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.

Comparative study of genome divergence in salmonids with various rates of genetic isolation

The aim of the study is a comparative investigation of changes that certain genome parts undergo during speciation. The research was focused on divergence of coding and noncoding sequences in different groups of salmonid fishes of the Salmonidae (Salmo, Parasalmo, Oncorhynchus, and Salvelinus genera) and the Coregonidae families under different levels of reproductive isolation. Two basic approaches were used: (1) PCR-RAPD with a 20–22 nt primer design with subsequent cloning and sequencing of the products and (2) a modified endonuclease restriction analysis. The restriction fragments were shown with sequencing to represent satellite DNA. Effects of speciation are found in repetitive sequences. The revelation of expressed sequences in the majority of the employed anonymous loci allows for assuming the adaptive selection during allopatric speciation in isolated char forms.

Molecular evolution of satellite DNA repeats and speciation of lizards of the genus Darevskia (Sauria: Lacertidae)

Satellite DNA repeats were studied in Caucasian populations of 18 rock lizard species of the genus Darevskia. Four subfamilies (Caucasian Lacerta satellites (CLsat)I-IV) were identified, which shared 70%-75% sequence similarity. The distribution of CLsat subfamilies among the species was studied. All the species could be divided into at least 3 clades, depending on the content of CLsat subfamilies in each genome: "saxicola", "rudis", and "mixta" lizards. CLsatI was found in all studied species, but in very different quantities; the "saxicola" group contained this subfamily predominantly. The "rudis" group also contained CLsatIII, and the "mixta" group carried considerable amounts of CLsatII. The highest concentrations of CLsatI and CLsatII were detected in 2 ground lizards--D. derjugini and D. praticola, respectively. D. parvula predominantly carried CLsatIII. CLsatIV was found only in the Crimean species D. lindholmi. The distribution patterns of satellite subfamilies show possible postglacial speciation within the genus Darevskia. A hybrid origin of species that possess 2 or 3 CLsat subfamilies and important clarifications to the systematics of the genus are proposed.