LOCALIZATION AND ACTIVITY OF RDNA GENES IN TIGER BEETLES (COLEOPTERA,CICINDELINAE)

Silver staining of male meiotic nuclei of six species of the tiger bee tle genus Cicindela (tribe Cicindelini), with multiple sex chromosomes , reveals the presence of active nucleolar organizing regions (NORs) i n the sex vesicle. In one species, Cicindela melancholica, fluorescenc e in situ hybridization (FISH) with a ribosomal probe showed that rDNA genes are in one of the three X chromosomes and in the Y chromosome. Silver staining and FISH show that the related species Cicindela palud osa with a male XO system, has NORs located in one pair of autosomes. In Megacephala euphratica (tribe Megacephalini) these techniques indic ate that NORs are located in three autosomal pairs but not in the sing le X chromosome of males. In all these species the nucleolus can be se en from the onset of meiosis to the end of the diffuse stage; it disap pears from diplotene to the end of meiosis and appears again during th e spermatid stage. From these results it is concluded that: (i) the nu cleolus does not seem to play a major role in the pairing and associat ion of the multiple sex chromosomes during first meiotic prophase and metaphase; () the occurrence of NORs in the heterosomes of species hav ing multiple sex chromosomes is thought to be an ancestral condition f or the genus Cicindela; and (iii) changes of location of NORs from the heterosomes to the autosomes have occurred within species of this gen us, at least in species showing extensive karyotypic repatterning.