Diversity of tuco-tucos (Ctenomys, Rodentia) in the Northeastern wetlands from Argentina: mitochondrial phylogeny and chromosomal evolution

Tuco-tucos (small subterranean rodents of the genus Ctenomys) that inhabit sandy soils of the area under the influence of the second largest wetland of South America, in Northeastern Argentina (Corrientes province), are a complex of species and forms whose taxonomic status were not defined, nor are the evolutionary relationships among them. The tuco-tuco populations of this area exhibit one of the most ample grades of chromosomal variability within the genus. In order to analyze evolutionary relationships within the Corrientes group and its chromosomal variability, we completed the missing karyotypic information and performed a phylogenetic analysis. We obtained partial sequences of three mitochondrial markers: D-loop, cytochrome b and cytochrome oxidase I. The Corrientes group was monophyletic and split into three main clades that grouped related karyomorphs. The phylogeny suggested an ancestral condition of the karyomorph with diploid number (2n) 70 and fundamental number (FN) 84 that has evolved mainly via reductions of the FN although amplifications occurred in certain lineages. We discuss the relationship between patterns of chromosomal variability and species and groups boundaries. From the three main clades the one named iberá exhibited a remarkable karyotypic homogeneity, and could be considered as an independent and cohesive evolutionary lineage. On the contrary, the former recognized species C. dorbignyi is a polyphyletic lineage and hence its systematic classification should be reviewed.     

Intraspecific chromosome variation between different populations ofCtenomys dorbignyi (Rodentia, Ctenomyidae) from Argentina

We used banding techniques to analyze the karyotypes of 17 individuals ofCtenomys dorbignyi Contreras and Contreras, 1984, from populations in Corrientes (Mbarigüí, the type locality, and Sarandicito) belonging to the previously known range of the species, and Entre Ríos (Tiro Federal and Paso Vera) representing a new geographically isolated group of populations. All known populations have 2n=70 although the extreme geographic isolation of the different localities suggested the possibility of chromosomal divergence. We found three different karyomorphs; two of them (Mbarigüí and Sarandicito) had 6 pairs of biarmed autosomes and 28 pairs of telocentric autosomes, with an FN=80. Pair 20 (telocentric) was the carrier of the only detected NOR. However, pair 2 was clearly different in each of these two, being metacentric in Sarandicito and submetacentric in Mbarigüí. The third fixed karyomorph differed significantly from the others, showing 8 pairs of biarmed autosomes and 26 pairs of telocentric autosomes, with an FN=84. Pair 3 (biarmed) was the carrier of the single NOR detected. The NOR carrier also showed a marked heteromorphism (Corrientes vs Entre Ríos) evidenced by differences in the length of the short arm. These observations revealed a chromosomal polytypism that was expected owing to the disjunct geographic distribution of the species.     

Genetic differentiation among distinct karyomorphs of the wolf fish Hoplias malabaricus species complex (Characiformes,Erythrinidae) and report of unusual hybridization with natural triploidy

In this study, genetic differentiation between karyomorphs A (2n = 42) and D (2n = 39/40) of the wolf fish Hoplias malabaricus, which is comprised of several cryptic species that present a wide variety of diploid chromosome numbers and sex chromosome systems, resulting in the identification of seven distinct karyomorphs (A–G), was investigated using a combination of molecular and cytogenetic tools. Deep sequence divergences for both karyomorphs were observed and indicate a long period of reproductive isolation between karyomorphs A and D. Additionally, one individual with 61 chromosomes was identified, which, as far as is known, is the first case of natural triploidy resulting from the hybridization between these highly differentiated karyomorphs of H. malabaricus. Molecular and cytogenetic analyses revealed that this allotriploid specimen carries two sets of maternal chromosomes from karyomorph D (2n = 40) and one set of chromosomes from karyomorph A (n = 21). Moreover, ribosomal sites and active nucleolus organizer regions from both parental contributors were found in the triploid hybrid. Considering the significant genetic distances between karyomorphs A and D, one of the primary reasons for the lack of recurrent reports of hybridization in the H. malabaricus species complex may be due to post‐zygotic barriers, such as hybrid sterility or unviability.     

