Meiotic chromosomes, synaptonemal complexes (SC) in the cryptic forms of the Euroasian complex Zootoca vivipara with multiple sex chromosomes
Among lacertid species, Zootoca vivipara is a rare case possessing both simple and multiple sex chromosomes (male 2n=36, Z1Z1Z2Z2/ Z1Z2W female 2n=35). Some changing in W sex chromosome (morphology, cytogenetic structure) accompany active form-formation and subspeciation in the Z. vivipara complex. Alterations in some characters of sex chromosomes, in particular multiple sex chromosomes, may influence the process of meiosis and may play a role in isolation and speciation. Therefore, early spermato- and oogenesis of the western cryptic form (reorganized W sex chromosome) have been firstly examined. The data obtained have been compared with previous studies of Safronova, Kupriyanova and colleagues on the males and females of eastern (Russian) cryptic form as well as with studies on males of Takydromus species – a closely related to Zootoca genus. The correlation in the process of meiosis of both forms of Zootoca were observed: in males (2n=36), all 18 synaptonemal complexes’ (SCs) bivalents, including SCs Z1Z1Z2Z2 sex chromosomes, appeared to be fully synapted; moreover, their regular segregation with forming of haploid spermatocytes, 18 chromosomes at the metaphase 1l stage, were constantly revealed. However, the mitotic and meiotic characteristics of the Takydromus species differed.
In eastern (Russian) cryptic form of Z. vivipara (2n=35), unlike males, 19 SC elements at the pachytena – diplotena prophase1 stage of female meiosis were identified (16 SCs fully synapted autobivalents and 3 SCs elements may be a sex chromosomes’ univalents). The lampbrush chromosomes have been observed in the eastern and the western cryptic forms, but, in the later, their exact number is still unknown. However, at the telophase-anaphase stages, some disturbances in the segregation of chromosomes have been revealed. Finally, some complex and even ambiguous behavior of sex chromosomes in female meiosis of Z. vivipara, related to the problems of female meiotic drive and subspeciation, need future studies.