Gut Microbiota of Drosophila subobscura Contributes to Its Heat Tolerance and Is Sensitive to Transient Thermal Stress

Impact of high temperature and drought stress on the microbial community in wolf spiders

High temperatures and drought present significant abiotic challenges that can limit the survival of many arthropods, including wolf spiders, which are ectothermic and play a crucial role in controlling pest populations. However, the impact of these stress factors on the microbiota of spiders remains poorly understood. In this study, we utilized 16 S rRNA gene sequencing to explore the diversity and composition of bacterial communities within Pardosa pseudoannulata under conditions of high temperature and drought stress. We found that Firmicutes, Bacteroidetes, and Proteobacteria were the predominant bacterial phyla present. Analyses of alpha diversity indicated an increase in bacterial diversity under combined stress conditions, as reflected by various diversity indices such as Ace, Chao1, Shannon, and Simpson. Furthermore, co-occurrence network analysis highlighted intricate interactions among the microbial taxa (e.g., Enterobacter, Chitinophaga, and Eubacterium), revealing the adaptive complexity of the spider's microbiome to environmental stress. Functional prediction analysis suggested that combined stress conditions might enhance key metabolic pathways, particularly those related to oxidative phosphorylation and amino acid metabolism. Using Random Forest analysis, we determined that changes in three heat shock proteins were largely attributed to variations in bacterial communities, with Firmicutes being notably influential. Collectively, this in-depth analysis offers novel insights into the responses of microbial communities within spider microbiomes to combined abiotic stresses, providing valuable information for understanding extreme climate impacts and informing ecological management strategies.

Experimental Evolution in a Warming World: The Omics Era

A comprehensive understanding of the genetic mechanisms that shape species responses to thermal variation is essential for more accurate predictions of the impacts of climate change on biodiversity. Experimental evolution with high-throughput resequencing approaches (evolve and resequence) is a highly effective tool that has been increasingly employed to elucidate the genetic basis of adaptation. The number of thermal evolve and resequence studies is rising, yet there is a dearth of efforts to integrate this new wealth of knowledge. Here, we review this literature showing how these studies have contributed to increase our understanding on the genetic basis of thermal adaptation. We identify two major trends: highly polygenic basis of thermal adaptation and general lack of consistency in candidate targets of selection between studies. These findings indicate that the adaptive responses to specific environments are rather independent. A review of the literature reveals several gaps in the existing research. Firstly, there is a paucity of studies done with organisms of diverse taxa. Secondly, there is a need to apply more dynamic and ecologically relevant thermal environments. Thirdly, there is a lack of studies that integrate genomic changes with changes in life history and behavioral traits. Addressing these issues would allow a more in-depth understanding of the relationship between genotype and phenotype. We highlight key methodological aspects that can address some of the limitations and omissions identified. These include the need for greater standardization of methodologies and the utilization of new technologies focusing on the integration of genomic and phenotypic variation in the context of thermal adaptation.

Humidity determines penetrance of a latitudinal gradient in genetic selection on the microbiota by Drosophila melanogaster

The fruit fly Drosophila melanogaster is a model for understanding how hosts and their microbial partners interact as the host adapts to wild environments. These interactions are readily interrogated because of the low taxonomic and numeric complexity of the flies' bacterial communities. Previous work has established that host genotype, the environment, diet, and interspecies microbial interactions can all influence host fitness and microbiota composition, but the specific processes and characters mediating these processes are incompletely understood. Here, we compared the variation in microbiota composition between wild-derived fly populations when flies could choose between the microorganisms in their diets and when flies were reared under environmental perturbation (different humidities). We also compared the colonization of the resident and transient microorganisms. We show that the ability to choose between microorganisms in the diet and the environmental condition of the flies can influence the relative abundance of the microbiota. There were also key differences in the abundances of the resident and transient microbiota. However, the microbiota only differed between populations when the flies were reared at humidities at or above 50% relative humidity. We also show that elevated humidity determined the penetrance of a gradient in host genetic selection on the microbiota that is associated with the latitude the flies were collected from. Finally, we show that the treatment-dependent variation in microbiota composition is associated with variation in host stress survival. Together, these findings emphasize that host genetic selection on the microbiota composition of a model animal host can be patterned with the source geography, and that such variation has the potential to influence their survival in the wild.

