Flexible Thermal Sensitivity of Mitochondrial Oxygen Consumption and Substrate Oxidation in Flying Insect Species

Environmental contaminants and insects: Genetic strategies for ecosystem and agricultural sustainability

Insects, with their vast biodiversity and essential ecological roles, are crucial to agriculture, textile production, and environmental stability. As pollinators, decomposers, and bioindicators, they support ecosystem functions and human industries. Their short generation time, high reproductive rates, and genetic adaptability make them valuable models for studying human diseases like cancer. However, contaminants pose significant threats to industrially important insects, impacting ecosystems and industries alike. Excessive pesticide use disrupts ecological balance, contributing to the global decline of insect populations. Understanding how contaminants affect insect physiology is critical for assessing their broader implications on agriculture, food security, and biodiversity. This interdisciplinary review integrates entomology, genetics, and environmental science to explore these impacts. Additionally, it examines the potential of genetic interventions to mitigate contaminant-induced harm, ensuring the sustainability of insect-mediated services. To safeguard these vital species, a comprehensive approach that integrates conservation and sustainable utilization strategies is essential.

Can Ahiflower® (Buglossoides arvensis) seed-oil supplementation help overcome the adverse effects of imidacloprid in honey bees?

In this study, we investigated the effects of nutritional supplementation as a strategy to mitigate the impacts of imidacloprid (neonicotinoid) on honey bees by using Ahiflower® (Buglossoides arvensis) seed-oil. This oil is rich in stearidonic-acid (SDA, 18:4n3), which is a precursor to eicosapentaenoic-acid (EPA) and docosahexaenoic-acid (DHA) that are known for their beneficial and protective effects. Specifically, we chronically fed newly emerged worker bees with sucrose syrup and pollen patties (control) that we supplemented with (i) imidacloprid (0.375 ng·μl-1), (ii) Ahiflower® oil (5 %) + imidacloprid (0.375 ng·μl-1), and (iii) Ahiflower® oil (5 %). Survival was recorded, and after 21 days, worker bees were sampled to measure mitochondrial respiration, ATP5A1 content, adenylate energy charge, lipid peroxidation in thorax as well as fatty acid composition and peroxidation index in whole bees. Our results indicate that (i) imidacloprid mostly hampers mitochondria, increases saturated fatty acids and decreases survival, (ii) oxidation of alternative substrates allows full recovery of mitochondrial respiration in the imidacloprid-treated group demonstrating mitochondrial flexibility, (iii) Ahiflower® oil in combination with imidacloprid partially restores mitochondrial respiration at the level of complexes I and II, restores fatty acid composition but fails to restore survival. These findings confirm the deleterious effects of imidacloprid on mitochondria while highlighting, for the first time, the potential benefits of Ahiflower® oil in mitochondrial function, though not on honey bee survival. In addition, this study highlights the importance of mitochondrial flexibility when organisms are exposed to toxicants at environmentally relevant levels.

Temperature-driven trade-off between mitochondrial activity and efficiency in live rotifers representing different thermal histories

Mitochondria generate up to 90% of cellular ATP, making it critical to understand how abiotic factors affect mitochondrial function under varying conditions. Using clones of the rotifer Lecane inermis with known thermal preferences, we investigated mitochondrial bioenergetic responses to four thermal regimes: standard temperature, optimal temperature, low suboptimal temperature and high suboptimal temperature. The study aimed to determine how mitochondrial parameters in intact organisms vary with temperature shifts and whether these responses differ across experimental populations. We assessed key bioenergetic parameters: routine respiration (representing overall metabolic rate), electron transport system capacity (indicative of oxidative phosphorylation potential) and proton leak rates (reflecting the energetic costs of maintaining mitochondrial membrane potential). Our results showed that populations with different thermal preferences displayed distinct mitochondrial responses to temperature changes, particularly at suboptimal temperatures. In contrast, responses were more uniform under standard and optimal conditions. Our findings demonstrated that metabolic plasticity in changing environments often involves trade-offs between mitochondrial efficiency and maintenance. By studying mitochondrial respiration at the whole-organism level, we revealed the complex temperature dependence of bioenergetic traits, providing insights beyond isolated mitochondria studies. This research highlights how a cascade of plastic responses spanning from mitochondrial responses to overall growth patterns is triggered by temperature changes, offering a valuable perspective in the context of global warming and organismal adaptation.

