Meiotic studies of male common shrews (Sorex araneus L.) from a hybrid zone between chromosome races

Thirty-three adult male common shrews (Sorex araneus L.) were collected from a hybrid zone between two chromosomal races that differed in Robertsonian metacentrics. Anaphase I nondisjunction frequencies were estimated on the basis of metaphase II counts. RIV and CV complex heterozygotes (four-element rings and five-element chains at meiosis I, respectively) had substantially higher nondisjunction rates than homozygotes and simple Robertsonian heterozygotes. However, at least in the case of RIV-forming hybrids, increased nondisjunction frequency did not result from malsegregation of the heterozygous complex. Extra elements found in hyperploid spreads were most frequently acrocentrics, that could not originate from a fully metacentric multivalent. Complex heterozygotes were also characterized by higher frequencies of univalents observed at diakinesis I. However, univalents did not originate from complex configurations, which were regularly formed with usually one chiasma per chromosome arm. Hence, we suppose that the presence of multivalents in the cell affects pairing and segregation of other elements at meiosis I.     

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.     

Cytogenetic control of a hybrid zone of between two Sorex araneus chromosome races before breeding season

Two chromosome races of common shrew, Moscow and Seliger, differ in the arm combination in 11 diagnostic chromosomes (Robertsonian metacentrics/acrocentrics). Homozygotes of both pure races, simple Robertsonian heterozygotes of Seliger race, and complex heterozygotes (FI hybrids) were detected in the found earlier between hybrid zone of these races, in the spring before the breeding seasonbreeding season. The g/oheterozygote was first discovered in race Seliger, whose chromosome formula typically contains acrocentrics g and o. The m/q heterozygote was recorded for the second time. Meiosis was studied in 16 males representing five detected karyotypic categories. No abnormal in pairing of homologs in either sex trivalent common for the species (XY1Y2) or autosome trivalents (g/o and m/q) was detected at diakinesis--metaphase I. Two hybrids displayed a theoretically expected and unimpaired meiotic configuration in a form of a very long chain comprising 11 monobrachial homologs (g/gm/mq/qp/pr/rk/ki/ih/hn/no/o). The results are discussed in terms of hypotheses on fertility of complex heterozygotes and limited gene flow in hybrid zone.     

Variability of a cytochrome b region in different chromosome races and populations of the common shrew Sorex araneus L., 1758

The nucleotide sequence (572 bp) of the cytochrome b gene of the common shrew Sorex araneus was analyzed. In total, 92 animals of five chromosome races from 12 localities were studied. The median haplotype network has a pronounced star-like structure. The central haplotype common for all samples, except for the southern island sample of the race Sok, accounts for about 36%. The main characteristics of molecular variation in our work correspond to those obtained in other studies. We revealed the lack of a correlation between the genetic and geographic distances and also population structurization of the species. On the basis of variation of the haplotypes in the samples, a scenario of colonization of the postglacial territories by females of one or several close matrilines with subsequent rapid subdivision of the population into independent populations is discussed.     

The complex hybrid zone between the Abisko and Sidensjö chromosome races of Sorex araneus in Sweden

Six chromosome races of the common shrew occur in Sweden, each with its characteristic arm combination of metacentric chromosomes. G-banded karyotypes were analysed from 201 common shrews in 14 localities of the northern hybrid zone in Sweden. Analyses from another 64 shrews from seven localities outside the hybrid zone w ere included for comparison. The shrews were classified with respect to karyotype into any of five categories: (1) Abisko race, (2) Sidensjö race, (3) hybrids between the parental races, (4) pseudohybrids (a type of hybrid), and (5) AT with all race-specific chromosomes (h, i, n, o, p, r) present as telocentrics. Hybrids occurred at a frequency close to Hardy-Weinberg expectation in the centre of the hybrid zone. Chromosome polymorphism of Robertsonian type was common and 43 different karyotypes were found among the specimens studied. The polymorphism involved six metacentric pairs in the Abisko and three in the Sidensjö race. The frequency of the Sidensjö race-specific metacentric hi decreased and the frequency of the Abisko race-specific hn increased from south-west to north-east along a transect across the hybrid zone. The number of race-specific telocentrics reached a peak 13 km north-east of the hi-hn cline centre. The estimated standardized cline width for chromosomes hi and hn was 16.0 km. The extension of the Sidensjö race is comparatively narrow [c. 50 km in the region of the investigation), and it is regarded to be a 'hybrid race' between the Uppsala race, which colonized Sweden from the south-west, and the Abisko race which arrived from the north-east after the most recent glaciation. The origin of the Sidensjö race is thus less than 10 000 years old, because earlier this area was covered by glacial ice.     