Importance

The fruit fly Drosophila melanogaster is a model for understanding how hosts and their microbial partners interact as hosts adapt in wild environments. Our understanding of what causes geographic variation in the fruit fly microbiota remains incomplete. Previous work has shown that the D. melanogaster microbiota has relatively low numerical and taxonomic complexity. Variation in the fly microbiota composition can be attributed to environmental characters and host genetic variation, and variation in microbiota composition can be patterned with the source location of the flies. In this work we explored three possible causes of patterned variation in microbiota composition. We show that host feeding choices, the host niche colonized by the bacteria, and a single environmental character can all contribute to variation in microbiota composition. We also show that penetrance of latitudinally-patterned host genetic selection is only observed at elevated humidities. Together, these results identify several factors that influence microbiota composition in wild fly genotypes and emphasize the interplay between environmental and host genetic factors in determining the microbiota composition of these model hosts.

Microbial communities are thermally more sensitive in warm-climate lizards compared with their cold-climate counterparts

Environmental temperature affects the composition, structure, and function of the gut microbial communities in host animals. To elucidate the role of gut microbiota in thermal adaptation, we designed a 2 species × 3 temperatures experiment, whereby we acclimated adult males of two agamid lizard species (warm-climate Leiolepis reevesii and cold-climate Phrynocephalus przewalskii) to 20, 28, and 36°C for 2 weeks and then collected their fecal and small-intestinal samples to analyze and compare the microbiota using 16S rRNA gene amplicon sequencing technology. The fecal microbiota displayed more pronounced interspecific differences in microbial community than the small-intestinal microbiota in the two species occurring in thermally different regions. The response of fecal and small-intestinal microbiota to temperature increase or decrease differed between the two species, with more bacterial taxa affected by acclimation temperature in L. reevesii than in P. przewalskii. Both species, the warm-climate species in particular, could cope with temperature change by adjusting the relative abundance of functional categories associated with metabolism and environmental information processing. Functional genes associated with carbohydrate metabolism were enhanced in P. przewalskii, suggesting the contribution of the fecal microbiota to cold-climate adaptation in P. przewalskii. Taken together, our results validate the two hypotheses tested, of which one suggests that the gut microbiota should help lizards adapt to thermal environments in which they live, and the other suggests that microbial communities should be thermally more sensitive in warm-climate lizards than in cold-climate lizards.

Cross-species gut microbiota transplantation predictably affects host heat tolerance

The gut microbiome is known to influence and have regulatory effects in diverse physiological functions of host animals, but only recently has the relationship between host thermal biology and gut microbiota been explored. Here, we examined how early-life manipulations of the gut microbiota in larval amphibians influenced their critical thermal maximum (CTmax) at different acclimation temperatures. We stripped the resident microbiome from egg masses of wild-caught wood frogs (Lithobates sylvaticus) via an antibiotic wash, and then inoculated the eggs with pond water (control), no inoculation, or the intestinal microbiota of another species that has a wider thermal tolerance - green frogs (Lithobates clamitans). We predicted that this cross-species transplant would increase the CTmax of the recipient wood frog larvae relative to the other treatments. In line with this prediction, green frog microbiome-recipient larvae had the highest CTmax while those with no inoculum had the lowest CTmax. Both the microbiome treatment and acclimation temperature significantly influenced the larval gut microbiota communities and α-diversity indices. Green frog microbiome-inoculated larvae were enriched in Rikenellaceae relative to the other treatments, which produce short-chain fatty acids and could contribute to greater energy availability and enhanced heat tolerance. Larvae that received no inoculation had a higher relative abundance of potentially pathogenic Aeromonas spp., which negatively affects host health and performance. Our results are the first to show that cross-species gut microbiota transplants alter heat tolerance in a predictable manner. This finding has repercussions for the conservation of species that are threatened by climate change and demonstrates a need to further explore the mechanisms by which the gut microbiota modulate host thermal tolerance.

Effects of heat tolerance on the gut microbiota of Sarcophaga peregrina (Diptera: Sarcophagidae) and impacts on the life history traits

BACKGROUND

Heat tolerance is a distinct abiotic factor affecting the distribution and abundance of insects. Gut microbiota can contribute to host fitness, thereby increasing resistance to abiotic stress conditions. In this study, Sarcophaga peregrina is closely associated with human life in ecological habits and shows remarkable adaptability to daily and seasonal temperature fluctuations. To date, the role of gut microbiota in S. peregrina response to heat stress and its influence on the host phenotypic variability remain poorly studied.