Optimal Neuromuscular Performance Requires Motor Neuron Phosphagen Kinases

Phosphagen systems are crucial for muscle bioenergetics - rapidly regenerating ATP to support the high metabolic demands of intense musculoskeletal activity. However, their roles in motor neurons that drive muscle contraction have received little attention. Here, we knocked down expression of the primary phosphagen kinase [Arginine Kinase 1; ArgK1] in Drosophila larval motor neurons and assessed the impact on presynaptic energy metabolism and neurotransmission in situ . Fluorescent metabolic probes showed a deficit in presynaptic energy metabolism and some glycolytic compensation. Glycolytic compensation was revealed through a faster elevation in lactate at high firing frequencies, and the accumulation of pyruvate subsequent to firing. Our performance assays included two tests of endurance: enforced cycles of presynaptic calcium pumping, and, separately, enforced body-wall contractions for extended periods. Neither test of endurance revealed deficits when ArgK1 was knocked down. The only performance deficits were detected at firing frequencies that approached, or exceeded, twice the firing frequencies recorded during fictive locomotion, where both electrophysiology and SynaptopHluorin imaging showed an inability to sustain neurotransmitter release. Our computational modeling of presynaptic bioenergetics indicates that the phosphagen system's contribution to motor neuron performance is likely through the removal of ADP in microdomains close to sites of ATP hydrolysis, rather than the provision of a deeper reservoir of ATP. Taken together, these data demonstrate that, as in muscle fibers, motor neurons rely on phosphagen systems during activity that imposes intense energetic demands.

Integrative transcriptomic, proteomic and metabolomic analyses yields insights into muscle fiber type in cattle

Muscle fiber is an important factor in beef quality. Here, we compared fast-type longissimus dorsi muscle and slow-type psoas major muscle from cattle using transcriptomic, proteomic and metabolomic analyses. A total of 1717 differentially expressed genes (DEGs), 297 differentially abundant proteins (DAPs) and 193 differentially abundant metabolites (DAMs) were identified between LD and PM tissue, respectively. For verification, we selected 10 DEGs for qRT-PCR and 6 DAPs for western blotting, and showed they were consistent between the two approaches. GO and KEGG enrichment analyses revealed that some DEGs, DAPs and DAMs were enriched in muscle fiber type-associated GO terms and pathways. Many of them are involved in glycolysis, TCA and fatty acid metabolism. Integrated multi-omics analysis showed a correlation coefficient of 0.6244 between the transcriptome and proteome. This study provides a new understanding of molecular mechanisms involved in the determination of bovine muscle fiber type and meat quality.

Effects of oxygen level on thermal tolerance in Amazonian catfishes with bimodal respiration: physiological and behavioural changes

The degree of tolerance to adverse conditions ultimately shapes a species' vulnerability to environmental changes. Some studies have reported limited thermal tolerance due to hypoxia in fish employing aquatic respiration. However, there is a lack of information regarding the effects of hypoxia on thermal tolerance in fish exhibiting bimodal respiration. A set of Amazonian fish species has adaptations to breathe air when oxygen in water is not enough to fulfil demand. Additionally, loricariid species within this group possess stomach adaptations for air breathing. The Loricariidae family exhibits varying stomach types and observed morphological differences could influence their ability to obtain oxygen from the air. This ability may, in turn, have consequences for the thermal tolerance of these species. Our objective was to assess the effects of hypoxia on thermal tolerance, along with the physiological (whole-animal metabolic rates and mitochondrial respiration) and behavioural mechanisms involved, in two facultative air-breathing species: Pterygoplichthys pardalis and Ancistrus dolichopterus. These species showcase morphological distinctions in their stomachs, with the former having a higher capacity to obtain oxygen from the air. Thermal tolerance in P. pardalis remained unaffected by dissolved oxygen in the water when air access was available but decreased when access to the water surface was restricted, specifically in hypoxic conditions. Conversely, the thermal tolerance of A. dolichopterus decreased below the critical oxygen partial pressure (Pcrit), even with access to air, highlighting their limited ability to obtain oxygen through their adapted stomach. Our results underscore that air breathing enhances thermal tolerance, but this effect is prominent only in species with a higher capacity for air breathing.

