First record of Arionvulgaris Moquin-Tandon, 1855 (Arionidae) from Armenia.

Background: Arionvulgaris Moquin-Tandon, 1855 is amongst the fastest-spreading terrestrial slugs Europe-wide. In recent years, it has been recorded in Canada, Mexico and continues to expand eastwards into Eurasia. Renowned for its high invasiveness, combatting its swift spread creates significant challenges in organising effective preventative measures. New information: This study presents the first record of Arionvulgaris from Armenia, which is the second record of this species' invasion of the Caucasus. In 2022, a substantial population of A.vulgaris was observed close to the City of Stepanavan, which is also the first record in Armenia of the family Arionidae. How the species was introduced to Armenia remains unknown. Identification of Arionvulgaris was conducted, based on external and genital morphology and mitochondrial CO1 (cytochrome c oxidase subunit 1) gene sequencing, revealing notable similarities with Central European clades. Our results confirm the introduction and distribution of A.vulgaris to Armenia. Invasion of such species into Armenia will require additional monitoring and would be aided by further research on Armenia's mollusc fauna in the future.

Variants of a major DNA satellite discriminate parental subgenomes in a hybrid parthenogenetic lizard Darevskia unisexualis (Darevsky, 1966).

Hybrid parthenogenetic animals are an exceptionally interesting model for studying the mechanisms and evolution of sexual and asexual reproduction. A diploid parthenogenetic lizard Darevskia unisexualis is a result of an ancestral cross between a maternal species Darevskia raddei nairensis and a paternal species Darevskia valentini and presents a unique opportunity for a cytogenetic and computational analysis of a hybrid karyotype. Our previous results demonstrated a significant divergence between the pericentromeric DNA sequences of the parental Darevskia species; however, an in-depth comparative study of their pericentromeres is still lacking. Here, using target sequencing of microdissected pericentromeric regions, we reveal and compare the repertoires of the pericentromeric tandem repeats of the parental Darevskia lizards. We found species-specific sequences of the major pericentromeric tandem repeat CLsat, which allowed computational prediction and experimental validation of fluorescent DNA probes discriminating parental chromosomes within the hybrid karyotype of D. unisexualis. Moreover, we have implemented a generalizable computational method, based on the optimization of the Levenshtein distance between tandem repeat monomers, for finding species-specific fluorescent probes for pericentromere staining. In total, we anticipate that our comparative analysis of Darevskia pericentromeric repeats, the species-specific fluorescent probes that we found and the pipeline that we developed will form a basis for the future detailed cytogenomic studies of a wide range of natural and laboratory hybrids.

Evolution of parthenogenetic reproduction in Caucasian rock lizards: A review.

Despite numerous works devoted to hybrid origin of parthenogenesis in reptiles, the causes of hybridization between different species, resulting in the origin of parthenogenetic forms, remain uncertain. Recent studies demonstrate that sexual species considered parental to parthenogenetic rock lizards (Darevskia spp.) avoid interspecific mating in the secondary overlap areas. A specific combination of environmental factors during last glaciation period was critical for ectotherms, which led to a change in their distribution and sex ratio. Biased population structure (e.g., male bias) and limited available distributional range favored the deviation of reproductive behavior when species switched to interspecific mates. To date, at least 7 diploid parthenogenetic species of rock lizards (Darevskia, Lacertidae) originated through interspecific hybridization in the past. The cytogenetic specifics of meiosis, in particular the weak checkpoints of prophase I, may have allowed the formation of hybrid karyotypes in rock lizards. Hybridization and polyploidization are 2 important evolutionary forces in the genus Darevskia. At present, throughout backcrossing between parthenogenetic and parental species, the triploid and tetraploid hybrid individuals appear annually, but no triploid species found among Darevskia spp. on current stage of evolution. The speciation by hybridization with the long-term stage of diploid parthenogenetic species, non-distorted meiosis, together with the high ecological plasticity of Caucasian rock lizards provide us with a new model for considering the pathways and persistence of the evolution of parthenogenesis in vertebrates.

