Can social partnerships influence the microbiome? Insights from ant farmers and their trophobiont mutualists

Influence of Endogenous Bacteria on Behavioral Responses in Leptocybe invasa: An Analysis of mVOCs

Microorganisms within insects play a vital role in maintaining the basal physiological functions of the insects, with olfactory signals as critical components of insect survival strategies. Leptocybe invasa (L. invasa), an invasive alien pest inflicting significant damage to eucalyptus trees, harbors a rich and varied bacterial community within its body. However, the impact of its endogenous bacteria and their microbial Volatile Organic Compounds (mVOCs) on the behavioral preferences of L. invasa remains unexplored to date. This study focused on nine cultivable and dominant endogenous bacterial strains within L. invasa. Using a Y-tube olfactometer, we investigated the behavioral responses of female L. invasa to the mVOCs emitted by these bacteria. Concurrently, gas chromatography-mass spectrometry (GC-MS) was employed to quantify the mVOCs produced by these endogenous bacteria. Our findings revealed that Staphylococcus sp. exhibited the highest attractiveness of L. invasa, whereas Microbacterium sp. and E. cloacae exerted the most significant avoidance effects. The analysis of the mVOCs further highlighted the significance of aldehyde compounds, notably 2,3,6-trichlorobenzaldehyde, and alkane compounds, such as eicosane, in mediating the repellency and attraction effects. These results contribute to a deeper understanding of the invasion mechanism of L. invasa and provide a scientific basis for developing novel biopesticides or elicitors.

Wolbachia Interactions with Diverse Insect Hosts: From Reproductive Modulations to Sustainable Pest Management Strategies

Effective in a variety of insect orders, including dipteran, lepidopteran, and hemipteran, Wolbachia-based control tactics are investigated, noting the importance of sterile and incompatible insect techniques. Encouraging approaches for controlling Aedes mosquitoes are necessary, as demonstrated by the evaluation of a new SIT/IIT combination and the incorporation of SIT into Drosophila suzukii management. For example, Wolbachia may protect plants from rice pests, demonstrating its potential for agricultural biological vector management. Maternal transmission and cytoplasmic incompatibility dynamics are explored, while Wolbachia phenotypic impacts on mosquito and rice pest management are examined. The importance of host evolutionary distance is emphasised in recent scale insect research that addresses host-shifting. Using greater information, a suggested method for comprehending Wolbachia host variations in various contexts emphasises ecological connectivity. Endosymbionts passed on maternally in nematodes and arthropods, Wolbachia are widely distributed around the world and have evolved both mutualistic and parasitic traits. Wolbachia is positioned as a paradigm for microbial symbiosis due to advancements in multiomics, gene functional assays, and its effect on human health. The challenges and opportunities facing Wolbachia research include scale issues, ecological implications, ethical conundrums, and the possibility of customising strains through genetic engineering. It is thought that cooperative efforts are required to include Wolbachia-based therapies into pest management techniques while ensuring responsible and sustainable ways.

Microbial symbionts are shared between ants and their associated beetles

The transmission of microbial symbionts across animal species could strongly affect their biology and evolution, but our understanding of transmission patterns and dynamics is limited. Army ants (Formicidae: Dorylinae) and their hundreds of closely associated insect guest species (myrmecophiles) can provide unique insights into interspecific microbial symbiont sharing. Here, we compared the microbiota of workers and larvae of the army ant Eciton burchellii with those of 13 myrmecophile beetle species using 16S rRNA amplicon sequencing. We found that the previously characterized specialized bacterial symbionts of army ant workers were largely absent from ant larvae and myrmecophiles, whose microbial communities were usually dominated by Rickettsia, Wolbachia, Rickettsiella and/or Weissella. Strikingly, different species of myrmecophiles and ant larvae often shared identical 16S rRNA genotypes of these common bacteria. Protein-coding gene sequences confirmed the close relationship of Weissella strains colonizing army ant larvae, some workers and several myrmecophile species. Unexpectedly, these strains were also similar to strains infecting dissimilar animals inhabiting very different habitats: trout and whales. Together, our data show that closely interacting species can share much of their microbiota, and some versatile microbial species can inhabit and possibly transmit across a diverse range of hosts and environments.

