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1. Host genomic variation shapes gut microbiome diversity in threespine stickleback fish

   https://doi.org/10.1128/mbio.00219-23  

   Small, Clayton M.; Beck, Emily A.; Currey, Mark C.; Tavalire, Hannah F.; Bassham, Susan; Cresko, William A. (January 2023, mBio)

   Barbour, Alan G. (Ed.)

   A major focus of host-microbe research is to understand how genetic differences, of various magnitudes, among hosts translate to differences in their microbiomes. This has been challenging for animal hosts, including humans, because it is difficult to control environmental variables tightly enough to isolate direct genetic effects on the microbiome. Our work in stickleback fish is a significant contribution because our experimental approach allowed strict control over environmental factors, including standardization of the microbiome from the earliest stage of development and unrestricted co-housing of fish in a truly common environment. Furthermore, we measured host genetic variation over 2,000 regions of the stickleback genome, comparing this information and microbiome composition data among fish from very similar and very different genetic backgrounds. Our findings highlight how differences in the host genome influence microbiome diversity and make a case for future manipulative microbiome experiments that use host systems with naturally occurring genetic variation. 

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2. Wild microbiomes of striped plateau lizards vary with reproductive season, sex, and body size

   https://doi.org/10.1038/s41598-022-24518-6  

   Bunker, Marie E.; Arnold, A. Elizabeth; Weiss, Stacey L. (December 2022, Scientific Reports)

   Abstract Long-term studies of animal microbiomes under natural conditions are valuable for understanding the effects of host demographics and environmental factors on host-associated microbial communities, and how those effects interact and shift over time. We examined how the cloacal microbiome of wild Sceloporus virgatus (the striped plateau lizard) varies under natural conditions in a multi-year study. Cloacal swabs were collected from wild-caught lizards across their entire active season and over three years in southeastern Arizona, USA. Analyses of 16S rRNA data generated on the Illumina platform revealed that cloacal microbiomes of S. virgatus vary as a function of season, sex, body size, and reproductive state, and do so independently of one another. Briefly, microbial diversity was lowest in both sexes during the reproductive season, was higher in females than in males, and was lowest in females when they were vitellogenic, and microbiome composition varied across seasons, sexes, and sizes. The pattern of decreased diversity during reproductive periods with increased sociality is surprising, as studies in other systems often suggest that microbial diversity generally increases with sociality. The cloacal microbiome was not affected significantly by hibernation and was relatively stable from year to year. This study highlights the importance of long term, wide-scale microbiome studies for capturing accurate perspectives on microbiome diversity and composition in animals. It also serves as a warning for comparisons of microbiomes across species, as each may be under a different suite of selective pressures or exhibit short-term variation from external or innate factors, which may differ in a species-specific manner. 

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3. Microbiome metabolic capacity is buffered against phylotype losses by functional redundancy

   https://doi.org/10.1128/aem.02368-24  

   Cross, Kayla; Beckman, Noelle; Jahnes, Benjamin; Sabree, Zakee L (February 2025, Applied and Environmental Microbiology)

   Rudi, Knut (Ed.)

   ABSTRACT Many animals contain a species-rich and diverse gut microbiota that likely contributes to several host-supportive services that include diet processing and nutrient provisioning. Loss of microbiome taxa and their associated metabolic functions as result of perturbations may result in loss of microbiome-level services and reduction of metabolic capacity. If metabolic functions are shared by multiple taxa (i.e., functional redundancy), including deeply divergent lineages, then the impact of taxon/function losses may be dampened. We examined to what degree alterations in phylotype diversity impact microbiome-level metabolic capacity. Feeding two nutritionally imbalanced diets to omnivorousPeriplaneta americanaover 8 weeks reduced the diversity of their phylotype-rich gut microbiomes by ~25% based on 16S rRNA gene amplicon sequencing, yet PICRUSt2-inferred metabolic pathway richness was largely unaffected due to their being polyphyletic. We concluded that the nonlinearity between taxon and metabolic functional losses is due to microbiome members sharing many well-characterized metabolic functions, with lineages remaining after perturbation potentially being capable of preventing microbiome “service outages” due to functional redundancy. IMPORTANCEDiet can affect gut microbiome taxonomic composition and diversity, but its impacts on community-level functional capabilities are less clear. Host health and fitness are increasingly being linked to microbiome composition and further modeling of the relationship between microbiome taxonomic and metabolic functional capability is needed to inform these linkages. Invertebrate animal models like the omnivorous American cockroach are ideal for this inquiry because they are amenable to various diets and provide high replicates per treatment at low costs and thus enabling rigorous statistical analyses and hypothesis testing. Microbiome taxonomic composition is diet-labile and diversity was reduced after feeding on unbalanced diets (i.e., post-treatment), but the predicted functional capacities of the post-treatment microbiomes were less affected likely due to the resilience of several abundant taxa surviving the perturbation as well as many metabolic functions being shared by several taxa. These results suggest that both taxonomic and functional profiles should be considered when attempting to infer how perturbations are altering gut microbiome services and possible host outcomes. 

