Contents: Volume 6 (1) 2007 (Printed 27 December 2007)

Minina J.M., Borodin P.M., Searle J.B., Volobouev V.T., Zhdanova N.S.

P. 3-6

A DAPI-banding technique was used to characterise the individual patterns of each chromosome of the Novosibirsk race of the common shrew (Sorex araneus) which has become a model for comparative gene mapping. In order to outline the main identifying characteristics of the individual chromosomes and to make comparisons to previously published G-banded karyotypes, we analysed DAPI-banded chromosomes with different degrees of condensation. On the basis of this analysis we constructed idiograms of chromosomes at a 300 band stage of resolution.

Zhdanova N.S., Minina J.M., Karamysheva T.V., Rubtsov N.B.

P. 007-013

It is widely believed that Robertsonian rearrangements have played a key role in the chromosome evolution of species of the Sorex araneus group. We present FISH data relating to the distribution of telomeric repeats and 18S rDNA on the chromosomes of Sorex araneus and Sorex granarius, which have karyotypes with almost identical chromosome arms. All chromosomes in S. araneus (Novosibirsk race) are metacentrics, whereas S. granarius has an acrocentric karyotype with two metacentric exceptions. In FISH experiments we revealed telomeric repeats at the ends of all S. araneus chromosomes but only on the short arms of S. granarius acrocentrics, which, as we have shown earlier, amount up to 300 kb in length. FISH signals of the (TTAGGG)n probe and the probe derived by microdissection of the pericentric regions of S. granarius acrocentrics a and b were co-localised or sequentially localised on distinct chromatin fibres of S. granarius. 18S rDNA clusters were found at the ends of short arms of 12 out of 16 S. granarius acrocentric pairs. In S. araneus primary cell culture fibroblasts rDNA was found at the ends of the q, t and u arms. However, after long cultivation of these cells an additional FISH signal of rDNA was found at the distal end of the o arm of chromosome go. In some regions the FISH signal of rDNA coincided with the signal of the telomeric probe. We suppose that rapid concerted evolution of telomeric and rDNA led to the repatterning of these repetitive DNA fractions in the sibling species S. araneus and S. granarius as well as the formation of “large” telomeres with unusual structure at the ends of the S. granarius chromosomes.

Karamysheva T.V., Belonogova N.M., Rodionova M.I., Rubtsov N.B., Polyakov A.V., Searle J.B., Borodin P.M.

P. 015-019

Chromosome pairing and recombination at meiosis involves scheduled formation and repair of double-strand breaks of DNA. Rad51, the eukaryotic homologue of the bacterial RecA protein, plays a crucial role in these processes. We used antibodies against human Rad51 to examine the temporal and spatial distribution of Rad51 in the spermatocytes of the common shrew Sorex araneus (Eulipotyphla, Soricidae). We found that hundreds of Rad51 foci appeared at leptotene. At the beginning of zygotene their close association with the axial elements of the synaptonemal complex became apparent. From early to late zygotene the number of Rad51 foci gradually decreased. At pachytene we observed a further dramatic decrease in the number of foci. They were distributed irregularly along autosomal bivalents. We detected a prevalence of Rad51 signals on the original X and autosomal arms of the sex trivalent at late pachytene. We did not detect a preferential association of Rad51 foci with unpaired or non-homologously paired regions of lateral elements of synaptonemal complexes in Robertsonian multivalents.

White Th.A., Searle J.B.

P. 021-025

Populations of many species are currently being fragmented and reduced by human interactions. These processes will tend to reduce genetic diversity within populations due to genetic drift, inbreeding and reduced migration. Conservation biologists need to know the effect of population size on genetic diversity as this is likely to influence a population’s ability to persist. Island populations represent an ideal natural experiment with which to study this problem. In a study of common shrews (Sorex araneus) on offshore Scottish islands, 147 individuals from 6 islands of different sizes and 2 mainland sites were trapped and genotyped at 10 microsatellite loci. Pairwise FST values (between 0.06 and 0.56) showed that all the island populations were significantly genetically divergent from one another. All island populations exhibited lower allelic diversity and heterozygosity than the mainland populations, and these measures of genetic diversity were positively correlated with log island size.

Illarionova N.A., Potapov S.G., Orlov V.N.

P. 027-033

We analysed genetic divergence between species of the genus Sorex (S. araneus, S. caecutiens, S. minutus and S. minutissimus) using the RAPD (random amplified polymorphic DNA) method. We also examined RAPDs in 26 individuals of six chromosome races of the common shrew (Moscow, Ilomantsi, St. Petersburg, Neroosa, Penza, and Sok) from the European part of Russia. Nine primers were used for the detection of 24 to 79 fragments. The number of clearly identified DNA fragments by all primers was 539. Loci specific for different chromosome races of S. araneus were revealed. On the basis of summary matrices of the RAPD spectrum for nine primers, trees showing the genetic divergence were constructed. This study demonstrated the value of RAPDs for the analysis of relationship between species and chromosome races in Sorex.