The mixed liver and kidney transcriptome dataset of Darevskia valentini rock lizard.

OBJECTIVES: This study is performed in the frame of a bigger study dedicated to genomics and transcriptomics of parthenogenesis in vertebrates. Among vertebrates, obligate parthenogenesis was first described in the lizards of the genus Darevskia. In this genus, all found parthenogenetic species originated via interspecific hybridization. It remains unknown which genetic or genomic factors play a key role in the generation of parthenogenetic organisms. Comparative genomic and transcriptomic analysis of parthenogens and their parental species may elucidate this problem. Darevskia valentini is a paternal species for four (of seven) parthenogens of this genus, which we promote as a particularly important species for the generation of parthenogenetic forms. DATA DESCRIPTION: Total cellular RNA was isolated from kidney and liver tissues using the standard Trizol Tissue RNA Extraction protocol. Sequencing of transcriptome libraries prepared by random fragmentation of cDNA samples was performed on an Illumina HiSeq2500. Obtained raw sequences contained 117,6 million reads with the GC content of 47%. After preprocessing, raw data was assembled by Trinity and produced 491,482 contigs.

First Genome of Rock Lizard Darevskia valentini Involved in Formation of Several Parthenogenetic Species.

The extant reptiles are one of the most diverse clades among terrestrial vertebrates and one of a few groups with instances of parthenogenesis. Due to the hybrid origin of parthenogenetic species, reference genomes of the parental species as well as of the parthenogenetic progeny are indispensable to explore the genetic foundations of parthenogenetic reproduction. Here, we report on the first genome assembly of rock lizard Darevskia valentini, a paternal species for several parthenogenetic lineages. The novel genome was used in the reconstruction of the comprehensive phylogeny of Squamata inferred independently from 7369 trees of single-copy orthologs and a supermatrix of 378 conserved proteins. We also investigated Hox clusters, the loci that are often regarded as playing an important role in the speciation of animal groups with drastically diverse morphology. We demonstrated that Hox clusters of D. valentini are invaded with transposons and contain the HoxC1 gene that has been considered to be lost in the amniote ancestor. This study provides confirmation for previous works and releases new genomic data that will contribute to future discoveries on the mechanisms of parthenogenesis as well as support comparative studies among reptiles.

Application of land snail Helix lucorum for evaluation of genotoxicity of soil pollution.

Application of native species as sentinels allows environmental scientists to determine real genotoxic impact of environmental pollutants. The present study aims at investigating the DNA damage in the land snail Helix lucorum as a biomarker of soil pollution. For this reason, the genotoxic impact of contaminated soil on H. lucorum, collected from different polluted areas, was investigated using the comet assay in haemocytes and digestive gland cells. An increase in DNA damage was found in the snails sampled from polluted sites compared with the reference one. Strong correlations between DNA damage in haemocytes and digestive gland cells with the level of contamination indicate pollution-induced genotoxic effects in both tissues. At the same time, the digestive gland was more sensitive towards pollutants compared with haemolymph. A direct relationship between concentrations of Cu, As and Mo in soil and the number of damaged cells for hаemolymph and digestive gland tissue was found. However, the data obtained reflect the total genotoxicity of all pollutants in the studied areas. Significant correlations between the DNA damage measured by the comet assay and metal contents in soil indicate that it is a suitable biomarker in ecotoxicological studies. Our results indicate the effectiveness of H. lucorum in biomonitoring of environmental pollution.

Parthenogenesis in Darevskia lizards: A rare outcome of common hybridization, not a common outcome of rare hybridization.