METHODS

We exposed S. peregrina to heat stress at 40 °C for 3 h every day throughout the developmental stages from newly hatched larva to adult, after which gut DNA was extracted from third-instar larvae, early pupal stage, late pupal stage, and newly emerged adults, respectively. Then, 16S rRNA microbial community analyses were performed.

RESULTS

Firstly, we analyzed whether heat stress could have an impact on the life history traits of S. peregrina and showed that the growth rate of larvae was higher and the developmental time was significantly shorter after heat stress. We then proposed the role of the gut microbiota in the heat tolerance of S. peregrina, which indicated that the bacterial abundance and community structure changed significantly after heat tolerance. In particular, the relative abundance of Wohlfahrtiimonas and Ignatzschineria was higher in the third-instar larval larvae; the former increased and the latter decreased significantly after heat stress. To further explore the effect of disturbing the microbial community on thermotolerant phenotype, newly hatched larvae were fed with amikacin under heat stress, which indicated that the larval length and the whole developmental cycle was significantly shorter.

CONCLUSION

This study indicated that Wohlfahrtiimonas and Ignatzschineria should play an important role in the post-feeding stage under heat stress, but further study is still needed. In general, heat tolerance can affect the gut microbial community structure, which in turn affects the fitness of the host.

Climate change drives loss of bacterial gut mutualists at the expense of host survival in wild meerkats

Climate change and climate-driven increases in infectious disease threaten wildlife populations globally. Gut microbial responses are predicted to either buffer or exacerbate the negative impacts of these twin pressures on host populations. However, examples that document how gut microbial communities respond to long-term shifts in climate and associated disease risk, and the consequences for host survival, are rare. Over the past two decades, wild meerkats inhabiting the Kalahari have experienced rapidly rising temperatures, which is linked to the spread of tuberculosis (TB). We show that over the same period, the faecal microbiota of this population has become enriched in Bacteroidia and impoverished in lactic acid bacteria (LAB), a group of bacteria including Lactococcus and Lactobacillus that are considered gut mutualists. These shifts occurred within individuals yet were compounded over generations, and were better explained by mean maximum temperatures than mean rainfall over the previous year. Enriched Bacteroidia were additionally associated with TB exposure and disease, the dry season and poorer body condition, factors that were all directly linked to reduced future survival. Lastly, abundances of LAB taxa were independently and positively linked to future survival, while enriched taxa did not predict survival. Together, these results point towards extreme temperatures driving an expansion of a disease-associated pathobiome and loss of beneficial taxa. Our study provides the first evidence from a longitudinally sampled population that climate change is restructuring wildlife gut microbiota, and that these changes may amplify the negative impacts of climate change through the loss of gut mutualists. While the plastic response of host-associated microbiotas is key for host adaptation under normal environmental fluctuations, extreme temperature increases might lead to a breakdown of coevolved host-mutualist relationships.

Hotter days, stronger immunity? Exploring the impact of rising temperatures on insect gut health and microbial relationships

Climate change can generate cascading effects on animals through compounding stressors. As ectotherms, insects are particularly susceptible to variation in temperature and extreme events. How insects respond to temperature often occurs with respect to their environment, and a pertinent question involves how thermal stress integrates with insect capabilities to resolve interactions with gut microorganisms (microbiome and gut pathogens). We explore the impact of elevated temperatures and the impact of the host physiological response influencing immune system regulation and the gut microbiome. We summarize the literature involving how elevated temperature extremes impact insect gut immune systems, and how in turn that alters potential interactions with the gut microbiome and potential pathogens. Temperature effects on immunity are complex, and ultimate effects on microbial components can vary by system. Moreover, there are multiple questions yet to explore in how insects contend with simultaneous abiotic stressors and potential trade-offs in their response to opportunistic microbiota.