Symbiotic Bacteria Regulating Insect-Insect/Fungus/Virus Mutualism

Bacteria associated with insects potentially provide many beneficial services and have been well documented. Mutualism that relates to insects is widespread in ecosystems. However, the interrelation between "symbiotic bacteria" and "mutualism" has rarely been studied. We introduce three systems of mutualism that relate to insects (ants and honeydew-producing Hemiptera, fungus-growing insects and fungi, and plant persistent viruses and vector insects) and review the species of symbiotic bacteria in host insects, as well as their functions in host insects and the mechanisms underlying mutualism regulation. A deeper understanding of the molecular mechanisms and role of symbiotic bacteria, based on metagenomics, transcriptomics, proteomics, metabolomics, and microbiology, will be required for describing the entire interaction network.

Differential transport of a guild of mutualistic root aphids by the ant Lasius flavus

Mutually beneficial associations are widespread in ecological networks. They are typically assembled as multispecies guilds of symbionts that compete for one or more host species. The ant Lasius flavus engages in an intriguing and obligate mutualistic association with a community of aphids that are cultivated on plant roots in its nests. The ant displays a repertoire of amicable behaviors toward the aphids, including their transport. I examined whether L. flavus preferentially carried some of the root aphids. Using a no-choice and a choice experiment, I comparatively analyzed the transport rate of 5 obligate and one loosely associated species back to the ant nest and used the transport rate of the ant larvae as a reference. All associated root aphids were carried back to the nest, but in a clear preferential hierarchy. Geoica utricularia, Forda Formicaria, and Trama rara were rapidly transported, but slower than the own larvae. Tetraneura ulmi and Geoica setulosa were collected at a moderate rate and the loosely associated Aploneura lentisci was slowly retrieved. In contrast, different species of unassociated aphids were not transported and even provoked aggressive behavior in L. flavus. This study revealed that co-occurring symbionts may induce different degrees of host attraction, which ultimately may affect the coexistence and assembly of ant-symbiont communities.

Perianal Structures in Non-Myrmecophilous Aphids (Hemiptera, Aphididae)

Mutualistic relation with ants is one of the leading features of aphid ecology. For some aphid species, it is a crucial association enhancing their survival capability, while the life mode of some others is completely independent of ants. It was broadly accepted that during the evolution of aphids, the ones relying on ants developed special morphological adaptations for this mutualism, the so-called trophobiotic organ. Its exact structuring, however, posed some explanatory difficulties because many non-myrmecophilous aphids had structural modifications accordant with the trophobiotic organ, while some myrmecophilous did not. Here we present an evaluation of the morphology of perianal structures in 25 non-myrmecophilous aphid species with reference to previous, similar studies on myrmecophilous species based on scanning electron microscopy. We conclude that the trophobiotic organ is an existing adaptation, but its definition requires revision.

Host phylogeny and ecological associations best explain Wolbachia host shifts in scale insects

Wolbachia are among the most prevalent and widespread endosymbiotic bacteria on Earth. Wolbachia's success in infecting an enormous number of arthropod species is attributed to two features: the range of phenotypes they induce in their hosts, and their ability to switch between host species. Whilst much progress has been made in elucidating their induced phenotypes, our understanding of Wolbachia host-shifting is still very limited: we lack answers to even fundamental questions concerning Wolbachia's routes of transfer and the importance of factors influencing host shifts. Here, we investigate the diversity and host-shift patterns of Wolbachia in scale insects, a group of arthropods with intimate associations with other insects that make them well suited to studying host shifts. Using Illumina multitarget amplicon sequencing of Wolbachia-infected scale insects and their direct associates we determined the identity of all Wolbachia strains. We then fitted a generalized additive mixed model to our data to estimate the influence of host phylogeny and the geographical distribution on Wolbachia strain sharing among scale insect species. The model predicts no significant contribution of host geography but strong effects of host phylogeny, with high rates of Wolbachia sharing among closely related species and a sudden drop-off in sharing with increasing phylogenetic distance. We also detected the same Wolbachia strain in scale insects and several intimately associated species (ants, wasps and flies). This indicates putative host shifts and potential routes of transfers via these associates and highlights the importance of ecological connectivity in Wolbachia host-shifting.

