The genus Chimarrogale is an ideal group to study the evolutionary mechanisms of semi-aquatic adaptation, but there is a lack of data on its mitochondrial genome, and the molecular mechanisms. Using Illumina high-throughput sequencing, this study addressed this gap, reporting assembled mitogenomes of C. himalayica and C. styani (newly characterized) alongside C. leander, covering all Chinese Chimarrogale species. Results showed that the three mitochondrial genomes were all closed circular double stranded structure, with full length of 17,202-18,567bp, including 37 typical genes, including 13 protein-coding genes (PCGs), 22 tRNAs, 2 rRNAs and D-loop region. There were 9 overlapping regions and 14 intergenic spacer regions identified, showing obvious at AT bias (64.68% -65.07%). Relative synonymous codon usage analysis (RSCU) showed that Serine (Ser) was used most frequently. Selection pressure analysis showed that the Ka/Ks ratios of PCGs in 44 Soricidae mitogenomes were less than 1, which were generally subject to purification selection. Among them, the evolution rate of ATP8 gene was the fastest. In the selection pressure analysis of 5 semi-aquatic adaptive Soricidae species in China, the ATP8 evolution rate of Nectogale elegans was significantly higher than that of the three Chimarrogale species, which may be related to its characteristics with the highest degree of aquatic adaptation among semi-aquatic shrews (such as its specialized webbed feet). The phylogenetic analysis using Maximum Likelihood (ML) and Bayesian Inference (BI) methods showed that the three Chimarrogale species clustered into a monophyletic clade, which formed a sister group with N. elegans, whereas the Neomys fodiens was identified as the basal taxon within the semi-aquatic group. This study filled the gap of mitochondrial genome data of semi-aquatic shrew and provided key genetic data for exploring the molecular mechanism of semi-aquatic adaptability and phylogenetic relationship of shrews.

The gut microbiomes of the host are large and complex communities, which helps to maintain homeostasis, improves digestive efficiency, and promotes the development of the immune system. The small mammals distributed in Sichuan Province are the most popular species for biodiversity research in Southwest China. However, the effects of different diets on the structure and function of the gut microbial community of these small mammals are poorly understood. In this study, whole-metagenome shotgun sequencing has been used to analyze the composition and functional structures of the gut microbiota of seven small mammals in Laojunshan National Nature Reserve, Sichuan Province, China. Taxonomic classification revealed that the most abundant phyla in the gut of seven small mammals were Bacteroides, Proteobacteria and Firmicutes. Moreover, Hafnia, Raoultella and Aeromonas were most abundant genus in the gut microbiomes of these seven species. At the functional level, we annotated a series of KEGG functional pathways, six Cazy categories and 46,163 AROs in the gut microbiomes of the seven species. Comparative analysis found that the difference in the gut microbiomes between the Soricidea and Muridae concentrated on the increase in the F/B (Firmicutes/Bacteroides) ratio in the Soricidea group, probably driven by the high fat and calorie digestive requirements due to their insectivorous diet. The comparative functional profiling revealed that functions related to metabolism and carbohydrates were significantly more abundant in Muridae group, which may be attributed to their high carbohydrate digestion requirements caused by their herbivorous diet. These data suggested that different diets in the host may play an important role in shaping the gut microbiota, and lay the foundation for teasing apart the influences of heritable and environmental factors on the evolution of gut microbial communities.