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The ecological and genetic changes that underlie the evolution of host–microbe interactions remain elusive, primarily due to challenges in disentangling the variables that alter microbiome composition. To understand the impact of host habitat, host genetics, and evolutionary history on microbial community structure, we examined gut microbiomes of river‐ and three cave‐adapted morphotypes of the Mexican tetra, Astyanax mexicanus, in their natural environments and under controlled laboratory conditions. Field‐collected samples were dominated by very few taxa and showed considerable interindividual variation. We found that lab‐reared fish exhibited increased microbiome richness and distinct composition compared to their wild counterparts, underscoring the significant influence of habitat. Most notably, however, we found that morphotypes reared on the same diet throughout life developed distinct microbiomes suggesting that genetic loci resulting from cavefish evolution shape microbiome composition. We observed stable differences in Fusobacteriota abundance between morphotypes and demonstrated that this could be used as a trait for quantitative trait loci mapping to uncover the genetic basis of microbial community structure. [ABSTRACT FROM AUTHOR]

Different host species associate with distinct gut microbes in mammals, a pattern sometimes referred to as phylosymbiosis. However, the processes shaping this host specificity are not well understood. One model proposes that barriers to microbial transmission promote specificity by limiting microbial dispersal between hosts. This model predicts that specificity levels measured across microbes is correlated to transmission mode (vertical vs. horizontal) and individual dispersal traits. Here, we leverage two large publicly available gut microbiota data sets (1490 samples from 195 host species) to test this prediction. We found that host specificity varies widely across bacteria (i.e., there are generalist and specialist bacteria) and depends on transmission mode and dispersal ability. Horizontally‐like transmitted bacteria equipped with traits that facilitate switches between host (e.g., tolerance to oxygen) were found to be less specific (more generalist) than microbes without those traits, for example, vertically‐like inherited bacteria that are intolerant to oxygen. Altogether, our findings are compatible with a model in which limited microbial dispersal abilities foster host specificity. see also the Perspective by Elizabeth K. Mallott [ABSTRACT FROM AUTHOR]

Although knowledge of the functions of the gut microbiome has increased greatly over the past few decades, our understanding of the mechanisms governing its ecology and evolution remains obscure. While host genetic distance is a strong predictor of the gut microbiome in large‐scale studies and captive settings, its influence has not always been evident at finer taxonomic scales, especially when considering among the recently diverged animals in natural settings. Comparing the gut microbiome of 19 populations of Japanese macaques Macaca fuscata across the Japanese archipelago, we assessed the relative roles of host genetic distance, geographic distance and dietary factors in influencing the macaque gut microbiome. Our results suggested that the macaques may maintain a core gut microbiome, while each population may have acquired some microbes from its specific habitat/diet. Diet‐related factors such as season, forest, and reliance on anthropogenic foods played a stronger role in shaping the macaque gut microbiome. Among closely related mammalian hosts, host genetics may have limited effects on the gut microbiome since the hosts generally have smaller physiological differences. This study contributes to our understanding of the relative roles of host phylogeography and dietary factors in shaping the gut microbiome of closely related mammalian hosts. Research Highlights: Japanese macaques may maintain a core gut microbiome, while each population may have acquired some microbes from its specific habitat/diet.Among closely related mammalian hosts, host genetics may have limited effects on the gut microbiome since the hosts generally have smaller physiological differences.The effect of diet quality, which is influenced the forest type, season and reliance on anthropogenic foods, was more pronounced and may have affected the distribution of specific microbial taxa. [ABSTRACT FROM AUTHOR]