The microsatellite polymorphism and gene flow in the contact zone of four common shrew (Sorex araneus L., Mammalia) chromosome races

The variation of microsatellite loci in 130 individuals of four common shrew chromosome races (Moscow, Western Dvina, Seliger, and St. Petersburg) contacting on the Valdai Hills was studied. A low level of genetic differences between the chromosome races, which differ at three-five fixed diagnostic metacentric chromosomes, was found. The genetic differentiation within the races is more considerable as compared with that between the races. A high deficiency in heterozygotes was recorded; presumably, this is connected with regular variation in the population sizes. It is assumed that the fixation of centric chromosome fusions was supported by selection (drive) in the evolution of the common shrew against the background of a neutral evolution of the microsatellite loci.     

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.     

Contribution to the knowledge of home range in common shrew Sorex araneus L.

Summary Population density of shrews in a clearing in the submountain spruce forest was established per 1 hectare 17.5 individuals of common shrew, 4.6 of pygmy shrew and 1.1 of alpin shrew. The mean radius of activity in common shrew amounts to 13 m. The ratio of shrew to rodents was 1:3 or 1:2 in summer and autum respectively. Theoretical home range reached 532 m². The importance of home range studies for synecological studies and theory of natural focality was demonstrated.District Station of Hygiene and Epidemiology, Olomouc, SSR.     

Contact zones between chromosome races of the common shrew Sorex araneus L. (insectivora, mammalia) at the margins of the Veps stage of the Valdai ice sheet

Cytogenetic analysis of the common shrew populations in the Valdai Hills revealed the presence of four distinct chromosome races (Western Dvina, Seliger, St. Petersburg, and Moscow). The geographic distribution of these races relative to the borders of the Late Valdai glaciation area is described and discussed. Five contact zones between chromosomal races were found, located directly on the ice-marginal formations of the Veps stage. Two races, Seliger and St. Petersburg, are located exclusively in the former ice sheet area. Attention is drawn to the fact that many of the races located in the last glacial area from the Valdai Hills through Scandinavia are characterized by endemic chromosomes (gi, gp, mo, or, etc.). It is concluded that the situation in the former glaciation area could favor the preservation of tundra or forest vegetation refuges and populations of some small mammal species.     

Biotope distribution of cestodes from the common shrew Sorex araneus in southern Karelia

Specific features in the formation of cestode species composition in the common shrew in different biotopes have been analyzed. Four categories of parasites have been recognized depending on a degree of dominance: dominants (Neoskrjabinolepis singularis, Molluscotaenia crassiscolex), subdominants (Ditestolepis diaphana), adominants A (Staphylocystis furcata, Vigisolepis spinulosa, adominants B (Hymenolepis scutigera, Dilepis undula, D. secunda, Taenia mustelae). A significant similarity was discovered between the species diversity and the dominance characteristics of cestodes. It was found that the distribution of mass species of parasites in the host population corresponds to the gamma distribution model. In regard to cestodes examined, a hypothesis considering the spatial structure and size of territory occupied by stable parasitic system is put forward.     

Craniometric study of the common shrew (Sorex araneus L. 1758) from different localities and chromosomal races across Germany and Europe

A total of 440 skulls of common shrews, Sorex araneus, from Germany and Europe (Croatia, Hungary, Austria, and Norway) were studied. The material represented six chromosomal races (Ulm, Laska, Drnholec, Mooswald, Jütland, and Abisko) assignable to the Western European and Northern European karyotypic groups. The race of a few samples was not determined. Twenty-one linear measurements were taken on skulls and mandibles and used in this study. Pearson correlations and multiple linear regressions were used to see the relationship of the cranial variables to altitude, latitude, the chromosomal race, and the geographic location. The results from the tested samples differed; the most negative correlations to latitude were found in the samples assigned to the Western European karyotypic group (WEK), the least negative ones in the samples of the Ulm race. These results indicate the converse of Bergmann's rule. But taking into consideration all the samples of the different karyotypic groups across Europe, the correlations to latitude included positive ones, which would indicate that Sorex follows Bergmann's rule in some of the variables. The studied material of different karyotypic groups could not be differentiated in discriminant analyses. The separation of the studied races within the WEK alone was slightly better, but about 30 % of ungrouped cases remained. Only the separation of the regional samples within one chromosomal race revealed better results but was still very different between the races. This indicates that within the races, regional differences might be strong enough for a separation of the samples and that within a karyotypic group, and even more so across karyotypic groups, regional differences conceal racial differences.     

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.     

