Temperature induces changes in Drosophila energy stores

Evolution and development of Drosophila melanogaster under different thermal conditions affected cell sizes and sensitivity to paralyzing hypoxia

Environmental gradients cause evolutionary and developmental changes in the cellular composition of organisms, but the physiological consequences of these effects are not well understood. Here, we studied experimental populations of Drosophila melanogaster that had evolved in one of three selective regimes: constant 16 °C, constant 25 °C, or intergenerational shifts between 16 °C and 25 °C. Genotypes from each population were reared at three developmental temperatures (16 °C, 20.5 °C, and 25 °C). As adults, we measured thorax length and cell sizes in the Malpighian tubules and wing epithelia of flies from each combination of evolutionary and developmental temperatures. We also exposed flies from these treatments to a short period of nearly complete oxygen deprivation to measure hypoxia tolerance. For genotypes from any selective regime, development at a higher temperature resulted in smaller flies with smaller cells, regardless of the tissue. At every developmental temperature, genotypes from the warm selective regime had smaller bodies and smaller wing cells but had larger tubule cells than did genotypes from the cold selective regime. Genotypes from the fluctuating selective regime were similar in size to those from the cold selective regime, but their cells of either tissue were the smallest among the three regimes. Evolutionary and developmental treatments interactively affected a fly's sensitivity to short-term paralyzing hypoxia. Genotypes from the cold selective regime were less sensitive to hypoxia after developing at a higher temperature. Genotypes from the other selective regimes were more sensitive to hypoxia after developing at a higher temperature. Our results show that thermal conditions can trigger evolutionary and developmental shifts in cell size, coupled with changes in body size and hypoxia tolerance. These patterns suggest links between the cellular composition of the body, levels of hypoxia within cells, and the energetic cost of tissue maintenance. However, the patterns can be only partially explained by existing theories about the role of cell size in tissue oxygenation and metabolic performance.

Cell cycle re-entry in the aging Drosophila brain

The brain is an organ comprised mostly of long-lived, quiescent cells that perform vital functions throughout an animal's life. Due to the brain's limited regenerative ability, these long-lived cells must engage unique mechanisms to cope with accumulated damage over time. We have shown that a subset of differentiated neuronal and glial cells in the fruit fly brain become polyploid during adulthood. Cell cycle re-entry in the brain has previously been associated with neurodegeneration, but there may be a more complex relationship between polyploidy and cell fitness in the brain. Here, we examine how known lifespan modifiers influence the accumulation of polyploidy in the aging fly brain. Flies aged at a low temperature, or with a low protein diet, accumulate polyploid cells in the brain more slowly than expected if this phenotype were solely regulated by lifespan mechanisms. Despite the slower accumulation of polyploid cells, animals under conditions that extend lifespan eventually reach similar levels of polyploidy in the brain as controls. Our work suggests known lifespan modifiers can influence the timing of cell cycle re-entry in the adult brain, indicating there is a flexible window of cell cycle plasticity in the aging brain.

Decoding the connection between lncRNA and obesity: Perspective from humans and Drosophila

Background

Obesity is a burgeoning global health problem with an escalating prevalence and severe implications for public health. New evidence indicates that long non-coding RNAs (lncRNAs) may play a pivotal role in regulating adipose tissue function and energy homeostasis across various species. However, the molecular mechanisms underlying obesity remain elusive.

Scope of review

This review discusses obesity and fat metabolism in general, highlighting the emerging importance of lncRNAs in modulating adipogenesis. It describes the regulatory networks, latest tools, techniques, and approaches to enhance our understanding of obesity and its lncRNA-mediated epigenetic regulation in humans and Drosophila.

Major conclusions

This review analyses large datasets of human and Drosophila lncRNAs from published databases and literature with experimental evidence supporting lncRNAs role in fat metabolism. It concludes that lncRNAs play a crucial role in obesity-related metabolism. Cross-species comparisons highlight the relevance of Drosophila findings to human obesity, emphasizing their potential role in adipose tissue biology. Furthermore, it discusses how recent technological advancements and multi-omics data integration enhance our capacity to characterize lncRNAs and their function. Additionally, this review briefly touches upon innovative methodologies like experimental evolution and advanced sequencing technologies for identifying novel genes and lncRNA regulators in Drosophila, which can potentially contribute to obesity research.

Salt concentration in substrate modulates the composition of bacterial and yeast microbiomes of Drosophila melanogaster

Aim: Microbiomes influence the physiology and behavior of multicellular organisms and contribute to their adaptation to changing environmental conditions. However, yeast and bacterial microbiota have usually been studied separately; therefore, the interaction between bacterial and yeast communities in the gut of Drosophila melanogaster (D. melanogaster) is often overlooked. In this study, we investigate the correlation between bacterial and yeast communities in the gut of D. melanogaster. Methods: We studied the shifts in the joint microbiome of Drosophila melanogaster, encompassing both yeasts and bacteria, during adaptation to substrate with varying salt concentrations (0%, 2%, 4%, and 7%) using plating for both yeasts and bacteria and NGS-sequencing of variable 16S rRNA gene regions for bacteria. Results: The microbiome of flies and their substrates was gradually altered at moderate NaCl concentrations (2% and 4% compared with the 0% control) and completely transformed at high salt concentrations (7%). The relative abundance of Acetobacter, potentially beneficial to D. melanogaster, decreased as NaCl concentration increased, whereas the relative abundance of the more halotolerant lactobacilli first increased, peaking at 4% NaCl, and then declined dramatically at 7%. At this salinity level, potentially pathogenic bacteria of the genera Leuconostoc and Providencia were dominant. The yeast microbiome of D. melanogaster also undergoes significant changes with an increase in salt concentration in the substrate. The total yeast abundance undergoes nonlinear changes: it is lowest at 0% salt concentration and highest at 2%-4%. At a 7% concentration, the yeast abundance in flies and their substrate is lower than at 2%-4% but significantly higher than at 0%. Conclusions: The abundance and diversity of bacteria that are potentially beneficial to the flies decreased, while the proportion of potential pathogens, Leuconostoc and Providencia, increased with an increase in salt concentration in the substrate. In samples with a relatively high abundance and/or diversity of yeasts, the corresponding indicators for bacteria were often lowered, and vice versa. This may be due to the greater halotolerance of yeasts compared to bacteria and may also indicate antagonism between these groups of microorganisms.

