Do aquatic barriers reduce male‐mediated gene flow in a hybrid zone of the common shrew (Sorex araneus)?

摘要

The common shrew, Sorex araneus, a small terrestrial mammal offers unique opportunity to study evolutionary processes due to its great chromosome variation. This insectivorous species is subdivided into numerous chromosome races (Wójcik et al. 2003). The diploid number of chromosomes varies within the species from 2n = 20 to 2n = 33, while fundamental number remains constant at FN = 40 (Wójcik et al. 2002).Many processes may be responsible for genetic structuring of the common shrew populations. Ecological (e.g. mating system, food resources) and geographical (e.g. lakes, mountain ridges, rivers) constraints affect gene flow, thereby shaping patterns of population-genetic structuring. Distances between the common shrew populations may be large and landscape features may provide obstacles between populations. Furthermore, life-history characteristics that may contribute to their genetic diversity and population structure include a polygamous mating system and male-biased dispersal of the common shrew (Dobson 1982; Searle 1990).The ??gucki M?yn and Popielno chromosome races meet and hybridize in the northeast of Poland. The presence of the hybrid zone may account for significant genetic structuring. In the ??gucki M?yn/Popielno hybrid zone, specific topographic conditions (presence of two lakes and the Krutynia river) occur. This may affect gene flow between the neighbouring races. The cytogenetic study carried out by Moska (2003) showed that the ranges of both races along the Krutynia river could be displaced (it is a so called ‘pocket effect’). The pocket effect takes place when the area of contact between races is limited on three sides by barriers inhibiting free contact between individuals. Free migration of individuals is possible only on one side, and the pocket ends with a barrier that precludes or severely limits migration. Although inter-racial gene flow is reduced (Lugon-Moulin et al. 1999), successful inter-racial matings take place, as shown by the finding of karyotypic hybrids on both sides of the hybrid zone (Brünner and Hausser 1996).The aim of the study was to investigate if isolation by distance and aquatic geographical barriers may influence gene flow between the ??gucki M?yn and Popielno chromosome races.