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

Abstract

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, Xyp, 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.

Chromosome mapping of 28S ribosomal genes in 11 species of Cassidinae (Coleoptera: Chrysomelidae)

“…The species with interstitial and/or centromeric rDNA cistrons are mainly members of the families Scarabaeidae and Chrysomelidae (subfamily Alticinae). As recorded in the present study, the changes in the location of the sites of rDNA are described in species with similar karyotype characteristics (Virkki, 1983;Yadav et al, 1992;Bione et al, 2005;Almeida et al, 2006Almeida et al, , 2010Arcanjo et al, 2009Arcanjo et al, , 2013Silva et al, 2009;Cabral de Mello et al, 2010, 2011bOliveira et al, 2010Oliveira et al, , 2012b. The differences in the location of rDNA in closely related species with similar chromosomal characteristics may be a result of small chromosomal rearrangements, which change the position of the ribosomal site without modifying the metacentric chromosomal morphology.…”

Molecular cytogenetic studies in the ladybird beetle Henosepilachna argus Geoffroy, 1762 (Coleoptera, Coccinellidae, Epilachninae)

“…In the first one the NOR region appears on the sex chromosomes ( Maffei et al 2001 ), nevertheless in the second one the NOR region appears on one pair of autosomes ( Maffei et al 2004 ). The variable location of the NORs has been observed in other Coleopteran families as Carabidae , Melolonthidae , Tenebrionidae or Scarabaeidae that show that rDNA sequences are located on the sex chromosomes, autosomes or both depending on the species ( Oliveira et al 2012 , Arcanjo et al 2013 ).…”