Interspecific faecal microbiota transplantation tests microbial contributions to thermal physiology in lizards

While the influence of microorganisms in the thermal physiology of animals is increasingly recognised, the role of the gut microbiome in enhancing phenotypic plasticity remains underexplored, particularly in ectotherms. Here, we tested the effect of gut microbiomes in modulating the physiological response of lizards to sudden temperature fluctuations. In captivity, we conducted an experiment with wild-caught Podarcis lizards: Mediterranean Podarcis liolepis (n=9) adapted to warm and dry environments, and Atlantic P. muralis (n=18) adapted to cooler and wetter conditions. Animals were assigned to three groups (intervention, control-cold and control-warm) and subjected to microbiota manipulations using antibiotics and faecal microbiota transplants (FMT). In the intervention group, cold-adapted P. muralis received faecal suspension from warm-adapted P. liolepis, while control-cold and control-warm groups received intraspecific transplants. Microbiome variation was analysed through genome-resolved metagenomics of 162 faecal samples, yielding 313 MAGs across 15 phyla, containing almost 1M annotated genes. One week after transplantation, microbiomes of control animals differed from their original state, whereas those of the intervention group (P. muralis), transitioned to a state resembling P. liolepis. After two weeks, both control groups showed trends of reversing their microbiomes to their original states. However, the intervention group displayed a distinct trajectory, resembling the microbial donors'. Although potentially relevant trends were observed, these microbiome alterations did not translate into detectable significant differences in their thermal physiology. Nevertheless, our results provide proof of concept for microbial transplants in lizards, and opportunities to further explore the link between gut microbes and host physiological responses in ectotherms.