Dexmedetomidine alleviates host ADHD-like behaviors by reshaping the gut microbiota and reducing gut-brain inflammation

Attention-deficit/hyperactivity disorder (ADHD) is one of the most prevalent psychiatric disorders that affects children and even continues into adulthood. Dexmedetomidine (DEX), a short-term sedative, can selectively activate the α2-adrenoceptor. Treatment with α2-adrenergic agonists in patients with ADHD is becoming increasingly common. However, the therapeutic potential of DEX for the treatment of ADHD is unknown. Here, we evaluated the effect of DEX on ADHD-like behavior in spontaneously hypertensive rats (SHRs), a widely used animal model of ADHD. DEX treatment ameliorated hyperactivity and spatial working memory deficits and normalized θ electroencephalogram (EEG) rhythms in SHRs. We also found that DEX treatment altered the gut microbiota composition and promoted the enrichment of beneficial gut bacterial genera associated with anti-inflammatory effects in SHRs. The gut pathological scores and permeability and the level of inflammation observed in the gut and brain were remarkably improved after DEX administration. Moreover, transplantation of fecal microbiota from DEX-treated SHRs produced effects that mimicked the therapeutic effects of DEX administration. Therefore, DEX is a promising treatment for ADHD that functions by reshaping the composition of the gut microbiota and reducing inflammation in the gut and brain.

Thermal and latitudinal patterns in pace-of-life traits are partly mediated by the gut microbiome

The integration of life-history, physiological and behavioural traits into the pace-of-life generates a powerful framework to understand trait variation in nature both along environmental gradients and in response to environmental stressors. While the gut microbiome has been hypothesized as a candidate mechanism to underlie differentiation in the pace-of-life, this has been rarely studied. We investigated the role of the gut microbiome in contributing to the differentiation in pace-of-life and in thermal adaptation between populations of Ischnura elegans damselfly larvae inhabiting warmer low latitudes and colder high latitudes. We carried out a common-garden experiment, whereby we manipulated the exposure of the damselfly larvae to two key global warming factors: 4 °C warming and a 30 °C heat wave. Comparing the bacterial composition of the food source and the bacterioplankton indicated that damselfly larvae differentially take up bacteria from the surrounding environment and have a resident and functionally relevant microbiome. The gut microbiome differed between larvae of both latitudes, and this was associated with the host's latitudinal differentiation in activity, a key pace-of-life trait. Under heat wave exposure, the gut microbial community composition of high-latitude larvae converged towards that of the low-latitude larvae, with an increase in bacteria that likely are important in providing energy to cope with the heat wave. This suggests an adaptive latitude-specific shift in the gut microbiota matching the better ability of low-latitude hosts to deal with heat extremes. In general, our study provides evidence for the gut microbiome contributing to latitudinal differentiation in both the pace-of-life and in heat adaptation in natural populations.

The microbiome buffers tadpole hosts from heat stress: a hologenomic approach to understand host-microbe interactions under warming

Phenotypic plasticity is an important strategy that animals employ to respond and adjust to changes in their environment. Plasticity may occur via changes in host gene expression or through functional changes in their microbiomes, which contribute substantially to host physiology. Specifically, the presence and function of host-associated microbes can impact how animals respond to heat stress. We previously demonstrated that 'depleted' tadpoles, with artificially disrupted microbiomes, are less tolerant to heat than 'colonized' tadpoles, with more natural microbiomes. However, the mechanisms behind these effects are unclear. Here, we compared gene expression profiles of the tadpole gut transcriptome, and tadpole gut microbial metagenome, between colonized and depleted tadpoles under cool or warm conditions. Our goal was to identify differences in host and microbial responses to heat between colonized and depleted tadpoles that might explain their observed differences in heat tolerance. We found that depleted tadpoles exhibited a much stronger degree of host gene expression plasticity in response to heat, while the microbiome of colonized tadpoles was significantly more heat sensitive. These patterns indicate that functional changes in the microbiome in response to heat may allow for a dampened host response, ultimately buffering hosts from the deleterious effects of heat stress. We also identified several specific host and microbial pathways that could be contributing to increased thermal tolerance in colonized tadpoles including amino acid metabolism, vitamin biosynthesis and ROS scavenging pathways. Our results demonstrate that the microbiome influences host plasticity and the response of hosts to environmental stressors.