Fasting as a precursor to high-fat diet enhances mitochondrial resilience in Drosophila melanogaster

Changes in diet type and nutrient availability can impose significant environmental stress on organisms, potentially compromising physiological functions and reproductive success. In nature, dramatic fluctuations in dietary resources are often observed and adjustments to restore cellular homeostasis are crucial to survive this type of stress. In this study, we exposed male Drosophila melanogaster to two modulated dietary treatments: one without a fasting period before exposure to a high-fat diet and the other with a 24-h fasting period. We then investigated mitochondrial metabolism and molecular responses to these treatments. Exposure to a high-fat diet without a preceding fasting period resulted in disrupted mitochondrial respiration, notably at the level of complex I. On the other hand, a short fasting period before the high-fat diet maintained mitochondrial respiration. Generally, transcript abundance of genes associated with mitophagy, heat-shock proteins, mitochondrial biogenesis, and nutrient sensing pathways increased either slightly or significantly following a fasting period and remained stable when flies were subsequently put on a high-fat diet, whereas a drastic decrease of almost all transcript abundances was observed for all these pathways when flies were exposed directly to a high-fat diet. Moreover, mitochondrial enzymatic activities showed less variation after the fasting period than the treatment without a fasting period. Overall, our study sheds light on the mechanistic protective effects of fasting prior to a high-fat diet and highlights the metabolic flexibility of Drosophila mitochondria in response to abrupt dietary changes and have implication for adaptation of species to their changing environment.

An evolving roadmap: using mitochondrial physiology to help guide conservation efforts

The crucial role of aerobic energy production in sustaining eukaryotic life positions mitochondrial processes as key determinants of an animal's ability to withstand unpredictable environments. The advent of new techniques facilitating the measurement of mitochondrial function offers an increasingly promising tool for conservation approaches. Herein, we synthesize the current knowledge on the links between mitochondrial bioenergetics, ecophysiology and local adaptation, expanding them to the wider conservation physiology field. We discuss recent findings linking cellular bioenergetics to whole-animal fitness, in the current context of climate change. We summarize topics, questions, methods, pitfalls and caveats to help provide a comprehensive roadmap for studying mitochondria from a conservation perspective. Our overall aim is to help guide conservation in natural populations, outlining the methods and techniques that could be most useful to assess mitochondrial function in the field.

Insect Flight: State of the Field and Future Directions

The evolution of flight in an early winged insect ancestral lineage is recognized as a key adaptation explaining the unparalleled success and diversification of insects. Subsequent transitions and modifications to flight machinery, including secondary reductions and losses, also play a central role in shaping the impacts of insects on broadscale geographic and ecological processes and patterns in the present and future. Given the importance of insect flight, there has been a centuries-long history of research and debate on the evolutionary origins and biological mechanisms of flight. Here, we revisit this history from an interdisciplinary perspective, discussing recent discoveries regarding the developmental origins, physiology, biomechanics, and neurobiology and sensory control of flight in a diverse set of insect models. We also identify major outstanding questions yet to be addressed and provide recommendations for overcoming current methodological challenges faced when studying insect flight, which will allow the field to continue to move forward in new and exciting directions. By integrating mechanistic work into ecological and evolutionary contexts, we hope that this synthesis promotes and stimulates new interdisciplinary research efforts necessary to close the many existing gaps about the causes and consequences of insect flight evolution.

Flies on the rise: acclimation effect on mitochondrial oxidation capacity at normal and high temperatures in Drosophila melanogaster

Increased average temperatures and extreme thermal events (such as heatwaves) brought forth by climate change impose important constraints on aerobic metabolism. Notably, mitochondrial metabolism, which is affected by both long- and short-term temperature changes, has been put forward as an important determinant for thermal tolerance of organisms. This study examined the influence of phenotypic plasticity on metabolic and physiological parameters in Drosophila melanogaster and the link between mitochondrial function and their upper thermal limits. We showed that D. melanogaster acclimated to 15°C have a 0.65°C lower critical thermal maximum (CTmax) compared with those acclimated to 24°C. Drosophila melanogaster acclimated to 15°C exhibited a higher proportion of shorter saturated and monounsaturated fatty acids, concomitant with lower proportions of polyunsaturated fatty acids. No mitochondrial quantitative changes (fractional area and number) were detected between acclimation groups, but changes of mitochondrial oxidation capacities were observed. Specifically, in both 15°C- and 24°C-acclimated flies, complex I-induced respiration was increased when measured between 15 and 24°C, but drastically declined when measured at 40°C. When succinate and glycerol-3-phosphate were added, this decrease was however compensated for in flies acclimated to 24°C, suggesting an important impact of acclimation on mitochondrial function related to thermal tolerance. Our study reveals that the use of oxidative substrates at high temperatures is influenced by acclimation temperature and strongly related to upper thermal tolerance as a difference of 0.65°C in CTmax translates into significant mitochondrial changes.