Fish represent a large part of the taxonomic diversity of vertebrates and are of high commercial value. However, the factors influencing the gut microbiota composition of freshwater fish over large spatial scales remain unclear. Therefore, this study explored gut microbiome diversity in 24 fish species from the Yellow River, which spans over 1500 km across China. The results showed that geographical distance, host phylogeny and diet significantly influenced gut microbial community diversity, whereas sex, body length and body weight had minimal influence. Geographical distance was the primary factor shaping gut microbiota, and dissimilarity in microbial community structure increased with an increase in geographical distance, which was mainly driven by dispersal limitation. The microbial communities were more homogeneous at higher host taxonomic resolutions due to the dominant role of homogeneous selection in community convergence. Phylosymbiosis was observed across all host species, with a stronger pattern in Cypriniformes, which harbour host‐specific microbial taxa. Host diet explained little variation in gut microbiome diversity, although it was significant for all diversity metrics tested. These findings collectively suggest that the geographical and host‐based patterns of fish gut microbiota tend to be shaped by different ecological forces across the Yellow River. The present work provides a robust assessment of multiple factors driving fish gut microbial community assembly and offers insight into the mechanisms underlying shifts in fish gut microbiota in rivers across large spatial scales. [ABSTRACT FROM AUTHOR]

Understanding the factors that shape microbiomes can provide insight into the importance of host–symbiont interactions and on co‐evolutionary dynamics. Unlike for mammals, previous studies have found little or no support for an influence of host evolutionary history on avian gut microbiome diversity and instead have suggested a greater influence of the environment or diet due to fast gut turnover. Because effects of different factors may be conflated by captivity and sampling design, examining natural variation using large sample sizes is important. Our goal was to overcome these limitations by sampling wild birds to compare environmental, dietary and evolutionary influences on gut microbiome structure. We performed faecal metabarcoding to characterize both the gut microbiome and diet of 15 wood‐warbler species across a 4‐year period and from two geographical localities. We find host taxonomy generally explained ~10% of the variation between individuals, which is ~6‐fold more variation of any other factor considered, including diet diversity. Further, gut microbiome similarity was more congruent with the host phylogeny than with host diet similarity and we found little association between diet diversity and microbiome diversity. Together, our results suggest evolutionary history is the strongest predictor of gut microbiome differentiation among wood‐warblers. Although the phylogenetic signal of the warbler gut microbiome is not very strong, our data suggest that a stronger influence of diet (as measured by diet diversity) does not account for this pattern. The mechanism underlying this phylogenetic signal is not clear, but we argue host traits may filter colonization and maintenance of microbes. [ABSTRACT FROM AUTHOR]

Associations between host genotype and host‐associated microbiomes have been shown in a variety of animal clades, but studies on teleosts mostly show weak associations. Our study aimed to explore these relationships in four sympatric Serrasalmidae (i.e., piranha) teleosts from an Amazonian lake, using data sets from the hosts genomes (single nucleotide polymorphisms from genotyping by sequencing), skin and gut microbiomes (16S rRNA gene metataxonomics) and diets (COI metabarcoding) from the same fish individuals. First, we investigated whether there were significant covariations of microbiome and fish genotypes at the inter‐ and intraspecific levels. We also assessed the extent of covariation between Serrasalmidae diet and microbiome, to isolate genotypic from dietary effects on community structure. We observed a significant covariation of skin microbiomes and host genotypes at interspecific (R2 = 24.4%) and intraspecific (R2 = 6.2%) levels, whereas gut microbiomes correlated poorly with host genotypes. Serrasalmidae diet composition was significantly correlated to fish genotype only at the interspecific level (R2 = 5.4%), but did not covary with gut microbiome composition (Mantel R = −.04). Second, we investigated whether the study of interspecific differentiation could benefit from considering host‐associated microbial communities in addition to host genotypes. By using a nonmetric multidimensional scaling (NMDS) ordination‐based approach, we observed that ordinations from skin‐ and gut species‐specific bacterial biomarkers identified through a random forest algorithm could significantly increase the average interspecific differentiation detected through host genotype data alone. Although future studies encompassing additional species and environments are needed, our results suggest Serrasalmidae microbiomes could constitute an insightful trait to be considered when studying the interspecific differences between members of this clade. [ABSTRACT FROM AUTHOR]

