Effects of Extreme Temperature Stress on the Gut Microbiota of Light-Vented Bulbul (Pycnonotus sinensis)

Temperature variation is a key environmental factor affecting the physiology and ecology of wild birds; however, experimental evidence for how sustained temperature exposure shapes the gut microbiota of wild passerines remains limited. In this study, 18 adult light-vented bulbuls (Pycnonotus sinensis) were randomly assigned to low temperature (LT, 0 °C), room temperature (RT, 24 °C), or high temperature (HT, 40 °C) groups for 60 days. Fecal microbiota were profiled by 16S rRNA gene amplicon sequencing of the V3–V4 region. After quality filtering and removal of non-bacterial sequences, 1490 amplicon sequence variants (ASVs) were retained. Firmicutes and Proteobacteria dominated all samples, together accounting for more than 90% of the relative abundance, with no significant differences among groups. At the genus level, Candidatus Arthromitus was most abundant in all groups and peaked in the LT group (75.39%), whereas Ligilactobacillus was significantly enriched in the HT group relative to the RT group (19.68%, adjusted p = 0.028). Alpha diversity analyses showed that observed ASVs and Faith’s phylogenetic diversity were significantly higher in the LT group than in the RT and HT groups, whereas Shannon, Simpson, and Pielou evenness did not differ significantly among groups. Beta diversity based on Aitchison distances revealed a significant shift in community structure among treatments (PERMANOVA, R2 = 0.326, p = 0.014), with no significant difference in within-group dispersion (PERMDISP, p = 0.559). LEfSe identified 25 differentially abundant genera, 16 of which were enriched in the LT group, while PICRUSt2-based functional prediction detected no significant differences in KEGG pathways after FDR correction. These results indicate that sustained temperature exposure, particularly low temperature, reshapes the gut microbiota of light-vented bulbuls primarily at the genus level and increases richness and phylogenetic diversity, whereas predicted functional profiles remain similar among treatments.