Changes in the numbers of chromosomes and sex determination system in bushcrickets of the genus Odontura (Orthoptera: Tettigoniidae: Phaneropterinae)

Chromosomes of the males of five species of Odontura, belonging to the subgenera Odontura and Odonturella, were analyzed. Intensive evolution of the karyotype was recorded, both in terms of changes in the numbers of chromosomes (from 2n = 31 to 27) and the sex chromosome system (from X0 to neo-XY and X0 to neo-X1X2Y). Karyotype evolution was accompanied by tandem autosome fusions and interspecific autosomal and sex chromosome differentiation involving changes in the locations of nucleolar organizer regions, NORs, which were revealed by silver impregnation and confirmed by FISH using an 18S rDNA probe. O. (Odonturella) aspericauda is a polytypic species with X0 and neo-X1X2Y sex determination. The latter system is not common in tettigoniids. It possibly originated by a translocation of a distal segment of the original X chromosome onto a medium sized autosome, resulting in a shortened neo-X-1 and a metacentric neo-Y. The remaining autosome homologue became the neo-X-2 chromosome. This shift from X0 to neo-X1X2Y is supported by the length of the X chromosome and location of the NOR/rDNA.