Longitudinal Gut Microbiota Assembly in Mothers and Children: Diversity Dynamics, Taxon-Richness Scaling, and Ecological Maturation Drivers

This project executed a longitudinal biostatistical evaluation of human gut microbiota development, contrasting the ecological assembly of infant and early childhood gut communities against the mature, resilient microbial ecosystems of mothers across $>1,200$ distinct bacterial taxa derived from 16S rRNA gene sequencing ($N = 1,124$ total profiles; $n = 757$ child, $n = 367$ mother). The primary analytical objectives were twofold: first, to map the temporal trajectories of microbial richness ($S$) and Shannon diversity ($H'$) across key developmental timepoints (10 days, 3 months, 1 year, 2 years, and maternal pregnancy); and second, to interrogate whether ecological richness scaling is driven by specific taxonomic expansions—specifically the short-chain fatty acid (SCFA)-producing family Lachnospiraceae—or governed by macro-ecological constraints like total microbial load.Data preprocessing and quality control protocols involved standardizing taxonomic nomenclature, converting zero-counts, log-transforming raw abundances, and performing sample-wise centering to stabilize high right-skewness and total count variance. Four complementary alpha diversity metrics were engineered: Species Richness, Total Abundance (microbial load), Shannon Index, and Pielou's Evenness ($J'$). Taxa belonging to Lachnospiraceae were aggregated into a unified family-level abundance metric to isolate its functional contribution to overall community complexity.Longitudinal diversity tracking revealed starkly contrasting ecological trajectories between cohorts. Infants initiated life with extremely simple, low-diversity pioneer communities at 10 days (mean richness $= 22.38 \pm 9.34$), followed by a progressive, non-linear expansion in taxonomic complexity through 1 year ($58.64 \pm 15.90$) and 2 years ($87.64 \pm 21.46$). A transient dip in diversity observed at 3 months ($79.71 \pm 59.07$) captured a critical window of early-life ecological turnover, likely reflecting dietary transitions, immune priming, or pioneer species replacement. Conversely, maternal gut communities exhibited persistent homeostatic stability, maintaining elevated richness ($129.87 \pm 37.43$ during pregnancy) and steady Shannon diversity across all sampling periods, illustrating a fully saturated and resilient climax ecosystem.To determine the ecological forces governing community assembly, non-parametric Spearman rank correlations and multivariable linear interaction models were deployed. The expansion of Lachnospiraceae was strongly correlated with overall community richness across the full dataset ($r = 0.732$), but group-stratified analyses demonstrated that this relationship was uniquely driven by the child cohort ($r = 0.776$ in children vs. $r = 0.188$ in mothers). A formal interaction model (Lachnospiraceae $\times$ Host Group) yielded a statistically significant interaction term ($p < 0.05$), confirming that Lachnospiraceae proliferation acts as an age-specific biological hallmark of microbiome maturation during early childhood. Conversely, total microbial load shared an inverse relationship with richness in both children ($r = -0.476$) and mothers ($r = -0.237$). The total abundance $\times$ host group interaction was not statistically significant, demonstrating that high-load single-taxon dominance constraints operate as a universal, age-invariant ecological mechanism that suppresses species evenness across all life stages.Model diagnostics—including residual Q-Q plots, fitted-versus-residual checks, and Shapiro-Wilk testing—highlighted expected non-normality and heteroscedasticity inherent to sparse microbiome count data. To account for repeated measures, within-subject temporal dependencies, and sample size imbalances across timepoints, linear mixed-effects models (lme4/lmerTest in R) with random intercepts per participant were implemented, validating the non-parametric findings and ensuring rigorous statistical inference.