Molecular variability in the commom shrew Sorex araneus L. from European Russia and Siberia inferred from the length polymorphism of DNA regions flanked by short interspersed elements (Inter-SINE PCR) and the relationships between the Moscow and Seliger chromosome races

Genetic exchange among chromosomal races of the common shrew Sorex araneus and the problem of reproductive barriers have been extensively studied by means of such molecular markers as mtDNA, microsatellites, and allozymes. In the present study, the interpopulation and interracial polymorphism in the common shrew was derived, using fingerprints generated by amplified DNA regions flanked by short interspersed repeats (SINEs)-interSINE PCR (IS-PCR). We used primers, complementary to consensus sequences of two short retroposons: mammalian element MIR and the SOR element from the genome of Sorex araneus. Genetic differentiation among eleven populations of the common shrew from eight chromosome races was estimated. The NP and MJ analyses, as well as multidimensional scaling showed that all samples examined grouped into two main clusters, corresponding to European Russia and Siberia. The bootstrap support of the European Russia cluster in the NJ and MP analyses was respectively 76 and 61%. The bootstrap index for the Siberian cluster was 100% in both analyses; the Tomsk race, included into this cluster, was separated with the bootstrap support of NJ/MP 92/95%.     

Morphometric differentiation between the Manturovo and Serov chromosome races of the common shrewSorex araneus

Morphometric differentiation between the Manturovo and Serov chromosome races of the common shrewSorex araneus Linnaeus, 1758, in Northeastern European Russia was studied using 27 measurements of the skull in 953 specimens. Discriminant and cluster analyses showed that shrews belonging to different chromosome races were well differentiated. No regular dependence between morphological changes of the skull and longitude was observed and there was no association between geographic and morphological distance. Multiple regression analysis revealed that 24.7% of the total morphological variance could be explained by seven geoclimatic variables. We suggest that karyotypic divergence may play a significant role in differentiating skull morphology in the Manturovo and Serov races of the common shrew. We also suppose that selection may affect the skull morphology of different chromosome races in this species.     

Identification of a novel WART-like chromosome rearrangement in complex heterozygotes in an interracial hybrid zone of the common shrew Sorex araneus L.

Karyotypes uncharacteristic of pure races or hybrids were identified in the interracial hybrid zones of the common shrew Sorex araneus L. that were recently discovered in the European part of Russia. This suggests the actual existence in natural populations of WART-like rearrangements (whole-arm reciprocal trans-ocations) along with Robertsonian fusions of acrocentrics. Demonstration of new and still rare chromosome variants is the aim of this communication.     

Multilevel subdivision in the <Emphasis Type="Italic">araneus</Emphasis> species group of the genus <Emphasis Type="Italic">Sorex</Emphasis>: 1. Chromosomal differentiation

This review summarizes the available data on multilevel differentiation in the araneus species group of the genus Sorex (Eulipotyphla, Mammalia). Communication 1 gives basic information about the biology and morphological and karyotypic differentiation of some species belonging to this genus, as well as about the subdivision of one of the species, the common shrew (Sorex araneus), into intraspecific chromosomal races. The list of the 75 races known so far is included (26 of them dwell in Russia).     

Genetic and morphological variation in a partially isolated population of Caucasian shrew <Emphasis Type="Italic">Sorex satunini</Emphasis> (Mammalia)

Morphological and genetic variation at microsatellite loci of Caucasian shrew Sorex satunini Ogn. is examined and compared with that of the common shrew S. araneus L. Genetic distance at microsatellite loci between the common shrew and Caucasian shrew proved to be threefold higher than between chromosome races of the common shrew. The Caucasian shrew manifested low polymorphism in studies of both microsatellites and morphometric mandibular traits. The heterozygote deficit was also typical. These properties may be a consequence of partial isolation of the population and gene drift.     

