Phylogenetic relationship betweenCallosciurus canicepsandC. inornatus(Rodentia, Sciuridae): Implications for zoogeographical isolation by the Mekong River

Abstract

To test the riverine barrier hypothesis in small arboreal mammals, we examined phylogenetic relationship between two Callosciurus squirrel species (C. caniceps and C. inornatus) geographically isolated in the northeastern part of the Indochina Peninsula by the Mekong River. We did this by comparing complete mitochondrial DNA cytochrome b gene sequences of these two squirrels and five other Callosciurus species: C. erythraeus, C. finlaysonii, C. nigrovittatus, C. notatus, and C. prevostii. Phylogenetic trees showed that there are three major lineages: (1) a lineage containing C. caniceps, C. erythraeus, C. finlaysonii, and C. inornatus; (2) a C. notatus lineage; and (3) a lineage containing C. nigrovittatus and C. prevostii. Callosciurus caniceps was most closely related to C. inornatus. Based on transversional divergence rate at the third codon position of cytochrome b gene, they diverged about 1.2 million years ago. The drastic eastward shift of the Mekong River may have isolated ancestors of C. caniceps and C. inornatus. Then, these two species might have evolved in the different environments of each side of the Mekong River. This phylogeographic history suggests a typical case of allopatric speciation.

Molecular identification and phylogenetic analysis of aCallosciurus notatuscomplete mitogenome from Peninsular Malaysia

“…This finding is consistent with the landscape of S.E. Asia, and in particular the marine barriers between the different land masses, which almost certainly affect the dispersal and genetic connectivity for small mammals such as Callosciurus species (Oshida et al 2011;Brunke et al 2019). In addition, Callosciurus notatus has also been reported as a genetically diverse species subdivided into several subspecies around Southeast Asia (Chah 2007;Sari et al 2020).…”

“…Asia, and in particular the marine barriers between the different land masses, which almost certainly affect the dispersal and genetic connectivity for small mammals such as Callosciurus species (Oshida et al. 2011 ; Brunke et al. 2019 ).…”

Messing about on the river: the role of geographic barriers in shaping the genetic structure of Bornean small mammals in a fragmented landscape

“…Recent studies in other regions of the world have demonstrated the importance of rivers as barriers to gene flow (Oshida et al 2011;Rocha et al 2011;Ćosić et al 2013), and verified the strong effect of anthropogenically modified landscapes on dispersal capabilities and genetic connectivity in small mammals (Gerlach and Musolf 2000;Trizio et al 2005;Stephens et al 2013;Bani et al 2017). But most studies investigating the effect of geographic barriers on dispersal and genetic structure have mainly focused on a single species (Patton et al 1994;Colombi et al 2010;Nicolas et al 2011;Ćosić et al 2013;Russo et al 2016), or few species from the same genus (Kennis et al 2011;Oshida et al 2011;Rocha et al 2014). This study is to our knowledge the first investigating the influence of different landscape features on migration and population connectivity in a comprehensive community of Bornean small mammals.…”

Zoogeographical barriers causing discontinuous osteometrical variations in the northern treeshrew skulls

“…It was suggested that the Mekong River has acted as a zoogeographical barrier at least in small mammals during the Pliocene and Pleistocene [ 27 ]. The cases of Callosciurus squirrels [ 30 , 31 , 32 ], genetic differentiation or speciation has been demonstrated between both sides of this river. In northern treeshrew of North Vietnam population, however, the t -test using raw data demonstrated that the total number of the siginificantly different measurements were few between Y and 2, Y and 3, and Y and 4 in both sexes and Y and 7 in male ( Table 7 ).…”