Blarinella, Thomas, 1911, Thomas, 1911

Chen, Shunde, Liu, Shaoying, Liu, Yang, He, Kai, Chen, Weicai, Zhang, Xiuyue, Fan, Zhenxin, Tu, Feiyun, Jia, Xiaodong & Yue, Bisong, 2012, Molecular phylogeny of Asiatic Short-Tailed Shrews, genus Blarinella Thomas, 1911 (Mammalia: Soricomorpha: Soricidae) and its taxonomic implications, Zootaxa 3250 (1), pp. 43-53 : 50-51

Relationships of

B. griselda and B. quadraticauda . In the present study, B. griselda was paraphyletic with respect to B. quadraticauda . The average cyt -b genetic distance between samples of B. griselda and B. quadraticauda was 4.23%, which is similar to the intraspecific genetic distance found in the genera Blarina (4.3%; Brant & Orti 2002) and Sorex (5.21 ± 0.75%; Fumagalli et al. 1999). For the ApoB gene, there were two shared allele types and little sequence difference between the two species. These results indicate a close phylogenetic relationship between the two species.

Given the lack of reciprocal monophyly, one possibility is that the two species are synonymous and B. quadraticauda might be a geographic subspecies of B. griselda . B. quadraticauda differs from B. griselda in its generally larger size and in its proportionately and absolutely longer tail ( Jiang et al. 2003). No qualitative character, however, can be found to distinguish the two species, and the karyotype of B. quadraticauda is still unknown. Size alone might not be a good indicator for species delimitation of small mammals because it may be phenotypically plastic and influenced by the individual rearing environment ( Rhymer 2004; Maldonado 2004; Frafjord 2007). Intraspecific size variation, for instances, was found in other shrew species, such as Sorex araneus (see Frafjord 2007) and Sorex ornatus (see Maldonado 2004); thus the larger size of B. quadraticauda could be due to yearly, seasonal, local, regional or microhabitat variation, or phenotypic drift. Comprehensive morphological analyses are still required to assess the pattern of morphological variation found in this complex.

Jiang et al. (2003) indicated that B. griselda had a partially sympatric distribution with B. quadraticauda . However, in this study, no sympatric distribution was observed between the two species in the 17 sampling localities. There was no shared haplotype between B. griselda and B. quadraticauda in the cyt -b network. Sharing of the predominant allele type, A1, in ApoB could be explained by the slower evolutionary rate of the nuclear gene than the mitochondrial gene rather than hybridization ( Brown et al. 1979).

Another possible explanation for the phylogenetic pattern is incomplete lineage sorting, which also leads to lack of reciprocal monophyly between species (Pamilo & Nei 1988). In this case, B. quadraticauda may be under a "budding" speciation scenario ( Funk & Omland 2003): the budding species is a spatially restricted and isolated population, and its shared alleles will be lost at a faster rate than the parental species; the budding species’ monophyletic set is expected to be embedded within the paraphyletic parental species (see Figure 1k in Funk & Omland 2003). In this study, B. quadraticauda is embedded within the widely distributed B. griselda , and it is a monophyletic group in the phylogenetic trees and an haplogroup in the network. Thus, B. quadraticauda may be a descendent species of the paraphyletic B. griselda .

Further studies about the chromosomes of B. quadraticauda and phylogenetic analysies of multiple unlinked genes and extensive samples from the Southwest of China would be beneficial to clarify the classification and relationships of the B. griselda and B. quadraticauda complex.

Phylogeographic patterns of B. griselda and B. quadraticauda . In this study, all mitochondrial haplotypes of the Blarinella species were restricted to limited geographical regions ( Figure 1 , Table 1). This significant phylogeographic pattern might be due to their middle-high elevation distribution and the complicated topography in Southwest China. Mountains in this region have dramatic variations in topography and are isolated by five major rivers, which run parallel to one another in a North-South direction ( Chen et al. 2010). Mountain ridges and river valleys may act as geographical barriers, resulting in genetic isolation ( Fu & Zeng 2008).

As with other small mammals inhabiting the middle-high altitude in this region ( Chen et al. 2011), dispersal of Blarinella species can be limited by this complex topography. B. quadraticauda is locally distributed in the Qionglai Mountains, which are surrounded by two major river systems, the Dadu River and the Min River. Thus, we can expect that the two river systems, functioning as geographical barriers, may have created a vicariance event between B. quadraticauda and B. griselda . The lack of reciprocal monophyly between the two putative species could be attributed to a recent timing. Additional samples and study in the regional distribution of genetic diversity are needed to test these hypotheses.

Figures

FIGURE 1. Map of China showing collecting localities of all individuals used in this study. The sampling localities and site number correspond to sample codes described in Table 1.