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4. Host phylogeny and functional traits differentiate gut microbiomes in a diverse natural community of small mammals

   https://doi.org/10.1111/mec.16874  

   Brown, Bianca R. P.; Goheen, Jacob R.; Newsome, Seth D.; Pringle, Robert M.; Palmer, Todd M.; Khasoha, Leo M.; Kartzinel, Tyler R. (February 2023, Molecular Ecology)

   Abstract Differences in the bacterial communities inhabiting mammalian gut microbiomes tend to reflect the phylogenetic relatedness of their hosts, a pattern dubbed phylosymbiosis. Although most research on this pattern has compared the gut microbiomes of host species across biomes, understanding the evolutionary and ecological processes that generate phylosymbiosis requires comparisons across phylogenetic scales and under similar ecological conditions. We analysed the gut microbiomes of 14 sympatric small mammal species in a semi‐arid African savanna, hypothesizing that there would be a strong phylosymbiotic pattern associated with differences in their body sizes and diets. Consistent with phylosymbiosis, microbiome dissimilarity increased with phylogenetic distance among hosts, ranging from congeneric sets of mice and hares that did not differ significantly in microbiome composition to species from different taxonomic orders that had almost no gut bacteria in common. While phylosymbiosis was detected among just the 11 species of rodents, it was substantially weaker at this scale than in comparisons involving all 14 species together. In contrast, microbiome diversity and composition were generally more strongly correlated with body size, dietary breadth, and dietary overlap in comparisons restricted to rodents than in those including all lineages. The starkest divides in microbiome composition thus reflected the broad evolutionary divergence of hosts, regardless of body size or diet, while subtler microbiome differences reflected variation in ecologically important traits of closely related hosts. Strong phylosymbiotic patterns arose deep in the phylogeny, and ecological filters that promote functional differentiation of cooccurring host species may disrupt or obscure this pattern near the tips. 

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5. Association between the gut microbiome and carotenoid plumage phenotype in an avian hybrid zone

   https://doi.org/10.1098/rspb.2024.0238  

   Baiz, Marcella D; Wood, Andrew W; Toews, David PL (April 2024, Proceedings of the Royal Society B: Biological Sciences)

   Vertebrates host complex microbiomes that impact their physiology. In many taxa, including colourful wood-warblers, gut microbiome similarity decreases with evolutionary distance. This may suggest that as host populations diverge, so do their microbiomes, because of either tight coevolutionary dynamics, or differential environmental influences, or both. Hybridization is common in wood-warblers, but the effects of evolutionary divergence on the microbiome during secondary contact are unclear. Here, we analyse gut microbiomes in two geographically disjunct hybrid zones between blue-winged warblers (Vermivora cyanoptera) and golden-winged warblers (Vermivora chrysoptera). We performed 16S faecal metabarcoding to identify species-specific bacteria and test the hypothesis that host admixture is associated with gut microbiome disruption. Species identity explained a small amount of variation between microbiomes in only one hybrid zone. Co-occurrence of species-specific bacteria was rare for admixed individuals, yet microbiome richness was similar among admixed and parental individuals. Unexpectedly, we found several bacteria that were more abundant among admixed individuals with a broader deposition of carotenoid-based plumage pigments. These bacteria are predicted to encode carotenoid biosynthesis genes, suggesting birds may take advantage of pigments produced by their gut microbiomes. Thus, host admixture may facilitate beneficial symbiotic interactions which contribute to plumage ornaments that function in sexual selection. 

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