Aphid species specializing on milkweed harbor taxonomically similar bacterial communities that differ in richness and relative abundance of core symbionts

Host plant range is arguably one of the most important factors shaping microbial communities associated with insect herbivores. However, it is unclear whether host plant specialization limits microbial community diversity or to what extent herbivores sharing a common host plant evolve similar microbiomes. To investigate whether variation in host plant range influences the assembly of core herbivore symbiont populations we compared bacterial diversity across three milkweed aphid species (Aphis nerii, Aphis asclepiadis, Myzocallis asclepiadis) feeding on a common host plant (Asclepias syriaca) using 16S rRNA metabarcoding. Overall, although there was significant overlap in taxa detected across all three aphid species (i.e. similar composition), some structural differences were identified within communities. Each aphid species harbored bacterial communities that varied in terms of richness and relative abundance of key symbionts. However, bacterial community diversity did not vary with degree of aphid host plant specialization. Interestingly, the narrow specialist A. asclepiadis harbored significantly higher relative abundances of the facultative symbiont Arsenophonus compared to the other two aphid species. Although many low abundance microbes were shared across all milkweed aphids, key differences in symbiotic partnerships were observed that could influence host physiology or additional ecological variation in traits that are microbially-mediated. Overall, this study suggests overlap in host plant range can select for taxonomically similar microbiomes across herbivore species, but variation in core aphid symbionts within these communities may still occur.

Insect-Microorganism Interaction Has Implicates on Insect Olfactory Systems

Olfaction plays an essential role in various insect behaviors, including habitat selection, access to food, avoidance of predators, inter-species communication, aggregation, and reproduction. The olfactory process involves integrating multiple signals from external conditions and internal physiological states, including living environments, age, physiological conditions, and circadian rhythms. As microorganisms and insects form tight interactions, the behaviors of insects are constantly challenged by versatile microorganisms via olfactory cues. To better understand the microbial influences on insect behaviors via olfactory cues, this paper summarizes three different ways in which microorganisms modulate insect behaviors. Here, we deciphered three interesting aspects of microorganisms-contributed olfaction: (1) How do volatiles emitted by microorganisms affect the behaviors of insects? (2) How do microorganisms reshape the behaviors of insects by inducing changes in the synthesis of host volatiles? (3) How do symbiotic microorganisms act on insects by modulating behaviors?

Microbiome of the Aphid Genus Dysaphis Börner (Hemiptera: Aphidinae) and Its Relation to Ant Attendance

Among mutualistic relationships of aphids with other organisms, there are two that seem to be of major importance: trophobiosis with ants and endosymbiosis of bacteria. While the former is well studied, the latter is the subject of an increasing amount of research constantly revealing new aspects of this symbiosis. Here, we studied the possible influence of ant attendance on the composition of aphid microbiota on primary and secondary hosts exploited by the aphid genus Dysaphis. The microbiome of 44 samples representing 12 aphid species was studied using an Illumina HiSeq 4000 with the V3-V4 region of 16S rRNA. The results showed a higher abundance of common facultative symbionts (Serratia, Regiella, Fukatsuia) in aphid species unattended by ants, but also on secondary hosts. However, in colonies attended by ants, the general species composition of bacterial symbionts was more rich in genera than in unattended colonies (Wolbachia, Gilliamella, Spiroplasma, Sphingomonas, Pelomonas). The results indicate a huge variability of facultative symbionts without clear correlation with ant attendance or aphid species. The possibility of multiple routes of bacterial infection mediated by ant-made environmental conditions is discussed.

