A POSSIBLE CYTOGENETIC ANALOGY TO GENOMIC «SPECIATION ISLANDS¼ AS REVEALED BY CHROMOSOME STUDY OF A NATURAL HYBRID VOLE.

Chromosome analysis in mammals over the last half century has largely focused on species identification. A growing number of hybrid zones of karyotypically differentiated cryptic taxa have been described. A good example is provided by two karyoforms of the 46-chromosome common vole (long known as «arvalis¼ and «obscurus¼) that make contact longitudinally from the north to the south of European Russia. The hybrid F1 karyotype displays genomic markers which distinguish arvalis and obscurus and which are cytogenetically detectable as minor variants. The apparent insignificance of the genomic region of heterozygosity associated with these markers perhaps does not prevent hybrid chromosome pair formation at meiosis but may reflect a site resistant to gene flow. A cytogenetic analogy with so-called «speciation islands¼, based, for example, on the study of the corvine hybrid zone and represented by a small number of limited genomic sites (occupying less than 1 % of the genome) (Poelstra et al., 2014), may be relevant.

[The role of hybrid zones in speciation: a case study on chromosome races of the house mouse Mus domesticus and common shrew Sorex araneus].

Although diverse complexes of chromosome races are of rather rare occurrence in mammals, that does not reduce its importance to insignificant phenomenon not worthy of studying as some unique case without direct analogy. Moreover, these complexes present virtually ideal models for estimation of the impact of hybridization on the process of microevolution. The chromosome races are characterized by almost zero level of genetic differentiation and well-defined distinctions, usually induced by chromosome rearrangements only. The presented review shows the valuable contribution of the studies on Sorex araneus and Mus domesticus chromosome Robertsonian systems into our understanding of varied impacts of hybridization on the speciation process. Particularly, it promotes better understanding of such evolutionary phenomena as "reinforcement" of reproductive isolation in secondary contact zones between divergent populations, speciation without geographic separation ("divergence with gene flow"), and "zonal raciation".

[Molecular cytogenetic markers of cryptic species and hybrids of the common vole superspecies complex Microtus arvalis s. l].

Molecular markers of cryptic cytogenetical differentiation were shown in chromosomal polymorphic Pan-European model group of rodents Microtus arvalis s. l. by FISH analysis. The polytypy of 46-chromosomes karyotypes determined by the sites of interstitial telomeric sequences (ITS) and ribosomal DNA emphasizes the genetical isolation of M. arvalis s. s. and M. obscurus.

Three new karyotypes extend a Robertsonian fan in Ethiopian spiny mice of the genus Acomys I. Geoffroy, 1838 (Mammalia, Rodentia).

Three new karyotypes (2n=40, 44, 52) are described revealing what are probably new cryptic species of Ethiopian spiny mice. Two other diploid numbers have already been reported for the country (2n=36 and 68) and, overall, the five known karyotypic forms constitute a common lineage differentiated by a Robertsonian process. Such arrays of karyotypic forms are known as a 'Robertsonian fan'. This view of the situation in Ethiopian Acomys I. Geoffroy, 1838 is based on standard chromosomal morphology that reveals a constant FN (68) and needs further investigation of chromosome homology by differential staining and/or molecular cytogenetic techniques as well as further molecular phylogenetic analysis.

[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.

[Genomic versus chromosomal polytypy in studies of mitochondrial and nuclear DNA markers in the Microtus arvalis group].

Common voles of the Microtus arvalis group distributed over the territory of European Russia are represented by three karyotypic categories, i.e., sympatric sibling species with 2n = 46 and 54, and two allopatric karyoforms in one of them, 2n = 46. For each category, molecular markers were found. For two 46-chromosome forms (arvalis and obscurus), DNA was for the first time studied in karyotypes and non-karyotyped specimens for a parapatric hybrid zone, where high diversity of intermediate karyotypes was recorded. Preferential migration of the mitochondrial markers in arvalis and significant differences in the cline width for chromosomal and nuclear markers in obscurus were shown. The hybrid zone examined exhibited unusual combination of such features as the practically complete absence of "pure" representatives of the original parental forms and a clear deficiency of the first generation hybrids. The mtDNA divergence for the arvalis and obscurus karyogroups (4.6%) is comparable to the lowest limit for interspecies differences within the large and complex genus Microtus.

[Cytogenetic study of the parapatric contact zone between two 46-chromosomal forms of the common vole in European Russia].

Since the first description of sympatric sibling species and allopatric chromosomal forms of the common vole (Microtus arvalis group) in 1969, the search of their range boundaries has been Continually going on up to the present time. Based on the cytogenetic material presented in the present study, the geographical distribution of two karyoforms (2n = 46: NF = 84 and NF = 72) was examined in 20 geographic localities of European Russia (within the interval between the longitude 34 degrees-56 degrees East and 51 degrees-61 degrees). The places of findings of two karyoforms, "arvalis" and "obscurus", in Russia have been supplemented and were shown to be significantly closer; whereas the well-known distribution boundaries for the "obscurus" form were specified in the northern and southern parts of Russia.A direct evidence of parapatric distribution and hybrid zone formation between the "arvalis" and "obscurus" karyoforms was obtained, which suggests the possibility of studying the evolutionary relations ships between two genomes in the Russian part of the group range under the natural experimental conditions-the hybrid zone at the boundary between the "arvalis" and "obscurus".

[Polyploid races of earthworms (Lumbricidae, Oligochaeta) in the East European plain and Siberia].