Hybridization is a common evolutionary process with multiple possible outcomes. In vertebrates, interspecific hybridization has repeatedly generated parthenogenetic hybrid species. However, it is unknown whether the generation of parthenogenetic hybrids is a rare outcome of frequent hybridization between sexual species within a genus or the typical outcome of rare hybridization events. Darevskia is a genus of rock lizards with both hybrid parthenogenetic and sexual species. Using capture sequencing, we estimate phylogenetic relationships and gene flow among the sexual species, to determine how introgressive hybridization relates to the origins of parthenogenetic hybrids. We find evidence for widespread hybridization with gene flow, both between recently diverged species and deep branches. Surprisingly, we find no signal of gene flow between parental species of the parthenogenetic hybrids, suggesting that the parental pairs were either reproductively or geographically isolated early in their divergence. The generation of parthenogenetic hybrids in Darevskia is, then, a rare outcome of the total occurrence of hybridization within the genus, but the typical outcome when specific species pairs hybridize. Our results question the conventional view that parthenogenetic lineages are generated by hybridization in a window of divergence. Instead, they suggest that some lineages possess specific properties that underpin successful parthenogenetic reproduction.

De novo transcriptome assembly and annotation of parthenogenetic lizard Darevskia unisexualis and its parental ancestors Darevskia valentini and Darevskia raddei nairensis.

Darevskia rock lizards include 29 sexual and seven parthenogenetic species of hybrid origin distributed in the Caucasus. All seven parthenogenetic species of the genus Darevskia were formed as a result of interspecific hybridization of only four sexual species. It remains unknown what are the main advantages of interspecific hybridization along with switching on parthenogenetic reproduction in evolution of reptiles. Data on whole transcriptome sequencing of parthenogens and their parental ancestors can provide value impact in solving this problem. Here we have sequenced ovary tissue transcriptomes from unisexual parthenogenetic lizard D. unisexualis and its parental bisexual ancestors to facilitate the subsequent annotation and to obtain the collinear characteristics for comparison with other lizard species. Here we report generated RNAseq data from total mRNA of ovary tissues of D. unisexualis, D. valentini and D. raddei with 58932755, 51634041 and 62788216 reads. Obtained RNA reads were assembled by Trinity assembler and 95141, 62123, 61836 contigs were identified with N50 values of 2409, 2801 and 2827 respectively. For further analysis top Gene Ontology terms were annotated for all species and transcript number was calculated. The raw data were deposited in the NCBI SRA database (BioProject PRJNA773939). The assemblies are available in Mendeley Data and can be accessed via doi:10.17632/rtd8cx7zc3.1.

Does reproductive mode affect sexually-selected coloration? Evaluating UV-blue spots in parthenogenetic and bisexual lizards of the genus Darevskia.

Sexual selection often leads to evolution of conspicuous signals, raising the chances of attracting not only potential mates, but also predators. In lacertid lizards, ultraviolet (UV)-blue spots on flanks and shoulders represent such a trait. Some level of correlation between male and female ornamentation is also known to exist. Therefore, the phenotype of females may change in the absence of sexual selection. We tested this hypothesis on a complex of parthenogenetic and bisexual lizards of the genus Darevskia. We evaluated area, counts, and chromatic properties (UV opponency, saturation) of UV-blue spots and compared the values between the clones and their bisexual progenitor species. We found a fair heterogeneity between the parthenogenetic species, but no general tendency toward higher crypsis or conspicuousness. Values of the parthenogens were not significantly different from the values of sexual females. A possible explanation is that the changes in selective forces associated with parthenogenetic reproduction are too small to affect the resulting pattern of selective pressures on the studied traits, or that the phenotypes of the parthenogens result from the unique combination of parental genomes and are conserved by clonal reproduction.

Meiotic synapsis of homeologous chromosomes and mismatch repair protein detection in the parthenogenetic rock lizard Darevskia unisexualis.

