause” to a “post-diapause” transcriptional profile occurred within 12 h of the termination stimulus. Transcriptional changes signaling the end of diapause were activated within one-hour post collection and included the up-regulation of genes involved in the 20E cascade pathway, the TCA cycle and RNA metabolism in combination with the down-regulation of genes associated with chromatin silencing. By 12 h, females exhibited a post-diapause phenotype characterized by the up-regulation of genes involved in cell division, cell differentiation and multiple developmental processes. By seven days post collection, the reproductive program was fully activated as indicated by up-regulation of genes involved in oogenesis and energy metabolism, processes that were enriched among the differentially expressed genes.

Conclusions

The analysis revealed a finely structured, precisely orchestrated sequence of transcriptional changes that led to rapid changes in the activation of biological processes paving the way to the successful completion of the reproductive program. Our findings lead to new hypotheses related to potentially universal mechanisms that terminate diapause before an organism can resume its developmental program.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07557-7.