Summary: Plants evolved in association with a diverse community of microorganisms. The effect of plant phylogeny and domestication on host–microbiome co‐evolutionary dynamics are poorly understood.Here we examined the effect of domestication and plant lineage on the composition of the endophytic microbiome of 11 Malus species, representing three major groups: domesticated apple (M. domestica), wild apple progenitors, and wild Malus species.The endophytic community of M. domestica and its wild progenitors showed higher microbial diversity and abundance than wild Malus species. Heirloom and modern cultivars harbored a distinct community composition, though the difference was not significant. A community‐wide Bayesian model revealed that the endophytic microbiome of domesticated apple is an admixture of its wild progenitors, with clear evidence for microbiome introgression, especially for the bacterial community. We observed a significant correlation between the evolutionary distance of Malus species and their microbiome.This study supports co‐evolution between Malus species and their microbiome during domestication. This finding has major implications for future breeding programs and our understanding of the evolution of plants and their microbiomes. [ABSTRACT FROM AUTHOR]

As for most of the life that inhabits our planet, microorganisms play an essential role in insect nutrition, reproduction, defence, and support their host in many other functions. More recently, we assisted to an exponential growth of studies describing the taxonomical composition of bacterial communities across insects' phylogeny. However, there is still an outstanding question that needs to be answered: Which factors contribute most to shape insects' microbiomes? This study tries to find an answer to this question by taking advantage of publicly available sequencing data and reanalysing over 4000 samples of insect‐associated bacterial communities under a common framework. Results suggest that insect taxonomy has a wider impact on the structure and diversity of their associated microbial communities than the other factors considered (diet, sex, life stage, sample origin and treatment). However, when specifically testing for signatures of codiversification of insect species and their microbiota, analyses found weak support for this, suggesting that while insect species strongly drive the structure and diversity of insect microbiota, the diversification of those microbial communities did not follow their host's phylogeny. Furthermore, a parallel survey of the literature highlights several methodological limitations that need to be considered in the future research endeavours. [ABSTRACT FROM AUTHOR]

Premise: Foliar fungal endophytes vary in their distributions across landscapes or plant host taxa, indicative of specialized ecologies and host specific adaptations. Accounts of specialization, however, depend on the taxonomic breadth and geographic range of the host plants included in each study. A broad region‐scale study or deep sampling of diverse potential host species still remains relatively rare but is becoming increasingly possible with high‐throughput sequencing. Methods: Amplicon sequencing was used to rapidly identify the fungal endophytic community among six pine (Pinus, Pinaceae) species co‐occurring across northeastern United States and to test for site and host specialization. We focused on the endophytic genus Lophodermium (Rhytismataceae), whose species members are thought to specialize on different pine species, to test if amplicon sequencing could rapidly verify previously implied or discover new patterns of host specificity. Results: While amplicon sequencing could analyze more samples at greater depths and recover greater numbers of unique Lophodermium taxa than when endophyte communities were surveyed with traditional culturing methods, patterns of specialization were not better supported. This may be because amplicon sequencing can indiscriminately capture non‐host specific organisms found incidentally from plant tissues or because we have overestimated host‐specificity in the past with biased culturing techniques. Conclusions: Amplicon sequencing can quickly identify patterns of host specificity by allowing large‐scale surveys but has limitations in quantifying the level of intimacy of these relationships. [ABSTRACT FROM AUTHOR]