Minimally destructive hDNA extraction method for retrospective genetics of pinned historical Lepidoptera specimens

The millions of specimens stored in entomological collections provide a unique opportunity to study historical insect diversity. Current technologies allow to sequence entire genomes of historical specimens and estimate past genetic diversity of present-day endangered species, advancing our understanding of anthropogenic impact on genetic diversity and enabling the implementation of conservation strategies. A limiting challenge is the extraction of historical DNA (hDNA) of adequate quality for sequencing platforms. We tested four hDNA extraction protocols on five body parts of pinned false heath fritillary butterflies, Melitaea diamina, aiming to minimise specimen damage, preserve their scientific value to the collections, and maximise DNA quality and yield for whole-genome re-sequencing. We developed a very effective approach that successfully recovers hDNA appropriate for short-read sequencing from a single leg of pinned specimens using silica-based DNA extraction columns and an extraction buffer that includes SDS, Tris, Proteinase K, EDTA, NaCl, PTB, and DTT. We observed substantial variation in the ratio of nuclear to mitochondrial DNA in extractions from different tissues, indicating that optimal tissue choice depends on project aims and anticipated downstream analyses. We found that sufficient DNA for whole genome re-sequencing can reliably be extracted from a single leg, opening the possibility to monitor changes in genetic diversity maintaining the scientific value of specimens while supporting current and future conservation strategies.

Investigating the thermal sensitivity of key enzymes involved in the energetic metabolism of three insect species

The metabolic responses of insects to high temperatures have been linked to their mitochondrial substrate oxidation capacity. However, the mechanism behind this mitochondrial flexibility is not well understood. Here, we used three insect species with different thermal tolerances (the honey bee, Apis mellifera; the fruit fly, Drosophila melanogaster; and the potato beetle, Leptinotarsa decemlineata) to characterize the thermal sensitivity of different metabolic enzymes. Specifically, we measured activity of enzymes involved in glycolysis (hexokinase, HK; pyruvate kinase, PK; and lactate dehydrogenase, LDH), pyruvate oxidation and the tricarboxylic acid cycle (pyruvate dehydrogenase, PDH; citrate synthase, CS; malate dehydrogenase, MDH; and aspartate aminotransferase, AAT), and the electron transport system (Complex I, CI; Complex II, CII; mitochondrial glycerol-3-phosphate dehydrogenase, mG3PDH; proline dehydrogenase, ProDH; and Complex IV, CIV), as well as that of ATP synthase (CV) at 18, 24, 30, 36, 42 and 45°C. Our results show that at high temperature, all three species have significantly increased activity of enzymes linked to FADH2 oxidation, specifically CII and mG3PDH. In fruit flies and honey bees, this coincides with a significant decrease of PDH and CS activity, respectively, that would limit NADH production. This is in line with the switch from NADH-linked substrates to FADH2-linked substrates previously observed with mitochondrial oxygen consumption. Thus, we demonstrate that even though the three insect species have a different metabolic regulation, a similar response to high temperature involving CII and mG3PDH is observed, denoting the importance of these proteins for thermal tolerance in insects.

Extracellular freezing induces a permeability transition in the inner membrane of muscle mitochondria of freeze-sensitive but not freeze-tolerant Chymomyza costata larvae

