Effects of spatially heterogeneous warming on gut microbiota, nutrition and gene flow of a heat-sensitive ungulate population.

Effects of climate warming on trophic cascades are increasingly reported for large herbivores occupying northern latitudes. During the last 40 years, moose (Alces alces) in northeast China have lost nearly half of their historical distribution through their habitat shifting northwards. There are many possible causes of bottom-up and top-down effects of temperature and for moose in northeast China they are poorly understood. Of particular relevance are the effects of extrinsic environmental factors on gene flow, nutritional adaptions, and gut microbiota that occur as moose populations retreat northwards. We combined molecular biology, nutritional ecology and metagenomics to gain deeper mechanistic insights into the effects of temperature on moose populations. In this study, we revealed that the direction and intensity of gene flow is consistent with global warming driving retreats of moose populations. We interpret this as evidence for the northward movement of moose populations, with cooler northern populations receiving more immigrants and warmer southern populations supplying emigrants. Comparison across latitudes showed that warmer late spring temperatures were associated with plant community composition and facilitated related changes in moose protein and carbohydrate intake through altering forage availability, forage quality and diet composition. Furthermore, these nutrient shifts were accompanied by changes in gut microbial composition and functional pathways related to nutrient metabolism. This study provided insights into mechanisms driving effects of spatial heterogeneous warming on genetic, nutritional and physiological adaptions related to key demographic rates and patterns of survival of heat-sensitive ungulates along a latitude gradient. Understanding such changes helps to identify key habitat areas and plant species to ensure accurate assessment of population status and targeted management of moose populations.