Genome instability of Chironomus riparius Mg. and Chironomus piger Strenzke (Diptera, Chironomidae)

Intra and interspecific variation was evaluated in two Bulgarian populations (Pancharevo, and Kokalijane) of the two sibling and homosequential species Chironomus riparius Mg. and Chironomus piger Strenzke, by analyzing structural and functional alterations in salivary gland polytene chromosomes. In both species genome instability was demonstrated, which was expressed by structural and functional somatic chromosomal alterations. In the C. riparius population from Pancharevo, living in sediments containing high concentrations of Cu, Pb and Zn, salivary gland cells containing somatic rearrangements appeared at a significantly higher frequency (51.92 %) than in the Kokalijane C. piger population, living in heavy metal-unpolluted sediments (21.3 %). In the C. riparius population, somatic aberrations were distributed at different points along the chromosomes while in the C. piger population, somatic rearrangements were concentrated in the pericentromeric regions of chromosomes CD, EF and in proximal part of arms D and F At the cytological level using FISH analysis, both species can be identified also by the different location of tandem-repetitive minisatellite DNA clusters of Alu and Hinf families, and insertion sites of the LINE retrotransposon NLRCTh1. While location of the former is fixed, NLRCth1 appeared to have both fixed and inter-individually variable positions in both species. On average, 19.0 +/- 9.5 insertions of NLRCth1 per individual were observed in C riparius and 5.57 +/- 2.09 in C. piger. In both species locations of minisatellite DNA clusters, NLRCth1 retrotransposons and aberration breakpoints concentrated in proximal regions of chromosomes, and the majority of the breakpoints were located in sections containing blocks of repetitive DNA clusters.