Multiple autosomal polymorphism in populations of Akodon simulator simulator Thomas, 1916 from Tucumán,Argentina (Rodentia,Cricetidae)

Cytogenetic analysis was performed on twenty seven specimens of Akodon simulator simulator collected in three different localities of Tucumán Province, Argentina. Diploid number, chromosomal morphology and C and G banding patterns were studied. Eight different karyomorphs were found, with diploid numbers of 2n=38, 39, 40, 41, and 42. All individuals showed the same number of chromosomal arms (FN=42). G-bands enable to identify chromosomal pairs (1, 10, 11, 12, 13, and 14) involved in three centric fusions. C-bands revealed that the heterochromatin is located in centromeric regions of the telocentric and biarmed chromosomes. The present study allowed us to document a new example of a floating multiple Robertsonian fusion polymorphism. The data are discussed in relation to the occurrence of Robertsonian polymorphism in natural populations.

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Resumen Polimorfismo autosómico múltiple en poblaciones de Akodon simulator simulator Thomas, 1916 de Tucumán, Argentina (Rodentia, Cricetidae). Se realizó un análisis citogenético de 27 especímenes de Akodon simulator simulator colectados en tres localidades diferentes de la provincia de Tucumán, Argentina. Se determinó el número diploide, la morfología cromosómica y los patrones de bandeo C y G. Se encotraron 8 cariomorfos differentes, con números diploides de 2n=38, 39, 40, 41, y 42. Todos los individuos presentaron el mismo número de brazos cromosómicos (FN=42). Las bandas G permitieron identificar los pares cromosómicos (1, 10, 11, 12, 13, y 14) involucrados en tres fusiones céntricas y las bandas C revelaron que la heterocromatina está localizada en las regiones centroméricas de los cromosomas telocéntricos y de los cromosomas bibraquiados. El presente estudio nos permite analizar un nuevo ejemplo de un polimorfismo robertsoniano. Los datos son discutidos en relación con la presencia de los polimorfismos robertsonianos en la naturaleza.

     

Chromosome spreading of associated transposable elements and ribosomal DNA in the fish Erythrinus erythrinus. Implications for genome change and karyoevolution in fish

Background  

The fish, Erythrinus erythrinus, shows an interpopulation diversity, with four karyomorphs differing by chromosomal number, chromosomal morphology and heteromorphic sex chromosomes. Karyomorph A has a diploid number of 2n = 54 and does not have differentiated sex chromosomes. Karyomorph D has 2n = 52 chromosomes in females and 2n = 51 in males, and it is most likely derived from karyomorph A by the differentiation of a multiple X₁X₂Y sex chromosome system. In this study, we analyzed karyomorphs A and D by means of cytogenetic approaches to evaluate their evolutionary relationship.     

Discovery of a diploid population of theHemidactylus garnotii-vietnamensis complex (Reptilia: Gekkonidae)

A diploid member of the parthenogenetic gekkonid species complexHemidactylus garnotii-vietnamensis was discovered for the first time from Thailand. This gecko, seemingly unisexual and parthenogenetic, possesses 2n=2x=38 chromosomes, showing distinct heteromorphisms. The absence of bisexual congeneric species with a combination of karyomorphs to produce this karyotype indicates the occurrence of chromosomal rearrangements after the initial estabilishment of a diploid clonal lineage of hybrid origin. Results of karyotypic comparisons of the present sample and the three known triploid species belonging to theH. garnotii-vietnamensis complex suggest that a triploid karyomorph similar to that ofH. vietnamensis has first emerged through an insemination of the diploid parthenogen's egg by the sperm from a bisexual species having 44 chromosomes (all telocentric), and that the karyomorph subsequently experienced some minor chromosomal aberrations to produce the karyomorphs ofH. vietnamensis andH. garnotii. The origin of theH. stejnegeri karyotype still remains an open question for future studies.     

Loss of nucleolar organizer regions during chromosomal evolution in the South American cricetid Graomys griseoflavus

Graomys griseoflavus is a South American phyllotine rodent having a remarkable Robertsonian polymorphism which may have produced reproductive isolation between 2n=42–41 and 2n=38–34 karyomorphs. Analysis of nucleolar organizer region (NOR) locations both by silver staining (Ag-NOR) and in situ hybridization revealed that 2n=42 individuals exhibit highly variable Ag-NOR patterns, while specimens of the 2n=38–34 karyomorphic group showed a single Ag-NOR pattern. The latter animals underwent two NOR deletions in reference to the 2n=42 karyomorphs, one of which would be the consequence of a Robertsonian fusion and the other would be produced by the unequal crossing-over mechanism. The differential NOR homogenization supports the hypothesis that G. griseoflavus karyomorphs are evolving separately towards the acquisition of separate species status.     

