Evolutionary dynamics of heterochromatin in the genome of Dichotomius beetles based on chromosomal analysis.

We comparatively analyzed six Dichotomius species (Coleoptera: Scarabainae) through cytogenetic methods and mitochondrial genes sequencing in the aim to identify patterns of chromosomal evolution and heterochromatin differentiation in the group. The chromosomal data were accessed through the classical analysis of heterochromatin and mapping of high and moderately repeated DNAs (C (0) t-1 DNA fraction). Mitochondrial data were obtained from nucleotide sequences of the cytochrome oxidase I (COI) and 16S rRNA genes. The heterochromatin distribution was conserved but revealed variability in the base pair richness and repetitive DNA content, and an intense turnover of heterochromatic associated sequences seems to have occurred during Dichotomius speciation. Specifically for D. bos, an interesting pattern was observed, indicating apparently the presence of heterochromatic sequences composed of low copy-number sequences. Moreover, highly conserved terminal/sub-terminal sequences that could act as a telomeric or telomere-associated DNA were observed. The heterochromatin diversification patterns observed in Dichotomius were not accomplished by the diversification of the species studied, which may be a consequence of the intense dynamics that drive the evolution of repeated DNA clusters in the genome. Finally our findings also suggest that the use of C (0) t-1 DNA fraction represents a powerful, inexpensive and not time consuming tool to be applied in understanding heterochromatin and repetitive DNA organization.