Complete Mitogenome of Chimarrogale styani, Phylogenetic Placement Within Soricinae, and Exploratory Mitogenomic Comparisons

Background/Objectives: Semi-aquatic lifestyles may impose distinct energetic and physiological demands, but their association with mitochondrial genome evolution remains poorly understood in soricines. This study aimed to characterise the complete mitochondrial genome of the Chinese water shrew, Chimarrogale styani, clarify its mitochondrial phylogenetic placement within Soricinae, and evaluate whether mitochondrial genomic characteristics differ between semi-aquatic and terrestrial soricines after accounting for phylogenetic non-independence. Methods: An adult C. styani specimen collected from Hongpo Village, Deqin County, Yunnan Province, China, was used for mitochondrial genome sequencing. The complete mitogenome was assembled and annotated; Soricinae relationships were reconstructed using 13 protein-coding genes and two rRNA genes, and mitochondrial composition, codon usage, amino-acid properties, and Ka/Ks ratios were compared between selected semi-aquatic and terrestrial soricines. Phylogenetic generalized least-squares analyses were used to account for phylogenetic non-independence. Results: The C. styani mitogenome is 17,207 bp long and contains the typical vertebrate mitochondrial gene set. Phylogenetic analyses supported Soricinae monophyly and placed Chimarrogale as sister to Nectogale, with C. styani clustering with C. leander. Semi-aquatic taxa had higher AT content and T3s values, whereas terrestrial taxa showed stronger bias toward preferred synonymous codons. Semi-aquatic taxa also showed slightly higher average protein hydrophobicity. Most compositional and codon-usage differences remained significant after phylogenetic correction. Evolutionary-rate differences were gene-specific: COX1 and ND6 showed higher Ka/Ks ratios, whereas ND3 and ND4L showed lower ratios in semi-aquatic taxa; all mitochondrial protein-coding genes remained under purifying selection. Conclusions: These results provide a genomic resource for C. styani and support lifestyle-associated mitochondrial variation in soricines, while indicating heterogeneous gene-specific evolutionary responses. Broader taxon sampling, additional independent ecological transitions, and nuclear genomic data are needed to further evaluate the relationship between lifestyle and mitochondrial genome evolution.