Origin and evolution of Parthenogenetic reproduction in the grasshopper Maraba virgo (Eumastacidae: Morabinae)

The virgo group of morabine grasshoppers includes the parthenogenetic, all. female species virgo from western New South Wales and north-western Victoria, together with four bisexual species from arid regions of Western Australia. The karyotypes of three of these bisexual species are compared with that of virgo and the origin of the various kinds of genetic heterozygosity found in the latter is discussed. It has been shown by tritiated thymidine autoradiography that virgo, in addition to being heterozygous for various structural rearrangements, is a permanent heterozygote for certain late-replicating DNA segments in the AB and CD chromosomes. The total amount of DNA per diploid nucleus is slightly lower in virgo than in its bisexual relatives. It is probable that the evolution of the virgo karyotype under conditions of parthenogenetic reproduction has involved inactivation of some segments (as suggested by late-labelling) and actual deletion of others. There have been two different X-autosome fusions in the phylogeny of the virgo group (one in the ancestry of virgo itself), two fusions between autosomes, and a translocation (or dissociation plus fusion). A numerical system to designate these and other chromosomal rearrangements in the morabine grasshoppers is put forward.