Evolution of the common shrewSorex araneus:

We review data on the chromosomal variation in the common shrewSorex araneus Linnaeus, 1758 in the context of recent molecular findings. The article considers all aspects of chromosomal variation in this species: within-population polymorphism, karyotypic races, hybrid zones between karyotypic races, chromosomal evolution, and speciation. The recent molecular data provide vital information on different evolutionary processes such as inbreeding, genetic drift, population expansion, and selective forces. In particular, the molecular data challenge traditional models for the fixation of chromosomal variants, provide new insights into the manner of spread of such variants once they are formed and allow in-depth analysis of gene exchange between karyotypic races.     

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.     

A mosaic XY1Y2/XY1Y2Y2 common shrewSorex araneus

XY₁Y₂/XY₁Y₂Y₂ mosaicism was found in a wild adult common shrewSorex araneus (Linnaeus, 1758) in lymphocytes from spleen. The multiple sex chromosome system in the common shrew was the result of an X-autosome translocation and the Y₂ chromosome was the unpaired autosome present in males. The external phenotype of the shrew was that of a mormal male. The histological picture of its testis showed complete spermatogenic breakdown on the stage of primary spermatocytes, hence the shrew was sterile. The possible causes of spermatogenic arrest in a mosaic shrew are dis cussed.     

Phylogeographical structure, postglacial recolonization and barriers to gene flow in the distinctive Valais chromosome race of the common shrew (Sorex araneus)

Using one male‐inherited and eight biparentally inherited microsatellite markers, we investigate the population genetic structure of the Valais chromosome race of the common shrew (Sorex araneus) in the Central Alps of Europe. Unexpectedly, the Y‐chromosome microsatellite suggests nearly complete absence of male gene flow among populations from the St‐Bernard and Simplon regions (Switzerland). Autosomal markers also show significant genetic structuring among these two geographical areas. Isolation by distance is significant and possible barriers to gene flow exist in the study area. Two different approaches are used to better understand the geographical patterns and the causes of this structuring. Using a principal component analysis for which testing procedure exists, and partial Mantel tests, we show that the St‐Bernard pass does not represent a significant barrier to gene flow although it culminates at 2469 m, close to the highest altitudinal record for this species. Similar results are found for the Simplon pass, indicating that both passes represented potential postglacial recolonization routes into Switzerland from Italian refugia after the last Pleistocene glaciations. In contrast with the weak effect of these mountain passes, the Rhône valley lowlands significantly reduce gene flow in this species. Natural obstacles (the large Rhône river) and unsuitable habitats (dry slopes) are both present in the valley. Moreover, anthropogenic changes to landscape structures are likely to have strongly reduced available habitats for this shrew in the lowlands, thereby promoting genetic differentiation of populations found on opposite sides of the Rhône valley.     

A wild common shrew (Sorex araneus) with an XXY sex chromosome constitution

An adult male common shrew with an XXY sex chromosome constitution was found in a natural population. The external appearance of the animal and size of the accessory glands were normal but the testes were as small as those of immature shrews. Histological preparations of the testis revealed seminiferous tubules containing only one type of cell, probably Sertoli cells, and interstitial cell hyperplasia.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Seasonality of leptin levels in the BAT of the common shrew (Sorex araneus)

Leptin concentrations in the interscapular brown adipose tissue (IBAT) of the common shrew (Sorex araneus) were measured in different seasons. The leptin concentrations in IBAT were much higher than in the liver, where leptin is supposed to be of blood origin. In the heart muscle no detectable amount of leptin was found. There were clear seasonal variations in the leptin concentrations in IBAT. Leptin levels in IBAT were the lowest in November at the beginning of the winter. The concentrations increased, however, strongly after the onset of the permanent snow cover, and the highest concentrations were measured in December-January, when the weight of the animals was very low. In April-May, at the time when shrews attain sexual maturity, leptin concentrations in IBAT were lower than in the mid-winter, but significantly higher than in November. In overwintered adults the leptin concentrations were at the same level as in nonwintered subadults. Leptin originating from BAT may inform the central nervous system about the amount of nonshivering thermogenesis as well as the amount of feeding necessary for survival in the winter months.     

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.