Chromosomal basis for a bilateral gynandromorph in Pycnogaster inermis (Rambur, 1838) (Orthoptera, Tettigoniidae)

Abstract

Morphological and cytogenetic analyses of a spontaneous gynandromorph of Pycnogaster inermis, found in a natural population in the Spanish Sierra Nevada, have shown that the left side was male and the right side female, with almost perfect bilateral symmetry. Ventral valves of the ovipositor were very short, appearing as two spurs; dorsal valves were longer but still shorter than normal. The specimen had an apparently normal testis on the left side and a well-developed ovary on the right side. Cytogenetic analysis revealed the presence of 2n = 28 + X0 chromosomes in the testis and 2n = 28 + XX in the ovary, the same as standard 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 binucleate egg by second-polar-body reactivation and subsequent fertilization by two spermatozoa, one male-and the other female-determining; however, the most parsimonious explanation is the elimination of one X chromosome in a female-determined zygote (XX) at the first cleavage division.