Bet-hedging in parasitoids: when optimization is not the best strategy to cope with climatic extremes

Bet-hedging occurs when unreliable environments select for genotypes exhibiting a lower variance in fitness at the cost of a lower mean fitness for each batch of progeny. This means that at the level of the genotype, the production of mostly non-optimal phenotypes may be favored when at least some phenotypes are successful. As extreme unreliable climatic events are increasing because of climate change, it is pertinent to investigate the potential of bet-hedging strategies that allow insects to cope with climate change. Evidence for bet-hedging is scarce in most insects, including parasitoids, but the unique lifestyle and biology of parasitoids leads to the expectation that bet-hedging may occur frequently. Here, we evaluate a range of parasitoid traits for which a bet-hedging strategy could be envisioned even if bet-hedging has not been identified as such yet. Under-identification of bet-hedging in nature could have resulted from a major focus of studies on parasitoid life history evolution and foraging behavior on optimality models, predicting how mean fitness can be maximized. Most environmental factors, however, vary unpredictably. Life history and behavioral adaptations are thus expected to be affected by environmental stochasticity. In this paper, we review different aspects of parasitoid behavior, physiology, and life histories and ask the question whether parasitoid traits could have evolved under selection by environmental stochasticity.

Among- and Within-Individual Variance in Metabolic Thermal Reaction Norms

AbstractIn ectotherms, temperature has a strong effect on metabolic rate (MR), yet the extent to which the thermal sensitivity of MR varies among versus within individuals is largely unknown. This is of interest because significant among-individual variation is a prerequisite for the evolution of metabolic thermal sensitivity. Here, we estimated the repeatability (R) of the thermal sensitivity of MR in individual virgin, adult male Drosophila melanogaster (N = 316 ) by taking repeated overnight measures of their MRs at two temperatures (~24°C and ~27°C). At the population level, thermal sensitivity decreased with locomotor activity, and older individuals showed a higher thermal sensitivity of MR than younger individuals. Taking these effects (and body mass) into account, we detected significant repeatability in both the centered intercept (R int = 0.52 ± 0.04 ) and the slope (R slp = 0.21 ± 0.07 ) of the metabolic thermal reaction norms, which respectively represent average MR and thermal sensitivity of MR. Furthermore, individuals with a higher overall MR also displayed greater increases in MR as temperature increased from ~24°C to ~27°C (r ind = 0.32 ± 0.14 ). Average MR and thermal sensitivity of MR were also positively correlated within individuals (r e = 0.15 ± 0.07 ). Our study represents a point of departure for future larger studies, in which more complex protocols (e.g., wider temperature range, breeding design) can be applied to quantify the causal components of variation in thermal sensitivity that are needed to make accurate predictions of adaptive responses to global warming.

Life History Traits and Metabolic Pool Variation in Neotropical Species of Drosophila (Diptera, Drosophilidae)

The differential exploration of natural resources by Drosophila species has effects on fitness, with changes in life history and metabolic traits. There is a lack of research on the variation in these characters in different environments in Neotropical species of Drosophila. The purpose of this study was to evaluate the profile of life history traits, including viability, development time, and dry weight (as a measure of size), as well as the metabolic pools of triglyceride, glycogen, and protein, in populations from the southern and southeastern regions of Brazil of four Neotropical Drosophila species: D. willistoni, of the Sophophora subgenus, and D. mercatorum, D. maculifrons, and D. ornatifrons, which belong to the Drosophila subgenus. Life history and metabolic traits showed interpopulational variation in at least one species. When significant differences in life history parameters occurred, species of the same subgenus presented similar profiles, i.e., southern populations were larger, less viable, and showed longer development time. This was also observed for triglyceride. However, for the other two metabolic pools (glycogen and total proteins), D. maculifrons and D. ornatifrons presented inverse patterns to the other two species, with the highest values in southeastern populations and the lowest in southern populations. These populational variations indicate plasticity of the examined life history traits, which allows distinctive responses to different environmental conditions shared by speciesof the same subgenus. Nevertheless, interspecific comparisons did not reflect phylogenetic relationships, with the highest viability being found for D. willistoni and D. mercatorum, which is probably correlated to the ability of these species to explore a broader variety of habitats. On the other hand, the storage capability of metabolic pools seems to be species specific, determined by the adaptive history to the quality and availability of resources, with D. mercatorum (low) and D. ornatifrons (high) having opposing capacities to store metabolites from their diets.

Strong Sex-Dependent Effects of Malnutrition on Life- and Healthspan in Drosophila melanogaster

Insufficient intake of essential nutrients, malnutrition is a major issue for millions of people and has a strong impact on the distribution and abundance of species in nature. In this study, we investigated the effect of malnutrition on several fitness components in the vinegar fly Drosophila melanogaster. Four diets with different nutritional values, including three diluted diets of an optimal nutritional balanced diet, were used as feed sources. The effect of malnutrition on fitness components linked to healthspan, the period of life spent in good health conditions, was evaluated by quantifying the flies' lifespan, locomotor activity, heat stress tolerance, lipid content, and dry weight. The results showed that malnutrition had severe negative impact, such as reduced lifespan, locomotor activity, heat stress tolerance, fat content, and dry weight. The negative phenotypic effects were highly sex-dependent, with males being more negatively impacted by malnutrition compared to females. These findings highlight important detrimental and sex-specific effects of malnutrition not only on lifespan but also on traits related to healthspan.