Bacterial gut microbiomes of aculeate brood parasites overlap with their aculeate hosts', but have higher diversity and specialization

Despite growing interest in gut microbiomes of aculeate Hymenoptera, research so far focused on social bees, wasps, and ants, whereas non-social taxa and their brood parasites have not received much attention. Brood parasitism, however, allows to distinguish between microbiome components horizontally transmitted by spill-over from the host with such inherited through vertical transmission by mothers. Here, we studied the bacterial gut microbiome of adults in seven aculeate species in four brood parasite-host systems: two bee-mutillid (host-parasitoid) systems, one halictid bee-cuckoo bee system, and one wasp-chrysidid cuckoo wasp system. We addressed the following questions: (1) Do closely related species possess a more similar gut microbiome? (2) Do brood parasites share components of the microbiome with their host? (3) Do brood parasites have different diversity and specialization of microbiome communities compared with the hosts? Our results indicate that the bacterial gut microbiome of the studied taxa was species-specific, yet with a limited effect of host phylogenetic relatedness and a major contribution of shared microbes between hosts and parasites. However, contrasting patterns emerged between bee-parasite systems and the wasp-parasite system. We conclude that the gut microbiome in adult brood parasites is largely affected by their host-parasite relationships and the similarity of trophic food sources between hosts and parasites.

Multiple generations of antibiotic exposure and isolation influence host fitness and the microbiome in a model zooplankton species

Chronic antibiotic exposure impacts host health through changes to the microbiome. The detrimental effects of antibiotic perturbation on microbiome structure and function after one host generation of exposure have been well-studied, but less is understood about multigenerational effects of antibiotic exposure and subsequent recovery. In this study, we examined microbiome composition and host fitness across five generations of exposure to antibiotics in the model zooplankton host Daphnia magna. By utilizing a split-brood design where half of the offspring from antibiotic-exposed parents were allowed to recover and half were maintained in antibiotics, we examined recovery and resilience of the microbiome. Unexpectedly, we discovered that isolation of single host individuals across generations exerted a strong effect on microbiome composition, with microbiome diversity decreasing over generations regardless of treatment while host body size and cumulative reproduction increased across generations. Though antibiotics did cause substantial changes to microbiome composition within a generation, recovery generally occurred in one generation regardless of the number of prior generations spent in antibiotics. Our results demonstrate that isolation of individual hosts leads to stochastic extinction of less abundant taxa in the microbiome, suggesting that these taxa are likely maintained via transmission in host populations.

Beyond specialization: re-examining routes of host influence on symbiont evolution

Our understanding of host influence on microbial evolution has focused on symbiont specialization and the genomic streamlining that often accompanies it. However, a vast diversity of symbiotic lineages facultatively interact with hosts or associate with multiple hosts. Yet, there are no clear expectations for how host association influences the niche of these symbionts or their evolution. Here, we discuss how weak or variable selection on microbial symbiotic associations, horizontal transmission, and low costs of adaptation to novel host habitats are predicted to promote the expansion or maintenance of microbial niches. This broad perspective will aid in developing better and more general predictions for evolution in microbial symbioses.