Metasilicate-based alkaline mineral water confers diarrhea resistance in maternally separated piglets via the microbiota-gut interaction

Stress or stress-induced intestinal disturbances, especially diarrhea, are the main triggers for inflammatory bowel disease and irritable bowel syndrome. Diarrhea and intestinal inflammatory disease afflict patients around the world, and it has become a huge burden on the global health care system. Drinking sodium metasilicate-based alkaline mineral water (SM-based AMW) exerts a potential therapeutic effect in gastrointestinal disorders, including gut inflammation, and diarrhea, but the supportive evidence on animal studies and mechanism involved remain unreported. The maternally separated (MS) piglet (Newly weaned piglet) is an excellent model to investigate the treatment of diarrhea in infant. This study aims to determine whether drinking SM-based AMW confers diarrhea resistance in maternally separated (MS) piglets under weaning stress and what the underlying mechanisms are involved. 240 newly weaned piglets were randomly divided into the Control group and the sodium metasilicate pentahydrate (SMP) group. A decreased diarrhea incidence was observed in SMP treatment piglets. The intestine injury and activated stress hormones (COR and ACTH) induced by weaning was alleviated by SM-based AMW. This may be related to the improvement of intestinal microflora structure and function by SMP, especially the increase of s_copri abundance. Meanwhile, SMP maintained the integrity of the duodenal mucus barrier in MS piglets. Importantly, by targeting NF-κB inhibition via the microbiota-gut interaction, SM-based AMW alleviated intestinal inflammation, maintained fluid homeostasis by modulating aquaporins and fluid transporter expression, and enhanced barrier integrity by suppressing MLCK/p-MLC signaling. Therefore, drinking metasilicate-based alkaline mineral water confers diarrhea resistance in MS piglets via the microbiota-gut interaction.

Experimental temperatures shape host microbiome diversity and composition

Global climate change has led to more extreme thermal events. Plants and animals harbour diverse microbial communities, which may be vital for their physiological performance and help them survive stressful climatic conditions. The extent to which microbiome communities change in response to warming or cooling may be important for predicting host performance under global change. Using a meta-analysis of 1377 microbiomes from 43 terrestrial and aquatic species, we found a decrease in the amplicon sequence variant-level microbiome phylogenetic diversity and alteration of microbiome composition under both experimental warming and cooling. Microbiome beta dispersion was not affected by temperature changes. We showed that the host habitat and experimental factors affected microbiome diversity and composition more than host biological traits. In particular, aquatic organisms-especially in marine habitats-experienced a greater depletion in microbiome diversity under cold conditions, compared to terrestrial hosts. Exposure involving a sudden long and static temperature shift was associated with microbiome diversity loss, but this reduction was attenuated by prior-experimental lab acclimation or when a ramped regime (i.e., warming) was used. Microbial differential abundance and co-occurrence network analyses revealed several potential indicator bacterial classes for hosts in heated environments and on different biome levels. Overall, our findings improve our understanding on the impact of global temperature changes on animal and plant microbiome structures across a diverse range of habitats. The next step is to link these changes to measures of host fitness, as well as microbial community functions, to determine whether microbiomes can buffer some species against a more thermally variable and extreme world.

Gut bacterial communities and their assembly processing in Cnaphalocrocis medinalis from different geographic sources

Introduction

The insect gut harbors numerous microorganisms that may have functions in development and reproduction, digestion, immunity and protection, and detoxification. Recently, the influence factors on gut microbiota were evaluated in the rice leaffolder Cnaphalocrocis medinalis, a widespread insect pest in paddy fields. However, the relationship between gut microbiota composition and geography is poorly understood in C. medinalis.

Methods

To reveal the patterns of C. medinalis gut bacterial communities across geographic sources and the ecological processes driving the patterns, C. medinalis were sampled from six geographic sources in China, Thailand, and Vietnam in 2016, followed by gut bacterial 16S ribosomal RNA gene sequencing.

Results

A total of 22 bacterial phyla, 56 classes, 84 orders, 138 families, 228 genera, and 299 species were generated in C. medinalis from six geographic sources. All alpha diversity indices differed among the samples from different geographic sources. Analysis of similarity (ANOSIM) and permutational multivariate analysis of variance (PERMANOVA) both revealed significant differences in the gut microbiota of C. medinalis from six geographic sources. A total of 94 different taxa were screened as indicators for the gut microbiota of C. medinalis from six geographic sources by linear discriminant analysis effect size (LEfSe). The gene ontology (GO) pathways of the gut microbiota in C. medinalis differed among geographic sources. In total, the bacterial communities within geographic sources were mainly determined by stochastic processes, and those between geographic sources were mainly determined by deterministic processes.