Craniometric differences between karyotypic races of the common shrew Sorex araneus (Mammalia) as a result of limited hybridization

The contact points of four karyotypic races (St. Petersburg, Moscow, Seliger and West Dvina) of the common shrew Sorex araneus L. were studied at the Valdai Hills (European Russia) in an area unimpeded by geographic barriers. The populations of the races are separated by narrow hybrid zones that represent the most complex heterozygous hybrid karyotypes. At these points of contact, the morphometric differentiation of karyotype races was examined in 12 cranial measurements in 190 shrews of a known karyotype. A comparison of the mean values in studied samples of immature shrews revealed statistically significant differences and the correlation of some measurements which describe the level of musculus temporalis. It has been proposed that morphometric differences in the karyotypic races were preserved and accumulated because of a 50% reduction of the frequencies of hybrids. The deviation from the Hardy-Weinberg ration in the frequencies of the genotype and haploid sets of chromosomes in the hybrid zones can be attributed to a number of fatalities of hybrid embryos or the nonrandom mating of karyotypic races. The ethological isolation might arise in the evolution of some karyotypic races from the reduced fitness of the hybrids.     

Intraspecific Phylogenetic Relationships in Sorex araneus L.: The Southern Baltic Subgroup of Chromosome Races

Results of chromosome G-banding were used to identify two new karyotypic races of the common shrew (Sorex araneus L.) in the European part of Russia. The chromosomal diagnosis of race St. Petersburg included five metacentrics (hk, ip, jl, mq, and nr) and two acrocentrics (g and o) (2Na = 20); the diagnosis of race West Dvina included six metacentrics (gm, hk, ip, jl, no, and qr) (2Na = 18). The phylogenetic significance of the chromosomal markers gm, hk, and ip is considered and the possibility of reticulate evolution in the species S. araneus is discussed.     

Chromosomal Evolution of the Common Shrew Sorex araneusL. from the Southern Urals and Siberia in the Postglacial Period

This paper summarizes a series of studies on chromosomal geography of the common shrew Sorex araneusL. in Siberia and the Southern Urals. Chromosomal races inhabiting the Southern Urals and the Western Siberian Plain sequentially replace each other in the latitudinal direction. In this region, karyotypes of each two adjacent races differ from each other by a single whole-arm reciprocal translocation. In the Eastern Siberian and Altai branches, the neighboring races differ mainly in the number or set of metacentric chromosomes. Analysis of the race distribution in the common shrew in the context of paleoecology of the glacial and postglacial period allowed us to reconstruct the sequence of events leading to the establishment of the present-day structure of the species S. araneus.     

The First Record of a Chigger Mite of the Genus <Emphasis Type="Italic">Neotrombicula</Emphasis> (Acariformes: Trombiculidae) in the Northwest of European Russia

A chigger mite species, Neotrombicula absoluta Schluger, 1966, previously known only from its type locality in Transcarpathian Region of Ukraine, was found in the vicinity of Kurgolovo Village (Kingisepp District, Leningrad Province, Russia). A single specimen of this species was collected off the common shrew Sorex araneus L. This is the first record of the genus Neotrombicula (which includes the most usual causative agents of trombiculiasis of humans and domestic animals in Europe) in the northwestern part of European Russia.     

A new chromosomal race of the common shrew <Emphasis Type="Italic">Sorex araneus</Emphasis> (Lipotyphla,Mammalia) found in Russia

Karyotyping of the common shrews Sorex araneus from the poorly studied region of the Northwest of Russia revealed the belonging of individuals to two chromosomal races, Lemi and St. Petersburg. The Lemi race, previously known only from Finland, was discovered for the first time on the territory of Russia and thus replenished the list of S. araneus chromosomal races that are distributed within the Russian part of the species range (27 races out of 74 known in the whole species range at the moment). The studied individuals showed a high level of chromosomal polymorphism, caused by Rb translocations.     

