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.     

Nondisjunction frequencies in Robertsonian heterozygotes from natural populations of the common shrew, Sorex araneus L

Pregnant female common shrews were collected from an area of Robertsonian polymorphism, involving five different arm combinations, around Oxford (England). The females and their fetuses were karyotyped, and the karyotypes of the sires were deduced. Ten pregnancies where at least one parent was known to be either a single or double Robertsonian heterozygote were available for analysis. From these pregnancies, upper and lower estimates of anaphase I nondisjunction arising from Robertsonian heterozygosity were calculated to be 1.0-2.5% per heterozygous arm combination and 1.5-3.7% per heterozygous parent. One trisomic fetus with retarded development was identified. This trisomy can be attributed to anaphase I nondisjunction of a trivalent in a female Robertsonian heterozygote.     

Meiotic studies of Robertsonian heterozygotes from natural populations of the common shrew, Sorex araneus L

Adult male common shrews, both Robertsonian heterozygotes and homozygotes, were collected from Oxford and elsewhere in Britain. In both simple Robertsonian heterozygotes and Robertsonian heterozygotes with monobrachial homology, regular chain configurations were observed at meiosis I; only 1-2% were incomplete such that univalents were observed. On the average, there was one chiasma per chromosome arm among those that displayed Robertsonian variation, including both chain configurations and bivalents. According to one hypothesis, a single chiasma per chromosome arm may facilitate proper disjunction of chain trivalents of simple Robertsonian heterozygotes. Based on metaphase II counts, anaphase I nondisjunction frequency can be estimated as 1.0% per heterozygous individual and 0.7% per heterozygous arm combination.     

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.     

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.     

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.     

Spermatogenesis in heterozygotes for Robertsonian chromosomal rearrangements from natural populations of the common shrew, Sorex araneus

Twenty-two adult male common shrews were collected from 5 sites in the vicinity of Oxford (UK) close to the zone of hybridization between two karyotypic races. The shrews were subdivided into 3 karyotypic categories: homozygotes, simple Robertsonian heterozygotes (which form one or more trivalents at prophase I of meiosis) and complex Robertsonian heterozygotes (which form a quadrivalent). The ratio of primary spermatocytes to round spermatids was determined from transverse sections of seminiferous tubules, to provide an indication of germ cell death. In no individual was there severe germ cells loss. Homozygotes had the highest mean spermatocyte: spermatid ratio and complex heterozygotes the lowest, but there was substantial individual variation and the differences were not significant. Complex heterozygotes also had a higher proportion of defective seminiferous tubules and lower testis weights than did other categories and it is reasonable to propose that, as a population, complex heterozygotes had reduced fitness relative to other categories on the basis of spermatogenic performance. However, there is no evidence from studies of spermatogenesis that simple Robertsonian heterozygotes are less fit than homozygotes.     

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.     

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.     

Evidence for echolocation in the common shrew, Sorex araneus

In this laboratory experiment it is shown that, like four North American soricid shrew species, the European common shrew Sorex araneus L. is able to use echolocation to identify open and closed tubes at a distance of 200 mm.
Three common shrews captured in Sweden were used for the experiments, which were carried out in darkness and within a sound-proof box. The experimental set-up eliminated orientation using sight, sound or scent from outside the experimental cage. Echolocation calls consisted of broadband ultrasonic clicks at low sound pressure. These were recorded using an ultrasound detector.
The ecological significance of echolocation in shrews is discussed. It is proposed that common shrews use echolocation to locate protective cover, thus minimizing the risk to be taken by, e.g. owls.
Echolocation may also be used for detecting obstacles in subterranean tunnels. Hence, echolocation could be of certain importance when abandoned burrows in the periphery of the tunnel system are restored during periods of increasing population densities. Since density peaks in most populations occur regularly each summer, and may reach extreme magnitudes in cyclic populations, the ecological significance of echolocation in shrews may be considerabl.     

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.     

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.     

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.     

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.     

Factors responsible for a karyotypic polymorphism in the common shrew, Sorex araneus

A Robertsonian karyotypic polymorphism in the common shrew in the Oxford area, first described in the 1950s, was re-examined. The polymorphism involves chromosome arm combinations kq, no and pr (characteristic of the Oxford karyotypic race), ko (characteristic of the Hermitage karyotypic race) and jl (found in both races). The polymorphism for jl was sporadic along a north-south transect through the Oxford area, with the frequency of the twin-acrocentric morph never exceeding 10%. The frequency of the Oxford race-specific metacentrics decreased and the frequency of the Hermitage race-specific metacentric ko increased from north to south along the transect. At a latitudinal grid reference of about 180 km, there was a high frequency of individuals with chromosome arms k, n, o and q in the ancestral acrocentric state. This was coincident with the area of occurrence of ko-kq and ko-no Oxford-Hermitage hybrids. Such hybrids are double Robertsonian heterozygotes with monobrachial homology and are likely to suffer reduced fertility in consequence. It is proposed that this is a source of selection against the monobrachial hybrids and hence results in an increase in frequency of the acrocentric morphs. This scheme goes some way to explain the clines of polymorphism for arm combinations kq, no and ko, but it is suggested that other selective factors are involved. It cannot explain the cline of polymorphism for pr, which is in general terms similar to that for kq and no, but is more shallow and centred further north.