Exposure to heat stress leads to striking clone-specific nymph deformity in pea aphid

Climatic changes, such as heatwaves, pose unprecedented challenges for insects, as escalated temperatures above the thermal optimum alter insect reproductive strategies and energy metabolism. While thermal stress responses have been reported in different insect species, thermo-induced developmental abnormalities in phloem-feeding pests are largely unknown. In this laboratory study, we raised two groups of first instar nymphs belonging to two clones of the pea aphid Acyrthosiphon pisum, on fava beans Vicia faba. The instars developed and then asexually reproduced under constant exposure to a sub-lethal heatwave (27°C) for 14 days. Most mothers survived but their progenies showed abnormalities, as stillbirths and appendageless or weak nymphs with folded appendages were delivered. Clone N116 produced more deceased and appendageless embryos, contrary to N127, which produced fewer dead and more malformed premature embryos. Interestingly, the expression of the HSP70 and HSP83 genes differed in mothers between the clones. Moreover, noticeable changes in metabolism, e.g., lipids, were also detected and that differed in response to stress. Deformed offspring production after heat exposure may be due to heat injury and differential HSP gene expression, but may also be indicative of a conflict between maternal and offspring fitness. Reproductive altruism might have occurred to ensure some of the genetically identical daughters survive. This is because maintaining homeostasis and complete embryogenesis could not be simultaneously fulfilled due to the high costs of stress. Our findings shine new light on pea aphid responses to heatwaves and merit further examination across different lineages and species.

Molecular and Neural Mechanisms of Temperature Preference Rhythm in Drosophila melanogaster

Temperature influences animal physiology and behavior. Animals must set an appropriate body temperature to maintain homeostasis and maximize survival. Mammals set their body temperatures using metabolic and behavioral strategies. The daily fluctuation in body temperature is called the body temperature rhythm (BTR). For example, human body temperature increases during wakefulness and decreases during sleep. BTR is controlled by the circadian clock, is closely linked with metabolism and sleep, and entrains peripheral clocks located in the liver and lungs. However, the underlying mechanisms of BTR are largely unclear. In contrast to mammals, small ectotherms, such as Drosophila, control their body temperatures by choosing appropriate environmental temperatures. The preferred temperature of Drosophila increases during the day and decreases at night; this pattern is referred to as the temperature preference rhythm (TPR). As flies are small ectotherms, their body temperature is close to that of the surrounding environment. Thus, Drosophila TPR produces BTR, which exhibits a pattern similar to that of human BTR. In this review, we summarize the regulatory mechanisms of TPR, including recent studies that describe neuronal circuits relaying ambient temperature information to dorsal neurons (DNs). The neuropeptide diuretic hormone 31 (DH31) and its receptor (DH31R) regulate TPR, and a mammalian homolog of DH31R, the calcitonin receptor (CALCR), also plays an important role in mouse BTR regulation. In addition, both fly TPR and mammalian BTR are separately regulated from another clock output, locomotor activity rhythms. These findings suggest that the fundamental mechanisms of BTR regulation may be conserved between mammals and flies. Furthermore, we discuss the relationships between TPR and other physiological functions, such as sleep. The dissection of the regulatory mechanisms of Drosophila TPR could facilitate an understanding of mammalian BTR and the interaction between BTR and sleep regulation.

Comparison of neuronal GAL4 drivers along with the AGES (auxin-inducible gene expression system) and TARGET (temporal and regional gene expression targeting) systems for fine tuning of neuronal gene expression in Drosophila

Spatial and temporal control of gene expression in Drosophila is essential in elucidating gene function. Spatial control is facilitated by the UAS/GAL4 system, and this can be coupled with additional adaptations for precise temporal control and fine tuning of gene expression levels. Here we directly compare the level of pan-neuronal transgene expression governed by nSyb-GAL4 and elav-GAL4, as well as mushroom body-specific expression alongside OK107-GAL4. We also compare the temporal modulation of gene expression in neurons with the auxin-inducible gene expression system (AGES) and temporal and regional gene expression targeting (TARGET) systems.

The dual role of heme oxygenase in regulating apoptosis in the nervous system of Drosophila melanogaster

Accumulating evidence from mammalian studies suggests the dual-faced character of heme oxygenase (HO) in oxidative stress-dependent neurodegeneration. The present study aimed to investigate both neuroprotective and neurotoxic effects of heme oxygenase after the ho gene chronic overexpression or silencing in neurons of Drosophila melanogaster. Our results showed early deaths and behavioral defects after pan-neuronal ho overexpression, while survival and climbing in a strain with pan-neuronal ho silencing were similar over time with its parental controls. We also found that HO can be pro-apoptotic or anti-apoptotic under different conditions. In young (7-day-old) flies, both the cell death activator gene (hid) expression and the initiator caspase Dronc activity increased in heads of flies when ho expression was changed. In addition, various expression levels of ho produced cell-specific degeneration. Dopaminergic (DA) neurons and retina photoreceptors are particularly vulnerable to changes in ho expression. In older (30-day-old) flies, we did not detect any further increase in hid expression or enhanced degeneration, however, we still observed high activity of the initiator caspase. In addition, we used curcumin to further show the involvement of neuronal HO in the regulation of apoptosis. Under normal conditions, curcumin induced both the expression of ho and hid, which was reversed after exposure to high-temperature stress and when supplemented in flies with ho silencing. These results indicate that neuronal HO regulates apoptosis and this process depends on ho expression level, age of flies, and cell type.

Signaling through the dystrophin glycoprotein complex affects the stress-dependent transcriptome in Drosophila

Deficiencies in the human dystrophin glycoprotein complex (DGC), which links the extracellular matrix with the intracellular cytoskeleton, cause muscular dystrophies, a group of incurable disorders associated with heterogeneous muscle, brain and eye abnormalities. Stresses such as nutrient deprivation and aging cause muscle wasting, which can be exacerbated by reduced levels of the DGC in membranes, the integrity of which is vital for muscle health and function. Moreover, the DGC operates in multiple signaling pathways, demonstrating an important function in gene expression regulation. To advance disease diagnostics and treatment strategies, we strive to understand the genetic pathways that are perturbed by DGC mutations. Here, we utilized a Drosophila model to investigate the transcriptomic changes in mutants of four DGC components under temperature and metabolic stress. We identified DGC-dependent genes, stress-dependent genes and genes dependent on the DGC for a proper stress response, confirming a novel function of the DGC in stress-response signaling. This perspective yields new insights into the etiology of muscular dystrophy symptoms, possible treatment directions and a better understanding of DGC signaling and regulation under normal and stress conditions.