Discussion

This study elucidates that geography plays a crucial role in shaping the gut microbiota of C. medinalis. Thus, it enriches our knowledge of gut bacteria in C. medinalis and sheds light on the mechanisms underlying C. medinalis gut microbial shifts across geography.

Sustained Drought, but Not Short-Term Warming, Alters the Gut Microbiomes of Wild Anolis Lizards

As rising temperatures threaten biodiversity across the globe, tropical ectotherms are thought to be particularly vulnerable due to their narrow thermal tolerance ranges. Nevertheless, physiology-based models highlighting the vulnerability of tropical organisms rarely consider the contributions of their gut microbiota, even though microbiomes influence numerous host traits, including thermal tolerance. We combined field and lab experiments to understand the response of the slender anole lizard (Anolis apletophallus) gut microbiome to climatic shifts of various magnitude and duration. First, to examine the effects of long-term climate warming in the wild, we transplanted lizards from the mainland Panama to a series of warmer islands in the Panama Canal and compared their gut microbiome compositions after three generations of divergence. Next, we mimicked the effects of a short-term "heat-wave" by using a greenhouse experiment and explored the link between gut microbiome composition and lizard thermal physiology. Finally, we examined variation in gut microbiomes in our mainland population in the years both before and after a naturally occurring drought. Our results suggest that slender anole microbiomes are surprisingly resilient to short-term warming. However, both the taxonomic and predicted functional compositions of the gut microbiome varied by sampling year across all sites, suggesting that the drought may have had a regional effect. We provide evidence that short-term heat waves may not substantially affect the gut microbiota, while more sustained climate anomalies may have effects at broad geographic scales. IMPORTANCE As climate change progresses, it is crucial to understand how animals will respond to shifts in their local environments. One component of this response involves changes in the microbial communities living in and on host organisms. These "microbiomes" can affect many processes that contribute to host health and survival, yet few studies have measured changes in the microbiomes of wild organisms experiencing novel climatic conditions. We examined the effects of shifting climates on the gut microbiome of the slender anole lizard (Anolis apletophallus) by using a combination of field and laboratory studies, including transplants to warm islands in the Panama Canal. We found that slender anole microbiomes remain stable in response to short-term warming but may be sensitive to sustained climate anomalies, such as droughts. We discuss the significance of these findings for a species that is considered highly vulnerable to climate change.

Temperature Acclimation Alters the Thermal Tolerance and Intestinal Heat Stress Response in a Tibetan Fish Oxygymnocypris stewarti

Numerous studies have shown that thermal tolerance and intestinal heat resistance are strongly associated with temperature acclimation. However, few reports have successfully conducted similar research on fishes from the Qinghai–Tibetan Plateau, an area that is facing the threat of climate warming. Therefore, the present study determined the growth, thermal tolerance, and intestinal heat stress (exposure to 30°C) responses in juveniles of a Tibetan fish, Oxygymnocypris stewarti, acclimated to three temperature levels (10°C, 15°C, and 20°C, named as T10, T15, and T20, respectively) for 30 days. The fastest growth was recorded in the T15 group. At 1°C/30 min heating rate, the critical thermal maximum (CT_Max) ranged from 31.3°C to 32.3°C, and the lethal thermal maximum (LT_Max) ranged from 31.8°C to 32.6°C among the three acclimation temperatures. According to the results of thermal tolerance tests, the heat stress temperature was set to 30°C. When the water temperature reached 30°C, the expression of the intestinal heat shock protein 70 (HSP70) gene as well as the intestinal microbiome and histology of experimental fish were monitored at 0, 2, 6, and 12 h. The expression of HSP70 reached the highest level at 2 h in all three temperature treatments. The histological analysis showed damage to intestinal cells, including diffuse infiltration of lymphocytes, villi epithelial cell swelling, decrease of intestinal villi length, and cytoplasmic light staining at 2 h in all three temperature treatments. In terms of the intestinal microbiome, phyla Proteobacteria and Firmicutes dominated the treatments at each monitored time in the T10 and T15 groups and at 0 h in T20 group, while phyla Fusobacteria, Proteobacteria, and Cyanobacteria were dominant in treatments at 2, 6, and 12 h in the T20 group. The overall results indicated that acclimation temperature could affect the growth, thermal tolerance, and intestinal heat stress response of O. stewarti juveniles. As the first report on intestinal heat stress response associated with temperature acclimation in a Tibetan fish, this study will help to understand the potential effects of climate change on highland fishes.

