Comparative cytogenetics of three species of Dichotomius (Coleoptera, Scarabaeidae)

Meiotic and mitotic chromosomes of Dichotomius nisus, D. semisquamosus and D. sericeus were analyzed after conventional staining, C-banding and silver nitrate staining. In addition, Dichotomius nisus and D. semisquamosus chromosomes were also analyzed after fluorescent in situ hybridization (FISH) with an rDNA probe. The species analyzed had an asymmetrical karyotype with 2n = 18 and meta-submetacentric chromosomes. The sex determination mechanism was of the Xy p type in D. nisus and D. semisquamosus and of the Xyr type in D. sericeus. C-banding revealed the presence of pericentromeric blocks of constitutive heterochromatin (CH) in all the chromosomes of the three species. After silver staining, the nucleolar organizer regions (NORs) were located in autosomes of D. semisquamosus and D. sericeus and in the sexual bivalent of D. nisus. FISH with an rDNA probe confirmed NORs location in D. semisquamosus and in D. nisus. Our results suggest that chromosome inversions and fusions occurred during the evolution of the group.

Karyotype, C-and fluorescence banding pattern, NOR location and FISH study of five Scarabaeidae (Coleoptera) species

Meiotic chromosomes obtained from members of the coleopteran subfamilies Rutelinae and Dynastinae were studied using standard and silver nitrate staining, C-banding, base-specific fluorochromes and fluorescent in situ hybridization (FISH). The study presents detailed karyotipic descripitions of three Rutelinae species (Geniates borelli, Macraspis festiva and Pelidnota pallidipennis), and two Dynastinae species (Lygirus ebenus and Strategus surinamensis hirtus) with special emphasis on the distribution and variability of constitutive heterochromatin and the nucleolar organizer region (NOR). We found that for G. borelli, P. pallidipennis, L. ebenus and S. s hirtus the karyotype was 2n = 20 (9II + Xy p), with G. borelli, P. pallidipennis and L. ebenus showed meta-submetacentric chromosomes which gradually decreased in size. For Macraspis festiva the karyotype was 2n = 18 (8II + Xy p). In L. ebenus we found that the NOR was located on an autosome, but in the other four species it occurred on the sex bivalents. In all five species the constitutive heterochromatin (CH) was predominantly pericentromeric while the X chromosomes were almost completely heterochomatic, although CMA3/DA/DAPI staining showed intra and interspecific variation in the bright fluorescence of the constitutive heterochromatin. The FISH technique showed rDNA sites on the X chromosome of the Rutelinae species.

A study of the constitutive heterochromatin and nucleolus organizer regions of Isocopris inhiata and Diabroctis mimas (Coleoptera: Scarabaeidae, Scarabaeinae) using C-banding, AgNO3 staining and FISH techniques

Meiotic and mitotic chromosomes of Isocopris inhiata and Diabroctis mimas were studied by standard staining procedures, C-banding, silver nitrate staining and FISH using Apis mellifera 28S rDNA as probe. Isocopris inhiata presented a 2n = 18 (8II+ Xy p) karyotype, composed of meta-submetacentric chromosomes with gradual reduction in size. The karyotype of D. mimas was 2n = 20 (9II+ Xy p), composed of meta-submetacentric (pairs 1, 2, 3, 4 and 7) and acrocentric (pairs 5, 6, 8 and 9) chromosomes, with gradual reduction in size. Analysis of constitutive heterochromatin revealed similar C-banding patterns for both species, showing pericentromeric and telomeric bands and diphasic chromosomes. In addition, the X chromosomes of these species were found to be almost completely heterochromatic. The presence of chromocenters was checked in one or more phases of prophase I of these species. All heterochromatin reacted positively for the silver stain. By FISH analysis we were able to locate the rDNA in medium-size autosome pairs in both species and in the X chromosome of D. mimas.