In 1996 the International Sorex araneus Cytogenetics Committee (ISACC) published a comprehensive list of 50 chromosome races of the common shrew Sorex araneus (Zima et . 1996). Since that time twenty one new races have been described and three races have been removed from the list. The present list summarises the data about races described since the 1996 publication. The rules introduced by Searle et ai (1991) and Hausser et al (1994) were followed in the compilation of the list. It can be considered a reference for further studies of evolutionary relationships between the chromosome races of Sorex araneus. A summary table of all the 68 known races, arranged alphabetically according to their names, is given. RESUMEEn suivant les principes de nomenclature des chromosomes de Sorex araneus (Searle et al. 1991) et ceux de la definition de ses races chromosomiques , PISACC (International Sorex araneus Cytogenetics Committee) a public en 1996 la premiere liste de races chromosomiques de 5. araneus (Zima et al., 1996). Elle comprenait 50 races chromosomiques. Depuis, 21 race nouvelles ont etc decrites et trois races ont etc eliminees de cette liste. Nous presentons ici la liste revisee des races chromosomiques de 5. araneus qui comprend actuellement 68 races.

Two parapatric chromosomal races of the common shrew (Sorex araneus) in Poland differ in their complement of metacentric arm combinations: hk, io, gr, nm (race IV), and hi, ko, gm, np (race II). In hybrids, these eight race-diagnostic metacentrics form two randomly segregating complexes. The first complex (C ) occurs in the form of a ring configuration ok/kh/hi/io, or a chain o/ok/kh/hi/i (when there is Robertsonian polymorphism of the element io). The second complex (C ) always takes the form of a six-element chain configuration r/rg/gm/mn/np/p. The C complex may be shortened to five or even four elements, when acrocentrics g, m and n are present. In the contact zone we found shrews of pure races (race II or IV), as well as hybrids with C or C complexes, and recombinants hi, ko, gr, nm. Complex heterozygotes are likely to suffer reduced fertility due to malsegregation at meiosis. However, the C hybrids with ring configurations occur with a high frequency throughout the contact zone. This suggest that their fitness is only slightly lowered relative to pure race individuals, in contrast to the hybrids with C or C chain configurations, which presumably have a more heavily reduced fertility. On the other hand, at the center of the zone there is a high proportion of recombinants, which, being chromosomal homozygotes, should display normal meiotic segregation. Furthermore, the high frequencies of recombinants within the contact zone should facilitate gene flow between the races. The occurrence of recombinants plays a similar role as the appearance of the maximum frequencies of acrocentric homozygotes described in several contact zones of S. araneus.

The list of chromosome races of the common shrew (Sorex araneus) was compiled, the vast literature has been scrutinized, and unpublished data have been added. Altogether, 50 chromosome races could be listed. The name and its synonyms, chromosomal constitution, author of the description, type locality, known distribution range, and additional information are reported for individual races. The present list should be considered a working document that will be regularly updated and supplemented.

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Editorial comment. The common shrew, one of the characteristic small mammal species of Europe and neighbouring Asia, has for decades been a focus of cytogenetic investigation due to remarkable chromosome variation at an individual as well as at a population level. It is a fi ne example of long-term international collaboration through a scientifi c grouping founded in 1987 as the International Sorex araneus Cytogenetics Committee (ISACC). The cytogenetic characterisation of common shrews over the whole species range, from Britain in the west to the Lake Baikal in the east, was predicated on standard rules developed by the Committee. Thus, the basic nomenclature for Sorex araneus chromosomes and chromosome races was published in the proceedings of the second ISACC meeting held in Lausanne, Switzerland in 1990 and published in a local journal not available to many young people involved in chromosome studies of the species, in particular those based in Russia. The Editorial Board thanks Société vaudoise des Sciences Naturelles for permission to republish this paper here. Original: © Mém. Soc. Vaudoise Sci. Natur. 19: 13-22 (1991). Abstract.A G-band composite karyotype has been prepared for the common shrew (Sorex araneus Linnaeus, 1758). This includes multiple cut-outs of each chromosome arm (in different stages of contraction) derived from chromosome spreads prepared by a variety of methods by the different authors. The important features of each chromosome arm are described. The nomenclature for the chromosome arms follows that of Halkka et al. (1974) as clarifi ed by Fredga, Nawrin (1977) and subsequent authors, i.e. italicised letters of the alphabet are used with a as the largest chromosome arm. Different authors have used a variety of methods to describe the karyotype of (a) individuals and (b) the pattern of variation within populations. Also, defi nitions of chromosomal 'race' differ. We suggest a standardised scheme for the description of individuals, populations and chromosomal races.