Parthenogenetic species of Caucasian rock lizards of the genus Darevksia are important evidence for reticulate evolution and speciation by hybridization in vertebrates. Female-only lineages formed through interspecific hybridization have been discovered in many groups. Nevertheless, critical mechanisms of oogenesis and specifics of meiosis that provide long-term stability of parthenogenetic species are still unknown. Here we report cytogenetic characteristics of somatic karyotypes and meiotic prophase I nuclei in the diploid parthenogenetic species Darevskia unisexualis from the new population "Keti" in Armenia which contains an odd number of chromosomes 2n = 37, instead of the usual 2n = 38. We revealed 36 acrocentric chromosomes and a single metacentric autosomal chromosome, resulting from Robertsonian translocation. Comparative genomic hybridization revealed that chromosome fusion occurred between two chromosomes inherited from the maternal species, similar to another parthenogenetic species D. rostombekowi. To trace the chromosome behaviour in meiosis, we performed an immunocytochemical study of primary oocytes' spread nuclei and studied chromosome synapsis during meiotic prophase I in D. unisexualis based on analysis of synaptonemal complexes (SCs). We found meiotic SC-trivalent composed of one metacentric and two acrocentric chromosomes. We confirmed that the SC was assembled between homeologous chromosomes inherited from two parental species. Immunostaining of the pachytene and diplotene nuclei revealed a mismatch repair protein MLH1 loaded to all autosomal SC bivalents. Possible mechanisms of meiotic recombination between homeologous chromosomes are discussed.

New records and geographic distribution of the sympatric zones of unisexual and bisexual rock lizards of the genus Darevskia in Armenia and adjacent territories.

BACKGROUND: Caucasian rock lizards of the genus Darevskia are unique taxa, including both bisexual and parthenogenetic species. The parthenogenetic species have originated as a result of natural hybridisation between females and males of different bisexual species. The species involved in interspecific hybridisation are called parental. However, sympatric zones (SZ) of unisexual and bisexual rock lizards of the Caucasus are still poorly studied, although they are very important for understanding the role of hybrid individuals of different origin in reticulate evolution. This paper presents the location of the SZs of parthenogenetic and their parental bisexual rock lizards of the genus Darevskia in Armenia and adjacent territories of Georgia and Nagorno-Karabakh. We summarised the locations of the SZs identified from 1957 to the present, based on our field survey data gathered in 2018-2019 and records from publications and museum collections. This dataset includes 39 SZs of three types: SZ of parental bisexual species, SZ of parental species with unisexual species and SZ of the parthenogenetic species. For each zone, species composition, geographical and altitudinal distribution are presented. New records expand our knowledge of the geographical and altitudinal distribution of SZs in these species and provide additional data for understanding the mechanisms of reticulate evolution and hybridogeneous speciation in the past, present and future. NEW INFORMATION: The new records, including geographical and altitudinal distributions of three types of SZs, are presented, which expand the previously-known list to 39 locations of contact zones for parthenogenetic and its bisexual parental species of rock lizards of the genus Darevskia in Armenia and the adjacent territories of Georgia and Nagorno-Karabakh.

Evolution of the parthenogenetic rock lizard hybrid karyotype: Robertsonian translocation between two maternal chromosomes in Darevskia rostombekowi.

Darevskia rostombekowi, the most outstanding of the seven known parthenogenetic species in the genus Darevskia, is the result of an ancestral cross between two bisexual species Darevskia raddei and Darevskia portschinskii. The chromosomal set of this species includes a unique submetacentric autosomal chromosome; the origin of this chromosome was unresolved as only acrocentric chromosomes are described in the karyotypes of Darevskia genus normally. Here, we applied a suite of molecular cytogenetic techniques, including the mapping of telomeric (TTAGGG) n repeats using fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), and whole-chromosome painting (WCP) in both D. rostombekowi and parental (D. portschinskii and D. raddei) species. The obtained results in total suggest that a de novo chromosomal rearrangement via Robertsonian translocation (centric fusion) between two maternal (D. raddei) acrocentric chromosomes of different size was involved in the formation of this unique submetacentric chromosome present in the parthenogenetic species D. rostombekowi. Our findings provide new data in specific and rapid evolutional processes of a unisexual reptile species karyotype.

