A Brief Review of Meiotic Chromosomes in Early Spermatogenesis and Oogenesis and Mitotic Chromosomes in the Viviparous Lizard Zootoca vivipara (Squamata: Lacertidae) with Multiple Sex Chromosomes

SIMPLE SUMMARY: The wide-ranging Eurasian species Zootoca vivipara (Lichtenstein, 1823), of the family Lacertidae (Reptilia), is a rare species within the family, possessing multiple sex chromosomes (male Z(1)Z(2)Z(1)Z(2)/Z(1)Z(2)W female). In addition, the intense reorganization of this W sex chromosome is accompanied by active subspeciation and the formation of 4–5 cryptic taxa. In the females of two cryptic forms having a similar system of multiple sex chromosomes (Z(1)Z(2)W) but with different morphology, the cytogenetic and specific genomic structures of the W sex chromosome’s early oogenesis and meiosis have standard occurrence. Despite the ambiguous behavior of the three presumed sex chromosomes at the early stages of meiotic prophase I, variability in their number of bivalents and chromosomes and significant disturbances in chromosome segregation have not been discovered. Because in Z. vivipara the W sex chromosome, unlike all the other chromosomes, does not have several identified SINE-Zv and TE elements, we may assume that the specific genomic structure of this chromosome may be one of the factors ensuring meiotic stability in the cryptic taxa of the species with the multiple sex chromosomes. The question of female meiotic drive in the meiosis of the cryptic forms of the Z. vivipara complex is still obscure. ABSTRACT: This brief review is focused on the viviparous lizard Zootoca vivipara (Lichtenstein, 1823), of the family Lacertidae, which possesses female heterogamety and multiple sex chromosomes (male 2n = 36, Z(1)Z(1)Z(2)Z(2)/Z(1)Z(2)W, female 2n = 35, with variable W sex chromosome). Multiple sex chromosomes and their changes may influence meiosis and the female meiotic drive, and they may play a role in reproductive isolation. In two cryptic taxa of Z. vivipara with different W sex chromosomes, meiosis during early spermatogenesis and oogenesis proceeds normally, without any disturbances, with the formation of haploid spermatocytes, and in female meiosis with the formation of synaptonemal complexes (SCs) and the lampbrush chromosomes. In females, the SC number was constantly equal to 19 (according to the SC length, 16 SC autosomal bivalents plus three presumed SC sex chromosome elements). No variability in the chromosomes at the early stages of meiotic prophase I, and no significant disturbances in the chromosome segregation at the anaphase–telophase I stage, have been discovered, and haploid oocytes (n = 17) at the metaphase II stage have been revealed. There should be a factor/factors that maintain the multiple sex chromosomes, their equal transmission, and the course of meiosis in these cryptic forms of Z. vivipara.