Association of Gut Microbiota With Metabolism in Rainbow Trout Under Acute Heat Stress

Global warming is one of the most common environmental challenges faced by cold-water fish farming. Heat stress seriously affects the feeding, growth, immunity, and disease resistance of fish. These changes are closely related to the destruction of intestinal barrier function, the change of intestinal microbiota, and metabolic dysfunction. However, the causal relationship between the phenotypic effects of heat stress as well as intestinal and metabolic functions of fish is unknown. In the current study, the optimal growth temperature (16°C) of rainbow trout was used as the control group, while the fish treated at 22.5°C, 23.5°C, and 24.5°C for 24 h, respectively, were the treatment groups. The 16S rRNA gene sequencing analysis showed that with the increase in temperature, the relative abundance and diversity of intestinal microbiota decreased significantly, while the number of Mycoplasma, Firmicutes, and Tenericutes increased significantly. Non-targeted metabolomics analysis by liquid chromatography-mass spectrometry analysis and correlation analysis showed that the changes of metabolites related to amino acids, vitamins, and short-chain fatty acids in serum of rainbow trout under acute heat stress were strongly correlated with the decrease of relative abundance of various intestinal microbiota, especially Morganella, Enterobacter, Lactobacillus, Lawsonia, and Cloacibacterium. In addition, we also found that acute heat stress seriously affected the intestinal structure and barrier function, and also caused the pathological damage of epithelial cells. These results indicate that the gut microbiome of acute heat-stressed rainbow trout could mediate metabolite transfer through the gut barrier by affecting its integrity. Significant changes in gut morphology, permeability, antioxidant capacity, and pro-inflammatory cytokine levels were observed. Therefore, it is necessary to explore the changes of intestinal microbiota under heat stress to help understand the regulatory mechanism of heat stress and protect the intestinal health of rainbow trout from the negative effects of rising water temperature.

Experimental manipulation of microbiota reduces host thermal tolerance and fitness under heat stress in a vertebrate ectotherm

Identifying factors that influence how ectothermic animals respond physiologically to changing temperatures is of high importance given current threats of global climate change. Host-associated microbial communities impact animal physiology and have been shown to influence host thermal tolerance in invertebrate systems. However, the role of commensal microbiota in the thermal tolerance of ectothermic vertebrates is unknown. Here we show that experimentally manipulating the tadpole microbiome through environmental water sterilization reduces the host's acute thermal tolerance to both heat and cold, alters the thermal sensitivity of locomotor performance, and reduces animal survival under prolonged heat stress. We show that these tadpoles have reduced activities of mitochondrial enzymes and altered metabolic rates compared with tadpoles colonized with unmanipulated microbiota, which could underlie differences in thermal phenotypes. These results demonstrate a strong link between the microbiota of an ectothermic vertebrate and the host's thermal tolerance, performance and fitness. It may therefore be important to consider host-associated microbial communities when predicting species' responses to climate change.

Drosophila Model for Studying Gut Microbiota in Behaviors and Neurodegenerative Diseases

Mounting evidence indicates that the gut microbiota is linked to several physiological processes and disease development in mammals; however, the underlying mechanisms remained unexplored mostly due to the complexity of the mammalian gut microbiome. The fruit fly, Drosophila melanogaster, is a valuable animal model for studying host-gut microbiota interactions in translational aspects. The availability of powerful genetic tools and resources in Drosophila allowed the scientists to unravel the mechanisms by which the gut microbes affect fitness, health, and behavior of their hosts. Drosophila models have been extensively used not only to study animal behaviors (i.e., courtship, aggression, sleep, and learning & memory), but also some human related neurodegenerative diseases (i.e., Alzheimer's disease and Parkinson's disease) in the past. This review comprehensively summarizes the current understanding of the gut microbiota of Drosophila and its impact on fly behavior, physiology, and neurodegenerative diseases.