Genotypic similarities among the parthenogenetic Darevskia rock lizards with different hybrid origins.

BACKGROUND: The majority of parthenogenetic vertebrates derive from hybridization between sexually reproducing species, but the exact number of hybridization events ancestral to currently extant clonal lineages is difficult to determine. Usually, we do not know whether the parental species are able to contribute their genes to the parthenogenetic vertebrate lineages after the initial hybridization. In this paper, we address the hypothesis, whether some genotypes of seven phenotypically distinct parthenogenetic rock lizards (genus Darevskia) could have resulted from back-crosses of parthenogens with their presumed parental species. We also tried to identify, as precise as possible, the ancestral populations of all seven parthenogens. RESULTS: We analysed partial mtDNA sequences and microsatellite genotypes of all seven parthenogens and their presumed ansectral species, sampled across the entire geographic range of parthenogenesis in this group. Our results confirm the previous designation of the parental species, but further specify the maternal populations that are likely ancestral to different parthenogenetic lineages. Contrary to the expectation of independent hybrid origins of the unisexual taxa, we found that genotypes at multiple loci were shared frequently between different parthenogenetic species. The highest proportions of shared genotypes were detected between (i) D. sapphirina and D. bendimahiensis and (ii) D. dahli and D. armeniaca, and less often between other parthenogens. In case (ii), genotypes at the remaining loci were notably distinct. CONCLUSIONS: We suggest that both observations (i-ii) can be explained by two parthenogenetic forms tracing their origin to a single initial hybridization event. In case (ii), however, occasional gene exchange between the unisexual and the parental bisexual species could have taken place after the onset of parthenogenetic reproduction. Indeed, backcrossed polyploid hybrids are relatively frequent in Darevskia, although no direct evidence of recent gene flow has been previously documented. Our results further suggest that parthenogens are losing heterozygosity as a result of allelic conversion, hence their fitness is expected to decline over time as genetic diversity declines. Backcrosses with the parental species could be a rescue mechanism which might prevent this decline, and therefore increase the persistance of unisexual forms.

Origin, clonal diversity, and evolution of the parthenogenetic lizard Darevskia unisexualis.

BACKGROUND: The hybridization of female D. raddei and male D. valentini gave rise to the parthenogenetic Caucasian rock lizard Darevskia unisexualis. A previously identified genetic polymorphism in the species consisted of one common and two allozyme clones. Analysis of microsatellites and single nucleotide polymorphisms (SNPs) from the three species yields estimates of clonal diversity and tests the hypothesis of a single origin for D. unisexualis. RESULTS: Genotyping and sequencing of four microsatellite-containing loci for 109 specimens of D. unisexualis, 17 D. valentini, and 45 D. raddei nairensis identified 12 presumptive clones, including one widespread and 11 rare clones. Most individuals in some localities had a rare clone. Clone-specific alleles in D. unisexualis were compared with those of the parental species. The results inferred a single hybridization event. Post-formation mutations best explain the less common clones. CONCLUSIONS: Interspecific analyses identify alleles inherited by D. unisexualis from its bisexual ancestors. SNP analyses fail to reject the hypothesis of a single interspecific origin of D. unisexualis, followed by microsatellite mutations in this initial clone. Microsatellites detect higher clonal diversity in D. unisexualis compared to allozymes and identify the likely origins of clones. Our approach may be applicable to other unisexual species whose origins involve interspecific hybridization.

Cytogenetic mechanisms of unisexuality in rock lizards.

