Altitude shapes gut microbiome composition accounting for diet, thyroid hormone levels, and host genetics in a subterranean blind mole rat
The animal gut microbiome acts as a crucial link between the host and its environment, playing a vital role in diet consumption, metabolism, physiology, and fitness. Using 16S rRNA metabarcoding, we investigated the effect of altitude on the microbiome composition of Anatolian Blind Mole Rats (ABMR, Nannospalax xanthodon) across six locations and three altitudinal groups in the Central Taurus Mountains. To explore the other potentially important aspects that vary with the altitude, we also factored in the host diet resolved on the basis of 18S rRNA metabarcodes, as well as host microsatellite genotypes and thyroid hormone levels. The altitude had a major effect on microbiome composition, with notable differences in the relative abundance of several bacterial taxa across elevations. In contrast to prior research, no substantial difference was observed in the abundance of strictly anaerobic bacteria among altitudinal groups, while the facultatively anaerobic bacteria were still more prevalent in high-altitude animals. Interestingly, the previously reported altitude-linked bacterial genus Prevotella was absent in our dataset. Microbiome alpha diversity reached its maximum in the middle altitude group, which was composed predominantly of the elements found at either low or high elevations. The beta diversity showed significant association with the altitude, and large differences were observed between the two high-altitude locations. Altitude had a significant effect on the diet composition but not on its alpha diversity, likely reflecting the variation in local plant communities. No distinct altitude-related genetic structure was evident among the host populations, and no correlation was revealed between the host genetic relatedness and microbiome composition nor between the host microbiome and the diet. Free thyroxine (FT4) levels increased almost linearly with the altitude but none of the bacterial ASVs were found to be specifically associated with hormone levels. Total thyroxine (TT4) levels correlated positively with microbiome diversity, while FT4/TT4 levels showed the opposite pattern. Although we detected correlation between certain components of the thyroid hormone levels and the microbiome beta diversity, the pattern of their relationship remains inconclusive.