Analysis of chromosomal polymorphism in Tityus confluens 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

Tityus confluens occurs in northern Argentina, Bolivia, southern Brazil and Paraguay. Previous cytogenetic studies on this species revealed 2n=6 in females of Catamarca, Argentina and 2n=13 in males of Piauí, Brazil. However, the latter specimens may not correspond to T. confluens, but to a closely related, undescribed, species. In this work we analyzed the chromosome variability in males of a population of Tityus confluens from Reserva Natural Formosa (Formosa, Argentina). Chromosome preparations were made from testes. Conventional staining with Giemsa, C-banding stained with DAPI and silver staining were performed. Tityus confluens shows holokinetic chromosomes and achiasmatic male meiosis, as is characteristic of Buthidae. Mitotic and meiotic cells revealed intrapopulation structural and numerical chromosome variations, comprising four cytotypes: A) 2n=6 with one bivalent and one chain quadrivalent at meiosis I (eight males); B) 2n=5 with one chain pentavalent (three males); C) 2n=5 with a different chain pentavalent (one male); D) 2n=6 with a chain hexavalent (one male). C-banding revealed blocks of heterochromatin of different sizes, located at terminal and interstitial regions of all chromosomes in the four cytotypes. In cytotype A, silver staining on mitotic cells revealed NORs at the terminal region of two middle-sized chromosomes, which presumably form the bivalent. In cytotype B, NORs were detected at the terminal region of one middle-sized chromosome and one large chromosome. In cytotype C, NORs were detected at the terminal region of one middle-sized chromosome and in an interstitial region of the largest chromosome. In cytotype D, NORs were detected at the terminal region of one middle-sized chromosome and one large chromosome. The analysis of chromosome size, C-banding pattern and NORs location allowed us to propose an origin for each cytotype, involving different rearrangements. Cytotype A may have arisen from a hypothetical ancestral complement of 2n=8 and 4II by the fusion of both members of a pair with two non-homologous chromosomes (excluding the NOR-pair), which originated the chain quadrivalent. In cytotypes B and C, one NOR chromosome participated in different fusions with the chromosomes that forms the quadrivalent, either involving the ends without or with NOR, respectively. Finally, cytotype D may have arisen from cytotype A by one reciprocal translocation between a NOR chromosome and one chromosome of the quadrivalent. The maintenance of the polymorphism in this population could be achieved by small deletions in heterozygous state as consequence of rearrangements or by a balanced lethal system.