Metabolic rate and hypoxia tolerance are affected by group interactions and sex in the fruit fly (Drosophila melanogaster): new data and a literature survey

Drosophila melanogaster as an Alternative Model to Higher Organisms for In Vivo Lung Research

COPD and asthma are lung diseases that cause considerable burden to more than 800 million people worldwide. As both lung diseases are so far incurable, it is mandatory to understand the mechanisms underlying disease development and progression for developing novel therapeutic approaches. Exposures to environmental cues such as cigarette smoke in earliest life are known to increase disease risks in the individual's own future. To explore the pathomechanisms leading to later airway disease, mammalian models are instrumental. However, such in vivo experiments are time-consuming and burdensome for the animals, which applies in particular to transgenerational studies. Along this line, the fruit fly Drosophila melanogaster comes with several advantages for research in this field. The short lifespan facilitates transgenerational studies. A high number of evolutionary conserved signaling pathways, together with a large toolbox for tissue-specific gene modification, has the potential to identify novel target genes involved in disease development. A well-defined airway microbiome could help to untangle interactions between disease development and microbiome composition. In the following article, Drosophila melanogaster is therefore presented and discussed as an alternative in vivo model to investigate airway diseases that can complement and/or replace models in higher organisms.

Airway specific deregulation of asthma-related serpins impairs tracheal architecture and oxygenation in D. melanogaster

Serine proteases are important regulators of airway epithelial homeostasis. Altered serum or cellular levels of two serpins, Scca1 and Spink5, have been described for airway diseases but their function beyond antiproteolytic activity is insufficiently understood. To close this gap, we generated fly lines with overexpression or knockdown for each gene in the airways. Overexpression of both fly homologues of Scca1 and Spink5 induced the growth of additional airway branches, with more variable results for the respective knockdowns. Dysregulation of Scca1 resulted in a general delay in fruit fly development, with increases in larval and pupal mortality following overexpression of this gene. In addition, the morphological changes in the airways were concomitant with lower tolerance to hypoxia. In conclusion, the observed structural changes of the airways evidently had a strong impact on the airway function in our model as they manifested in a lower physical fitness of the animals. We assume that this is due to insufficient tissue oxygenation. Future work will be directed at the identification of key molecular regulators following the airway-specific dysregulation of Scca1 and Spink5 expression.

Low-input PacBio sequencing generates high-quality individual fly genomes and characterizes mutational processes

Long-read sequencing, exemplified by PacBio, revolutionizes genomics, overcoming challenges like repetitive sequences. However, the high DNA requirement ( > 1 µg) is prohibitive for small organisms. We develop a low-input (100 ng), low-cost, and amplification-free library-generation method for PacBio sequencing (LILAP) using Tn5-based tagmentation and DNA circularization within one tube. We test LILAP with two Drosophila melanogaster individuals, and generate near-complete genomes, surpassing preexisting single-fly genomes. By analyzing variations in these two genomes, we characterize mutational processes: complex transpositions (transposon insertions together with extra duplications and/or deletions) prefer regions characterized by non-B DNA structures, and gene conversion of transposons occurs on both DNA and RNA levels. Concurrently, we generate two complete assemblies for the endosymbiotic bacterium Wolbachia in these flies and similarly detect transposon conversion. Thus, LILAP promises a broad PacBio sequencing adoption for not only mutational studies of flies and their symbionts but also explorations of other small organisms or precious samples.

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.

Apple Polyphenol Diet Extends Lifespan, Slows down Mitotic Rate and Reduces Morphometric Parameters in Drosophila Melanogaster: A Comparison between Three Different Apple Cultivars

Plant-derived polyphenols exhibit beneficial effects on physiological and pathological processes, including cancer and neurodegenerative disorders, mainly because of their antioxidant activity. Apples are highly enriched in these compounds, mainly in their peel. The Tuscia Red (TR) apple variety exhibits the peculiar characteristic of depositing high quantities of polyphenols in the pulp, the edible part of the fruit. Since polyphenols, as any natural product, cannot be considered a panacea per se, in this paper, we propose to assess the biological effects of TR flesh extracts, in comparison with two commercial varieties, in a model system, the insect Drosophila melanogaster, largely recognized as a reliable system to test the in vivo effects of natural and synthetic compounds. We performed a comparative, qualitative and quantitative analysis of the polyphenol compositions of the three cultivars and found that TR flesh shows the highest content of polyphenols, and markedly, anthocyanins. Then, we focused on their effects on a panel of physiological, morphometrical, cellular and behavioral phenotypes in wild-type D. melanogaster. We found that all the apple polyphenol extracts showed dose-dependent effects on most of the phenotypes we considered. Remarkably, all the varieties induced a strong relenting of the cell division rate.

