Chromosomal Breakpoints and Transposable-elemen tinsertion Sites in Salivary Gland Chromosomes of Chironomus riparius Meigen (Diptera, Chironomidae) from Trace Metal Polluted Stations

We studied the distributions of somatic chromosome rearrangements and copies of three transposable elements (NLRCth1, CTRT1 and TFB1) in the salivary-gland chromosomes of Chironomus riparius Mg. larvae. Larvae were collected from four stations (Chaya River and The Farm in Bulgaria, and Pazar fountain and Derincay River in Turkey), whose sediments had different concentrations of several trace metals. The number of cytogenetic aberrations was higher in larvae from those stations whose sediments had higher concentrations of trace metals. Through FISH analysis of the cytogenetic localization of the three transposable elements, we found fixed insertion sites in the centromere regions and many variable insertion sites. NLRCth1, CTRT1, TFB1 insertion sites and locations of somatic-rearrangements occurred significantly more often in the proximal than in the distal regions of the polytene chromosomes. In addition, some common breakpoints of aberrations co-localized with NLRCth1, CTRT1 or TFB1 insertion sites in the populations of C.riparius samples: from Pazar (for all studied TEs: from 35.7% to 57.1%); Derincay River (from 38.8% to 69.4%); The Farm (from 34.8% to 50%) and Chaya River (from 23.3% to 50%). We advance the hypothesis that chromosome instabilities induced by stress agents in the environment could be related to the position of the TEs in the genome of C. riparius.