The association with microbes in plants and animals is known to be beneficial for host's survival and fitness, but the generality of the effect of the microbiome is still debated. For some animals, similarities in microbiome composition reflect taxonomic relatedness of the hosts, a pattern termed phylosymbiosis. The mechanisms behind the pattern could be due to co‐evolution and/or to correlated ecological constraints. General conclusions are hampered by the fact that available knowledge is highly dominated by microbiomes from model species. Here, we addressed the issue of the generality of phylosymbiosis by analysing the species‐specificity of microbiomes across different species of freshwater zooplankton, including rotifers, cladocerans, and copepods, coupling field surveys and experimental manipulations. We found that no signal of phylosymbiosis was present, and that the proportion of "core" microbial taxa, stable and consistent within each species, was very low. Changes in food and temperature under laboratory experimental settings revealed that the microbiome of freshwater zooplankton is highly flexible and can be influenced by the external environment. Thus, the role of co‐evolution, strict association, and interaction with microbes within the holobiont concept highlighted for vertebrates, corals, sponges, and other animals does not seem to be supported for all animals, at least not for freshwater zooplankton. Zooplankton floats in the environment where both food and bacteria that can provide help in digesting such food are available. In addition, there is probably redundancy for beneficial bacterial functions in the environment, not allowing a strict host‐microbiome association to originate and persist. [ABSTRACT FROM AUTHOR]

Neotropical wood‐eating catfishes (family Loricariidae) can occur in diverse assemblages with multiple genera and species feeding on the same woody detritus. As such, they present an intriguing system in which to examine the influence of host species identity on the vertebrate gut microbiome as well as to determine the potential role of gut bacteria in wood digestion. We characterized the gut microbiome of two co‐occurring catfish genera and four species: Panaqolus albomaculatus, Panaqolus gnomus, Panaqolus nocturnus, and Panaque bathyphilus, as well as that of submerged wood on which they feed. The gut bacterial community did not significantly vary across three gut regions (proximal, mid, distal) for any catfish species, although interspecific variation in the gut microbiome was significant, with magnitude of interspecific difference generally reflecting host phylogenetic proximity. Further, the gut microbiome of each species was significantly different to that present on the submerged wood. Inferring the genomic potential of the gut microbiome revealed that the majority of wood digesting pathways were at best equivalent to and more often depleted or nonexistent within the catfish gut compared to the submerged wood, suggesting a minimal role for the gut microbiome in wood digestion. Rather, these fishes are more likely reliant on fiber degradation performed by microbes in the environment, with their gut microbiome determined more by host identity and phylogenetic history. [ABSTRACT FROM AUTHOR]

Gut microbial diversity is thought to reflect the co‐evolution of microbes and their hosts as well as current host‐specific attributes such as genetic background and environmental setting. To explore interactions among these parameters, we characterized variation in gut microbiome composition of California voles (Microtus californicus) across a contact zone between two recently diverged lineages of this species. Because this contact zone contains individuals with mismatched mitochondrial‐nuclear genomes (cybrids), it provides an important opportunity to explore how different components of the genotype contribute to gut microbial diversity. Analyses of bacterial 16S rRNA sequences and joint species distribution modelling revealed that host genotypes and genetic differentiation among host populations together explained more than 50% of microbial community variation across our sampling transect. The ranked importance (most to least) of factors contributing to gut microbial diversity in our study populations were: genome‐wide population differentiation, local environmental conditions, and host genotypes. However, differences in microbial communities among vole populations (β‐diversity) did not follow patterns of lineage divergence (i.e., phylosymbiosis). Instead, among‐population variation was best explained by the spatial distribution of hosts, as expected if the environment is a primary source of gut microbial diversity (i.e., dispersal limitation hypothesis). Across the contact zone, several bacterial taxa differed in relative abundance between the two parental lineages as well as among individuals with mismatched mitochondrial and nuclear genomes. Thus, genetic divergence among host lineages and mitonuclear genomic mismatches may also contribute to microbial diversity by altering interactions between host genomes and gut microbiota (i.e., hologenome speciation hypothesis). [ABSTRACT FROM AUTHOR]