The distribution of polyploid races of earthworms in the East European plain and Siberia was analyzed. Amphimictic autopolyploid races of two species of the Asian genus Eisenia, E. nordenskioldi and A. atlavinyteae, are widespread in Siberia, from its southern boundary to the arctic region, while polyploid Lumbricidae in the East-European plain, except for the Volga region, are represented mainly by parthenogenetic forms of other genera. This is presumably related to differences in the Pleistocene environmental history between the two adjacent geographic regions of Eurasia.

[Distribution of two chromosome races of the common shrew (Sorex araneus L.) in the hybrid zone: may a change of the dispersal mode maintain independent gene frequencies?].

Combination of different dispersal modes may itself, without external obstacles, lead to the appearance of subdivided populations and maintain the existence of independent population systems. The common shrew, a mammal convenient for studying different levels of intraspecific differentiation, was the object of the study. Empirical data have been used for simulation taking into account the change of dispersal modes in the population area. The obtained results agree with empirical data on the distribution of races and hybrids in the hybrid zone of chromosome races Moscow and Seliger. Change of the dispersal mode may maintain independent population dynamics and, in the case of chromosome races, prevent the migration of parental individuals into the territory of the other race.

[Cytogenetic control of a hybrid zone of between two Sorex araneus chromosome races before breeding season].

Two chromosome races of common shrew, Moscow and Seliger, differ in the arm combination in 11 diagnostic chromosomes (Robertsonian metacentrics/acrocentrics). Homozygotes of both pure races, simple Robertsonian heterozygotes of Seliger race, and complex heterozygotes (FI hybrids) were detected in the found earlier between hybrid zone of these races, in the spring before the breeding seasonbreeding season. The g/oheterozygote was first discovered in race Seliger, whose chromosome formula typically contains acrocentrics g and o. The m/q heterozygote was recorded for the second time. Meiosis was studied in 16 males representing five detected karyotypic categories. No abnormal in pairing of homologs in either sex trivalent common for the species (XY1Y2) or autosome trivalents (g/o and m/q) was detected at diakinesis--metaphase I. Two hybrids displayed a theoretically expected and unimpaired meiotic configuration in a form of a very long chain comprising 11 monobrachial homologs (g/gm/mq/qp/pr/rk/ki/ih/hn/no/o). The results are discussed in terms of hypotheses on fertility of complex heterozygotes and limited gene flow in hybrid zone.

[Molecular variability in the commom shrew Sorex araneus L. from European Russia and Siberia inferred from the length polymorphism of DNA regions flanked by short interspersed elements (Inter-SINE PCR) and the relationships between the Moscow and Seliger chromosome races].

Genetic exchange among chromosomal races of the common shrew Sorex araneus and the problem of reproductive barriers have been extensively studied by means of such molecular markers as mtDNA, microsatellites, and allozymes. In the present study, the interpopulation and interracial polymorphism in the common shrew was derived, using fingerprints generated by amplified DNA regions flanked by short interspersed repeats (SINEs)-interSINE PCR (IS-PCR). We used primers, complementary to consensus sequences of two short retroposons: mammalian element MIR and the SOR element from the genome of Sorex araneus. Genetic differentiation among eleven populations of the common shrew from eight chromosome races was estimated. The NP and MJ analyses, as well as multidimensional scaling showed that all samples examined grouped into two main clusters, corresponding to European Russia and Siberia. The bootstrap support of the European Russia cluster in the NJ and MP analyses was respectively 76 and 61%. The bootstrap index for the Siberian cluster was 100% in both analyses; the Tomsk race, included into this cluster, was separated with the bootstrap support of NJ/MP 92/95%.

[Intraspecies phylogenetic connections in Sorex araneus L.: a southern Baltic subgroup of chromosome races]. / Vnutrividovye filogeneticheskie sviazi u Sorex araneus L.: iuzhnobaltiiskaia podgruppa khromosomnykh ras.

Results of chromosome G-banding were used to identify two new karyotypic races of the common shrew (Sorex araneus L.) in the European part of Russia. The chromosomal diagnosis of race St. Petersburg included five metacentrics (hk, ip, jl, mq, and nr) and two acrocentrics (g and o) (2Na = 20); the diagnosis of race West Dvina included six metacentrics (gm, hk, ip, jl, no, and qr) (2Na = 18). The phylogenetic significance of the chromosomal markers gm, hk, and ip is considered and the possibility of reticulate evolution in the species S. araneus is discussed.

[Identification of structural rearrangements in the karyotype of Microtus oeconomus from Chernobyl by differential staining of chromosomes]. / Identifikatssiia strukturnoi perestroike v kariotipe polevki-ékonomki iz Chernobylia metodami differentsial'noi okraski khromosom.

Karyological studies of rodents within a 30-km radius of the Chernobyl' nuclear power plant revealed one female root vole (Microtus oeconomus) with an abnormal karyotype. The use of C, G, and AgNOR banding methods allowed us to determine that morphological changes in two nonhomologous autosomes, which were accompanied by rearrangements in distribution of G bands, heterochromatin, and NOR, are the result of a reciprocal translocation. Chromosomal aberrations were probably inherited or appeared in embryogenesis, since none of the analyzed cells of the studied vole had a normal karyotype. It is important to note that this rearrangement was detected five years after the meltdown. Both breaks and reunions of the chromosomes that participate in this rearrangement are probably located in regions that are not important for functioning of these chromosomes. Thus, it can be supposed that the detected rearrangement did not influence the viability of the vole. This karyotype was compared to a standard karyotype of a root vole from another area of the species range. The heteromorphism of the first pair of chromosomes in both voles, which was detected for the first time, is probably normal for the karyotype of M. oeconomus, and is not linked with any radiation-induced intrachromosomal aberrations.