Male and female meiosis in the mountain scorpion Zabius fuscus (Scorpiones, Buthidae): heterochromatin, rDNA and TTAGG telomeric repeats

Abstract

All cytogenetically studied scorpions present male achiasmatic meiosis and lack heteromorphic sex chromosomes. In contrast, information about female meiosis in scorpions is scarce due to the difficulty of finding meiotic cells. The genus Zabius includes three described species and no chromosome studies have been performed on it until now. We analyzed the constitutive heterochromatin distribution, NORs and telomeric sequences in mitosis and meiosis of males and females of different populations of Zabius fuscus. All specimens presented 2n = 18 holokinetic chromosomes that gradually decreased in size. Male meiosis presented nine bivalents and a polymorphism for one reciprocal translocation in one population. Telomeric signals were detected at every terminal region, confirming also the presence of a (TTAGG) n motif in Buthidae. Constitutive heterochromatin was found in three chromosome pairs at a terminal region; moreover, NORs were embedded in the heterochromatic region of the largest pair. Chromosome size and landmarks allowed us to propose the chromosomes involved in the rearrangement. In four females, cells at different prophase I stages were analyzed. We describe a diffuse stage and the presence of ring-shaped bivalents. We discuss the possible origin of these bivalents in the framework of chiasmatic or achiasmatic female meiosis. These results contribute to increase the scarce evidence of female meiosis in scorpions and raise new questions about its mechanism.

Sex-Linked Chromosome Heterozygosity in Males of Tityus confluens (Buthidae): A Clue about the Presence of Sex Chromosomes in Scorpions

“…Shanahan [5] proposed that the chromosomes involved in multivalents would adopt an alternate “above and below” orientation at metaphase I, ensuring a balanced segregation. The ability to undergo balanced segregation has also been described in many Buthidae species with multivalents at male meiosis [8, 10, 24], suggesting that this is a conserved feature of this group.…”

“…Most species studied of Buthidae present one terminal ribosomal DNA cluster in one chromosome pair (or two homologous chromosome segments, in the case of rearrangements), often associated with a conspicuous heterochromatin block [8, 10, 24, 25]. The specimens of T .…”

“…The telomeric probe was generated by PCR in the absence of a template [33]. The protocol was performed according to [34] with minor modifications in the design of primers and PCR mix as described by [10]. Labelling of both probes was carried out by PCR with biotin-16-dUTP.…”

“…Cytogenetic studies in the Bothriuridae, Buthidae, Scorpionidae and Urodacidae families of scorpions revealed the presence of achiasmatic male meiosis and a lack of recognizable sex chromosomes [3–10]. The only references to sex chromosomes in scorpions were in the mitosis of Leiurus quinquestriatus (Ehrenberg 1828) (Buthidae) and Nebo hierichonticus (Simon 1872) (Scorpionidae) [11, 12], where the presence of an XY/XX system is assumed but without any evidence to support it, and in the meiosis of Tityus bahiensis (Perty 1833) [13].…”

Karyotype diversity and chromosomal organization of repetitive DNA in Tityus obscurus (Scorpiones, Buthidae)

“…In Tityus obscurus the presence of two pairs of homologues bearing of the 45S rDNA in the terminal region differed from the pattern observed in the other Buthidae, which present ribosomal clusters in one pair of homologues [11, 12]. Some authors have proposed that the NOR terminal position is necessary for the stability and correct segregation of holokinetic chromosomes during cell division, once decondensed NORs constrictions could promote an interruption in the kinetochore plate [45].…”