Differentiation and evolutionary relationships in Erythrinus erythrinus (Characiformes, Erythrinidae): comparative chromosome mapping of repetitive sequences

Erythrinus erythrinus presents extensive karyotypic diversity, with four karyomorphs (A–D) differing in the number of chromosomes, karyotype structure or sex chromosomes systems. Karyomorph A has 2n = 54 chromosomes in males and females without heteromorphic sex chromosomes, while karyomorph C has 2n = 52 chromosomes in females and 2n = 51 chromosomes in males, due a X₁X₁X₂X₂/X₁X₂Y sex chromosome system. Three allopatric populations of the karyomorph A and one population of the karyomorph C were now in deep investigated by molecular cytogenetic analyses, using repetitive DNAs as probes. The results reinforced the relatedness among populations of the karyomorph A, despite their large geographic distribution. Karyomorph C, however, showed a remarkably difference in the genomic constitution, especially concerning the amount and distribution of the 5S rDNA and Rex3 sequences on chromosomes. In addition, although karyomorphs C and D share several features, exclusive chromosomal markers show the derivative evolutionary pathway between them. Thus, besides the classical chromosomal rearrangements, the repetitive DNAs were useful tools to reveal the biodiversity, relatedness and differentiation of this fish group. The chromosomal set strongly corroborates that E. erythrinus corresponds to a species complex instead of a single biological entity.     

Population and species boundaries in the South American subterranean rodent Ctenomys in a dynamic environment

Subterranean rodents of the genus Ctenomys are an interesting system to assess the effects of habitat instability on the genetic structure of populations. The perrensi group is a complex of three species (C. roigi, C. perrensi and C. dorbignyi) and several forms of uncertain taxonomic status, distributed in the vicinity of the Iberá wetland in Argentina. Because of limited availability of suitable dry habitat, Ctenomys populations are distributed patchily around a vast mosaic of marshes, swamps and lagoons and become connected or isolated over time, depending particularly on the precipitation regime. Genetic variation at 16 microsatellite loci in 169 individuals collected in the area revealed eight clusters of populations which are thought to be evolutionary units, but which do not fit previous species limits. We interpret this lack of congruence between taxonomy and genetic structure as the result of a dynamic population structure. Where populations become connected, hybridization is possible. Where populations become isolated, rapid genetic divergence may occur. In the perrensi group, it appears that both of these factors disrupt the association between different genetic and morphological characters. The study of multiple characters is crucial to the understanding of the recent evolutionary history for dynamic systems such as this. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 368–383.     

Molecular and karyotypic phylogeography in the Neotropical Hoplias malabaricus (Erythrinidae) fish in eastern Brazil

The sedentary, predatory characin Hoplias malabaricus has one of the widest distributions of freshwater fishes in South America and is characterized by seven karyomorphs (A–G) that occur in sympatric and allopatric populations. Karyotypical patterns of variation in wild populations have been interpreted as evidence of multiple lineages within this nominal species, a possibility that may limit the validity of experimental data for particular karyomorphs. This study used the phylogeographic and genealogical concordance between cytogenetic (N = 49) and molecular (mitochondrial DNA) (N = 73) data on 17 samples, collected in 12 basins from south‐eastern and north‐eastern Brazil, to assess the systematic value of cytogenetic data. Cytogenetic patterns show a sex chromosome system in the 2n = 40F karyomorph. Molecular and cytogenetic data indicate a long, independent evolutionary history of karyomorphs and a coastal origin of continental populations in south‐eastern Brazil. The lack of fit with molecular clock expectations of divergence between groups is likely to be due to strong demographic fluctuations during the evolution of this species complex. The results indicate that karyotypical identification provides a reliable baseline for placing experimental studies on Hoplias spp. in a phylogenetic context.     

