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

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, Z₁Z₁Z₂Z₂/Z₁Z₂W, 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.

Keywords: Zootoca vivipara; form and subspeciation; lizards; meiosis; multiple sex chromosomes; synaptonemal complex (SC).

Figure 1

Map showing the distribution of eastern (Russian) (●) and western (●) forms of Zootoca vivipara in the Baltic Sea basin based mainly on their karyotypes. Topography is adapted from the GEBCO world map 2014. The points of distribution are from reference [18] with additions.

Figure 2

Cells of male specimens of eastern (Russian) cryptic form of viviparous lizard Zootoca vivipara: (A)—meiotic testis cell at the diakinesis stage; bivalents, n = 18; (B)—synaptonemal complex (SC) karyotype of spermatocytes, n = 18. (B) from reference [30].

Figure 3

Cells of female specimens of eastern (Russian) form and of western form of viviparous lizard Zootoca vivipara: (A)—metaphase plate of eastern (Russian) form, specific DAPI stained, 2n = 35: 32 A + Z₁Z₂W. Arrow points to centromeric and interstitial DAPI blocks of acrocentric W sex chromosome. (A) from reference [30]; (B)—metaphase plate of western form, specific DAPI stained, 2n =35: 32 A + Z₁Z₂W. Arrow points to centromeric and weak interstitial DAPI blocks of submetacentric W sex chromosome; (C)—the spread oocyte nuclei of female of eastern (Russian) form at pachytene–diplotene stages. Incubation with antibody (SYPC3) and after incubation specific fluorochrome AT DAPI stained. Arrow points to the lampbrush chromosomes. (C) from reference [33]; (D)—SC karyotype of female eastern (Russian) form, n = 16 autosomal bivalents and 3 SC elements of presumed Z₁Z₂W sex chromosomes. (D) from reference [30].