Mosquito sex and mycobiota contribute to fructose metabolism in the Asian tiger mosquito Aedes albopictus

BACKGROUND

Plant floral nectars contain natural sugars such as fructose, which are a primary energy resource for adult mosquitoes. Despite the importance of carbohydrates for mosquito metabolism, a limited knowledge is available about the pathways involved in sugar assimilation by mosquitoes and their associated microbiota. To this end, we used 13C-metabolomic and stable isotope probing approaches coupled to high-throughput sequencing to reveal fructose-related mosquito metabolic pathways and the dynamics of the active gut microbiota following fructose ingestion.

RESULTS

Our results revealed significant differences in metabolic pathways between males and females, highlighting different modes of central carbon metabolism regulation. Competitive and synergistic interactions of diverse fungal taxa were identified within the active mycobiota following fructose ingestion. In addition, we identified potential cross-feeding interactions between this. Interestingly, there is a strong correlation between several active fungal taxa and the presence of fructose-derived metabolites.

CONCLUSIONS

Altogether, our results provide novel insights into mosquito carbohydrate metabolism and demonstrate that dietary fructose as it relates to mosquito sex is an important determinant of mosquito metabolism; our results also further highlight the key role of active mycobiota interactions in regulating the process of fructose assimilation in mosquitoes. This study opens new avenues for future research on mosquito-microbiota trophic interactions related to plant nectar-derived sugars. Video abstract.

Measurement of oxygen consumption in Tenebrio molitor using a sensitive, inexpensive, sensor-based coulometric microrespirometer

Coulometric respirometry is a highly sensitive method for measuring O2 consumption in small organisms but is not in widespread use among physiologists. Here we describe a coulometric microrespirometer based on a digital environmental sensor inside a sealed glass chamber and controlled by an Arduino™ microcontroller. As O2 is consumed, exhaled CO2 is removed, causing pressure to decrease in the chamber. The sensor detects the decreased pressure, and the controller activates electrolytic production of O2, returning pressure to the initial value. O2 consumption is calculated from electrolytic charge transfer. The effects of developmental stage, body mass, and temperature on O2 consumption of Tenebrio molitor beetles were easily measured by the apparatus. This straightforward design is a significant innovation in that it provides continuous data regarding environmental conditions inside the experimental chamber, can be fabricated easily, and is adaptable to a wide range of uses.

Phenotyping of Drosophila Melanogaster-A Nutritional Perspective

The model organism Drosophila melanogaster was increasingly applied in nutrition research in recent years. A range of methods are available for the phenotyping of D. melanogaster, which are outlined in the first part of this review. The methods include determinations of body weight, body composition, food intake, lifespan, locomotor activity, reproductive capacity and stress tolerance. In the second part, the practical application of the phenotyping of flies is demonstrated via a discussion of obese phenotypes in response to high-sugar diet (HSD) and high-fat diet (HFD) feeding. HSD feeding and HFD feeding are dietary interventions that lead to an increase in fat storage and affect carbohydrate-insulin homeostasis, lifespan, locomotor activity, reproductive capacity and stress tolerance. Furthermore, studies regarding the impacts of HSD and HFD on the transcriptome and metabolome of D. melanogaster are important for relating phenotypic changes to underlying molecular mechanisms. Overall, D. melanogaster was demonstrated to be a valuable model organism with which to examine the pathogeneses and underlying molecular mechanisms of common chronic metabolic diseases in a nutritional context.

Bugs on Drugs: A Drosophila melanogaster Gut Model to Study In Vivo Antibiotic Tolerance of E. coli

With an antibiotic crisis upon us, we need to boost antibiotic development and improve antibiotics’ efficacy. Crucial is knowing how to efficiently kill bacteria, especially in more complex in vivo conditions. Indeed, many bacteria harbor antibiotic-tolerant persisters, variants that survive exposure to our most potent antibiotics and catalyze resistance development. However, persistence is often only studied in vitro as we lack flexible in vivo models. Here, I explored the potential of using Drosophila melanogaster as a model for antimicrobial research, combining methods in Drosophila with microbiology techniques: assessing fly development and feeding, generating germ-free or bacteria-associated Drosophila and in situ microscopy. Adult flies tolerate antibiotics at high doses, although germ-free larvae show impaired development. Orally presented E. coli associates with Drosophila and mostly resides in the crop. E. coli shows an overall high antibiotic tolerance in vivo potentially resulting from heterogeneity in growth rates. The hipA7 high-persistence mutant displays an increased antibiotic survival while the expected low persistence of ΔrelAΔspoT and ΔrpoS mutants cannot be confirmed in vivo. In conclusion, a Drosophila model for in vivo antibiotic tolerance research shows high potential and offers a flexible system to test findings from in vitro assays in a broader, more complex condition.

