Ecomorphometric variation and sexual dimorphism in the common shrew (Sorex araneus)

We investigated the evolution of the biomechanics of the mandible in island and mainland populations of the common shrew on the west coast of Scotland. We predicted that climatic differences between populations should cause differences in prey composition leading to changes in the mechanical potential (MP) of the mandible. In females, MP was correlated with climate, with greater MP in warmer and drier habitats. In males, MP was significantly greater than in females but there was no relationship between male MP and climate. This led to increased sexual dimorphism in colder and wetter climates. The same pattern was found after a phylogenetic least squares analysis was conducted to account for shared phylogenetic history. We discuss possible reasons for this pattern, including male–male combat and the greater necessity of females to feed as efficiently as possible to meet their extremely high energy requirements during lactation.     

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.     

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.     

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.     

Recombination map of the common shrew, Sorex araneus (Eulipotyphla, Mammalia)

The Eurasian common shrew (Sorex araneus L.) is characterized by spectacular chromosomal variation, both autosomal variation of the Robertsonian type and an XX/XY(1)Y(2) system of sex determination. It is an important mammalian model of chromosomal and genome evolution as it is one of the few species with a complete genome sequence. Here we generate a high-precision cytological recombination map for the species, the third such map produced in mammals, following those for humans and house mice. We prepared synaptonemal complex (SC) spreads of meiotic chromosomes from 638 spermatocytes of 22 males of nine different Robertsonian karyotypes, identifying each autosome arm by differential DAPI staining. Altogether we mapped 13,983 recombination sites along 7095 individual autosomes, using immunolocalization of MLH1, a mismatch repair protein marking recombination sites. We estimated the total recombination length of the shrew genome as 1145 cM. The majority of bivalents showed a high recombination frequency near the telomeres and a low frequency near the centromeres. The distances between MLH1 foci were consistent with crossover interference both within chromosome arms and across the centromere in metacentric bivalents. The pattern of recombination along a chromosome arm was a function of its length, interference, and centromere and telomere effects. The specific DNA sequence must also be important because chromosome arms of the same length differed substantially in their recombination pattern. These features of recombination show great similarity with humans and mice and suggest generality among mammals. However, contrary to a widespread perception, the metacentric bivalent tu usually lacked an MLH1 focus on one of its chromosome arms, arguing against a minimum requirement of one chiasma per chromosome arm for correct segregation. With regard to autosomal chromosomal variation, the chromosomes showing Robertsonian polymorphism display MLH1 foci that become increasingly distal when comparing acrocentric homozygotes, heterozygotes, and metacentric homozygotes. Within the sex trivalent XY(1)Y(2), the autosomal part of the complex behaves similarly to other autosomes.     

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.     

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.     

XYY spermatogenesis in XO/XY/XYY mosaic mice

The relative frequencies of XYY and XY cells in XO/XY/XYY mosaic mice were compared between somatic cells (bone marrow) and spermatogonia, and between spermatogonia and pachytene or MI spermatocytes. The results indicated there was no selection either for or against XYY spermatogonia. There was, however, a strong selection against XYY spermatocytes during pachytene, with their almost total elimination by the first meiotic metaphase. At pachytene, most XYY cells had trivalent or X univalent/YY bivalent configurations. These findings are contrasted with previous studies of XYY spermatogenesis in mice and are discussed with respect to a model that invokes sex-chromosome univalence as the cause of XYY spermatogenic failure.     

Muscle capillary supply in hind limb and diaphragm of the common shrew (Sorex araneus)

Shrew species of the subfamily Soricinae have unusually high metabolic rates when compared to Crocidurinae shrews and other similar-sized mammals. The aim of this study was to clarify whether the high basal metabolic rate of Soricinae shrews is reflected in a high capillary density in their muscles. To this end, the capillary supply of four limb muscles and diaphragm of the common shrew (Sorex araneus) was quantified from cross-sectioned muscles. The capillary densities of the limb muscles were 2575 ± 329, 3111 ± 299, 2812 ± 197 and 2752 ± 173 capillaries mm⁻² fibre area in gastrocnemius lateralis, g. medialis, plantaris and soleus, respectively. Capillary density of the shrew diaphragm (6691 ± 1057) was double that of the limb muscles. This value is among the highest ever measured in mammals. In general, the capillary supply in the hind limb of the common shrew is about 3–4 times higher than commonly found in the leg muscles of the laboratory rat or other bigger mammals, but similar to those in Crocidurinae shrews and some small rodents. Thus the high resting metabolism of the common shrew is not associated with an extraordinarily high capillary density. The apparent disparity between basal metabolic rate and muscle capillary supply in S. araneus is probably due to the small aerobic scope of shrews in the subfamily Soricinae. Accepted: 22 January 1998     

Structure and seasonal dynamics of an ectoparasite community on the common shrew (Sorex araneus) in the Il'men'-Volkhov lowland