Abstract: The variation and taxonomic diversity among mammalian gut microbiomes raises several questions about the factors that contribute to the rates and patterns of change in these microbial communities. By comparing the microbiome compositions of 112 species representing 14 mammalian orders, we assessed how host and ecological factors contribute to microbiome diversification. Except in rare cases, the same bacterial phyla predominate in mammalian gut microbiomes, and there has been some convergence of microbiome compositions according to dietary category across all mammalians lineages except Chiropterans (bats), which possess high proportions of Proteobacteria and tend to be most similar to one another regardless of diet. At lower taxonomic ranks (families, genera, 97% OTUs), bacteria are more likely to be associated with a particular mammalian lineage than with a particular dietary category, resulting in a strong phylogenetic signal in the degree to which microbiomes diverge. Despite different physiologies, the gut microbiomes of several mammalian lineages have diverged at roughly the same rate over the past 75 million years; however, the gut microbiomes of Cetartiodactyla (ruminants, whales, hippopotami) have evolved much faster and those of Chiropterans much slower. Contrary to expectations, the number of dietary transitions within a lineage does not influence rates of microbiome divergence, but instead, some of the most dramatic changes are associated with the loss of bacterial taxa, such as those accompanying the transition from terrestrial to marine lifestyles and the evolution of hominids. [ABSTRACT FROM AUTHOR]

Abstract: Gut microbial communities provide many physiological functions to their hosts, especially in herbivorous animals. We still lack an understanding of how these microbial communities are structured across hosts in nature, especially within a given host species. Studies on laboratory mice have demonstrated that host genetics can influence microbial community structure, but that diet can overwhelm these genetic effects. We aimed to test these ideas in a natural system, the American pika (Ochotona princeps). First, pikas are high‐elevation specialists with significant population structure across various mountain ranges in the USA, allowing us to investigate whether similarities in microbial communities match host genetic differences. Additionally, pikas are herbivorous, with some populations exhibiting remarkable dietary plasticity and consuming high levels of moss, which is exceptionally high in fibre and low in protein. This allows us to investigate adaptations to an herbivorous diet, as well as to the especially challenging diet of moss. Here, we inventoried the microbial communities of pika caecal pellets from various populations using 16S rRNA sequencing to investigate structuring of microbial communities across various populations with different natural diets. Microbial communities varied significantly across populations, and differences in microbial community structure were congruent with genetic differences in host population structure, a pattern known as “phylosymbiosis.” Several microbial members (Ruminococcus, Prevotella, Oxalobacter and Coprococcus) were detected across all samples, and thus likely represent a “core microbiome.” These genera are known to perform a number of services for herbivorous hosts such as fibre fermentation and the degradation of plant defensive compounds, and thus are likely important for herbivory in pikas. Moreover, pikas that feed on moss harboured microbial communities highly enriched in Melainabacteria. This uncultivable candidate phylum has been proposed to ferment fibre for herbivores, and thus may contribute to the ability of some pika populations to consume high amounts of moss. These findings demonstrate that both host genetics and diet can influence the microbial communities of the American pika. These animals may be novel sources of fibre‐degrading microbes. Last, we discuss the implications of population‐specific microbial communities for conservation efforts in this species. [ABSTRACT FROM AUTHOR]

Many aspects of animal ecology and physiology are influenced by the microbial communities within them. The underlying forces contributing to the assembly and diversity of gut microbiotas include chance events, host-based selection and interactions among microorganisms within these communities. We surveyed 215 wild individuals from four sympatric species of Drosophila that share a common diet of decaying mushrooms. Their microbiotas consistently contained abundant bacteria that were undetectable or at low abundance in their diet. Despite their deep phylogenetic divergence, all species had similar microbiotas, thus failing to support predictions of the phylosymbiosis hypothesis. Communities within flies were not random assemblages drawn from a common pool; instead, many bacterial operational taxonomic units ( OTUs) were overrepresented or underrepresented relative to the neutral expectations, and OTUs exhibited checkerboard distributions among flies. These results suggest that selective factors play an important role in shaping the gut community structure of these flies. [ABSTRACT FROM AUTHOR]