From Genes to Greens: How Diet, Climate and Phylogeny Shape Freshwater Turtle Microbiotas.

Reptile microbiotas remain poorly understood despite their importance for host ecology and evolution. This study investigated how diet, climate and evolutionary history shape the gut microbiota of 234 Australian freshwater turtles spanning 10 species, four climatic zones and contrasting trophic strategies. It was found that turtles' microbiotas were dominated by Pseudomonadota, Actinobacteriota and Bacteroidota. Microbial richness and evenness varied significantly among species, diets and climates. Carnivorous turtles exhibited greater bacterial diversity than omnivores, while individuals from oceanic and humid subtropical zones had higher diversity than those from semi-arid and Mediterranean regions. Canonical Correspondence Analysis confirmed diet and climate as significant predictors of community composition, together explaining 2.76% of total variation. Omnivorous turtles were enriched in Bacteroidota, Myxococcota, Cyanobacteriota and Bacillota, whereas climatic effects drove distinct phylum-level signatures across habitats. Host phylogeny showed a weak but significant signal of phylosymbiosis, indicating an evolutionary imprint on microbial structure. Collectively, these findings reveal that turtle microbiotas are shaped by a complex interplay between ecological and evolutionary forces, underscoring the importance of integrating microbial data into conservation strategies for Australia's increasingly threatened freshwater turtles.