Fruit fly phylogeny imprints bacterial gut microbiota

One promising avenue for reconciling the goals of crop production and ecosystem preservation consists in the manipulation of beneficial biotic interactions, such as between insects and microbes. Insect gut microbiota can affect host fitness by contributing to development, host immunity, nutrition, or behavior. However, the determinants of gut microbiota composition and structure, including host phylogeny and host ecology, remain poorly known. Here, we used a well‐studied community of eight sympatric fruit fly species to test the contributions of fly phylogeny, fly specialization, and fly sampling environment on the composition and structure of bacterial gut microbiota. Comprising both specialists and generalists, these species belong to five genera from to two tribes of the Tephritidae family. For each fly species, one field and one laboratory samples were studied. Bacterial inventories to the genus level were produced using 16S metabarcoding with the Oxford Nanopore Technology. Sample bacterial compositions were analyzed with recent network‐based clustering techniques. Whereas gut microbiota were dominated by the Enterobacteriaceae family in all samples, microbial profiles varied across samples, mainly in relation to fly identity and sampling environment. Alpha diversity varied across samples and was higher in the Dacinae tribe than in the Ceratitinae tribe. Network analyses allowed grouping samples according to their microbial profiles. The resulting groups were very congruent with fly phylogeny, with a significant modulation of sampling environment, and with a very low impact of fly specialization. Such a strong imprint of host phylogeny in sympatric fly species, some of which share much of their host plants, suggests important control of fruit flies on their gut microbiota through vertical transmission and/or intense filtering of environmental bacteria.

Lactic Acid Bacteria Are Prevalent in the Infrabuccal Pockets and Crops of Ants That Prefer Aphid Honeydew

Ants are evolutionarily successful species and occupy diverse trophic and habitat niches on the earth. To fulfill dietary requirements, ants have established commensalism with both sap-feeding insects and bacteria. In this study, we used high-throughput sequencing of the bacterial 16S rRNA gene to characterize the bacterial composition and structure of the digestive tracts in three species of Formica ants and Lasius niger (Linnaeus)—species that predominantly feed on honeydew secreted by aphids. We found that bacterial communities displayed species- and colony-level signatures, and that bacterial communities in the infrabuccal pockets and crops were different from those in the midguts and hindguts. Lactobacillus and Wolbachia were dominant in the infrabuccal pockets and crops of workers, whereas Wolbachia was dominant in the midguts, hindguts and brood (larvae, pupae and cocoons). To learn more about the dominant Lactobacillus in ants, we assessed its prevalence in a wide range of aphid-tending ants using diagnostic PCR. We found that Lactobacillus was more prevalent in Formicinae than in Myrmicinae species. We also isolated four strains of lactic acid bacteria (Lactobacillus sanfranciscensis, Lactobacillus lindneri, Weissella cibaria and Fructobacillus sp.) from the infrabuccal pockets and crops of aphid-tending ants using a culture-dependent method. Two predominant lactic acid bacterial isolates, Lactobacillus sanfranciscensis (La2) and Weissella cibaria (La3), exhibited abilities in catabolizing sugars (sucrose, trehalose, melezitose and raffinose) known to be constituents of hemipteran honeydew. These findings contribute to further understanding the association between ants, aphids and bacteria, and provide additional information on the function of lactic acid bacteria in ants.

Molecular Rationale of Insect-Microbes Symbiosis-From Insect Behaviour to Mechanism

Insects nurture a panoply of microbial populations that are often obligatory and exist mutually with their hosts. Symbionts not only impact their host fitness but also shape the trajectory of their phenotype. This co-constructed niche successfully evolved long in the past to mark advanced ecological specialization. The resident microbes regulate insect nutrition by controlling their host plant specialization and immunity. It enhances the host fitness and performance by detoxifying toxins secreted by the predators and abstains them. The profound effect of a microbial population on insect physiology and behaviour is exploited to understand the host–microbial system in diverse taxa. Emergent research of insect-associated microbes has revealed their potential to modulate insect brain functions and, ultimately, control their behaviours, including social interactions. The revelation of the gut microbiota–brain axis has now unravelled insects as a cost-effective potential model to study neurodegenerative disorders and behavioural dysfunctions in humans. This article reviewed our knowledge about the insect–microbial system, an exquisite network of interactions operating between insects and microbes, its mechanistic insight that holds intricate multi-organismal systems in harmony, and its future perspectives. The demystification of molecular networks governing insect–microbial symbiosis will reveal the perplexing behaviours of insects that could be utilized in managing insect pests.

