Occurrence of pre‐nucleolar bodies and 45S rDNA location on the chromosomes of the ant Mycocepurus goeldii (Forel) (Formicidae, Myrmicinae, Attini)

The ant Mycocepurus goeldii (Forel) is known for having a relict karyotype with low chromosome number and the present study help the understanding of this ant cytogenetics by describing the occurrence of pre‐nucleolar bodies in their chromosomes using impregnation with silver nitrate (Ag‐NOR) and the location of 45S rDNA sites by means of the FISH (fluorescent in situ hybridization) technique. Several spots were observed surrounding all chromosomes when submitted to the Ag‐NOR technique. These unusual markings were observed in both chromatids of metaphase and early anaphase chromosomes, and are associated to the presence of pre‐nucleolar bodies, allowing the observation of the phenomenon of nucleologenesis. Although recent studies have shown that all chromosomes of M. goeldii exhibit centromeric or pericentromeric markings for the CMA3 fluorochrome, the FISH technique indicated the presence of 45S rDNA in only one pair of chromosomes that differed in the number of CMA3 markings observed for this species, pointing that the other markings observed with this fluorochrome do not match the sequences in ribosomal genes.