Balakirev A.E., Illarionova N.A., Potapov S.G., Orlov V.N.

P. 035-042

Genetic variation in the common shrew (Sorex araneus) in European Russia was studied using cytochrome b gene sequences. The genetic diversity, based on nucleotide substitutions (Kimura 2-parameter d=0.015±0.003, h=0.933), and the number of mtDNA haplotypes, was three times higher than described previously. However, levels of molecular divergence are often in contradiction with karyological data. While there are more than 20 karyotypic races in European Russia, only one clear phylogenetic group is revealed for cytochrome b (the North-eastern Group). The relationship of this group to other European S. araneus haplotypes is not clear. Over the main part of the European range of the common shrew geographic subdivision between haplotypes is lacking.

W?jcik J.M., Polly P.D., W?jcik A.M., Sikorski M.D.

P. 043-049

Epigenetic variation of the common shrew, Sorex araneus, was studied in three habitats (floodplain forest, wet sedge bog and dry meadow) at Bia?owie?a, north-eastern Poland. Previous chromosome and allozyme studies of the same population suggested that polymorphisms are related to environmental heterogeneity and that random factors influence frequencies of acrocentric chromosomes and alleles. In the present study we tested whether similar processes influence epigenetic variation. Thirty-one non-metric skull traits were scored in 274 individuals from samples collected in different biotopes. The specific aim of the study was to estimate non-metric trait frequencies and fluctuating asymmetry in shrews from different habitats, and to explain the factors involved in the maintenance of epigenetic polymorphism. Significant differences found among samples of shrews from different habitats indicated that important epigenetic variation exists within the population. This epigenetic variation in the common shrew appears to be related to environmental heterogeneity.

Mishta A.V.

P. 051-062

Comparisons were made of chromosomal and macro-morphological variation in two widespread chromosome races of the common shrew Sorex araneus Linnaeus, 1758 in the Ukraine using multivariate statistics. Representatives of the Kiev and Neroosa races cannot reliably be identified from craniometric characteristics. Within the two chromosome races, however, we observed a relationship between morphology and geography. About 60% of morphological variance could be explained by the influence of geoclimatic factors. It was confirmed that ecogeography is more important than karyotype as a morphological determinant in the common shrew. Highly differentiated southern Ukrainian forms of S. araneus may be regarded as ecotypes.

Okulova N.M., Balakirev A.E., Orlov V.N.

P. 063-071

Findings of gene flow across hybrid zones between karyotypic races of the common shrew, Sorex araneus Linnaeus, 1758, have contributed to the debate over the role of chromosomal changes in speciation. The correlation between chromosomal and morphological evolution was examined here across the full geographic range of the species. Previous studies on selected karyotypic races yielded ambiguous results: some found significant differences between races, but others concluded that local variation was more important than karyotype for morphological structuring. Forty three samples, representing 24 karyotypic races and three species were studied here. Geometric morphometrics were used to determine whether karyotypic, geographic or population-level structuring was present in the size and shape of molars, skulls and mandibles. Significant structuring was found in all traits among populations, among karyotypic races, among phylogenetic groups of karyotypic races and among species, greatest among populations (FST ranged from 0.08 to 0.11) and groups (FST 0.04 to 0.15). Within S. araneus structuring was greater in skull centroid size and molar shape than in skull or mandible shape. Large-scale east-to-west clines were found in molar and skull shape. The skull cline is probably associated with changes in the frequency of the upper fifth antemolar. Mandible shape was not highly differentiated between karyotypic races compared to molar shape, but it was better at discriminating among karyotypic groups and species. It is likely that fossil specimens can be determined to the level of karyotypic group, but not to a specific karyotypic race.

Polly P.D.

P. 073-084

Findings of gene flow across hybrid zones between karyotypic races of the common shrew, Sorex araneus Linnaeus, 1758, have contributed to the debate over the role of chromosomal changes in speciation. The correlation between chromosomal and morphological evolution was examined here across the full geographic range of the species. Previous studies on selected karyotypic races yielded ambiguous results: some found significant differences between races, but others concluded that local variation was more important than karyotype for morphological structuring. Forty three samples, representing 24 karyotypic races and three species were studied here. Geometric morphometrics were used to determine whether karyotypic, geographic or population-level structuring was present in the size and shape of molars, skulls and mandibles. Significant structuring was found in all traits among populations, among karyotypic races, among phylogenetic groups of karyotypic races and among species, greatest among populations (FST ranged from 0.08 to 0.11) and groups (FST 0.04 to 0.15). Within S. araneus structuring was greater in skull centroid size and molar shape than in skull or mandible shape. Large-scale east-to-west clines were found in molar and skull shape. The skull cline is probably associated with changes in the frequency of the upper fifth antemolar. Mandible shape was not highly differentiated between karyotypic races compared to molar shape, but it was better at discriminating among karyotypic groups and species. It is likely that fossil specimens can be determined to the level of karyotypic group, but not to a specific karyotypic race.