The Ubiquity and Development-Related Abundance Dynamics of Ophiocordyceps Fungi in Soft Scale Insects

Mutual relationships with symbionts play a crucial role in the evolution and ecology of plant-feeding hemipteran insects. However, there was no specific dominant bacterium observed in soft scales (Coccidae) in the previous studies, it is still unclear whether soft scales have specific primary symbionts. In this study, a nuclear ribosomal internal transcribed spacer (ITS)gene fragment was used to analyze the diversity of fungal communities in 28 Coccidae species based on next-generation sequencing (NGS). Furthermore, samples from different developmental stages of Ceroplastes japonicus were sequenced to illustrate the dynamics of fungal community. Our results showed that Coccidae-associated Ophiocordyceps fungi (COF) were prevalent in all 28 tested species with high relative abundance. Meanwhile, the first and second instars of C. japonicus, two important stages for growth and development, had high relative abundance of COF, while the relative abundances in other stages were low, ranging from 0.68% to 2.07%. The result of fluorescent in situ hybridization showed that the COF were widely present in hemolymph and vertically transmitted from mother to offspring. Our study confirms that the COF have intimate associations with the growth and development of soft scales, and provides new evidence to support that COF are primary fungal symbionts for Coccidae.

Formicine ants swallow their highly acidic poison for gut microbial selection and control

Animals continuously encounter microorganisms that are essential for health or cause disease. They are thus challenged to control harmful microbes while allowing the acquisition of beneficial microbes. This challenge is likely especially important for social insects with respect to microbes in food, as they often store food and exchange food among colony members. Here we show that formicine ants actively swallow their antimicrobial, highly acidic poison gland secretion. The ensuing acidic environment in the stomach, the crop, can limit the establishment of pathogenic and opportunistic microbes ingested with food and improve the survival of ants when faced with pathogen contaminated food. At the same time, crop acidity selectively allows acquisition and colonization by Acetobacteraceae, known bacterial gut associates of formicine ants. This suggests that swallowing of the poison in formicine ants acts as a microbial filter and that antimicrobials have a potentially widespread but so far underappreciated dual role in host-microbe interactions.

Endomicrobial Community Profiles of Two Different Mealybugs: Paracoccus marginatus and Ferrisia virgata

Mealybugs (Hemiptera: Coccomorpha: Pseudococcidae) harbour diverse microbial symbionts that play essential roles in host physiology, ecology, and evolution. In this study we aimed to reveal microbial communities associated with two different mealybugs, papaya mealybug (Paracoccus marginatus) and two-tailed mealybug (Ferrisia virgata) collected from the same host plant. Comparative analysis of microbial communities associated with these mealybugs revealed differences that appear to stem from phylogenetic associations and different nutritional requirements. This first report on both bacterial and fungal communities associated with these mealybugs provides a preliminary insight on factors affecting the endomicrobial communities. .

Characterization of the bacterial communities of psyllids associated with Rutaceae in Bhutan by high throughput sequencing

Background

Several plant-pathogenic bacteria are transmitted by insect vector species that often also act as hosts. In this interface, these bacteria encounter plant endophytic, insect endosymbiotic and other microbes. Here, we used high throughput sequencing to examine the bacterial communities of five different psyllids associated with citrus and related plants of Rutaceae in Bhutan: Diaphorina citri, Diaphorina communis, Cornopsylla rotundiconis, Cacopsylla heterogena and an unidentified Cacopsylla sp.

