Amplification of repetitive DNA and origin of a rare chromosomal sex bivalent in Deltochilum (Calhyboma) verruciferum (Coleoptera, Scarabaeidae)

Chromosomal diversification of diploid number, heterochromatin and rDNAs in two species of Phanaeus beetles (Scarabaeidae, Scarabaeinae)

The genus Phanaeus is included in the tribe Phanaeini, one of the most diverse tribes within the subfamily Scarabaeinae in terms of chromosomal characteristics. However, so far the species of this genus were not studied with differential cytogenetic techniques, limiting any inference of the probable mechanisms responsible for this diversity. In this work, several techniques were applied with the aim of cytogenetically characterizing two Phanaeus species. The karyotype found for Phanaeus (Notiophanaeus) chalcomelas was 2n = 12, neo-XY, and that of P. (N.) splendidulus was 2n = 20, Xy_p, considered primitive for the family Scarabaeidae. The chromosomes of both species showed a high amount of constitutive heterochromatin (CH), with blocks rich in base pairs GC (CMA₃⁺). Moreover, in P. (N.) chalcomelas the marks revealed by C-banding and fluorochrome staining were different in size, showing CH variability. Sites of 18S ribosomal DNA (rDNA) were identified in one autosomal pair of P. (N.) chalcomelas and in five autosomal pairs of P. (N.) splendidulus. On the other hand, only one autosomal pair exhibited 5S rDNA sequences in these species. The results suggest that the karyotype differentiation of the Phanaeus species studied here involved pericentric inversions and centric fusions, as well as mechanisms related to amplification and dispersion of CH and rDNA sequences.

Karyotype analysis of four jewel-beetle species (Coleoptera, Buprestidae) detected by standard staining, C-banding, AgNOR-banding and CMA3/DAPI staining

The male karyotypes of Acmaeodera pilosellae persica Mannerheim, 1837 with 2n=20 (18+neoXY), Sphenoptera scovitzii Faldermann, 1835 (2n=38-46), Dicerca aenea validiuscula Semenov, 1895 - 2n=20 (18+Xyp) and Sphaerobothris aghababiani Volkovitsh et Kalashian, 1998 - 2n=16 (14+Xyp) were studied using conventional staining and different chromosome banding techniques: C-banding, AgNOR-banding, as well as fluorochrome Chromomycin A3 (CMA3) and DAPI. It is shown that C-positive segments are weakly visible in all four species which indicates a small amount of constitutive heterochromatin (CH). There were no signals after DAPI staining and some positive signals were discovered using CMA3 staining demonstrating absence of AT-rich DNA and presence of GC-rich clusters of CH. Nucleolus organizing regions (NORs) were revealed using Ag-NOR technique; argentophilic material mostly coincides with positive signals obtained using CMA3 staining.

Cytogenetic analysis of two Coprophanaeus species (Scarabaeidae) revealing wide constitutive heterochromatin variability and the largest number of 45S rDNA sites among Coleoptera

The Coleopterans of Scarabaeinae clade presents Coprophanaeus (Megaphanaeus) ensifer and C. (Coprophanaeus) cyanescens (Scarabaeidae) when they are studied cytogenetically by different techniques. The species present symmetric karyotypes, diploid number of 2n=20, and meta-submetacentric chromosomes. C. (M.) ensifer present an XY sex-determining mechanism and C. (C.) cyanescens an XY(p) parachute mechanism. Analysis of constitutive heterochromatin (CH) in the two species revealed the presence of diphasic autosomes, with log arm heterochromatics. Moreover, an additional heterochromatic block in four autosomal bivalents were observed in C. (M.) ensifer. CMA(3)/DA/DAPI fluorochrome staining detected CMA(3) positive heterochromatic blocks restricted to the sex chromosomes in C. (C.) cyanescens, whereas in C. (M.) ensifer CMA(3) positive pericentromeric blocks were present in all autosomes, in the Y chromosome and in the four additional heterochromatic blocks. DAPI staining was neutral in both species. Silver nitrate (AgNO(3)) staining was inefficient for the detection of the nucleolar organizer region (NORs), but showed affinity for the heterochromatic regions. Fluorescence in situ hybridization (FISH) revealed the presence of 45S rDNA sites in the terminal region of the three autosomal bivalents of C. (C.) cyanescens and in seven bivalents and the Y chromosome of C. (M.) ensifer. These results contribute to a better understanding of chromosome evolution in the genus Coprophanaeus, and demonstrate a wide CH variability and the largest number of ribosomal sites among Coleoptera.