Darevskia rock lizards is a unique complex taxa, including more than thirty species, seven of which are parthenogenetic. In mixed populations of Darevskia lizards, tri- and tetraploid forms can be found. The most important issues in the theory of reticulate evolution of Darevskia lizards are the origin of parthenogenetic species and their taxonomic position. However, there is little data on how meiosis proceeds in these species. The present work reports the complex results of cytogenetics in a diploid parthenogenetic species - D. unisexualis. Here we detail the meiotic prophase I progression and the specific features оf mitotic chromosomes organization. The stages of meiosis prophase I were investigated by immunocytochemical analysis of preparations obtained from isolated primary oocytes of D. unisexualis in comparison with maternal species D. raddei nairensis. It has been shown that in D. unisexualis at the leptotene-zygotene stages the axial elements and the synaptonemal complex (SC) form typical "bouquets". At the pachytene-diplotene stage, 18 autosomal SC-bivalents and thickened asynapted sex Z and w univalents were observed. The presence of SYCP1 protein between the lateral elements of autosomal chromosomes proved the formation of assembled SCs. Comparative genomic hybridization (CGH) on the mitotic metaphase chromosomes of D. unisexualis was carried out using the genomic DNA isolated from the parental species D. raddei nairensis and D. valentini. In the pericentromeric regions of half of the mitotic chromosomes of D. unisexualis, specific regions inherited from maternal species have been found. Following our results, we suggest a model for diploid germ cells formation from diploid oocytes without premeiotic duplication of chromosomes in the oogenesis of diploid parthenogenetic lizards D. unisexualis. Taken as a whole, our findings confirm the hybrid nature of D. unisexualis and shed light on heterozygosity and automixis in diploid parthenogenetic forms.

Correction to: The role of hybridisation in the origin and evolutionary persistence of vertebrate parthenogens: a case study of Darevskia lizards.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Infection of parthenogenetic lizards by blood parasites does not support the "Red Queen hypothesis" but reveals the costs of sex.

Sexual organisms should be better suited than asexual ones in a context of continuous evolution in response to opposite organisms in changing environments ("Red Queen" hypothesis of sex). However, sex also carries costs associated with the maintenance of males and mating (sex cost hypothesis). Here, both non-mutually excluding hypotheses are tested by analysing the infestation by haemogregarines of mixed communities of Darevskia rock lizards composed of parthenogens generated by hybridisation and their bisexual relatives. Prevalence and intensity were recorded from 339 adult lizards belonging to six species from five syntopic localities and analysed using Generalized Mixed-Models (GLMM). Both infestation parameters depended on host-size (like due to longer exposure with age), sex and, for intensity, species. Once accounting for locality and species, males were more parasitized than conspecific females with bisexual species, but no signal of reproductive mode itself on parasitization was recovered. Essentially, male-male interactions increased haemogregarine intensity while females either sexual or asexual had similar reproductive costs when in the same conditions. These findings deviate from the predictions from "Red Queen" dynamics while asymmetric gender costs are here confirmed. Thus, increased parasitization pressure on males adds to other costs, such as higher social interactions and lower fecundity, to explain why parthenogenetic lizards apparently prevail in the short-term evolutionary scale. How this is translated in the long-term requires further phylogenetic analysis.

The role of hybridisation in the origin and evolutionary persistence of vertebrate parthenogens: a case study of Darevskia lizards.

Obligate parthenogenesis is found in only 0.1% of the vertebrate species, is thought to be relatively short lived and is typically of hybrid origin. However, neither the evolutionary persistence of asexuality in vertebrates, nor the conditions that allow the generation of new parthenogenetic lineages are currently well understood. It has been proposed that vertebrate parthenogenetic lineages arise from hybridisation between two divergent taxa within a specific range of phylogenetic distances (the 'Balance Hypothesis'). Moreover, parthenogenetic species often maintain a certain level of hybridisation with their closest sexual relatives, potentially generating new polyploid hybrid lineages. Here we address the role of hybridisation in the origin and evolutionary lifespan of vertebrate parthenogens. We use a set of microsatellite markers to characterise the origins of parthenogens in the lizard genus Darevskia, to study the distinctiveness of sexual and asexual taxa currently in sympatry, and to analyse the evolutionary consequences of interspecific hybridisation between asexual females and sexual males. We find that parthenogens result from multiple past hybridisation events between species from specific lineages over a range of phylogenetic distances. This suggests that the Balance Hypothesis needs to allow for lineage-specific effects, as envisaged in the Phylogenetic Constraint Hypothesis. Our results show recurrent backcrossing between sexual and parthenogenic Darevskia but neither gene flow nor formation of new asexual lineages. We suggest that, along with their demographic advantage, parthenogens gain additional leverage to outcompete sexuals in nature when the retention of sexual reproductive machinery allows backcrossing with their sexual ancestors.