Serotonergic control of feeding microstructure in Drosophila

To survive, animals maintain energy homeostasis by seeking out food. Compared to freely feeding animals, food-deprived animals may choose different strategies to balance both energy and nutrition demands, per the metabolic state of the animal. Serotonin mediates internal states, modifies existing neural circuits, and regulates animal feeding behavior, including in humans and fruit flies. However, an in-depth study on the neuromodulatory effects of serotonin on feeding microstructure has been held back for several technical reasons. Firstly, most feeding assays lack the precision of manipulating neuronal activity only when animals start feeding, which does not separate neuronal effects on feeding from foraging and locomotion. Secondly, despite the availability of optogenetic tools, feeding in adult fruit flies has primarily been studied using thermogenetic systems, which are confounded with heat. Thirdly, most feeding assays have used food intake as a measurement, which has a low temporal resolution to dissect feeding at the microstructure level. To circumvent these problems, we utilized OptoPAD assay, which provides the precision of optogenetics to control neural activity contingent on the ongoing feeding behavior. We show that manipulating the serotonin circuit optogenetically affects multiple feeding parameters state-dependently. Food-deprived flies with optogenetically activated and suppressed serotonin systems feed with shorter and longer sip durations and longer and shorter inter-sip intervals, respectively. We further show that serotonin suppresses and enhances feeding via 5-HT1B and 5-HT7 receptors, respectively.

Central and peripheral regulations mediated by short-chain fatty acids on energy homeostasis

The human gut microbiota influences obesity, insulin resistance, and the subsequent development of type 2 diabetes (T2D). The gut microbiota digests and ferments nutrients resulting in the production of short-chain fatty acids (SCFAs), which generate various beneficial metabolic effects on energy and glucose homeostasis. However, their roles in the central nervous system (CNS)-mediated outputs on the metabolism have only been minimally studied. Here, we explore what is known and future directions that may be worth exploring in this emerging area. Specifically, we searched studies or data in English by using PubMed, Google Scholar, and the Human Metabolome Database. Studies were filtered by time from 1978 to March 2022. As a result, 195 studies, 53 reviews, 1 website, and 1 book were included. One hundred and sixty-five of 195 studies describe the production and metabolism of SCFAs or the effects of SCFAs on energy homeostasis, glucose balance, and mental diseases through the gut-brain axis or directly by a central pathway. Thirty of 195 studies show that inappropriate metabolism and excessive of SCFAs are metabolically detrimental. Most studies suggest that SCFAs exert beneficial metabolic effects by acting as the energy substrate in the TCA cycle, regulating the hormones related to satiety regulation and insulin secretion, and modulating immune cells and microglia. These functions have been linked with AMPK signaling, GPCRs-dependent pathways, and inhibition of histone deacetylases (HDACs). However, the studies focusing on the central effects of SCFAs are still limited. The mechanisms by which central SCFAs regulate appetite, energy expenditure, and blood glucose during different physiological conditions warrant further investigation.

Comparative analysis of temperature preference behavior and effects of temperature on daily behavior in 11 Drosophila species

Temperature is one of the most critical environmental factors that influence various biological processes. Species distributed in different temperature regions are considered to have different optimal temperatures for daily life activities. However, how organisms have acquired various features to cope with particular temperature environments remains to be elucidated. In this study, we have systematically analyzed the temperature preference behavior and effects of temperatures on daily locomotor activity and sleep using 11 Drosophila species. We also investigated the function of antennae in the temperature preference behavior of these species. We found that, (1) an optimal temperature for daily locomotor activity and sleep of each species approximately matches with temperatures it frequently encounters in its habitat, (2) effects of temperature on locomotor activity and sleep are diverse among species, but each species maintains its daily activity and sleep pattern even at different temperatures, and (3) each species has a unique temperature preference behavior, and the contribution of antennae to this behavior is diverse among species. These results suggest that Drosophila species inhabiting different climatic environments have acquired species-specific temperature response systems according to their life strategies. This study provides fundamental information for understanding the mechanisms underlying their temperature adaptation and lifestyle diversification.

Loss of neurexin-1 in Drosophila melanogaster results in altered energy metabolism and increased seizure susceptibility

Although autism is typically characterized by differences in language, social interaction and restrictive, repetitive behaviors, it is becoming more well known in the field that alterations in energy metabolism and mitochondrial function are comorbid disorders in autism. The synaptic cell adhesion molecule, neurexin-1 (NRXN1), has previously been implicated in autism, and here we show that in Drosophila melanogaster, the homologue of NRXN1, called Nrx-1, regulates energy metabolism and nutrient homeostasis. First, we show that Nrx-1-null flies exhibit decreased resistance to nutrient deprivation and heat stress compared to controls. Additionally, Nrx-1 mutants exhibit a significantly altered metabolic profile characterized by decreased lipid and carbohydrate stores. Nrx-1-null Drosophila also exhibit diminished levels of nicotinamide adenine dinucleotide (NAD⁺), an important coenzyme in major energy metabolism pathways. Moreover, loss of Nrx-1 resulted in striking abnormalities in mitochondrial morphology in the flight muscle of Nrx-1-null Drosophila and impaired flight ability in these flies. Further, following a mechanical shock Nrx-1-null flies exhibited seizure-like activity, a phenotype previously linked to defects in mitochondrial metabolism and a common symptom of patients with NRXN1 deletions. The current studies indicate a novel role for NRXN1 in the regulation of energy metabolism and uncover a clinically relevant seizure phenotype in Drosophila lacking Nrx-1.