Results

The microbiomes of the psyllids largely comprised their obligate P-endosymbiont ‘Candidatus Carsonella ruddii’, and one or two S-endosymbionts that are fixed and specific to each lineage. In addition, all contained Wolbachia strains; the Bhutanese accessions of D. citri were dominated by a Wolbachia strain first found in American isolates of D. citri, while D. communis accessions were dominated by the Wolbachia strain, wDi, first detected in D. citri from China. The S-endosymbionts from the five psyllids grouped with those from other psyllid taxa; all D. citri and D. communis individuals contained sequences matching ‘Candidatus Profftella armatura’ that has previously only been reported from other Diaphorina species, and the remaining psyllid species contained OTUs related to unclassified Enterobacteriaceae. The plant pathogenic ‘Candidatus Liberibacter asiaticus’ was found in D. citri but not in D. communis. Furthermore, an unidentified ‘Candidatus Liberibacter sp.’ occurred at low abundance in both Co. rotundiconis and the unidentified Cacopsylla sp. sampled from Zanthoxylum sp.; the status of this new liberibacter as a plant pathogen and its potential plant hosts are currently unknown. The bacterial communities of Co. rotundiconis also contained a range of OTUs with similarities to bacteria previously found in samples taken from various environmental sources.

Conclusions

The bacterial microbiota detected in these Bhutanese psyllids support the trends that have been seen in previous studies: psyllids have microbiomes largely comprising their obligate P-endosymbiont and one or two S-endosymbionts. In addition, the association with plant pathogens has been demonstrated, with the detection of liberibacters in a known host, D. citri, and identification of a putative new species of liberibacter in Co. rotundiconis and Cacopsylla sp.

The topology and drivers of ant-symbiont networks across Europe

Intimate associations between different species drive community composition across ecosystems. Understanding the ecological and evolutionary drivers of these symbiotic associations is challenging because their structure eventually determines stability and resilience of the entire species network. Here, we compiled a detailed database on naturally occurring ant-symbiont networks in Europe to identify factors that affect symbiont network topology. These networks host an unrivalled diversity of macrosymbiotic associations, spanning the entire mutualism-antagonism continuum, including: (i) myrmecophiles - commensalistic and parasitic arthropods; (ii) trophobionts - mutualistic aphids, scale insects, planthoppers and caterpillars; (iii) social parasites - parasitic ant species; (iv) parasitic helminths; and (v) parasitic fungi. We dissected network topology to investigate what determines host specificity, symbiont species richness, and the capacity of different symbiont types to switch hosts. We found 722 macrosymbionts (multicellular symbionts) associated with European ants. Symbiont type explained host specificity and the average relatedness of the host species. Social parasites were associated with few hosts that were phylogenetically highly related, whereas the other symbiont types interacted with a larger number of hosts across a wider taxonomic distribution. The hosts of trophobionts were the least phylogenetically related across all symbiont types. Colony size, host range and habitat type predicted total symbiont richness: ant hosts with larger colony size, a larger distribution range or with a wider habitat range contained more symbiont species. However, we found that different sets of host factors affected diversity in the different types of symbionts. Ecological factors, such as colony size, host range and niche width predominantly determined myrmecophile species richness, whereas host phylogeny was the most important predictor of mutualistic trophobiont, social parasite and parasitic helminth species richness. Lastly, we found that hosts with a common biogeographic history support a more similar community of symbionts. Phylogenetically related hosts also shared more trophobionts, social parasites and helminths, but not myrmecophiles. Taken together, these results suggest that ecological and evolutionary processes structure host specificity and symbiont richness in large-scale ant-symbiont networks, but these drivers may shift in importance depending on the type of symbiosis. Our findings highlight the potential of well-characterized bipartite networks composed of different types of symbioses to identify candidate processes driving community composition.

