Cytogenetics of the hybrids of three 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 south-eastern Australia. Meiosis of hybrids between three of the members that occur on Kangaroo Island, South Australia, was studied. The three members were the taxonomically undescribed form P24(XY) and two chromosomal races of V. viatica. Hybrids were either collected from narrow overlap zones (viatica₁₉-viatica₁₇, viatica₁₉-P24 (XY), P24(XY)-vitica₁₇) or were reared from grasshoppers collected from areas close to the overlap zones. — Chromosomal heterozygotes were found in all three overlap zones, but were frequent only in the overlap 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, however, 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 of importance in the evolution of the group, particularly since the distortion favoured the original rather than the derived type of chromosome.