Spermatogenesis was studied in 56 shrews (Sorex araneus L.) from two chromosomal hybrid zones in Poland. The hybrid zones were formed between chromosome races that diered in Robertsonian metacentrics. Shrews were compared in four classes: homozygotes, simple Robertsonian heterozygotes, complex heterozygotes forming four-element rings in meiosis I, and complex heterozygotes forming four-or ®ve-element chains. There was a signi®cant eect of karyotype on the level of germ-cell death and chain-forming complex heterozygotes suered the greatest germ-cell loss. However, the estimated level of germ-cell death is probably insucient to in¯uence the fertility of these males.Keywords: chromosome races, common shrew, complex heterozygotes, hybrid zone, Sorex araneus, spermatogenesis. IntroductionThe common shrew (Sorex araneus L. 1758) shows exceptional chromosome variation at both the intraand interpopulation level. The variability of the common shrew karyotype is based on the occurrence of Robertsonian (centric) fusions and whole-arm reciprocal translocations (see Searle, 1993). Interpopulation chromosome variation manifests itself as the presence of chromosome races, that dier either in the chromosome arm combination of the metacentrics, or the number of these metacentrics relative to the ancestral acrocentric complement (for the list of races see Zima et al., 1996). Metacentrics speci®c to neighbouring races may show monobrachial homologies relative to one another (i.e. metacentrics have one arm in common). In consequence, interracial hybridization gives rise to hybrids that form chromosome multivalents at prophase I of meiosis. Chromosome multivalents consisting of meta-and acrocentrics form chain (CH) con®gurations, whereas ring (R) con®gurations are formed by the metacentrics only.It is commonly thought that a balance between dispersal and selection against hybrids maintains chromosomal hybrid zones. Selection against hybrids results from their lowered fertility caused by the presence of atypical con®gurations at meiosis I. Meiotic disorders, such as a failure of homologous chromosomes to pair accurately at prophase I and an increased level of nondisjunction at anaphase I, may lead to the greater germ-cell death and postzygotic loss of aneuploid embryos. Pairing irregularities may lead to germ-cell death as a result of inappropriate expression of genes at unpaired regions of autosomes (Miklos, 1974; Burgoyne & Baker, 1984) or as a consequence of interactions between the sex chromosomes in males and unsynapsed regions of autosomes (Forejt, 1984).Although the lower ®tness of hybrids may be inferred from the structure of many chromosomal hybrid zones (see Searle, 1993; Searle & Wo jcik, 1998), direct data on the fertility of hybrids of the common shrew are still scarce. This paper presents results of studies on spermatogenesis in male common shrews aimed to establish the relationship between level of germ-cell death and karyotype. The males come from two hybrid zones: one between the Drnholec (Dn) and èeË gucki Møyn (...

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.

We established the location of the contact zone between the Drnholec (diagnostic metacentrics hi, ko, gm, nr) and Bialowieza (hn, ik, gr, mp) races of the common shrew in eastern Poland. The hybrids in this zone form meiotic chain configurations consisting of a maximum of 10 elements. Moreover, we caught 13 different types of hybrids with shorter chain complexes, resulting because of a polymorphism for metacentrics ko, nr, gr. The Drnholec/Bialowieza contact zone is stabilized on an environmental barrier (a railway embankment). The sharp change in frequencies of diagnostic metdcentrics across the railtrack showed that it was a strong barrier to migration of the shrews. At present it is difficult to say whether there is any mechanism enhancing fertility in the hybrid populations.