Composition and stability of the gut microbiome are associated with thermal tolerance and its plasticity in <i>Anolis</i> lizards

Ectotherms are thought to be particularly vulnerable to climate change as they rely directly on environmental temperatures to regulate their physiology. One of the pathways by which ectotherms can alter their physiology in a warming environment is through phenotypic plasticity, which is usually treated as resulting from interactions between the organism's genetics and the environment. However, ectotherms also host communities of microbes which can change quickly within the host and affect host physiology. To date, little is known about the extent to which gut microbes affect thermal plasticity in the non-model host organisms that will be the most affected by climate change. We investigated relationships between gut microbiome composition and host heat tolerance plasticity in three species of Anolis lizards: Anolis cristatellus, Anolis sagrei and Anolis carolinensis. We brought wild-caught lizards into the lab and tested for (1) effects of experimental warming on the gut microbiomes and (2) associations between microbiome composition and compositional dynamics with heat tolerance and its plasticity across host individuals and species. We found that each anole species hosted a distinct gut microbial community, but that all host species had microbiomes that were largely resilient to temperature increases. However, several key aspects of microbiome composition were correlated with baseline host heat tolerance. Finally, microbiome composition and its stability were associated with the magnitude of plasticity in host heat tolerance. Our results indicate that gut microbes may play a role in the ability of ectotherms to mount plastic responses to rapidly changing thermal environments.