Background: Many insect species have evolved the ability to survive extracellular freezing. The search for the underlying principles of their natural freeze tolerance remains hampered by our poor understanding of the mechanistic nature of freezing damage itself. Objectives: Here, in search of potential primary cellular targets of freezing damage, we compared mitochondrial responses (changes in morphology and physical integrity, respiratory chain protein functionality, and mitochondrial inner membrane (IMM) permeability) in freeze-sensitive vs. freeze-tolerant phenotypes of the larvae of the drosophilid fly, Chymomyza costata. Methods: Larvae were exposed to freezing stress at -30°C for 1 h, which is invariably lethal for the freeze-sensitive phenotype but readily survived by the freeze-tolerant phenotype. Immediately after melting, the metabolic activity of muscle cells was assessed by the Alamar Blue assay, the morphology of muscle mitochondria was examined by transmission electron microscopy, and the functionality of the oxidative phosphorylation system was measured by Oxygraph-2K microrespirometry. Results: The muscle mitochondria of freeze-tolerant phenotype larvae remained morphologically and functionally intact after freezing stress. In contrast, most mitochondria of the freeze-sensitive phenotype were swollen, their matrix was diluted and enlarged in volume, and the structure of the IMM cristae was lost. Despite this morphological damage, the electron transfer chain proteins remained partially functional in lethally frozen larvae, still exhibiting strong responses to specific respiratory substrates and transferring electrons to oxygen. However, the coupling of electron transfer to ATP synthesis was severely impaired. Based on these results, we formulated a hypothesis linking the observed mitochondrial swelling to a sudden loss of barrier function of the IMM.

Mitochondrial phosphagen kinases support the volatile power demands of motor nerve terminals

Motor neurons are the longest neurons in the body, with axon terminals separated from the soma by as much as a meter. These terminals are largely autonomous with regard to their bioenergetic metabolism and must burn energy at a high rate to sustain muscle contraction. Here, through computer simulation and drawing on previously published empirical data, we determined that motor neuron terminals in Drosophila larvae experience highly volatile power demands. It might not be surprising then, that we discovered the mitochondria in the motor neuron terminals of both Drosophila and mice to be heavily decorated with phosphagen kinases - a key element in an energy storage and buffering system well-characterized in fast-twitch muscle fibres. Knockdown of arginine kinase 1 (ArgK1) in Drosophila larval motor neurons led to several bioenergetic deficits, including mitochondrial matrix acidification and a faster decline in the cytosol ATP to ADP ratio during axon burst firing. KEY POINTS: Neurons commonly fire in bursts imposing highly volatile demands on the bioenergetic machinery that generates ATP. Using a computational approach, we built profiles of presynaptic power demand at the level of single action potentials, as well as the transition from rest to sustained activity. Phosphagen systems are known to buffer ATP levels in muscles and we demonstrate that phosphagen kinases, which support such phosphagen systems, also localize to mitochondria in motor nerve terminals of fruit flies and mice. By knocking down phosphagen kinases in fruit fly motor nerve terminals, and using fluorescent reporters of the ATP:ADP ratio, lactate, pH and Ca2+ , we demonstrate a role for phosphagen kinases in stabilizing presynaptic ATP levels. These data indicate that the maintenance of phosphagen systems in motor neurons, and not just muscle, could be a beneficial initiative in sustaining musculoskeletal health and performance.

Pre-fertilization gamete thermal environment influences reproductive success, unmasking opposing sex-specific responses in Atlantic salmon (Salmo salar)

The environment gametes perform in just before fertilization is increasingly recognized to affect offspring fitness, yet the contributions of male and female gametes and their adaptive significance remain largely unexplored. Here, we investigated gametic thermal plasticity and its effects on hatching success and embryo performance in Atlantic salmon (Salmo salar). Eggs and sperm were incubated overnight at 2°C or 8°C, temperatures within the optimal thermal range of this species. Crosses between warm- and cold-incubated gametes were compared using a full-factorial design, with half of each clutch reared in cold temperatures and the other in warm temperatures. This allowed disentangling single-sex interaction effects when pre-fertilization temperature of gametes mismatched embryonic conditions. Pre-fertilization temperature influenced hatch timing and synchrony, and matching sperm and embryo temperatures resulted in earlier hatching. Warm incubation benefited eggs but harmed sperm, reducing the hatching success and, overall, gametic thermal plasticity did not enhance offspring fitness, indicating vulnerability to thermal changes. We highlight the sensitivity of male gametes to higher temperatures, and that gamete acclimation may not effectively buffer against deleterious effects of thermal fluctuations. From an applied angle, we propose the differential storage of male and female gametes as a tool to enhance sustainability within the hatcheries.

