Abstract Telomere has a central role in chromosomal stability events. Chromosome ends organized in telomere-loop prevent activation of DNA damage response (DDR) mechanisms, thus keeping the chromosome structure organized. On the other hand, free chromosome ends, dysfunctional telomeres, and interstitial telomeric sequences (ITS) can trigger chromosome rearrangements. Here, the telomere organization, function, and maintenance mechanisms, in addition to ITS types and their involvement in chromosome changes, were revisited. Despite a general (TTAGGG)n sequence being present in vertebrate telomeres, insects show more diversification of their telomere motif. The relation between ITS and chromosome rearrangements was observed in insects and vertebrates, demonstrating different types of genome organization and distribution. Some ITS cannot be considered relicts of chromosome rearrangements because probable they were inserted during a double-strand break repair mechanism. On the other hand, the involvement of telomere sequences participating or triggering chromosome rearrangements or organizing satellite DNA components in several species groups is evident. The genomic assembling advances and applying other methodologies over ITS, and their flanking regions, can help to understand the telomere participation in the chromosomal evolution in species groups with highly diversified karyotypes.

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.

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.