Autosomal and sex chromosomal polymorphisms with multiple rearrangements and a new karyotype in the genus Rhipidomys (Sigmodontinae, Rodentia)

Two diploid numbers and five karyomorphs were found in ten specimens of Rhipidomys (Sigmodontinae, Rodentia) from three states in Brazil: 2n = 50 from Amazonas, and 2n = 44 from Mato Grosso and Bahia. CBG, GTG, and RBG-banding and Ag-NOR analyses were performed, as well as fluorescence in situ: hybridization with (T2AG3)7 probes. The new diploid number of 2n = 50 was associated with two different fundamental numbers (FN = 71 and 72) as a result of pericentric inversions and addition/deletion of constitutive heterochromatin. The samples from two localities (Aripuan? and Vila Rica) in the state of Mato Grosso shared 2n = 44 and FN = 52, but their karyotypes differed because of pericentric inversions. Although the single specimen from Bahia had the same diploid number as the samples from Mato Grosso, its karyotype and FN were completely distinctive. Karyological comparison of GTG-banding patterns revealed total homology between the karyotypes of the specimens from Bahia and Mato Grosso, implying the occurrence of 14 autosomal pericentric inversions. Homologies between ten of the autosomes in the karyotypes with 2n = 50 (FN = 72) and 2n = 44 (from Vila Rica, MT) were demonstrated. The differentiation between 2n = 44 and 2n = 50 involved five pericentric inversions, addition/deletion of constitutive heterochromatin in both autosomes and sex chromosomes, at least one Robertsonian rearrangement and other not detected rearrangements. Despite the remarkable number of rearrangements, interstitial telomeric sites (ITS) were not detected. Sex chromosomes also exhibited polymorphism in size and morphology.     

Phylogenetic analysis of G-banded karyotypes among the South American subterranean rodents of the genus Ctenomys (Caviomorpha: Octodontidae), with special reference to chromosomal evolution and speciation

The chromosomes of subterranean rodents of the South American genus Ctenomys are highly variable with diploid numbers ranging from 10 to 70. The phylogenetic relationships of this group have been analysed cladistically using G-banded karyotypes as have the chromosomal rearrangements involved in its karyotypic differentiation. One group, called the 'Corrientes group', has very variable chromosomes but low allozymic and morphological differentiation among its members. This group has been analysed with respect to chromosomal speciation. Using a member of another subfamily (Octodontomys gliroides) as an outgroup, the results indicate that karyotypes with low diploid and fundamental numbers are plesiomorphic. The range of diploid numbers studied here is between 22 and 70, while the fundamental numbers are between 40 and 86. It was found that the main chromosomal rearrangement that transforms karyotypes towards higher diploid and fundamental numbers is the acquisition of new chromosomal material via unknown mechanisms, followed by pericentric inversions that generate new chromosomal arms, centric fusions and centric fissions. In spite of their low differentiation regarding allozymic and morphological features, it was found that the karyomorphs of the Corrientes group have enough chromosomal differentiation to consider them as distinct species. Beside the range of diploid and fundamental numbers of this group (42–70 and 80–84 respectively), their pairwise chromosomal differences are high. The most closely related of them differ in one nonhomologous arm, one Robertsonian change and a whole chromosome duplication. The most differentiated taxa differ in 20 arms with lack of homology, 12 Robertsonian changes (one with monobrachial homology), six pericentric inversions and the above mentioned probable arm duplication. For these reasons, it is probable that some kind of chromosomal speciation has occurred in the Corrientes group.     

Supernumerary chromosomes,Robertsonian rearrangement and variability of the sex chromosomes inNectomys squamipes (Cricetidae,Rodentia)

Chromosomes were analyzed in 91 specimens ofNectomys squamipes, collected in three distinct geographic regions of Brazil. Chromosomal polymorphism due to supernumerary chromosomes, Robertsonian rearrangement and variation of sex chromosomes is reported. Samples collected in the northeastern region had 2n=52, FN=52; 2n=53, FN=54; 2n=54, FN=56; 2n=55, FN=56; 2n=56, FN=56; 2n=57, FN=57. The specimens from the southeastern and southern regions showed 2n=55, FN=56; 2n=56, FN=56; 2n=57, FN=58; 2n=58, FN=60; 2n=59, FN=62. Seven different types of supernumeraries were observed. These vary in size, morphology and C-banding characteristics.The Brazilian populations ofNectomys squamipes are composed of at least two basic entities, one with 2n=52 and its increasing series up to 2n=55, the other with 2n=56, increasing to 2n=59. Both entities are characterized by variation from 0 to 3 supernumeraries. The X and Y chromosomes present polymorphisms in terms of the size, shape as well as the distribution of constitutive heterochromatin.This research was supported by CNPq-PIG (Projeto Integrado de Genética) and is part of the Rodent Cytogenetic Colaborative Study, developed by different Laboratories in Brazil.     

