Heterochromatin and karyotypic differentiation of some neotropical cactus-breeding species of the Drosophila repleta species group

Abstract

Metaphase chromosomes from neuroblasts of strains from both laboratory stocks and natural populations of D. serido, D. meridionalis, D. borborema and D. buzzatii have been studied using colcemid pretreatment, and air-drying followed by Giemsa staining. The two latter species both show a uniform ‘basic’ metaphase karyotype. D. serido and D. meridionalis, on the other hand, both include a number of different, geographically distinct, metaphase karyotypes involving differences in the major blocks of constitutive heterochromatin present on the sex chromosomes and/or the 6th chromosome (microchromosome). These chromosomal differences are largely due to the acquisition of extra heterochromatin though pericentric inversions appear to be responsible for some of the Y-chromosome variants in D. serido. Moreover, the cytological evidence demonstrates that populations of both species are far from continuous in distribution. The extent to which such cytological differences reflect the existence of subspecific or specific complexes with minimal morphological differentiation is under investigation.