Life History Traits in Two Drosophila Species Differently Affected by Microbiota Diversity under Lead Exposure

Simple Summary

Microbiota have a significant functional role in the life of the host, including immunity, lifespan and reproduction. Drosophila species are attractive model organisms for investigating microbiota diversity from different aspects due to their simple gut microbiota, short generation time and high fertility. Considering such an important role of the microbiota in the life of Drosophila, we investigated the extent to which lead (Pb), as one of the most abundant heavy metals in the environment, affects the microbiota and the fitness of this insect host. The results indicate that different factors, such as population origin and sex, may affect individual traits differently and this could be species-specific. In addition, there are members of microbiota that help the host to overcome environmental stress and they could play a key role in reducing the fitness cost in such situations. Studying the influence of microbiota on the adaptive response to heavy metals and the potential implications on overall host fitness is of great pertinence.

Abstract

Life history traits determine the persistence and reproduction of each species. Factors that can affect life history traits are numerous and can be of different origin. We investigated the influence of population origin and heavy metal exposure on microbiota diversity and two life history traits, egg-to-adult viability and developmental time, in Drosophila melanogaster and Drosophila subobscura, grown in the laboratory on a lead (II) acetate-saturated substrate. We used 24 samples, 8 larval and 16 adult samples (two species × two substrates × two populations × two sexes). The composition of microbiota was determined by sequencing (NGS) of the V3–V4 variable regions of the 16S rRNA gene. The population origin showed a significant influence on life history traits, though each trait in the two species was affected differentially. Reduced viability in D. melanogaster could be a cost of fast development, decrease in Lactobacillus abundance and the presence of Wolbachia. The heavy metal exposure in D. subobscura caused shifts in developmental time but maintained the egg-to-adult viability at a similar level. Microbiota diversity indicated that the Komagataeibacter could be a valuable member of D. subobscura microbiota in overcoming the environmental stress. Research on the impact of microbiota on the adaptive response to heavy metals and consequently the potential tradeoffs among different life history traits is of great importance in evolutionary research.

A perspective on insect-microbe holobionts facing thermal fluctuations in a climate-change context

Temperature influences the ecology and evolution of insects and their symbionts by impacting each partner independently and their interactions, considering the holobiont as a primary unit of selection. There are sound data about the responses of these partnerships to constant temperatures and sporadic thermal stress (mostly heat shock). However, the current understanding of the thermal ecology of insect-microbe holobionts remains patchy because the complex thermal fluctuations (at different spatial and temporal scales) experienced by these organisms in nature have often been overlooked experimentally. This may drastically constrain our ability to predict the fate of mutualistic interactions under climate change, which will alter both mean temperatures and thermal variability. Here, we tackle down these issues by focusing on the effects of temperature fluctuations on the evolutionary ecology of insect-microbe holobionts. We propose potentially worth-investigating research avenues to (i) evaluate the relevance of theoretical concepts used to predict the biological impacts of temperature fluctuations when applied to holobionts; (ii) acknowledge the plastic (behavioural thermoregulation, physiological acclimation) and genetic responses (evolution) expressed by holobionts in fluctuating thermal environments; and (iii) explore the potential impacts of previously unconsidered patterns of temperature fluctuations on the outcomes and the dynamic of these insect-microbe associations.

Experimental Warming Reduces Survival, Cold Tolerance, and Gut Prokaryotic Diversity of the Eastern Subterranean Termite, Reticulitermes flavipes (Kollar)

Understanding the effects of environmental disturbances on insects is crucial in predicting the impact of climate change on their distribution, abundance, and ecology. As microbial symbionts are known to play an integral role in a diversity of functions within the insect host, research examining how organisms adapt to environmental fluctuations should include their associated microbiota. In this study, subterranean termites [Reticulitermes flavipes (Kollar)] were exposed to three different temperature treatments characterized as low (15°C), medium (27°C), and high (35°C). Results suggested that pre-exposure to cold allowed termites to stay active longer in decreasing temperatures but caused termites to freeze at higher temperatures. High temperature exposure had the most deleterious effects on termites with a significant reduction in termite survival as well as reduced ability to withstand cold stress. The microbial community of high temperature exposed termites also showed a reduction in bacterial richness and decreased relative abundance of Spirochaetes, Elusimicrobia, and methanogenic Euryarchaeota. Our results indicate a potential link between gut bacterial symbionts and termite's physiological response to environmental changes and highlight the need to consider microbial symbionts in studies relating to insect thermosensitivity.