Characterization and evolutionary dynamics of a complex family of satellite DNA in the leaf beetle Chrysolina carnifex (Coleoptera, Chrysomelidae)

The present study characterizes the complex satellite DNA from the specialized phytophagous beetle species Chrysolina carnifex. The satellite DNA is formed by six monomer types, partially homologous but having diverged enough to be separate on the phylogenetic trees, since each monomer type is located on a different branch, having statistically significant bootstrap values. Its analysis suggests a common evolutionary origin of all monomers from the same 211-bp sequence mainly by means of base-substitution mutations evolutionarily fixed to each monomer type and duplications and/or deletions of pre-existing segments in the 211-bp sequence. The analysis of the sequences and Southern hybridizations suggest that the monomers are organized in three types of repeats: monomers (211-bp) and higher-order repeats in the form of dimers (477-bp) or even trimers (633-bp). These repetitive units are not isolated from others, and do not present the pattern characteristic for the regular tandem arrangement of satellite DNA. In-situ hybridization with biotinylated probes corresponding to the three types of repeats showed the pericentromeric location of these sequences in all meiotic bivalents, coinciding with the heterochromatic blocks revealed by C-banding, indicating in addition that each type of repeat is neither isolated from others nor located in specific chromosomes but rather that they are intermixed in the heterochromatic regions. The presence of this repetitive DNA in C. haemoptera, C. bankii and C. americana was also tested by Southern analysis. The results show that this satellite DNA sequence is specific to the C. carnifex genome but has not been found in three other species of Chrysolina occupying similar or different host plants.