Age-related flexibility of energetic metabolism in the honey bee Apis mellifera

The mechanisms that underpin aging are still elusive. In this study, we suggest that the ability of mitochondria to oxidize different substrates, which is known as metabolic flexibility, is involved in this process. To verify our hypothesis, we used honey bees (Apis mellifera carnica) at different ages, to assess mitochondrial oxygen consumption and enzymatic activities of key enzymes of the energetic metabolism as well as ATP5A1 content (subunit of ATP synthase) and adenylic energy charge (AEC). We also measured mRNA abundance of genes involved in mitochondrial functions and the antioxidant system. Our results demonstrated that mitochondrial respiration increased with age and favored respiration through complexes I and II of the electron transport system (ETS) while glycerol-3-phosphate (G3P) oxidation was relatively decreased. In addition, glycolytic, tricarboxylic acid cycle and ETS enzymatic activities increased, which was associated with higher ATP5A1 content and AEC. Furthermore, we detected an early decrease in the mRNA abundance of subunits of NADH ubiquinone oxidoreductase subunit B2 (NDUFB2, complex I), mitochondrial cytochrome b (CYTB, complex III) of the ETS as well as superoxide dismutase 1 and a later decrease for vitellogenin, catalase and mitochondrial cytochrome c oxidase subunit 1 (COX1, complex IV). Thus, our study suggests that the energetic metabolism is optimized with aging in honey bees, mainly through quantitative and qualitative mitochondrial changes, rather than showing signs of senescence. Moreover, aging modulated metabolic flexibility, which might reflect an underpinning mechanism that explains lifespan disparities between the different castes of worker bees.

Mitochondrial metabolism and oxidative stress in the tropical cockroach under fluctuating thermal regimes

The cockroach Gromphadorhina coquereliana can survive at low temperatures under extensive periods of cold stress. To assess energy management and insect adaptation in response to cold, we measured mitochondrial activity and oxidative stress in muscle and fat body tissues from G. coquereliana under a fluctuating thermal regime (FTR; stressed at 4°C for 3 h on 3 consecutive days, with or without 24 h recovery). Compared with our earlier work showing that a single exposure to cold significantly affects mitochondrial parameters, here, repeated exposure to cold triggered an acclimatory response, resulting in unchanged mitochondrial bioenergetics. Immediately after cold exposure, we observed an increase in the overall pool of ATP and a decrease in typical antioxidant enzyme activity. We also observed decreased activity of uncoupling protein 4 in muscle mitochondria. After 24 h of recovery, we observed an increase in expression of antioxidant enzymes in muscles and the fat body and a significant increase in the expression of UCP4 and HSP70 in the latter. This indicates that processes related to energy conversion and disturbance under cold stress may trigger different protective mechanisms in these tissues, and that these mechanisms must be activated to restore insect homeostasis. The mitochondrial parameters and enzymatic assays suggest that mitochondria are not affected during FTR but oxidative stress markers are decreased, and a 24 h recovery period allows for the restoration of redox and energy homeostasis, especially in the fat body. This confirms the crucial role of the fat body in intermediary metabolism and energy management in insects and in the response to repeated thermal stress.

Succinate oxidation rescues mitochondrial ATP synthesis at high temperature in Drosophila melanogaster

Decreased NADH-induced and increased reduced FADH2 -induced respiration rates at high temperatures are associated with thermal tolerance in Drosophila. Here, we determined whether this change was associated with adjustments of adenosine triphosphate (ATP) production rate and coupling efficiency (ATP/O) in Drosophila melanogaster. We show that decreased pyruvate + malate oxidation at 35°C is associated with a collapse of ATP synthesis and a drop in ATP/O ratio. However, adding succinate triggered a full compensation of both oxygen consumption and ATP synthesis rates at this high temperature. Addition of glycerol-3-phosphate (G3P) led to a huge increase in respiration with no further advantage in terms of ATP production. We conclude that succinate is the only alternative substrate able to compensate both oxygen consumption and ATP production rates during oxidative phosphorylation at high temperature, which has important implications for thermal adaptation.