First Insight into Microbiome Profiles of Myrmecophilous Beetles and Their Host, Red Wood Ant Formica polyctena (Hymenoptera: Formicidae)-A Case Study

Formica polyctena belongs to the red wood ant species group. Its nests provide a stable, food rich, and temperature and humidity controlled environment, utilized by a wide range of species, called myrmecophiles. Here, we used the high-throughput sequencing of the 16S rRNA gene on the Illumina platform for identification of the microbiome profiles of six selected myrmecophilous beetles (Dendrophilus pygmaeus, Leptacinus formicetorum, Monotoma angusticollis, Myrmechixenus subterraneus, Ptenidium formicetorum and Thiasophila angulata) and their host F. polyctena. Analyzed bacterial communities consisted of a total of 23 phyla, among which Proteobacteria, Actinobacteria, and Firmicutes were the most abundant. Two known endosymbionts-Wolbachia and Rickettsia-were found in the analyzed microbiome profiles and Wolbachia was dominant in bacterial communities associated with F. polyctena, M. subterraneus, L. formicetorum and P. formicetorum (>90% of reads). In turn, M. angusticollis was co-infected with both Wolbachia and Rickettsia, while in the microbiome of T. angulata, the dominance of Rickettsia has been observed. The relationships among the microbiome profiles were complex, and no relative abundance pattern common to all myrmecophilous beetles tested was observed. However, some subtle, species-specific patterns have been observed for bacterial communities associated with D. pygmaeus, M. angusticollis, and T. angulata.

A Risky Business? Habitat and Social Behavior Impact Skin and Gut Microbiomes in Caribbean Cleaning Gobies

The broadstripe cleaning goby Elacatinus prochilos has two alternative ecotypes: sponge-dwellers, which live in large groups and feed mainly upon nematode parasites; and coral-dwellers, that live in small groups or in solitude and behave as cleaners. Recent studies focusing on the skin and gut microbiomes of tropical fish showed that microbial communities are influenced mainly by diet and host species. Here, we compare the skin and gut microbiomes of the Caribbean broadstripe cleaning goby E. prochilos alternative ecotypes (cleaners and non-cleaners) from Barbados and predict that different habitat use and behavior (cleaning vs. non-cleaning) will translate in different bacterial profiles between the two ecotypes. We found significant differences in both alpha- and beta-diversity of skin and gut microbiomes belonging to different ecotypes. Importantly, the skin microbiome of obligate cleaners showed greater intra-sample diversity and harbored a significantly higher prevalence of potential fish pathogens. Likewise, potential pathogens were also more prevalent in the gut of obligate cleaners. We suggest that habitat use, diet, but also direct contact with potential diseased clientele during cleaning, could be the cause for these patterns.

Can social partnerships influence the microbiome? Insights from ant farmers and their trophobiont mutualists

Mutualistic interactions with microbes have played a crucial role in the evolution and ecology of animal hosts. However, it is unclear what factors are most important in influencing particular host–microbe associations. While closely related animal species may have more similar microbiota than distantly related species due to phylogenetic contingencies, social partnerships with other organisms, such as those in which one animal farms another, may also influence an organism's symbiotic microbiome. We studied a mutualistic network of Brachymyrmex and Lasius ants farming several honeydew‐producing Prociphilus aphids and Rhizoecus mealybugs to test whether the mutualistic microbiomes of these interacting insects are primarily correlated with their phylogeny or with their shared social partnerships. Our results confirm a phylogenetic signal in the microbiomes of aphid and mealybug trophobionts, with each species harbouring species‐specific endosymbiont strains of Buchnera (aphids), Tremblaya and Sodalis (mealybugs), and Serratia (both mealybugs and aphids) despite being farmed by the same ants. This is likely explained by strict vertical transmission of trophobiont endosymbionts between generations. In contrast, our results show the ants’ microbiome is possibly shaped by their social partnerships, with ants that farm the same trophobionts also sharing strains of sugar‐processing Acetobacteraceae bacteria, known from other honeydew‐feeding ants and which likely reside extracellularly in the ants’ guts. These ant–microbe associations are arguably more “open” and subject to horizontal transmission or social transmission within ant colonies. These findings suggest that the role of social partnerships in shaping a host's symbiotic microbiome can be variable and is likely dependent on how the microbes are transmitted across generations.