Constitutive heterochromatin and ribosomal DNA characterization in two parthenogenetic populations of Tityus trivittatus Kraepelin 1898 (Buthidae, Scorpiones)

ADILARDI RS; OJANGUREN AFFILASTRO AA; MARTÍ DA; MOLA LM

Guarujá

Congreso; 3ª Reunião Brasileira de Citogenética - IV SLACE - Simpósio Latino-Americano de Citogenética e Evolução; 2013

Sociedade Brasileira de Genetica

Tityus trivittatus is the most medically important scorpion species of Argentina, being also the southernmost species of the genus. It presents synantropic and parthenogenetic populations in most of the cities of northern and central Argentina, and it is responsible for several deceases every year. Nowadays about fifteen Tityus species were cytogenetically analyzed, but only in T. serrulatus a detailed karyotypic study of parthenogenetic populations was performed. We have studied the karyotype, heterochromatin distribution, and ribosomal DNA of specimens of Tityus trivittatus from urban populations of Ciudad Autónoma de Buenos Aires and Posadas, Misiones Province, Argentina. Chromosomes preparations were made from adult female?s ovaries and entire embryos by spreading technique. Giemsa staining, C-banding, NOR staining with AgNO3 and FISH with 28s rDNA probe were performed on the slides. Specimens of the two localities show 2n=6 with the same karyotype: two large and four middle-sized holokinetic chromosomes. C-banding is also alike and shows a complex pattern with terminal, subterminal and interstitial bands of different size. C-bands make it possible to identify three pairs of chromosomes. Hybridization signals of rDNA probes are observed in the terminal region of two middle sized chromosomes. Silver staining also reveal the presence of two active NORs, and sequential C-banding and silver staining reveal that the NORs co-locate with a conspicuous terminal C-band of a middle-sized chromosome pair. The number and location of NORs found in T. trivittatus were also observed in most of the other analyzed Tityus species. The association between NORs and constitutive heterochromatin is a feature also reported in T. bahiensis and T. serrulatus. The heterochromatin content is variable between species and terminal location is a common characteristic, although interstitial blocks are present in some species like in T. trivittatus. A high frequency of intra- and interpopulation chromosomal rearrangements is known in many Tityus species. Parthenogenetic reproduction may allow urban populations that differ in their chromosome characteristics to establish. Although, the two populations of Tityus trivittatus here analyzed, separated by a distance of 800 km, show the same karyotype. In distant parthenogenetic populations of T. serrulatus also karyotypic constancy was reported. These results could indicate that karyotypic uniformity may be somehow related with parthenogenesis in Tityus species.