Morphometric difference between the Novosibirsk and Tomsk chromosome races of<Emphasis Type="Italic">Sorex araneus</Emphasis> in a zone of parapatry

A hybrid zone between the Novosibirsk and Tomsk chromosome races of the common shrewSorex araneus Linnaeus, 1758 was found near Novosibirsk city (West Siberia, Russia) in an area unimpeded by geographic barriers. In this zone, the shrews of both races and their hybrids were trapped and karyotyped and 22 features of their cranial and postcranial skeleton were measured. Canonical discriminant analysis revealed 3 distinct groups of individuals, which corresponded to the 3 karyotypic categories involved in the analysis. The first discriminant function reflected the differences in the size of skeletal elements. The Novosibirsk shrews and the hybrids were significantly smaller than the Tomsk shrews. The second discriminant function was interpreted as a parameter of skeletal proportionality. The hybrids were significantly less proportional than the parental races. This study revealed one of the clearest examples of morphological differentiation between chromosome races of the common shrew.     

Hybrid zones between chromosome races of the common shrew in West Siberia

In West Siberia, the whole species range of the common shrew (Sorex araneus L.) is shared by two parapatric chromosome races — Novosibirsk and Tomsk. These races form a hybrid zone with each other. In addition, on the western margin of the range there is a hybrid zone between the Novosibirsk race and the Uralian race Serov, and in the east, the Tomsk race forms a hybrid zone with the East Siberian race Strelka hybrid. The structures of the three hybrid zones are very different and depend on the karyotypic state of the races in contact. A comparative analysis of the hybrid zones between the chromosome races of the common shrew in West Siberia is discussed together with the role of these zones in maintaining variability in natural populations.     

Structure and Seasonal Dynamics of the Ectoparasite Community of the Pygmy Shrew <Emphasis Type="Italic">Sorex minutus</Emphasis> in the Ilmen-Volkhov Lowland

The species composition and seasonal dynamics of ectoparasites of the pygmy shrew Sorex minutus L., 1756 were studied in coniferous and mixed forests of the Ilmen-Volkhov Lowland (Novgorod Province of Russia) in 1999–2003. Examination of 265 specimens of the pygmy shrew revealed 670 specimens of ectoparasites that belonged to 13 species: 8 species of fleas, 2 species of ixodid ticks, 1 species of gamasid mites, and 2 species of myobiid mites. In total, 55.8% of shrew specimens were infested with ectoparasites. No more than 4 species of ectoparasites were found simultaneously on one host, and most of the examined shrews (64.8%) were infested with only 1 ectoparasite species. The pygmy shrew had lower infestation intensity and species diversity of acarines and fleas as compared with those of the common shrew Sorex araneus L., 1758 and the bank vole Myodes glareolus (Schreber, 1780) (13 vs. 23 and 29 species, respectively). Unlike these two other hosts, the prevalent ectoparasite of the pygmy shrew was the tick Ixodes trianguliceps Birula, 1895.     

Allozyme variability in common shrew Sorex araneus of Western Siberia

The allozyme variability of the common shrew Sorex araneus of Western Siberia is studied. The small level of genetic variability and lack of reliable differences in indices of polymorphism for taiga, subtaiga, and forest-steppe populations are revealed. A significant level of genetic differentiation in populations belonging to adjacent chromosomal races—Novosibirsk and Serov (F _st = 0.3) — has been shown.     

Telomeric DNA allocation in chromosomes of common shrew (Sorex araneus, eulipotyphla)

Recently, we displayed an Iberian shrew species (Sorex granarius) with telomere structures unusual for mammals. Long telomeres on the short acrocentric arms contain an average of 213 kb of telomere repeats, whereas the other chromosomal ends have only 3.8 kb (Zhdanova et al., 2005; 2007). However, it is not clear whether these telomeres are typical for all shrew species or only for S. granarius. S. granarius and common shrew Sorex araneus are sibling species. In this study, using modified Q-FISH we demonstrated that telomeres in S. araneus from various chromosomal races distinguished by their number of metacentrics contain 6.8–15.2 kb of telomeric tracts. The S. araneus telomere lengths appear to correspond to telomere lengths in the majority of both shrew species and wild mammals, whereas S. granarius has telomeres with unique or rare structures. Using DNA and RNA high-specific modified probes to telomeric repeats (PNA and LNA), we showed that interstitial telomeric sites in S. araneus chromosomes contain mainly telomeric DNA and that their localization coincide with some evolutionary breakpoints. Interstitial telomeric DNA in S. granarius chromosomes was not revealed. Thus, the distribution of telomeric DNA may be significantly different, even in closely related species whose chromosomes are composed of almost identical chromosomal arms.     