Molecular analysis of populations of Ctenomys (Caviomorpha,Rodentia) with high karyotypic variability

The tuco-tucos (Ctenomys) are South American subterranean rodents that are some of the most chromosomally variable of all mammals. In this study we focus on Ctenomys of the "Corrientes species group" from that Argentine province and consisting of C. dorbignyi, C. perrensi, C. roigi and unnamed populations (Ctenomys sp.). A diploid range of 41-70 has been demonstrated for these taxa with multiple Robertsonian changes, pericentric inversions, heterochromatic modifications and other chromosomal rearrangements. To analyse the molecular variation in the Corrientes group, a 402 base pair fragment of mitochondrial cytochrome b was sequenced in 75 individuals from 26 populations. This generated 15 different haplotypes which were subjected to phylogenetic analysis. The different species within the Corrientes group failed to form monophyletic groups in the phylogenetic trees we generated and the divergences between haplotypes were low. Therefore, these molecular data demonstrate the recent subdivision of the Corrientes group with a substantial accumulation of chromosomal differences. Through our new chromosomal data and cytochrome b studies, we are able to subdivide the Ctenomys sp. populations into two groups and hypothesize on their relationships with the described Corrientes group species. Further studies are needed to establish the basis of the phenomenal chromosomal variation in this group.     

Phylogenetic relationships among Robertsonian karyomorphs of Graomys griseoflavus (Rodentia,Muridae) by mitochondrial cytochrome b DNA sequencing

Graomys griseoflavus (Waterhouse 1837) is a phyllotine murid rodent with a Robertsonian autosomal polymorphism, having been described 2n = 42, 41, 38, 37, 36, 35 and 34 karyomorphs, and proposed a chromosomal divergence pathway accounted by four sequential Robertsonian fusions. Sequences of a fragment (422 bp long) of the cytochrome b (cyt b) mitochondrial gene and its 5' flanking region (tRNA Glu) were obtained for 19 Graomys griseoflavus from different karyomorphs to infer phylogenetic relationships by using maximum parsimony. Outgroups considered for this analysis were the phyllotine rodents Phyllotis xanthopygus and Eligmodontia typus cyt b sequences. Three trees were produced showing the 2n = 38-34 karyomorphs grouped in a single clade while the 2n = 42-41 animals formed a different one. This is in agreement with a hypothesis of a single origin for 2n = 38-34 Robertsonian karyomorphs from the ancestral 2n = 42.     

Chromosomal evolution in Cervidae

On the basis of chromosome data obtained on 30 species and 20 subspecies of Cervidae, a report is submitted on the karyosystematics of this family. The primitive karyotype of Cervidae may be inferred to be composed of 35 acrocentric pairs (2n = 70 FN = 70). During the phyletic evolution of this family different types of chromosome rearrangements were probably selected and the group may have differentiated karyologically into three branches: (1) the Cervinae that fixed a centric fusion resulting in a metacentric pair of autosomes (2n = 68, FN = 70), as shown by the basic karyotype of Cervus elaphus, and where Robertsonian fusions are the preeminent type of chromosome rearrangement; (2) the Odocoileinae, in which pericentric inversions and Robertsonian fusions were favored, yielding first a submetacentric X and then a submetacentric autosome pair. The most representative karyotype is 2n = 70, FN = 74--as in Odocoileus hemionus; and (3) the Muntiacinae, in which centric and tandem fusions were the most common chromosome rearrangements. While Muntiacus reevesi has a karyotype 2n = 46, FN = 46, the chromosome number drops down to 2n = 6 in the females of the M. muntjak vaginalis subspecies group and M. rooseveltorum. Therefore, while the karyotypes are conserved within the subfamilies Cervinae and Odocoileinae; the subfamily Muntiacinae appears to be the most chromosomally diversified group. The few karyological data on the Moschus berezovskii suggest that the Moschinae should be placed in a separate family, the Moschidae.     

