Data: Consistent, not chaotic: Gut microbiota responses to winter warming in a temperate lizard

These data and codes are associated with a study examining the effects of winter warming on the gut microbiome of the common wall lizard (Podarcis muralis). This work was supported by the Natural Environment Research Council (NERC) Envision Doctoral Training Programme (project number: 2737291) and an Amphibian and Reptile Conservation Trust grant awarded to M.R. The corresponding raw sequence data is available at European Nucleotide Archive (project accession number: PRJEB108057). Any queries or questions, please direct them to miaryras [at] gmail.com or k.macleod [at] bangor.ac.uk. Content: Data, metadata, and R scripts used for the analysis of the gut microbiota alpha and beta diversity, differential taxon abundance, and microbiota dysbiosis in the common wall lizard (Podarcis muralis) under different winter warming regimes. Manuscript abstract: Environmental temperature shapes ectotherm gut microbiota through direct effects on community structure and indirect effects mediated by host physiology, with potential consequences for host health and performance. Due to climate change, winter temperatures are rising, in some regions faster than summer temperatures. However, warming effects on the microbiota during overwintering remain poorly understood compared to the active season, limiting predictions of host-microbiota responses across the annual cycle. We experimentally tested how winter warming influences gut microbiota diversity and community structure in the common wall lizard (Podarcis muralis). Thirty-nine lizards were overwintered under cold (4±1°C), mild (8±1°C), or fluctuating (5 days cold, 2 days mild) temperatures, and 80 faecal samples were collected post-emergence for 16S rRNA gene sequencing. Winter warming did not affect alpha diversity but resulted in differences in beta diversity and taxon abundance patterns relative to control lizards, with distinct responses under constant and fluctuating warming regimes. Constant mild temperatures enriched fewer taxa, including putatively opportunistic or pathogenic genera, whereas fluctuating warming and the cold control treatment enriched a broader suite of taxa associated with fermentative metabolism. Both warming treatments increased directional dysbiosis scores relative to cold reference treatment, but did not increase community dispersion or interindividual variability, providing no evidence for dysbiosis characterised by Anna Karenina-type destabilisation of the gut microbiota. Instead, winter warming was associated with consistent, treatment-specific restructuring of the gut microbiota. Our findings therefore highlight overwintering as an important, yet overlooked, period through which climate warming can alter host-microbiota dynamics.