Maternal body condition affects the response of larval spined toads’ faecal microbiome to a widespread contaminant

Glyphosate’s primary metabolite, aminomethylphosphonic acid (AMPA), is the most detected pollutant in surface waters. Recent studies have raised concerns about its toxicity, yet underlying mechanisms remain poorly understood. A disruption of the gut microbiome, which plays a crucial role in host health, could mediate most of the adverse effects. We investigated the impact of AMPA exposure on the gut microbiome of spined toad tadpoles ( Bufo spinosus ). We hypothesized that AMPA could alter the gut microbiota composition and that these effects could depend on the microbiota source. We exposed tadpoles to minute concentrations of AMPA and analyzed their faecal microbiota using 16S rRNA gene sequencing as a proxy of the gut microbiota. AMPA exposure decreased the gut bacterial biomass and affected the bacterial community composition of tadpole’s faeces. Furthermore, we observed interactions between AMPA exposure and maternal body condition on the Bacteroidota and Actinobacteriota phyla abundances. This suggests a maternal effect on early-life microbial colonizers that could influence the response of the gut microbiome to AMPA. These findings highlight the importance of considering the gut microbiome when studying the effects of environmental contaminants. Further research is needed to elucidate the long-term implications of this microbiome alteration for amphibian health. ### Competing Interest Statement The authors have declared no competing interest.