H. Hirai et al., MULTIPLICATION OF 28S RDNA AND NOR ACTIVITY IN CHROMOSOME EVOLUTION AMONG ANTS OF THE MYRMECIA-PILOSULA SPECIES COMPLEX, Chromosoma, 103(3), 1994, pp. 171-178
Chromosomal localization of rDNA in samples of five taxa of the Myrmec
ia pilosula species complex (Hymenoptera: Formicidae: Myrmeciinae) wit
h 2n=3 (M. croslandi), 8 (M. imaii), 10 (M. banksi), 18 (M. haskinsoru
m), and 27 (M. pilosula) was carried out by fluorescence in situ hybri
dization (FISH) using cloned M. croslandi rDNA (pMc.r2) including the
coding region for 28S rRNA. Results show that (1) the 28S rDNA in the
genome of these ants is repetitive and is localized in pericentromeric
C-bands, (2) the number of chromosomes carrying rDNA is two in M. cro
slandi, M. imaii and M. banksi, six in M. haskinsorum and ten in M. pi
losula, and (3) only one or two clusters of rRNA genes generate nucleo
li in each species. We suggest that the rDNA in the ancestral stock of
the M. pilosula complex was localized originally in a pericentromeric
C-band, and multiplied by chance with time during saltatory increases
in C-banding following episodes of centric fission. Most rDNA multipl
ied on various chromosomes seems to be inactivated and eliminated from
the genome, together with C-bands, by AM-inversion or centric fusion,
with the remnant rDNAs dispersed in the genome by centric fission and
AM-inversion.