Chilled, starved or frozen: Insect mitochondrial adaptations to overcome the cold

Physiological adaptations to tackle cold exposure are crucial for insects living in temperate and arctic environments and here we review how cold adaptation is manifested in terms of mitochondrial function. Cold challenges are diverse, and different insect species have evolved metabolic and mitochondrial adaptations to: i) energize homeostatic regulation at low temperature, ii) stretch energy reserves during prolonged cold exposure, and iii) preserve structural organization of organelles following extracellular freezing. While the literature is still sparse, our review suggests that cold-adapted insects preserve ATP production at low temperatures by maintaining preferred mitochondrial substrate oxidation, which is otherwise challenged in cold-sensitive species. Chronic cold exposure and metabolic depression during dormancy is linked to reduced mitochondrial metabolism and may involve mitochondrial degradation. Finally, adaptation to extracellular freezing could be associated with superior structural integrity of the mitochondrial inner membrane following freezing which is linked to cellular and organismal survival.

How does mitochondria function contribute to aerobic performance enhancement in lizards?

Aims: Aerobic exercise typically enhances endurance across vertebrates so that chronically high energy demands can be met. Some known mechanisms of doing this include increases in red blood cell numbers, angiogenesis, muscle fiber adaptions, mitochondria biogenesis, and changes to cellular metabolism and oxidative phosphorylation. We used green anole lizards (Anolis carolinensis) to test for an effect of aerobic exercise on metabolism, mitochondria densities, and mitochondrial function. Methods: We first tested the response of green anoles to endurance training and pyrroloquinoline quinone (PQQ) supplementation, which has been shown to increase mitochondria biogenesis. We also conducted a mitochondrial stress test to determine how training affected mitochondrial function in skeletal muscle fibers. Results: Aerobic exercise led to increased endurance and decreased standard metabolic rate (SMR), while PQQ did not affect endurance and increased SMR. In a second experiment, aerobic exercise increased endurance and decreased resting metabolic rate (RMR) in both male and female green anoles. Higher counts of mitochondrial gene copies in trained lizards suggested additional mitochondria adaptations to achieve increased endurance and decreased metabolism. A mitochondrial stress test revealed no effect on baseline oxygen consumption rates of muscle fibers, but untrained lizards had higher maximal oxygen consumption rates with the addition of metabolic fuel. Conclusion: It is likely that trained lizards exhibited lower maximal oxygen consumption rates by developing higher mitochondria efficiency. This adaptation allows for high ATP demand to be met by making more ATP per oxygen molecule consumed. On the other hand, it is possible that untrained lizards prioritized limiting reactive oxygen species (ROS) production at rest, while sacrificing higher levels of proton leak and higher oxygen consumption rates when working to meet high ATP demand.

Substrate use and temperature effects in flight muscle mitochondria from an endothermic insect, the hawkmoth Manduca sexta

Manduca sexta are endothermic insects, requiring adult thorax temperatures to be elevated above 35 °C for flight muscles to produce the wing beat frequencies necessary for flight. During flight, these animals rely on aerobic production of ATP by flight muscle mitochondria with several potential metabolic pathways providing the fuel. Along with typical carbohydrate substrates, mitochondria of other endothermic insects including bumblebees and wasps can use the amino acid proline or glycerol 3-phosphate (G3P) as metabolic fuel for prewarm up and flight. Here we examine flight muscle mitochondria physiology and the role of temperature and substrates in oxidative phosphorylation from 3-day old adult Manduca sexta. Mitochondria oxygen flux from flight muscle fibers were temperature sensitive with Q₁₀ values ranging from 1.99 to 2.90, with a large increase in LEAK respiration with increased temperature. Mitochondria oxygen flux was stimulated by carbohydrate-based substrates, with flux through Complex I substrates providing the greatest oxygen flux. Neither proline nor G3P produced an increase in oxygen flux of the flight muscle mitochondria. Unlike other endothermic insects, Manduca are unable to supplement carbohydrate oxidation with either proline or G3P entering through Coenzyme Q and rely on substrates entering at complex I and II.

