Population cytogenetics of the genus Caledia (orthoptera: acridinae)

Abstract

The distribution of constitutive heterochromatin has been investigated in four chromosomal races of the grasshopper Caledia captiva (2n= 23 ♂/24 ♀) by the C-banding technique. Each of the four races was found to have a distinctive banding pattern which is associated with the inter-racial differences in chromosomal rearrangements. — The “Ancestral” race has a telocentric chromosome complement with large procentric C-bands which are structurally double on six pairs of chromosomes. The centromeres are unstained. — The “General Purpose” race has a C-banding pattern very similar to that seen in other Acridine grasshoppers with the majority of its chromosomes showing a centromeric localisation of the bands. — The two southern races, which show a complex polymorphism for presumed pericentric inversions on all twelve chromosomes, also show an unusually high level of interstitial and terminal C-bands. The different locations and numbers of these bands allow unambiguous identification of all the chromosome pairs within the complement. — In two cases, there is good evidence to indicate that a C-band redistribution between acrocentric and metacentric chromosomes has occurred by pericentric inversion. Furthermore, C-band variation on the long arm of the metacentric X-chromosome indicates the presence of a large paracentric inversion. This double inversion system has involved over 95% of the X-chromosome. — The interstitial and terminal C-bands probably have not resulted from heterochromatin movement within the complement but, more likely, have arisen by saltatory duplication of pre-existing sequences on the chromosome. — A new nomenclature system for banded chromosomes is proposed which allows most kinds of chromosomal restructuring and rearrangement to be adequately enumerated.