Application of the comet assay, micronucleus test and global DNA methylation analysis in Darevskia lizards as a sentinel organism for genotoxic monitoring of soil pollution.

Widely distributed in Armenia bisexual and parthenogenetic species of Darevskia rock lizards have the potential to be considered as bioindicators of the effects of environmental pollutants. Juvenile and adult bisexual D. raddei and parthenogenetic D. armeniaca lizards were sampled from four locations with different levels of soil contamination. The comet assay, micronucleus (MN) test and global DNA methylation detection were applied in peripheral blood erythrocytes to assess genotoxic and epigenetic effects of pollutants. The concentrations of heavy metals were analyzed in the corresponding soil samples. In polluted areas levels of DNA damage were significantly higher and levels of global DNA methylation were significantly lower in both species than in reference sites. The levels of comets and global DNA methylation decreased with age but did not depend on sex. MN test did not show significant differences among localities or between sexes and age groups. The positive correlation between DNA damage and contents of Cr, Cu, As and Mo and negative correlation between global DNA methylation and contents of Cr, Cu, Zn, Mo and Pb were shown for D. raddei. The positive correlations between DNA damage and contents of Cr, Zn and Pb and negative correlations between global DNA methylation and contents of Cr, Zn, Mo, Cd and Pb were revealed for D. armeniaca. The correlation results for some metals are different in juveniles and adults. D. armeniaca showed higher sensitivity toward environmental pollution than D. raddei in their common habitat. Genetic homogeneity of parthenogenetic lizards permits to evaluate the effects of environmental pollutants independently from inter-individual genetic variation. In conclusion, the current study suggests that DNA damage and global DNA methylation may be applied to Darevskia lizards as a sentinel organism for assessing the effects of environmental pollutants.

Extraordinary centromeres: differences in the meiotic chromosomes of two rock lizards species Darevskia portschinskii and Darevskia raddei.

According to the synthesis of 30 years of multidisciplinary studies, parthenogenetic species of rock lizards of genus Darevskia were formed as a result of different combination patterns of interspecific hybridization of the four bisexual parental species: Darevskia raddei, D. mixta, D. valentini, and D. portschinskii. In particular, D. portschinskii and D. raddei are considered as the parental species for the parthenogenetic species D. rostombekowi. Here for the first time, we present the result of comparative immunocytochemical study of primary spermatocyte nuclei spreads from the leptotene to diplotene stages of meiotic prophase I in two species: D. portschinskii and D. raddei. We observed similar chromosome lengths for both synaptonemal complex (SC) karyotypes as well as a similar number of crossing over sites. However, unexpected differences in the number and distribution of anti-centromere antibody (ACA) foci were detected in the SC structure of bivalents of the two species. In all examined D. portschinskii spermatocyte nuclei, one immunostained centromere focus was detected per SC bivalent. In contrast, in almost every studied D. raddei nuclei we identified three to nine SCs with additional immunostained ACA foci per SC bivalent. Thus, the obtained results allow us to identify species-specific karyotype features, previously not been detected using conventional mitotic chromosome analysis. Presumably the additional centromere foci are result of epigenetic chromatin modifications. We assume that this characteristic of the D. raddei karyotype could represent useful marker for the future studies of parthenogenetic species hybrid karyotypes related to D. raddei.