TRACKING THE EVOLUTIONARY HISTORY OF DISTINCT SEX CHROMOSOME SYSTEMS IN FOUR SPECIES OF MELANOPLINAE (ORTHOPTERA, ACRIDIDAE) BASED ON THE MAPPING OF MULTIGENE FAMILIES AND TELOMERIC SEQUENCES

PALACIOS, OCTAVIO; CASTILLO ELIO R.D; DARDO A. MARTÍ; CABRAL DE MELLO D.C.

Ribeirão Preto

Congreso; II EPACITO; 2012

Species of Orthoptera are characterized by the presence in high frequency of 2n=23 diploid number and an X0 Sex Chromosome Determination System (SCDS) in males. However within Acrididade, Melanoplines show some variability regarding to SCDS. The main mechanism responsible of it origin are the Robertsoninan fusions (Rb) between the X chromosome and one member of an autosomal pair, replacing the ancient X0 sex chromosomal system by a derived neo-XY. Besides, neo-XY species underwent a second Rb-fusion event, resulting in a neo-X1X2Y complex sex chromosome system. Examples of X0 are observed in Chlorus species and Eurotettix brevicerci, while derived neo-XY and neo-X1X2Y were described in E. minor and all Dichromatos species respectively. In order to understand the evolutionary patterns of SCDS in Orthoptera, we mapped cytogenetically by fluorescent in situ hybridization (FISH) the 18S rRNA, U1 snRNA genes and the telomeric DNA sequences in five phylogenetically related Melanoplinae species. The 18S rDNA was located in the pericentromeric region of autosomal pairs 3 and the proximal region of pair 6 of Chlorus vittatus; in Eurotettix brevicerci and E. minor this cluster was observed in the pericentromeric regions in pair 3, and additionally the X chromosome of E. brevicerci; and in the two species of Dichromatos, D. lilloanus and D. schrottkyi three clusters were observed, two in the proximal region of pairs 5 and 4 respectively; and additionally in the centromere of X1 sex chromosome. The clusters of U1 gene were terminally located in the pair 4 of E. brevicerci and E. minor, and in the interstitial position of XR and Y sex chromosomes in E. minor. For D. lilloanus the U1 snRNA is restricted to the interstitial region of the autosomal pair 2, while in D. schrottkyi it was located in the terminal region of pair 3. The data obtained with the telomeric probe revealed the presence telomeric sequences only in the actual telomeres, confirming the previous hypothesis for the origin through Rb-fusions, involving chromosomal breaks, and loss of telomeric sequences. The occurrence of 18S rRNA in the centromere of X1 in D. lilloanus and D. schrottkyi suggests a common origin for the neo-X1X2Y sex chromosomes. On the other hand, the two multigene families mapped indicate a divergent origin between the neo-XY of E. minor and neo-X1X2Y of Dichromatos representatives. The possible mechanisms for this divergence could be attributed to occurrence of distinct Rb-fusions, sequence amplification and transposition. Additionally, the other differences observed to specific location of multigene families in the autosomes reinforce the possible occurrence of cited mechanisms and that the karyotypes of grasshoppers are not highly conserved, at least in the microgenomic point to view.