Endocrine control of glycogen and triacylglycerol breakdown in the fly model

Over the last decade, the combination of genetics, transcriptomic and proteomic approaches yielded substantial insights into the mechanisms behind the synthesis and breakdown of energy stores in the model organisms. The fruit fly Drosophila melanogaster has been particularly useful to unravel genetic regulations of energy metabolism. Despite the considerable evolutionary distance between humans and flies, the energy storage organs, main metabolic pathways, and even their genetic regulations remained relatively conserved. Glycogen and fat are universal energy reserves used in all animal phyla and several of their endocrine regulators, such as the insulin pathway, are highly evolutionarily conserved. Nevertheless, some of the factors inducing catabolism of energy stores have diverged significantly during evolution. Moreover, even within a single insect species, D. melanogaster, there are substantial developmental and context-dependent variances in the regulation of energy stores. These differences include, among others, the endocrine pathways that govern the catabolic events or the predominant fuel which is utilized for the given process. For example, many catabolic regulators that control energy reserves in adulthood seem to be largely dispensable for energy mobilization during development. In this review, we focus on a selection of the most important catabolic regulators from the group of peptide hormones (Adipokinetic hormone, Corazonin), catecholamines (octopamine), steroid hormones (20-hydroxyecdysone), and other factors (extracellular adenosine, regulators of lipase Brummer). We discuss their roles in the mobilization of energy reserves for processes such as development through non-feeding stages, flight or starvation survival. Finally, we conclude with future perspectives on the energy balance research in the fly model.

Behavior Individuality: A Focus on Drosophila melanogaster

Among individuals, behavioral differences result from the well-known interplay of nature and nurture. Minute differences in the genetic code can lead to differential gene expression and function, dramatically affecting developmental processes and adult behavior. Environmental factors, epigenetic modifications, and gene expression and function are responsible for generating stochastic behaviors. In the last decade, the advent of high-throughput sequencing has facilitated studying the genetic basis of behavior and individuality. We can now study the genomes of multiple individuals and infer which genetic variations might be responsible for the observed behavior. In addition, the development of high-throughput behavioral paradigms, where multiple isogenic animals can be analyzed in various environmental conditions, has again facilitated the study of the influence of genetic and environmental variations in animal personality. Mainly, Drosophila melanogaster has been the focus of a great effort to understand how inter-individual behavioral differences emerge. The possibility of using large numbers of animals, isogenic populations, and the possibility of modifying neuronal function has made it an ideal model to search for the origins of individuality. In the present review, we will focus on the recent findings that try to shed light on the emergence of individuality with a particular interest in D. melanogaster.

Characterization of Stress Responses in a Drosophila Model of Werner Syndrome

As organisms age, their resistance to stress decreases while their risk of disease increases. This can be shown in patients with Werner syndrome (WS), which is a genetic disease characterized by accelerated aging along with increased risk of cancer and metabolic disease. WS is caused by mutations in WRN, a gene involved in DNA replication and repair. Recent research has shown that WRN mutations contribute to multiple hallmarks of aging including genomic instability, telomere attrition, and mitochondrial dysfunction. However, questions remain regarding the onset and effect of stress on early aging. We used a fly model of WS (WRNexoΔ) to investigate stress response during different life stages and found that stress sensitivity varies according to age and stressor. While larvae and young WRNexoΔ adults are not sensitive to exogenous oxidative stress, high antioxidant activity suggests high levels of endogenous oxidative stress. WRNexoΔ adults are sensitive to stress caused by elevated temperature and starvation suggesting abnormalities in energy storage and a possible link to metabolic dysfunction in WS patients. We also observed higher levels of sleep in aged WRNexoΔ adults suggesting an additional adaptive mechanism to protect against age-related stress. We suggest that stress response in WRNexoΔ is multifaceted and evokes a systemic physiological response to protect against cellular damage. These data further validate WRNexoΔ flies as a WS model with which to study mechanisms of early aging and provide a foundation for development of treatments for WS and similar diseases.

Glutamate metabolism directs energetic trade-offs to shape host-pathogen susceptibility in Drosophila

Individual hosts within populations often show inter-individual variation in their susceptibility to bacterial pathogen-related diseases. Utilizing Drosophila, we highlight that phenotypic variation in host-pathogen susceptibility within populations is driven by energetic trade-offs, facilitated by infection-mediated changes in glutamate metabolism. Furthermore, host-pathogen susceptibility is conditioned by life history, which adjusts immunometabolic sensing in muscles to direct vitamin-dependent reallocation of host energy substrates from the adipose tissue (i.e., a muscle-adipose tissue axis). Life history conditions inter-individual variation in the activation strength of intra-muscular NF-κB signaling. Limited intra-muscular NF-κB signaling activity allows for enhanced infection-mediated mitochondrial biogenesis and function, which stimulates glutamate dehydrogenase-dependent synthesis of glutamate. Muscle-derived glutamate acts as a systemic metabolite to promote lipid mobilization through modulating vitamin B enzymatic cofactor transport and function in the adipose tissue. This energy substrate reallocation improves pathogen clearance and boosts host survival. Finally, life history events that adjust energetic trade-offs can shape inter-individual variation in host-pathogen susceptibility after infection.

Alternative models for transgenerational epigenetic inheritance: Molecular psychiatry beyond mice and man

Mental illness remains the greatest chronic health burden globally with few in-roads having been made despite significant advances in genomic knowledge in recent decades. The field of psychiatry is constantly challenged to bring new approaches and tools to address and treat the needs of vulnerable individuals and subpopulations, and that has to be supported by a continuous growth in knowledge. The majority of neuropsychiatric symptoms reflect complex gene-environment interactions, with epigenetics bridging the gap between genetic susceptibility and environmental stressors that trigger disease onset and drive the advancement of symptoms. It has more recently been demonstrated in preclinical models that epigenetics underpins the transgenerational inheritance of stress-related behavioural phenotypes in both paternal and maternal lineages, providing further supporting evidence for heritability in humans. However, unbiased prospective studies of this nature are practically impossible to conduct in humans so preclinical models remain our best option for researching the molecular pathophysiologies underlying many neuropsychiatric conditions. While rodents will remain the dominant model system for preclinical studies (especially for addressing complex behavioural phenotypes), there is scope to expand current research of the molecular and epigenetic pathologies by using invertebrate models. Here, we will discuss the utility and advantages of two alternative model organisms-Caenorhabditis elegans and Drosophila melanogaster-and summarise the compelling insights of the epigenetic regulation of transgenerational inheritance that are potentially relevant to human psychiatry.

