The complete mitochondrial genome of Sorex minutissimus (Eulipotyphla: Soricidae).

In this study, the complete mitochondrial genome of Sorex minutissimus was sequenced and deposited to GeneBank for the first time using muscle tissue. This mitochondrial genome is a circular molecule of 16,700 bp in length and sequence analysis showed it contains 2 rRNA genes, 22 tRNA genes, 13 protein-coding genes, rep_origin, and D_loop. Phylogenetic analysis on the basis of 12 protein-coding genes except ND6 of 13 Soricidae species' mitochondrial genomes using ML and BI demonstrated that S. minutissimus and other Sorex species were clustered into same clade.

The Sorex minutissimus is classified under order Eulipotyphla, family Soricidae and genus Sorex. It has a large range and habitats include forest-tundra zone, mixed forests, and forest-steppe and it feeds on small insects, spiders, grubs, and snails (Macdonald and Barrett 1993). In this study, the tissue sample of S. minutissimus was caught by pitfall traps through field survey and stored at biological specimens of Hulun Lake National Nature Reserve, Inner Mongolia, China, and the geo-spatial coordinates are 48°22′35″N latitude and 117°31′50″E longitude. All sampling procedures and experimental manipulations had the proper permits. After manually annotating, the mitochondrial genome was deposited in GeneBank with the accession number MK641805.

The complete mitochondrial genome of Sorex minutissimus is a double-circular DNA of 16,700 bp in length and contains 13 protein-coding genes, 22 tRNA genes, 16S rRNA, 12S rRNA, rep_origin, and D_loop. Among these genes, ND6 and 8 tRNA (tRNA, tRNA, tRNA, tRNA, tRNA, tRNA, tRNA, and tRNA) genes were encoded in L-strand and other genes were encoded in H-strand. The base composition is 33.0% for A, 28.9% for T, 13.3% for G, 24.8% for C and the percentage of A and T (61.9%) is higher than G and C (38.1%). This genes arrangement is similar to other species, such as Sorex araneus (Huang et al. 2016), Sorex tundrensis (Xu et al. 2015) and Ochotona dauurica (Yang et al. 2019).

Phylogenetic analysis of 9 Sorex species, 2 Episoriculus species, and 2 Blarinella species were analyzed using the maximum-likelihood (ML) and the Bayesian inference (BI) methods based on the 12 protein-coding genes except ND6 with Microtus arvalis (NC_038176) used as an outgroup. Using MrModeltest 3.7 (Nylander 2004), GTR + I + G was selected as the best-fitting nucleotide substitution mode according to the AIC criterion. These parameters were used in BI and the ML analysis by MrBayes 3.2.2 (Ronquist and Huelsenbeck 2003) with a bootstrap test of 100 replicates and PAUP 4.0b10 (Swofford 2002) was run for 1,000,000 cycles, respectively.

Phylogenetic analysis shows that the different tree-building methods (ML and BI) have the same topology (Figure 1), and three major phyletic lineages were present in Sorex. The S. minutissimus was close to S. sinalis, S. caecutiens, S. isodon, and S. gracillimus, and had the greatest difference with S. cylindricauda. Compared with Episoriculus, the Sorex was close to Blarinella in the family of Soricidae, which was also supported by several previous studies (Jin et al. 2017). We expect the data of the present study to be useful for further research and for phylogenetic relationships of Sorex.

Figure 1.

Phylogenetic tree of 13 species was obtained from maximum-likelihood (ML) and Bayesian phylogenetic inference (BI) methods, based on 12 protein-coding genes except ND6 and the BI posterior probabilities are shown on the nodes. The species accession numbers were downloaded from GenBank and are as follows: E. caudatus (NC_026131), E. macrurus (NC_029840), S. tundrensis (NC_025327), S. araneus (NC_027963), S. roboratus (NC_034808), S. sinalis (NC_037174), S. caecutiens (MF374796), S. isodon (NC_037894), S. gracillimus (NC_037859), S. cylindricauda (KT023074), B. quadraticauda (NC_023950), B. wardi (MF125692) and M. arvalis.