CHROMOSOMAL BASIS FOR A BILATERAL GYNANDROMORPH IN PYCNOGASTER-INERMIS (RAMBUR, 1838) (ORTHOPTERA, TETTIGONIIDAE)

Morphological and cytogenetic analyses of a spontaneous gynandromorph of Pycnogaster inermis, found in a natural population in the Spanish S ierra Nevada, have shown that the left side was male and the right sid e female, with almost perfect bilateral symmetry. Ventral valves of th e ovipositor were very short, appearing as two spurs; dorsal valves we re longer but still shorter than normal. The specimen had an apparentl y normal testis on the left side and a well-developed ovary on the rig ht side. Cytogenetic analysis revealed the presence of 2n = 28 + X0 ch romosomes in the testis and 2n = 28 + XX in the ovary, the same as sta ndard males and females, respectively, of this species. This suggests that the gynandromorphism occurred at a very early developmental stage . This gynandromorph could have originated from the formation of a bin ucleate egg by second-polar-body reactivation and Subsequent fertiliza tion by two spermatozoa, one male- and the other female-determining; h owever, the most parsimonious explanation is the elimination of one X chromosome in a female-determined zygote (XX) at the first cleavage di vision.