Ecological Stoichiometry of Bumblebee Castes, Sexes, and Age Groups

Ecological stoichiometry is important for revealing how the composition of chemical elements of organisms is influenced by their physiological functions and ecology. In this study, we investigated the elemental body composition of queens, workers, and males of the bumblebee Bombus terrestris, an important pollinator throughout Eurasia, North America, and northern Africa. Our results showed that body elemental content differs among B. terrestris castes. Young queens and workers had higher body nitrogen concentration than ovipositing queens and males, while castes did not differ significantly in their body carbon concentration. Furthermore, the carbon-to-nitrogen ratio was higher in ovipositing queens and males. We suggest that high body nitrogen concentration and low carbon-to-nitrogen ratio in young queens and workers may be related to their greater amount of flight muscles and flight activities than to their lower stress levels. To disentangle possible effects of stress in the agricultural landscape, further studies are needed to compare the elemental content of bumblebee bodies between natural habitats and areas of high-intensity agriculture.

Sex-specific effects of mitochondrial haplotype on metabolic rate in Drosophila melanogaster support predictions of the Mother's Curse hypothesis

Evolutionary theory proposes that maternal inheritance of mitochondria will facilitate the accumulation of mitochondrial DNA (mtDNA) mutations that are harmful to males but benign or beneficial to females. Furthermore, mtDNA haplotypes sampled from across a given species distribution are expected to differ in the number and identity of these 'male-harming' mutations they accumulate. Consequently, it is predicted that the genetic variation which delineates distinct mtDNA haplotypes of a given species should confer larger phenotypic effects on males than females (reflecting mtDNA mutations that are male-harming, but female-benign), or sexually antagonistic effects (reflecting mutations that are male-harming, but female-benefitting). These predictions have received support from recent work examining mitochondrial haplotypic effects on adult life-history traits in Drosophila melanogaster. Here, we explore whether similar signatures of male-bias or sexual antagonism extend to a key physiological trait-metabolic rate. We measured the effects of mitochondrial haplotypes on the amount of carbon dioxide produced by individual flies, controlling for mass and activity, across 13 strains of D. melanogaster that differed only in their mtDNA haplotype. The effects of mtDNA haplotype on metabolic rate were larger in males than females. Furthermore, we observed a negative intersexual correlation across the haplotypes for metabolic rate. Finally, we uncovered a male-specific negative correlation, across haplotypes, between metabolic rate and longevity. These results are consistent with the hypothesis that maternal mitochondrial inheritance has led to the accumulation of a sex-specific genetic load within the mitochondrial genome, which affects metabolic rate and that may have consequences for the evolution of sex differences in life history. This article is part of the theme issue 'Linking the mitochondrial genotype to phenotype: a complex endeavour'.

Sex-Specific Among-Individual Covariation in Locomotor Activity and Resting Metabolic Rate in Drosophila melanogaster

A key endeavor in evolutionary physiology is to identify sources of among- and within-individual variation in resting metabolic rate (RMR). Although males and females often differ in whole-organism RMR due to sexual size dimorphism, sex differences in RMR sometimes persist after conditioning on body mass, suggesting phenotypic differences between males and females in energy-expensive activities contributing to RMR. One potential difference is locomotor activity, yet its relationship with RMR is unclear and different energy budget models predict different associations. We quantified locomotor activity (walking) over 24 h and RMR (overnight) in 232 male and 245 female Drosophila melanogaster that were either mated or maintained as virgins between two sets of measurements. Accounting for body mass, sex, and reproductive status, RMR and activity were significantly and moderately repeatable (RMR: R=0.33±0.06; activity: R=0.58±0.03). RMR and activity were positively correlated among (rind=0.26±0.09) but not within (re=0.05±0.06) individuals. Moreover, activity varied throughout the day and between the sexes. Partitioning our analysis by sex and activity by time of day revealed that all among-individual correlations were positive and significant in males but nonsignificant or even significantly negative in females. Such differences in the RMR-activity covariance suggest fundamental differences in how the sexes manage their energy budget.