Karyology of the Atlantic forest rodent Juliomys (Cricetidae): A new karyotype from southern Brazil

Juliomys is a small rodent from the family Cricetidae which inhabits the Atlantic forest and forests from Argentina to eastern Brazil. The three species recognized so far have different karyotypes. In this paper, we describe a new karyotype with 2n = 32, FN = 48 found in Juliomys specimens from a high-altitude area in the Atlantic forest of southern Brazil. The karyotype was analyzed after G- and C-banding and silver staining of the nucleolus organizer regions (Ag-NOR) and its G-banding patterns were compared with those of the newly described species Juliomys ossitenuis (2n = 20, FN = 36). The 2n = 32 karyomorph presented peculiar features and was very different from those of the other species of the genus: J. pictipes (2n = 36, FN = 34), J. rimofrons (2n = 20, FN = 34) and J. ossitenuis (2n = 20, FN = 36). Differences were mostly due to centric and tandem fusions, pericentric inversion and loss of heterochromatin. The karyotype represents a powerful tool to differentiate Juliomys species and our data suggest that the karyotype described herein belongs to a new species.     

Whole chromosome painting reveals independent origin of sex chromosomes in closely related forms of a fish species

The wolf fish Hoplias malabaricus includes well differentiated sex systems (XY and X₁X₂Y in karyomorphs B and D, respectively), a nascent XY pair (karyomorph C) and not recognized sex chromosomes (karyomorph A). We performed the evolutionary analysis of these sex chromosomes, using two X chromosome-specific probes derived by microdissection from the XY and X₁X₂Y sex systems. A putative-sex pair in karyomorph A was identified, from which the differentiated XY system was evolved, as well as the clearly evolutionary relationship between the nascent XY system and the origin of the multiple X₁X₂Y chromosomes. The lack of recognizable signals on the sex chromosomes after the reciprocal cross-FISH experiments highlighted that they evolved independently from non-homologous autosomal pairs. It is noteworthy that these distinct pathways occur inside the same nominal species, thus exposing the high plasticity of sex chromosome evolution in lower vertebrates. Possible mechanisms underlying this sex determination liability are also discussed.     

Cytogenetical studies in five Atlantic Anguilliformes fishes

The order Anguilliformes comprises 15 families, 141 genera and 791 fish species. Eight families had at least one karyotyped species, with a prevalence of 2n = 38 chromosomes and high fundamental numbers (FN). The only exception to this pattern is the family Muraenidae, in which the eight species analyzed presented 2n = 42 chromosomes. Despite of the large number of Anguilliformes species, karyotypic reports are available for only a few representatives. In the present work, a species of Ophichthidae, Myrichthys ocellatus (2n = 38; 8m+14sm+10st+6a; FN = 70) and four species of Muraenidae, Enchelycore nigricans (2n = 42; 6m+8sm+12st+16a; FN = 68), Gymnothorax miliaris (2n = 42; 14m+18sm+10st; FN = 84), G. vicinus (2n = 42; 8m+6sm+28a; FN = 56) and Muraena pavonina (2n = 42; 6m+4sm+32a; FN = 52), collected along the Northeastern coast of Brazil and around the St Peter and St Paul Archipelago were analyzed. Typical large metacentric chromosomes were observed in all species. Conspicuous polymorphic heterochromatic regions were observed at the centromeres of most chromosomes and at single ribosomal sites. The data obtained for Ophichthidae corroborate the hypothesis of a karyotypic diversification mainly due to pericentric inversions and Robertsonian rearrangements, while the identification of constant chromosome numbers in Muraenidae (2n = 42) suggests a karyotype diversification through pericentric inversions and heterochromatin processes.     

Phylogeographic structure in the chromosomally polymorphic rodent Cricetulus barabensis sensu lato (Mammalia,Cricetidae)

Striped hamsters (Cricetulus barabensis sensu lato) represent a complex of chromosomally distinct allopatric lineages/taxa of either species or subspecies rank. They are widely distributed across the steppes of eastern and central Palearctic. Phylogenetic analysis of cytochrome b gene sequences based on 496 specimens from 112 localities revealed five well‐supported lineages divergent at 2%–4%. Two of them correspond to “griseus” (2n = 22) and “pseudogriseus” (2n = 24) karyomorphs and are placed as sister taxa. The “barabensis” (2n = 20) karyomorph is represented by three other branches and appears non‐monophyletic. All mtDNA lineages are distributed allopatrically or parapatrically; no indications of gene flow between populations of different chromosomal races were found. The results of the molecular clock analysis suggest that the main lineages diverged in the late Middle Pleistocene. The inferred evolutionary scenario implies that the common ancestor of the recent lineages belonged to the 2n = 20 karyomorph and originated in the eastern part of the contemporary range.