Links Between Environmental Quality, Gut Microbiota, and Host Performance in Nutrient-Impacted Springs.

In least killifish (Heterandria formosa) from Florida springs, females grew more slowly and males showed higher mass-specific metabolic rates in the most nutrient-loaded water.

• Why it matters: Nutrient-enriched freshwater habitats may rely on host–microbe interactions for stress adaptation, but how water chemistry and gut microbiota jointly affect performance is unclear.
• What they did: A full-factorial lab experiment manipulated water chemistry from four Florida springs and inoculated fish with gut microbiota from conspecifics at those sites, then used 16S rRNA sequencing to compare gut and ambient communities.
• The result: Gut richness was higher in less nutrient-loaded waters, gut composition differed from ambient water with enrichment of Pseudomonadota and Planctomycetota, and reproductive output per female nearly doubled when microbiota and water matched by site.

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