Species composition, seasonal dynamics, and a load of ectoparasites per individual and population of the common shrew Sorex araneus have been examined in coniferous and mixed forests of the Ilmen'-Volkhov lowland (a neighbourhood of Oskuy village, Chudovo district, Novgorod Province) during the period 1999-2003. Trapping of mammals was carried monthly, with exception of few accidental gaps. The Gero traps were used for catching micromammalian hosts. The lines of trap were checked 2 times a day, places of lines changed each 3-5 day. Total number of micromammalians collected during the period of study is 3215, including 1115 specimens of the common shrew S. araneus and 246 ones of the pigmy shrew S. minutus. Parasite fauna on the common shrew included 23 ectoparasite species: fleas--12, ixodid ticks--2, gamasid mites--7, and myobiid mites--2 species. Among recorded species, 9 fleas species and some gamasid species are accidental parasites. These accidental ectoparasite species are common to the bank vole Clethrionomys glareolus in the territory investigated. Species composition, occurrence and abundance indices of parasites changed during the year. In total, about 55% shrew specimens are infected with ectoparasites. The infracommunity of ectoparasites on the common shrew usually consists of 6 species or less. Mean number of all ectoparasite individuals per one host specimens varies from 4 to 83. The greatest number of parasites (50 and 83) was recorded on the shrews, which carried 5 and 4 parasites species, respectively. Biodiversity of parasite species in the ectoparasite community on the common shrew and the load of parasites per one host specimen are lower than those in the bank vole. In forest biotopes explored, the most part of temporary ectoparasite species found on the common shrew was also recorded on other small mammals, which could have contacts with this host. It is possible to conclude that among the parasite supracommunity in the explored ecosystem, the temporary ectoparasites represent a "fond" of temporary parasites, which are common for most small mammal species. A role of different shrew and rodent species as main of additional hosts changes depending on a population density of potential mammalian hosts and other environment factors.     

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.     

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.     

Meiotic drive favors Robertsonian metacentric chromosomes in the common shrew (Sorex araneus, Insectivora, mammalia)

Meiotic drive has attracted much interest because it concerns the robustness of Mendelian segregation and its genetic and evolutionary stability. We studied chromosomal meiotic drive in the common shrew (Sorex araneus, Insectivora, Mammalia), which exhibits one of the most remarkable chromosomal polymorphisms within mammalian species. The open question of the evolutionary success of metacentric chromosomes (Robertsonian fusions) versus acrocentrics in the common shrew prompted us to test whether a segregation distortion in favor of metacentrics is present in female and/or male meiosis. Performing crosses under controlled laboratory conditions with animals from natural populations, we found a clear trend toward a segregation distortion in favor of metacentrics during male meiosis, two chromosome combinations (gm and jl) being significantly preferred over their acrocentric homologs. Apart for one Robertsonian fusion (hi), this trend was absent in female meiosis. We propose a model based on recombination events between twin acrocentrics to explain the difference in transmission ratios of the same metacentric in different sexes and unequal drive of particular metacentrics in the same sex. Pooled data for female and male meiosis revealed a trend toward stronger segregation distortion for larger metacentrics. This is partially in agreement with the frequency of metacentrics occurring in natural populations of a chromosome race showing a high degree of chromosomal polymorphism.     

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.     

Morphometric variation of the common shrew (Sorex araneus) in Britain, in relation to karyotype and geography

A multivariate study of variation in mandible dimensions was conducted to determine whether common shrews of different karyotypic race (Aberdeen, Oxford, Hermitage) in Britain differ in morphology. Differences between samples from north and south Britain suggest that geography is more important than karyotype as a morphological determinant. However, the distinctiveness of hybrids in the 'Oxford-Hermitage' hybrid zone raises the possibility that there are genetic differences between the races.     

Living at the physiological limits: field and maximum metabolic rates of the common shrew (Sorex araneus)

Shrews (genus Sorex, small insectivorous mammals) are well known for their extremely high basal metabolic rates (BMRs) even when corrected for their small body size. We measured energy expenditure of the common shrew (Sorex araneus) under natural conditions (field metabolic rate [FMR]) by doubly labeled water method to test whether FMR is proportional to high BMR in this species. The study was performed in summer in northeastern Poland. In addition to the FMR, we also measured maximum metabolic rates induced by cold exposure and by intense activity (MMRCOLD and MMRRUN, respectively) to evaluate the aerobic reserve (MMR-FMR) in S. araneus. This aerobic reserve was used as an indicator of the potential for metabolic constraints. The FMR averaged 2.31+/-0.32 L CO2 d(-1) (+/-SD) or 58.1+/-8.0 kJ d(-1) in 8.2-g animals. This figure constituted 216%-258% of a value predicted for a "standard" mammal of the same body mass and was the highest mass-specific field metabolic rate in mammals. Because of the high BMR level in S. araneus, the FMR to BMR ratio (2.4) was not far off mammalian standards (median value of 3.1). The rate of water efflux determined in S. araneus (20.2 mL H2O d(-1) or 2.46 mL H2O g(-1) d(-1)) exceeded all figures reported to date in other mammals and was apparently linked to the high FMR level and relatively high water content of shrews' food. Maximal metabolic rates (MMRRUN of 18.1+/-1.6 mL O2 g(-1) h(-1) and MMRCOLD of 23.5+/-1.9 mL O2 g(-1) h(-1)) were not high in proportion to BMR or FMR that resulted in relatively narrow aerobic reserve in S. araneus: 20% when calculated against the MMRRUN and 39% when compared with the MMRCOLD. Our study reveals that S. araneus has high energy costs of living and operates close to its physiological limits.