Karyotype, C-banding, chromosomal location of active nucleolar organizing regions, and B-chromosomes in Lasius niger (Hymenoptera, Formicidae)

Abstract

The karyotype of Lasius niger (n = 15) was analysed using C-banding and observation of nucleolar organizing region (NOR) sites. C-banding showed the existence of heterochromatin in the paracentromeric regions of all chromosomes. Two sites with primary NORs were found in chromosomes 6 and 8. Chromosome 13 showed a secondary NOR. In both cases, the NORs were located in the paracentromeric region. B-chromosomes were found in male and female germ cells. They exhibited intra- and inter-individual numerical variation. No B-chromosomes were observed in somatic cells (cerebral ganglion cells) of all castes. The Bs are telocentric, small, and clearly distinguishable from the regular members of the complement. They show positive heteropycnosis in meiotic prophase and they are highly C-band positive. The activity of NORs does not change when Bs are present. Several aspects of the behaviour of these Bs are examined.Key words: C-bands, nucleolar organizing region (primary), nucleolar oganizing region (secondary), B-chromosomes, Formicidae.