Additive and non-additive effects of day and night temperatures on thermally plastic traits in a model for adaptive seasonal plasticity

Developmental plasticity can match organismal phenotypes to ecological conditions, helping populations to deal with the environmental heterogeneity of alternating seasons. In contrast to natural situations, experimental studies of plasticity often use environmental conditions that are held constant during development. To explore potential interactions between day and night temperatures, we tested effects of circadian temperature fluctuations on thermally plastic traits in a seasonally plastic butterfly, Bicyclus anynana. Comparing phenotypes for four treatments corresponding to a full-factorial analysis of cooler and warmer temperatures, we found evidence of significant interaction effects between day and night temperatures. We then focused on comparing phenotypes between individuals reared under two types of temperature fluctuations (warmer days with cooler nights, and cooler days with warmer nights) and individuals reared under a constant temperature of the same daily mean. We found evidence of additive-like effects (for body size), and different types of dominance-like effects, with one particular period of the light cycle (for development time) or one particular extreme temperature (for eyespot size) having a larger impact on phenotype. Differences between thermally plastic traits, which together underlie alternative seasonal strategies for survival and reproduction, revealed their independent responses to temperature. This study underscores the value of studying how organisms integrate complex environmental information toward a complete understanding of natural phenotypic variation and of the impact of environmental change thereon.

Daily temperature cycles prolong lifespan and have sex-specific effects on peripheral clock gene expression in Drosophila melanogaster

Circadian rhythms optimize health by coordinating the timing of physiological processes to match predictable daily environmental challenges. The circadian rhythm of body temperature is thought to be an important modulator of molecular clocks in peripheral tissues, but how daily temperature cycles affect physiological function is unclear. Here, we examined the effect of constant temperature (Tcon, 25°C) and cycling temperature (Tcyc, 28°C:22°C during light:dark) paradigms on lifespan of Drosophila melanogaster, and the expression of clock genes, heat shock protein 83 (Hsp83), Frost (Fst) and senescence marker protein-30 (smp-30). Male and female D. melanogaster housed at Tcyc had longer median lifespans than those housed at Tcon. Tcyc induced robust Hsp83 rhythms and rescued the age-related decrease in smp-30 expression that was observed in flies at Tcon, potentially indicating an increased capacity to cope with age-related cellular stress. Ageing under Tcon led to a decrease in the amplitude of expression of all clock genes in the bodies of male flies, except for cyc, which was non-rhythmic, and for per and cry in female flies. Strikingly, housing under Tcyc conditions rescued the age-related decrease in amplitude of all clock genes, and generated rhythmicity in cyc expression, in the male flies, but not the female flies. The results suggest that ambient temperature rhythms modulate D. melanogaster lifespan, and that the amplitude of clock gene expression in peripheral body clocks may be a potential link between temperature rhythms and longevity in male D. melanogaster. Longevity due to Tcyc appeared predominantly independent of clock gene amplitude in female D. melanogaster.

The effect of environmental stress on ageing in a termite species with low social complexity

Social insects seem to have overcome the almost universal trade-off between fecundity and longevity as queens can be highly fecund and at the same time reach lifespans of decades. By contrast, their non-reproducing workers are often short-lived. One hypothesis to explain the long lifespan of queens is that they are better protected against stress than their workers. However, evidence is controversial and experimental studies are scarce. We aimed at manipulating environmental stress and ageing by exposing colonies of the less-socially complex termite Cryptotermes secundus to temperature regimes that differed in variance. In contrast with expectation, constant temperatures imposed more stress than variable temperatures. Survival of queens and workers as well as queens' fecundity were partly reduced under constant conditions and both castes showed signs of ageing in the transcriptome signature under constant conditions. There was a clear oxidative stress defence signal under constant conditions that was, surprisingly, stronger for workers than queens. We discuss how our results relate to social complexity. We argue that workers that are totipotent to become reproductives, like in C. secundus, should invest more in 'anti-ageing' mechanisms than sterile workers because the former can still reproduce and have not reached maturity yet. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

Lower bioenergetic costs but similar immune responsiveness under a heat wave in urban compared to rural damselflies

There is mounting evidence that the widespread phenotypic changes in response to urbanization may reflect adaptations caused by rapid evolutionary processes driven by urban-related stressors. Compared to increased habitat fragmentation and pollution, adaptations towards another typical urban-related stressor, that is higher and longer lasting very high temperatures (heat waves), are much less studied. Notably, the sensitivities to heat waves of life-history traits and important fitness-related physiological traits such as immune responsiveness and bioenergetic variables (energy availability, energy consumption and their balance) have never been contrasted between urban and rural populations. By conducting a laboratory common-garden experiment, we compared effects of a simulated heat wave on life history (survival and growth rate), immune responsiveness and bioenergetic variables between three urban and three rural populations of the damselfly Coenagrion puella. Because energy-mediated trade-off patterns may only be detected under energetically costly manipulations, all larvae were immune-challenged by simulating ectoparasitism by water mites. As expected, the simulated heat wave caused negative effects on nearly all response variables. The immune responsiveness, on the other hand, increased under the heat wave, consistent with a trade-off pattern between immune function and growth, and this similarly between urban and rural populations. A key finding was that urban larvae suffered less from the simulated heat wave compared to the rural larvae in terms of a lower heat wave-induced depletion in energy availability. This suggests an adaptation of urban populations to better cope with the stronger and more frequent heat waves in cities. Notably, this urbanization-driven evolution in the bioenergetic variables was not apparent in the absence of a heat wave. Given that changes in energy budgets have strong fitness consequences, our findings suggest that the evolved higher ability to cope with heat waves is fundamental for the survival of urban damselfly populations.

