Molecular phylogeny and evolution of Sorex shrews (Soricidae: insectivora) inferred from mitochondrial DNA sequence data

Shrews of the genus Sorex are characterized by a Holarctic distribution, and relationships among extant taxa have never been fully resolved. Phylogenies have been proposed based on morphological, karyological, and biochemical comparisons, but these analyses often produced controversial and contradictory results. Phylogenetic analyses of partial mitochondrial cytochrome b gene sequences (1011 bp) were used to examine the relationships among 27 Sorex species. The molecular data suggest that Sorex comprises two major monophyletic lineages, one restricted mostly to the New World and one with a primarily Palearctic distribution. Furthermore, several sister-species relationships are revealed by the analysis. Based on the split between the Soricinae and Crocidurinae subfamilies, we used a 95% confidence interval for both the calibration of a molecular clock and the subsequent calculation of major diversification events within the genus Sorex. Our analysis does not support an unambiguous acceleration of the molecular clock in shrews, the estimated rate being similar to other estimates of mammalian mitochondrial clocks. In addition, the data presented here indicate that estimates from the fossil record greatly underestimate divergence dates among Sorex taxa.

The chromosome complement of Sorex granarius--the ancestral karyotype of the common shrew (Sorex araneus)?

We present the G-band karyotype of Sorex granarius (Miller, 1910). With minor exceptions, each of the acrocentric autosomes in this karyotype is completely homologous to one of the chromosome arms in the karyotype of the common shrew (Sorex araneus L., 1758). If, as is the simplest interpretation, the karyotypic evolution in S. araneus is by repeated Robertsonian fusion, the karyotype in S. granarius represents the ancestral condition. We urge breeding studies to establish whether the designation of S. granarius as a full species is justified.