Sex and age specific reduction in stress resistance and mitochondrial DNA copy number in Drosophila melanogaster

Environmental stresses such as extreme temperatures, dehydration and food deprivation may have distinct consequences for different age-classes and for males and females across species. Here we investigate a natural population of the model organism Drosophila melanogaster. Males and females at ages 3, 19 and 35 days were tested for stress resistance; i.e. the ability of flies to cope with starvation and both cold and hot temperatures. Further, we tested a measure of metabolic efficiency, namely mitochondrial DNA copy number (mtDNA CN) in both sexes at all three age-classes. We hypothesize that stress resistance is reduced at old age and more so in males, and that mtDNA CN is a biomarker for sex- and age-dependent reductions in the ability to cope with harsh environments. We show that: (1) males exhibit reduced starvation tolerance at old age, whereas older females are better in coping with periods without food compared to younger females, (2) heat tolerance decreases with increasing age in males but not in females, (3) cold tolerance is reduced at old age in both sexes, and (4) old males have reduced mtDNA CN whereas mtDNA CN slightly increases with age in females. In conclusion, our data provide strong evidence for trait and sex specific consequences of aging with females generally being better at coping with environmental stress at old age. The reduced mtDNA CN in old males suggests reduced metabolic efficiency and this may partly explain why males are less stress tolerant at old age than females. We suggest that mtDNA CN might be a suitable biomarker for physiological robustness. Our findings likely extend to other taxa than Drosophila and therefore we discuss the observations in relation to aging and sex specific lifespan across species.

Intraspecific variation in metabolic rate and its correlation with local environment in the Chinese scorpion Mesobuthus martensii

Scorpions are well known for their reduced resting metabolic rate (RMR) in comparison to typical arthropods. Since RMR is a key physiological trait linked with evolutionary fitness, it is expected that there may exist intraspecific RMR variation given the ecological and geographical heterogeneities across the distributional range of a species. Nevertheless, it is unclear whether RMR variation exists among scorpion populations. Here, we compared the RMR (VCO₂) of 21 populations of the Chinese scorpion Mesobuthus martensii (Scorpiones: Buthidae) at 25°C after at least 3 months of laboratory acclimation. The following results were obtained. First, there was significant difference in RMR between sexes when body-weight effects were factored out. Second, significant local variation in RMR was detected by analyses of both variance and covariance, with one population showing significantly reduced RMR and another significantly increased RMR. Third, regression analysis indicated that the local mean temperature and mean annual days of rainfall were the two significant factors associated with the aforementioned inter-population difference in RMR. The implication of such an association was discussed.

Summary: Metabolic rate variation is observed between the two sexes and among populations in the Chinese scorpion, with the latter being correlated negatively with local mean temperature and positively with annual days of rainfall.

Functional Hypoxia in Insects: Definition, Assessment, and Consequences for Physiology, Ecology, and Evolution

Insects can experience functional hypoxia, a situation in which O₂ supply is inadequate to meet oxygen demand. Assessing when functional hypoxia occurs is complex, because responses are graded, age and tissue dependent, and compensatory. Here, we compare information gained from metabolomics and transcriptional approaches and by manipulation of the partial pressure of oxygen. Functional hypoxia produces graded damage, including damaged macromolecules and inflammation. Insects respond by compensatory physiological and morphological changes in the tracheal system, metabolic reorganization, and suppression of activity, feeding, and growth. There is evidence for functional hypoxia in eggs, near the end of juvenile instars, and during molting. Functional hypoxia is more likely in species with lower O₂ availability or transport capacities and when O₂ need is great. Functional hypoxia occurs normally during insect development and is a factor in mediating life-history trade-offs.

Effect of localized hypoxia on Drosophila embryo development

Environmental stress, such as oxygen deprivation, affects various cellular activities and developmental processes. In this study, we directly investigated Drosophila embryo development in vivo while cultured on a microfluidic device, which imposed an oxygen gradient on the developing embryos. The designed microfluidic device enabled both temporal and spatial control of the local oxygen gradient applied to the live embryos. Time-lapse live cell imaging was used to monitor the morphology and cellular migration patterns as embryos were placed in various geometries relative to the oxygen gradient. Results show that pole cell movement and tail retraction during Drosophila embryogenesis are highly sensitive to oxygen concentrations. Through modeling, we also estimated the oxygen permeability across the Drosophila embryonic layers for the first time using parameters measured on our oxygen control device.