plasticity of gut microbiome under cold stress
The 'phenotypic plasticity hypothesis' believes that animals can adjust their own phenotypes when facing environmental pressure. Cold is a vital factor affecting the discrepancy of phenotypic plasticity between poikilotherm and homeotherm. Gut microbiota, as a microscopic phenotype, plays a crucial role in food metabolism and energy supply in response to cold, but the disparity of cold on gut microbiota in homeotherm and poikilotherm remains unsettled. Here, we used 16S rRNA gene sequencing and high-throughput quantitative PCR to explore the gut microbial plasticity in homeothermic (pika) and poikilothermic (fish) animals under cold stress. We found that cold caused 39.05% of the gut species variations in poikilotherm  intestines, but only 5.06% variations in homeotherm. The diversity of gut microbiota decreased significantly in poikilotherm but not in homeotherm under cold stress. Function prediction showed that cold immensely increased functional similarity and enriched metabolic functional pathways (such as lipid metabolism) in poikilotherm, while the functional pathways of homeotherm were relatively stable. Null model showed that cold had no distinct effect on the community assembly processes of the homeotherm, but caused poikilotherm gut community to shift from stochastic processes to deterministic processes. Similarly, cold significantly declined gut ARGs diversity in poikilotherm rather than homeotherm. These results reveal the gut microbiomes of poikilotherm exhibit greater plasticity than those of homeotherm under cold stress, and predict that frequent extreme weather probably causes more adverse consequences to gut microbiomes of poikilotherm than for homeotherm.