Temperature modulates immune gene expression in mosquitoes during arbovirus infection

The principal vector of dengue, Zika and chikungunya viruses is the mosquito Aedes aegypti, with its ability to transmit pathogens influenced by ambient temperature. We use chikungunya virus (CHIKV) to understand how the mosquito transcriptome responds to arbovirus infection at different ambient temperatures. We exposed CHIKV-infected mosquitoes to 18, 28 and 32°C, and found that higher temperature correlated with higher virus levels, particularly at 3 days post infection, but lower temperature resulted in reduced virus levels. RNAseq analysis indicated significantly altered gene expression levels in CHIKV infection. The highest number of significantly differentially expressed genes was observed at 28°C, with a more muted effect at the other temperatures. At the higher temperature, the expression of many classical immune genes, including Dicer-2, was not substantially altered in response to CHIKV. The upregulation of Toll, IMD and JAK-STAT pathways was only observed at 28°C. Functional annotations suggested that genes in immune response and metabolic pathways related to energy supply and DNA replication were involved in temperature-dependent changes. Time post infection also led to substantially different gene expression profiles, and this varied with temperature. In conclusion, temperature significantly modulates mosquito gene expression in response to infection, potentially leading to impairment of immune defences at higher temperatures.

Acclimation temperature affects thermal reaction norms for energy reserves in Drosophila

Organisms have evolved various physiological mechanisms to cope with unfavourable environmental conditions. The ability to tolerate non-optimal thermal conditions can be substantially improved by acclimation. In this study, we examined how an early-life acclimation to different temperatures (19 °C, 25 °C and 29 °C) influences thermal reaction norms for energy stores in Drosophila adults. Our results show that acclimation temperature has a significant effect on the amount of stored fat and glycogen (and their relative changes) and the optimal temperature for their accumulation. Individuals acclimated to 19 °C had, on average, more energy reserves than flies that were initially maintained at 25 °C or 29 °C. In addition, acclimation caused a shift in optimal temperature for energy stores towards acclimation temperature. We also detected significant population differences in this response. The effect of acclimation on the optimal temperature for energy stores was more pronounced in flies from the temperate climate zone (Slovakia) than in individuals from the tropical zone (India). Overall, we found that the acclimation effect was stronger after acclimation to low (19 °C) than to high (29 °C) temperature. The observed sensitivity of thermal reaction norms for energy reserves to acclimation temperature can have important consequences for surviving periods of food scarcity, especially at suboptimal temperatures.

Multigenerational experimental simulation of climate change on an economically important insect pest

Long-term multigenerational experimental simulations of climate change on insect pests of economically and socially important crops are crucial to anticipate challenges for feeding humanity in the not-so-far future. Mexican bean weevil Zabrotes subfasciatus, is a worldwide pest that attacks the common bean Phaseolus vulgaris seeds, in crops and storage. We designed a long term (i.e., over 10 generations), experimental simulation of climate change by increasing temperature and CO2 air concentration in controlled conditions according to model predictions for 2100. Higher temperature and CO2 concentrations favored pest's egg-to-adult development survival, even at high female fecundity. It also induced a reduction of fat storage and increase of protein content but did not alter body size. After 10 generations of simulation, genetic adaptation was detected for total lipid content only, however, other traits showed signs of such process. Future experimental designs and methods similar to ours, are key for studying long-term effects of climate change through multigenerational experimental designs.

Response of Mycorrhizal 'Touriga Nacional' Variety Grapevines to High Temperatures Measured by Calorespirometry and Near-Infrared Spectroscopy

Heat stress negatively affects several physiological and biochemical processes in grapevine plants. In this work, two new methods, calorespirometry, which has been used to determine temperature adaptation in plants, and near-infrared (NIR) spectroscopy, which has been used to determine several grapevine-related traits and to discriminate among varieties, were tested to evaluate grapevine response to high temperatures. 'Touriga Nacional' variety grapevines, inoculated or not with Rhizoglomus irregulare or Funneliformis mosseae, were used in this study. Calorespirometric parameters and NIR spectra, as well as other parameters commonly used to assess heat injury in plants, were measured before and after high temperature exposure. Growth rate and substrate carbon conversion efficiency, calculated from calorespirometric measurements, and stomatal conductance, were the most sensitive parameters for discriminating among high temperature responses of control and inoculated grapevines. The results revealed that, although this vine variety can adapt its physiology to temperatures up to 40 °C, inoculation with R. irregulare could additionally help to sustain its growth, especially after heat shocks. Therefore, the combination of calorespirometry together with gas exchange measurements is a promising strategy for screening grapevine heat tolerance under controlled conditions and has high potential to be implemented in initial phases of plant breeding programs.

Temperature dependency of predation: Increased killing rates and prey mass consumption by predators with warming

Temperature dependency of consumer-resource interactions is fundamentally important for understanding and predicting the responses of food webs to climate change. Previous studies have shown temperature-driven shifts in herbivore consumption rates and resource preference, but these effects remain poorly understood for predatory arthropods. Here, we investigate how predator killing rates, prey mass consumption, and macronutrient intake respond to increased temperatures using a laboratory and a field reciprocal transplant experiment. Ectothermic predators, wolf spiders (Pardosa sp.), in the lab experiment, were exposed to increased temperatures and different prey macronutrient content (high lipid/low protein and low lipid/high protein) to assess changes in their killing rates and nutritional demands. Additionally, we investigate prey mass and lipid consumption by spiders under contrasting temperatures, along an elevation gradient. We used a field reciprocal transplant experiment between low (420 masl; 26°C) and high (2,100 masl; 15°C) elevations in the Ecuadorian Andes, using wild populations of two common orb-weaver spider species (Leucauge sp. and Cyclosa sp.) present along the elevation gradient. We found that killing rates of wolf spiders increased with warmer temperatures but were not significantly affected by prey macronutrient content, although spiders consumed significantly more lipids from lipid-rich prey. The field reciprocal transplant experiment showed no consistent predator responses to changes in temperature along the elevational gradient. Transplanting Cyclosa sp. spiders to low- or high-elevation sites did not affect their prey mass or lipid consumption rate, whereas Leucauge sp. individuals increased prey mass consumption when transplanted from the high to the low warm elevation. Our findings show that increases in temperature intensify predator killing rates, prey consumption, and lipid intake, but the responses to temperature vary between species, which may be a result of species-specific differences in their hunting behavior and sensitivity to temperature.