Fredga K.

P. 085-096

To clarify the number, distribution and origin of chromosome races of common shrews in northern Scandinavia, 117 specimens were karyotyped from 12 new localities, six in Sweden and six in Norway. Including previous investigations, altogether 257 specimens from 26 localities in northern Fennoscandia have been analysed. Inspection of this complete dataset shows that the Abisko chromosome race, which occupies a wide range in northern Scandinavia, should be subdivided into three races: Abisko (Ai) in the north, Ammarnдs (Am) in the centre, and Hattsjц (Ha) in the south. The characteristics of these races and their distributions are described. The colonization of small mammals into northern Scandinavia is closely associated with the history of deglaciation. Most likely, common shrews of the Abisko race were the first to spread westwards along the northern coast of Norway. Later, when the ice and water had disappeared from northern Sweden, a new and wider immigration route from the east was opened for shrews of the Ammarnдs race. Another possibility is that northern Sweden and Norway were colonized from the west by shrews which had survived the last glaciation on the isle of Andцya in northwest Norway. The Hattsjц race, located between the Ammarnдs and Sidensjц races, may be regarded as a hybrid race.

Orlov V.N., Kozlovsky A.I., Okulova N.M., Balakirev A.E.

P. 097-104

The present distribution of common shrew chromosome races indicates that the region covered by the Late Valdai ice sheet was subsequently recolonised by populations from refugia near the glacial front. The similarity of chromosome races from Finland and the Urals can be considered convergent: identical karyotypes have been formed independently on the basis of metacentrics in common and the canalisation of karyotypes. Chromosome races that survived the glaciation in southern refugia (Kiev, Neroosa, Penza and Sok) did not contribute to the postglacial recolonisation of the region vacated by the ice sheet.

Bystrakova N.V., Shchipanov N.A., Bulatova N.S., Sheftel B.I., Nadjafova R.S., Pavlova S.V., Demidova T.B., Bobretsov A.V., Aleksandrov D.Yu., Kalinin A.A., Kouptsov A.V., Volkova A.T., Oleinichenko V.Yu., Searle J.B.

P. 105-109

New information is presented on the distributional ranges of the West Dvina, Moscow, Neroosa, Serov, Sok and Yuryuzan chromosome races in European Russia. Our study provides chromosome data on 67 common shrews from 28 localities in various parts of the East European Plain and foothills of the Ural Mountains. No new chromosome races were discovered but our data added substantially to the known geographic range of the Serov race both north- and southwards from the Asian slopes of the Ural Ridge where it was first described. This race also extends into northern Europe far to the west of the Ural Ridge. The known distribution of the Neroosa race has also been considerably extended. These data allow us to predict locations for contact zones between the following pairs of races: West Dvina – Moscow, Moscow – Neroosa, Sok – Serov.

Bulatova N.S., Shchipanov N.A., Searle J.B.

P. 111-116

We provide the first description of a hybrid zone between chromosome races of Sorex araneus in Central European Russia. In the area near Lake Seliger (Upper Volga), the locally-distributed Seliger race (diagnostic chromosomes hn, ik, mq, pr, g, o) meets and hybridises with the more widespread Moscow race (gm, hi, kr, no, pq). This hybrid zone appears to be narrow and constrained to the inter-lake isthmus between Lake Seliger and the River Volga system. The hybrid zone may be centred on a minor road. Hybrids occur between the two races but at low frequency. There were three F1 hybrids out of a total of 87 specimens. These were expected to form the maximally long meiotic chain that can be found in the common shrew: a chain-of-eleven (CXI). Such a configuration was observed in meiotic preparations from one adult male F1. Two other complex heterozygote karyotypes were found. The existence of these backcross individuals reflects Robertsonian polymorphism for certain race-specific chromosomes. It is presumed that these various hybrids have reduced fertility, consistent with the narrowness of the hybrid zone and bimodal structure. This is likely to be a “strong” hybrid zone with a greater probability of reduced gene flow and evolution of reproductive isolation than other hybrid zones in the common shrew.

Shchipanov N.A.

P. 117-122

Data on population density, dispersal and homing in common shrews of the Moscow chromosome race are discussed. A population of common shrews is regarded as a set of “independent populations” with each such independent population characterised by their distinctive dynamics in population density. These distinctive dynamics result from the restricted exchange of individuals between the independent populations. The movement of individuals that belong to an independent population is hypothesised to be driven by a network of signals resulting from common activity (tunnels, nest places, pathways etc.) and direct or indirect social interactions (aggression, acoustic communication, scent marks and so on), i.e. Naumov’s “signals field”. Data on year to year fluctuations of population density in two closely located sampling sites were used to reveal independent populations of this sort. Homing experiments were conducted to establish areas through which shrews are most likely to travel. Surveys of micromycetes on the fur support the idea of discontinuity between independent populations. The boundaries between different chromosome races in continuous forests may be explained in terms of the low probability of dispersal of shrews beyond the area of an independent population.