Abstract
Bacterial species within the mammalian gut microbiota exhibit considerable strain diversity associated with both geography and host genetic ancestry. However, because geography and ancestry are typically confounded, disentangling their contributions to the divergence of gut bacterial strains has remained challenging. Here we show that isolation by distance (IBD) promotes gut bacterial strain divergence within host species independently of host ancestry. Joint profiling of gut bacterial and mitochondrial genomes from wild-living populations of deer mice (Peromyscus maniculatus) sampled across the USA revealed significant IBD in 27 predominant gut bacterial species, including Muribaculaceae and Lachnospiraceae spp., but limited evidence for co-inheritance of gut bacterial genomes with mitochondria during the diversification of mouse populations. Spore-forming gut bacterial species exhibited reduced IBD, suggesting that adaptations facilitating bacterial dispersal can lessen geographic structuring of strain diversity. In contrast to conspecific hosts sampled at the same field site, hosts of different rodent genera sampled in sympatry with deer mice harboured divergent strains within shared gut bacterial species. These results indicate that geographic distance mediates the early stages of gut bacterial strain divergence between conspecific hosts, whereas effects of host ancestry on strain-level microbiota composition emerge over longer evolutionary timescales, such as those separating host genera.
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Data availability
All sequence data generated in this article has been deposited in the National Center for Biotechnology Information Sequence Read Archive under the BioProject accession PRJNA1306187. All bacterial MAGs generated in this study are available via Dryad at https://doi.org/10.5061/dryad.95x69p8z4 (ref. 63).
Code availability
The code used to set up and run the SGB diversification analyses is available via Zenodo at https://doi.org/10.5281/zenodo.19262353 (ref. 64).
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Acknowledgements
We thank W. Yan for assistance with DNA extractions from rodent faecal samples. The National Ecological Observatory Network is a programme sponsored by the US National Science Foundation and operated under cooperative agreement by Battelle. This material uses specimens and/or samples collected as part of the NEON Program and provided by the NEON Biorepository at Arizona State University. Funding was provided by the National Institutes of Health grants R35 GM138284 and R01 DK139214 to A.H.M.
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B.A.D designed the study, performed analyses and wrote and edited the paper. J.G.S designed the study and edited the paper. A.P.H and K.M.Y facilitated sample selection and provisioning and edited the paper. A.H.M supervised the project, designed the study, and wrote and edited the paper.
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Extended data
Extended Data Fig. 1 Consistent evidence for IBD in deer mice across field sites.
Scatter plots show IBD of deer mouse MT lineages across field sites. MT genetic distances and geographic distances are shown on the y- and x-axes, respectively. Each facet corresponds to a focal field site for which comparisons including that field site are shown. Points represent pairs of deer mice, with color denoting the non-focal field site. In each facet, trendline indicates best-fit linear regression and shading around trendline denotes standard error centered around the mean value predicted by regression. Asterisks indicate Mantel test FDR-corrected two-sided p-values; * < 0.05, ** < 0.01, *** < 0.001. All individual p-values are provided in Supplementary Table 2.
Extended Data Fig. 2 Minimal evidence for IBL on strain divergence within individual gut bacterial species.
Scatterplots and trendlines show lack of relationships between SGB conANI distances (residualized against geographic distances) and host MT distances for individual SGBs derived from deer mouse hosts. SGB ANI distances were residualized against the residuals from a GLS model with the formula: SGB ANI distance ~ geographic distance. Each facet represents an SGB. Colors denote the phylum to which each SGB belongs, as indicated by the key. Shading around each trendline shows standard error from the best-fit linear model. Standard error is centered around the mean value predicted by regression. No SGBs reached significance at the MRM FDR-corrected two-sided p-values < 0.05 threshold for either Pearson or Spearman based tests. All individual p-values are provided in Supplementary Table 4.
Extended Data Fig. 3 No difference in PTR ratio between SGBs showing or not showing significant evidence of IBD within deer mice.
Box plots the peak-to-trough ratios of SGBs (n = 248) either showing or not showing significant evidence of IBD within deer mice based on both Pearson and Spearman methods. Each boxplot shows minimum and maximum (whiskers), inner quartile range (lower and upper sides of box), and median (center line). Results of permutation t-test are shown; n.s. two-sided p-value > 0.05 (p-value = 0.4262).
Extended Data Fig. 4 Aggregating gut bacterial strain comparisons across SGBs indicates widespread IBD and relatively weaker IBL.
a) Scatter plot shows the relationship between strain genetic distance within SGBs (1 – conANI) and geographic distance (x-axis), after accounting for the effects of host MT genetic distance. Y-axis shows SGB genetic distance residualized against host MT genetic distances. b) Scatter plot shows the relationship between genetic distance similarity within SGBs (1 – conANI) and host MT genetic distance (x-axis), after accounting for the effects of geographic distance. Y-axis shows genetic distance (1 – conANI) residualized against geographic distances. In (A) and (B), trendlines and shading indicate best-fit linear regressions with standard errors. Asterisks indicate linear regression p-value; *** < 0.001 (p-value < 2.2e-16 in both A and B). Within each panel (a or b), p-values were derived from a single test and uncorrected.
Extended Data Fig. 5 Synteny scores indicate widespread IBD and relatively weaker IBL.
a) Scatter plot shows the relationship between strain average pairwise synteny score (APSS) distance (1-APSS) within SGBs and geographic distance (x-axis), after accounting for the effects of host MT genetic distance. Y-axis shows APSS distance residualized against host MT genetic distances. b) Scatter plot shows the relationship between strain APSS distance within SGBs and host MT genetic distance (x-axis), after accounting for the effects of geographic distance. Y-axis shows APSS distance within SGBs residualized against geographic distances. In (A) and (B), trendlines and shading indicate best-fit linear regressions with standard errors. Asterisks indicate regression p-value; *** < 0.001 (p-value < 2.2e-16 in A and p-value = 0.08148 in B). Within each panel (a or b), p-values were derived from a single test and uncorrected.
Extended Data Fig. 6 Traitar analyses confirm negative relationship between sporulation ability and strength of IBD.
Volcano plot shows the significance (y-axis, uncorrected p-values) of association between the presence of bacterial traits (points) and the strength of IBD (x-axis). The strength of IBD was measured as the MRM Pearson correlation coefficient describing the relationship between geographic distance and strain genomic divergence between mice within SGBs residualized against host MT genetic distances.
Supplementary information
Supplementary Tables 1–6. (download XLSX )
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Dillard, B.A., Sanders, J.G., Husain, A.P. et al. Isolation by distance promotes gut microbial strain divergence in wild mouse populations. Nat Ecol Evol (2026). https://doi.org/10.1038/s41559-026-03073-7
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DOI: https://doi.org/10.1038/s41559-026-03073-7