Lack of mitochondrial DNA divergence between chromosome races of the common shrew, Sorex araneus, in Sweden. Implications for interpreting chromosomal evolution and colonization history

The common shrew, Sorex araneus, has one of the most variable karyotypes among mammals, displaying numerous chromosome races throughout its distribution. The six chromosome races present in Sweden can be categorized in two different karyotypic groups, the west and north European karyotypic groups (western and northern). Three races belonging to the western group are considered to have arisen through whole arm reciprocal translocations (WARTs). Race formation through this process requires a bottleneck event. In the present study we sequenced a part of the mitochondrial DNA (mtDNA) genome to investigate molecular differences between the chromosome races in Sweden. We found no mtDNA differentiation between the mainland chromosome races or the karyotypic groups. Genetic variation is as large between populations within a race as between populations among the races or karyotypic groups, suggesting that the karyotypic groups might have originated in a common glacial refugium. The noticeable exception is the Oland race, which shows higher mtDNA diversity compared to the other Swedish races, indicating a divergent origin difficult to explain. Mitochondrial DNA variation in Sweden suggests that most haplotypes arose in situ and that the populations has undergone a rapid size expansion. Altogether, the mtDNA data are in agreement with the WART hypothesis, which still holds as the most plausible variant of karyotype evolution for three of the chromosome races of the common shrew in Sweden.     

Cases of coat colour anomalies in the common shrew, Sorex araneus L

Coat colour anomalies in the common shrew, Sorex araneus L., in the geographical range of this species, including Poland, are extremely rare. This study describes atypically coloured common shrews. Light colouration of the coat is a result of lack ofpigment in the entire hair or hair fragments. It appears that atypically coloured shrews occur more often in isolated populations whose gene transfer with neighboring populations is limited.     

Additional data for nuclear DNA give new insights into the phylogenetic position of Sorex granarius within the Sorex araneus group

Many species contain genetic lineages that are phylogenetically intermixed with those of other species. In the Sorex araneus group, previous results based on mtDNA and Y chromosome sequence data showed an incongruent position of Sorex granarius within this group. In this study, we explored the relationship between species within the S. araneus group, aiming to resolve the particular position of S. granarius. In this context, we sequenced a total of 2447 base pairs (bp) of X-linked and nuclear genes from 47 individuals of the S. araneus group. The same taxa were also analyzed within a Bayesian framework with nine autosomal microsatellites. These analyses revealed that all markers apart from mtDNA showed similar patterns, suggesting that the problematic position of S. granarius is best explained by an incongruent behavior by mtDNA. Given their close phylogenetic relationship and their close geographic distribution, the most likely explanation for this pattern is past mtDNA introgression from S. araneus race Carlit to S. granarius.     

Helminthofauna of the common shrew Sorex araneus L. (Soricidae) from Samarskaya Luka

Ecological analysis of the helminthofauna of common shrew Sorex araneus L. from Samarskaya Luka (Samara Region) has been carried out. Twenty-three helminth species are found including 3 species of trematodes, 8 cestodes, 10 nematodes, and 2 acanthocephales. Dependence of the structure of helminthofauna on the host age is revealed.     

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.     

Synaptonemal complexes of the common shrew, Sorex araneus L., in spermatocyte spreads

This paper presents an electron microscopic analysis of the behavior and morphology of the sex chromosomes and autosomes during prophase I in the common shrew, Sorex araneus L. The pairing patterns of the X/Y1Y2 and autosomal Robertsonian trivalents are described.     

A hybrid zone between the Kirillov and Petchora chromosomal races of the common shrew (Sorex araneus L., 1758) in northeastern European Russia: a preliminary description

Karyotypes of the Petchora and Kirillov chromosomal races of the common shrew differ by six Robertsonian metacentrics with monobrachial homology, such that interracial F₁ hybrids produce a ring-of-six configuration at meiosis I and are expected to suffer infertility. Mapping of 52 karyotyped individuals by using a unique global positioning system (GPS) revealed that the Kirillov-Petchora hybrid zone is positioned close to the river Mezen, which separated these races, and so may limit the migration of shrews across the contact zone. Although the population density of shrews was found to be markedly different with respect to habitats, the zone runs through a mosaic of habitats that are similar for both the Petchora and the Kirillov sides. This is one of the narrowest chromosomal hybrid zones among those studied in Sorex araneus with a standard cline width of about 1 km. The center of the cline is located on a bank occupied by the Petchora race at a distance of 0.4 km away from a riverine barrier. Interestingly, both the Kirillov race and hybrid individuals were found on a small island in the middle of a river fully flooded each spring. The frequencies of karyotypic variants allow us to consider the zone as an example of a bimodal zone. New Robertsonian and de novo whole-arm reciprocal translocations (WART) chromosomal variants found in the zone could be regarded as evidences of current evolutionary process in chromosomal hybrid zones.