CYTOGENETICS OF HYBRIDS OF 3 MEMBERS OF THE GRASSHOPPER GENUS VANDIEMENELLA "(ORTHOPTERA-EUMASTACIDAE-MORABINAE)

Certain members of the grasshopper genus Vandiemenella (earlier referred to as the viatica group) form a group of chromosomally distinct taxa with contiguous distributions through southeastern Australia. Meiosis of hybrids between 3 of the members that occur on Kangaroo Island, South Australia, was studied. The 3 members were the taxonomically undescribed form P24(XY) and 2 chromosomal races of V. viatica. Hybrids were either collected from narrow overlap zones (viatica19-viatica17, viatica19-P24(XY), P24(XY)-viatica17) or were reared from grasshoppers collected from areas close to the overlap zones. Chromosomal heterozygotes were found in all 3 overlap zones, but were frequent only in the overal zone of P24(XY) and viatica17. Male chromosomal heterozygotes of P24(XY) and viatica19 and of viatica17 and viatica19 had abnormalities of meiosis, such as asynapsis (or desynapsis), which were generally associated with the chromosomes that distinguish the taxa. These abnormalities would be expected to lead to a reduction of fertility and so may contribute to reproductive isolation. Analysis of embryos from female heterozygotes of P24(XY) and viatica17 indicated that similar abnormalities of meiosis occurred in these females. Very few meiotic abnormalities were seen in the corresponding male hybrids. The structurally different X chromosomes of female hybrids of P24(XY) and viatica17 were recovered in a distorted ratio in their embryos. The distortion was only slight and would not be expected to be important in the evolution of the group, particularly since the distortion favored the original rather than the derived type of chromosome.