Narrow hybrid zone between Moscow and Western Dvina chromosomal races and specific features of population isolation in common shrew <Emphasis Type="Italic">Sorex araneus</Emphasis> (Mammalia)

The contact zone between Moscow and Western Dvina chromosomal races of common shrew Sorex araneus L. at the south of the Valdai Hights was traced over a distance of 20 km. Within this, close to parapatric, contact zone of chromosomal races the width of sympatry zone was about 500 m (the narrowest among currently known hybrid zones), and the proportion of hybrids was 24.3%. It was shown that in bimodal hybrid zones between chromosomal races of common shrew the width of sympatry zones varied from 0.5 to 13 km. This width does not correlate with the cytogenetic features of the hybrids, and seems to be determined by competitive relations between the races. The hybrid proportion is determined by the type of hybrid heterozygosity, and decreased in the race sympatry zone from 33–40 to 21.5–25.2%. The decrease of the hybrid proportion can be associated with the abnormal fertility of either the first generation, or the backcross hybrids.     

Number and distribution of dominant species of common shrews of <Emphasis Type="Italic">Sorex</Emphasis> genus across Kuznetsk Alatau Ridge

The numbers of dominant shrew species, Sorex araneus and Sorex tundrensis, vary in various altitudinal belts of the Kuznetsk Alatau Ridge. The common shrew is the most abundant in dark-coniferous forests of herbaceous type, i.e. belongs to the mesophyte environmental complex. The greatest numbers of Sorex tundrensis are found in habitats of thinned tree layer with moderate humidification; therefore, this species is categorized xeromesophytic.     

No apparent reduction of gene flow in a hybrid zone between the West and North European karyotypic groups of the common shrew, Sorex araneus

The common shrew, Sorex araneus, exhibits an unusually high level of karyotypic variation. Populations with identical or similar karyotypes are defined as chromosome races, which are, in turn, grouped into larger evolutionary units, karyotypic groups. Using six microsatellite markers, we investigated the genetic structure of a hybrid zone between the Sidensjö and Abisko chromosome races, representatives of two distinct karyotypic groups believed to have been separated during the last glacial maximum, the West European karyotypic group (western group) and the North European karyotypic group (northern group), respectively. Significant F_ST values among populations suggest some weak genetic structure. All hierarchical levels show similar levels of genetic differentiation, equivalent to levels of genetic structure in several intraracial studies of common shrew populations from central Europe. Notably, genetic differentiation was of the same order of magnitude between and within karyotypic groups. Although the genetic differentiation was weak, the correlation between genetic and geographical distance was positive and significant, suggesting that the genetic variation observed between populations is a function of geographical distance rather than racial origin. Hence, considerable chromosomal differences do not seem to prevent extensive gene flow.     

Identification of a novel WART-like chromosome rearrangement in complex heterozygotes in an interracial hybrid zone of the common shrew Sorex araneus L

Karyotypes uncharacteristic of pure races or hybrids were identified in the interracial hybrid zones of the common shrew Sorex araneus L. that were recently discovered in the European part of Russia. This suggests the actual existence in natural populations of WART-like rearrangements (whole-arm reciprocal translocations) along with Robertsonian fusions of acrocentrics. Demonstration of new and still rare chromosome variants is the aim of this communication.     

Genetic and morphological variation in a partially isolated population of Caucasian shrew sorex Satunini (Mammalia)

Morphological and genetic variation at microsatellite loci of Caucasian shrew Sorex satunini Ogn. is examined and compared with that of the common shrew S. araneus L. Genetic distance at microsatellite loci between the common shrew and Caucasian shrew proved to be threefold higher than between chromosome races of the common shrew. The Caucasian shrew manifested low polymorphism in studies of both microsatellites and morphometric mandibular traits. The heterozygote deficit was also typical. These properties may be a consequence of partial isolation of the population and gene drift.