Cytogenetic analysis of two related Deltochilum (Coleoptera,Scarabaeidae) species: Diploid number reduction,extensive heterochromatin addition and differentiation

Male mitotic and meiotic chromosomes of two species of the genus Deltochilum (Scarabaeidae) were analyzed through conventional staining, C-banding, base-specific fluorochromes, silver nitrate staining (AgNO₃) and FISH (45S rDNA). The two species possessed karyotypes with 2n = 14, neo-XY and meta-submetacentric chromosomes. The analysis of constitutive heterochromatin (CH) revealed mainly diphasic chromosomes in the two species, showing heterochromatic long arms. Silver nitrate staining labeled the blocks corresponding to CH in D. (Deltohyboma) aff morbillosum while in D. (Deltohyboma) calcaratum, AgNO₃ staining revealed only the CH blocks of the diphasic autosomes. The fluorochrome staining revealed in D. (D.) calcaratum the diphasic autosomes and the sex chromosomes with CMA₃⁺ blocks, and in D. (D.) aff morbillosum, the GC-rich sequences were restricted to the terminal regions of the long arms of the pairs 1 and 2 and the X. The FISH revealed 45S rDNA sites in two autosomic pairs and in the X chromosome. The analyses performed allowed for the identification of cytogenetic markers and the discussion of possible chromosome rearrangements that have been involved in the karyotypic differentiation of these species mainly related to the repetitive genome.