Transcriptome analysis of Drosophila melanogaster laboratory strains of different geographical origin after long-term laboratory maintenance

Positive selection may be the main factor of the between-population divergence in gene expression. Expression profiles of two Drosophila melanogaster laboratory strains of different geographical origin and long-term laboratory maintenance were analyzed using microchip arrays encompassing probes for 18,500 transcripts. The Russian strain D18 and the North American strain Canton-S were compared. A set of 223 known or putative genes demonstrated significant changes in expression levels between these strains. Differentially expressed genes (DEG) were enriched in response to DDT (p = .0014), proteolysis (p = 2.285E-5), transmembrane transport (p = 1.03E-4), carbohydrate metabolic process (p = .0317), protein homotetramerization (p = .0444), and antibacterial humoral response (p = 425E-4). The expression in subset of genes from different categories was verified by qRT-PCR. Analysis of transcript abundance between Canton-S and D18 strains allowed to select several genes to estimate their participation in latitude adaptation. Expression of selected genes was analyzed in five D. melanogaster lines of different geographic origins by qRT-PCR, and we found two candidate genes that may be associated with latitude adaptation in adult flies-smp-30 and Cda9. Quite possible that several alleles of these genes may be important for insect survival in the environments of global warming. It is interesting that the number of genes involved in local adaptation demonstrates expression level appropriate to their geographical origin even after decades of laboratory maintenance.

Temperature and altitude modulate feeding attributes of Mexican beetle, Zygogramma bicolorata Pallister on Parthenium hysterophorus

Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) is an effective biocontrol agent of Parthenium hysterophorus L. which is an alien invasive herbaceous weed with a pan-tropical distribution. The present study aimed to assess the effects of temperature and altitude on feeding attributes (consumption rate, conversion efficiency and growth rate) of adults from the wild populations of Z. bicolorata inhabiting India and Nepal. Results revealed that adults inhabiting areas of low temperature (24°C ‒ 25°C) and high altitude (415 m ‒1400 m) were large and had higher food consumption rates. In contrast, those inhabiting areas of high temperature (34°C ‒ 36°C) and low altitude (81 m ‒ 229 m) were smaller and had higher food utilization efficiencies. In all the eco-climatic regions, females were larger than males and had higher feeding attributes than their counterparts. Temperature between 27°C and 30°C was found optimal for Z. bicolorata adults to convert and utilize the food biomass to body mass. Above the optimal temperature the feeding attributes decreased. Present results suggest that there exists a possibility for decrease in body size, and thereby weed biocontrol efficiency of Z. bicolorata adults with an increase in temperature due to global climate change.

Temperature and Sweet Taste Integration in Drosophila

Sugar-containing foods offered at cooler temperatures tend to be less appealing to many animals. However, the mechanism through which the gustatory system senses thermal input and integrates temperature and chemical signals to produce a given behavioral output is poorly understood. To study this fundamental problem, we used the fly, Drosophila melanogaster. We found that the palatability of sucrose is strongly reduced by modest cooling. Using Ca²⁺ imaging and electrophysiological recordings, we demonstrate that bitter gustatory receptor neurons (GRNs) and mechanosensory neurons (MSNs) are activated by slight cooling, although sugar neurons are insensitive to the same mild stimulus. We found that a rhodopsin, Rh6, is expressed and required in bitter GRNs for cool-induced suppression of sugar appeal. Our findings reveal that the palatability of sugary food is reduced by slightly cool temperatures through different sets of thermally activated neurons, one of which depends on a rhodopsin (Rh6) for cool sensation.

Temperature and Sugar Feeding Effects on the Activity of a Laboratory Strain of Aedes aegypti

Aedes aegypti is an invasive mosquito species that is expected to expand its global distribution through climate change. As poikilotherms, mosquitoes are greatly affected by the temperature of the environment which can impact host-seeking, blood-feeding, and flight activity as well as survival and ability to transmit pathogens. However, an important aspect of mosquito biology on which the effect of temperature has not been investigated is water and sugar-feeding and how access to a sugar source might affect the insect's activity and survival under different thermal conditions. To close this knowledge gap, we relied on actometer experiments to study the activity of both female and male Ae. aegypti at 20 °C, 25 °C, and 30 °C, providing either water or 10% sucrose to the insects. We then measured the total carbohydrate contents of alive mosquitoes using the anthrone protocol. Survival was assessed and compared between all groups. Results from this study will inform on the thermal biology of Ae. aegypti mosquitoes and how access to sugar affects their activity.

The Intestine of Drosophila melanogaster: An Emerging Versatile Model System to Study Intestinal Epithelial Homeostasis and Host-Microbial Interactions in Humans

In all metazoans, the intestinal tract is an essential organ to integrate nutritional signaling, hormonal cues and immunometabolic networks. The dysregulation of intestinal epithelium functions can impact organism physiology and, in humans, leads to devastating and complex diseases, such as inflammatory bowel diseases, intestinal cancers, and obesity. Two decades ago, the discovery of an immune response in the intestine of the genetic model system, Drosophila melanogaster, sparked interest in using this model organism to dissect the mechanisms that govern gut (patho) physiology in humans. In 2007, the finding of the intestinal stem cell lineage, followed by the development of tools available for its manipulation in vivo, helped to elucidate the structural organization and functions of the fly intestine and its similarity with mammalian gastrointestinal systems. To date, studies of the Drosophila gut have already helped to shed light on a broad range of biological questions regarding stem cells and their niches, interorgan communication, immunity and immunometabolism, making the Drosophila a promising model organism for human enteric studies. This review summarizes our current knowledge of the structure and functions of the Drosophila melanogaster intestine, asserting its validity as an emerging model system to study gut physiology, regeneration, immune defenses and host-microbiota interactions.