Ectotherm mitochondrial economy and responses to global warming

Temperature is a key abiotic factor affecting ecology, biogeography, and evolution of species. Alterations of energy metabolism play an important role in adaptations and plastic responses to temperature shifts on different time scales. Mitochondrial metabolism affects cellular bioenergetics and redox balance making these organelles an important determinant of organismal performances such as growth, locomotion, or development. Here I analyze the impacts of environmental temperature on the mitochondrial functions (including oxidative phosphorylation, proton leak, production of reactive oxygen species(ROS), and ATP synthesis) of ectotherms and discuss the mechanisms underlying negative shifts in the mitochondrial energy economy caused by supraoptimal temperatures. Owing to the differences in the thermal sensitivity of different mitochondrial processes, elevated temperatures (beyond the species- and population-specific optimal range) cause reallocation of the electron flux and the protonmotive force (Δp) in a way that decreases ATP synthesis efficiency, elevates the relative cost of the mitochondrial maintenance, causes excessive production of ROS and raises energy cost for antioxidant defense. These shifts in the mitochondrial energy economy might have negative consequences for the organismal fitness traits such as the thermal tolerance or growth. Correlation between the thermal sensitivity indices of the mitochondria and the whole organism indicate that these traits experience similar selective pressures but further investigations are needed to establish whether there is a cause-effect relationship between the mitochondrial failure and loss of organismal performance during temperature change.

Coping with global warming: Adult thermal thresholds in four pestiferous Anastrepha species determined under experimental laboratory conditions and development/survival times of immatures and adults under natural field conditions

Climate change, particularly global warming, is disturbing biological processes in unexpected ways and forcing us to re-study/reanalyze the effects of varying temperatures, among them extreme ones, on insect functional traits such as lifespan and fecundity/fertility. Here we experimentally tested, under both laboratory and field conditions, the effects of an extreme range of temperatures (5, 10, 15, 20, 30, 40, and 45 °C, and the naturally varying conditions experienced in the field), on survivorship/lifespan, fecundity, and fertility of four pestiferous fruit fly species exhibiting contrasting life histories and belonging to two phylogenetic groups within the genus Anastrepha: A. ludens, A. obliqua, A. striata, and A. serpentina. In the field, we also measured the length of the entire life cycle (egg to adult), and in one species (A. ludens), the effect on the latter of the host plant (mango and grapefruit). Under laboratory conditions, none of the adults, independent of species, could survive a single day when exposed to a constant temperature of 45 °C, but A. striata and A. serpentina females/males survived at the highly contrasting temperatures of 5 and 40 °C at least 7 days. Maximum longevity was achieved in all species at 15 °C (375, 225, 175 and 160 days in A. ludens, A. serpentina, A. striata and A. obliqua females, respectively). Anastrepha ludens layed many eggs until late in life (368 days) at 15 °C, but none eclosed. Eclosion was only observed in all species at 20 and 30 °C. Under natural conditions, flies lived ca. 100 days less than in the laboratory at 15 °C, likely due to the physiological cost of dealing with the highly varying environmental patterns over 24 h (minimum and maximum temperatures and relative humidity of ca. 10–40 °C, and 22–100%, respectively). In the case of A. ludens, the immature’s developmental time was shorter in mango, but adult survival was longer than in grapefruit. We discuss our results considering the physiological processes regulating the traits measured and tie them to the increasing problem of global warming and its hidden effects on the physiology of insects, as well as the ecological and pest management implications.

Overwintering in North American domesticated honeybees (Apis mellifera) causes mitochondrial reprogramming while enhancing cellular immunity

Many factors negatively impact domesticated honeybee (Apis mellifera) health causing a global decrease in their population year after year with major losses occurring during winter, and the cause remains thus far unknown. Here, we monitored for 12 months North American colonies of honeybees enduring important temperature variations throughout the year, to assess the metabolism and immune system of honeybees of summer and winter individuals. Our results show that in flight muscle, mitochondrial respiration via complex I during winter is drastically reduced compared to summer. However, the capacity for succinate and glycerol-3-phosphate (G3P) oxidation by mitochondria is increased during winter, resulting in higher mitochondrial oxygen consumption when complex I substrates, succinate and G3P were assessed altogether. Pyruvate kinase, lactate dehydrogenase, aspartate aminotransferase, citrate synthase and malate dehydrogenase tend to have reduced activity levels in winter unlike hexokinase, NADH dehydrogenase and pyruvate dehydrogenase. Transcript abundance of highly important immunity proteins like Vitellogenin and Defensin-1 were also increased in winter bees, and a stronger phagocytic response as well as a better hemocyte viability was observed during winter. Thus, a reorganization of substrate utilization favoring succinate and G3P while negatively affecting complex I of the ETS is occurring during winter. We suggest that this might be due to complex I transitioning to a dormant conformation through post-translational modification. Winter bees also have an increased response for antibacterial elimination in honeybees. Overall, this study highlights previously unknown cellular mechanisms between summer and winter honeybees that further our knowledge about this important species.