Chromosomal and rDNA variability in populations of Tityus argentinus (Borelli, 1899) (Buthidae, Scorpiones)

ADILARDI RS; OJANGUREN AFFILASTRO AA; MOLA LM

Atibaia, San Pablo

Congreso; 4ª Reunião Brasileira de Citogenética; 2015

Sociedad Brasileira de Genética

Genus Tityus, as all Buthidae scorpions, present holokinetic chromosomes, male achiasmatic meiosis and high incidence of chromosomal rearrangements evidenced as multivalents during meiosis I. The aim of this work was to characterize the cytogenetic diversity in populations of Tityus argentinus (Borelli, 1899). We studied males of T. argentinus from Parque Nacional Calilegua (Jujuy, Argentina) collected at three altitudes (600, 885 and 1700m.a.s.l.) which were considered as three different populations. Chromosome preparations were made from testes. Giemsa staining, C-banding and FISH with 28S rDNA and (TTAGG)n telomere probes were performed. Mitotic and meiotic cells revealed intra and interpopulation structural and numerical chromosome variations. Specimens from both lower altitude populations showed 2n=10 and 5II at meiosis I (nine males). In the third population (1700m), three different cytotypes were found: 2n=10 with 3II+IV (three males), 2n=10 with one ring decavalent (X) (four males) and 2n=9 with one bivalent plus one chain heptavalent (1II+VII) (three males). All metaphase II evidenced balanced segregation during meiosis. C-banding revealed constitutive heterochromatin in almost every terminal region of all chromosomes and a few interstitial blocks in some chromosomes. Hybridization with rDNA probes revealed signals at the terminal heterochromatic region of one bivalent in males with 5II and males with 3II+IV, and one signal at a terminal region of a single chromosome in the multivalents of males with 1II+VII and males with X. Additional smaller signals in only one chromosome were observed in one male with 5II and one male with X. FISH with telomere probes showed signals exclusively at terminal regions. High-altitude cytotypes may have arisen from specimens with 2n=10 and 5II by different rearrangements: one unequal reciprocal translocation originated the cytotype with one IV, two reciprocal translocations and one fusion (that reduced the diploid number) generated the cytotype with the heptavalent, and four reciprocal translocations originated the cytotype with the decavalent. The occurrence of only heterozygote specimens in this population could indicate the presence of coadapted genes associated with rearrangements, which can give a selective advantage at higher altitude environmental conditions. Tityus argentinus, as most Buthidae species, presented one chromosome pair with terminal NORs in some cytotypes. Although, only one NOR was found in the cytotypes where the NOR bivalent is involved in the rearrangement. Extra NORs were found in males with bivalents as well as with multivalents. Besides chromosomal rearrangement, the polymorphism for NORs could also be a result of transposition or ectopic recombination.