Inherited and somatic cytogenetic variability in Palearctic populations ofChironomus ripariusMeigen 1804 (Diptera, Chironomidae)

Abstract

Inter- and intracytogenetic variability was analyzed in 13 natural Palearctic populations of Chironomus riparius Meigen 1804 (syn. Chironomus thummi) by examining hereditary and somatic aberrations (mainly inversions) of the salivary gland polytene chromosomes. In total, 77 different types of inherited inversion sequences and 184 different types of somatic inversions were found. The median percent frequency of inherited inversions was 1.4% and karyotypic divergence between populations was very low. Most hereditary inversions were endemic and always in a heterozygous state. Only six inversion sequences, each of them shared by two very distant populations, may be considered a relic of very ancient ancestral inversions. Unlike inherited inversions, occurrence of somatic aberrations seems to increase with the overall rise in the level of heavy metal pollution of the sediments from which larvae were sampled. In contrast with what occurs in populations of other chironomid species, populations of C. riparius do not seem to undergo a process of cytogenetic differentiation.

Chironomids (Diptera) and their salivary gland chromosomes as indicators of trace-metal genotoxicity

“…These were the cases where the sediments analyzed were considered polluted (e.g., Michailova et al 1996;Michailova et al 2009a,b,c). Sometimes the concentrations of trace-metal pollutants were similar to or lower than that of the fossil reference data (Sella et al 2004). These were the station sediments that were considered unpolluted.…”

“…Since samples do not always have the same size for all analyzed populations, the degree of somatic cytogenetic variability of a population can be quantified by dividing the number of observed different types of somatic inversions by the number of sampled larvae in a given population. Such a ratio is called the S index (Sella et al 2004).…”

“…Aberrations are considered inherited when they affect all cells in both salivary glands of the same individual. Generally they occur at low (∼1%) frequencies in C. riparius and C. piger (Michailova et al 1996;Sella et al 2004;Michailova et al 2009a) or at >1% frequencies in C. plumosus (Butler et al 1999;Gunderina et al 1999). Inherited aberrations can result either from an aberration that occurred in the zygote or from the heritage of the parents.…”

“…Figure 3 illustrates the sediment concentrations of Cu, Cr, Ni, Zn and Pb and the frequencies of the different types of somatic chromosome aberrations of 535 C. riparius larvae from nine different stations in Italy, Russia and Bulgaria (Sella et al 2004). Because of the heterogeneity of the trace metal concentrations in the sediments of the nine water basins, it was impossible to correlate the overall level of trace metal pollution of the sediment in each station in relation to the S value of the larvae living on it.…”

The effect of long-term contamination by heavy metals on community and genome alterations of Chironomidae (Diptera) in a stream with mine drainage water (southern Poland)

“…Chromosome aberrations occurring in only a few cells were considered somatic aberrations (Sella et al 2004) and were presented as percentages. On the basis of the observed somatic chromosome Table 1 The cytogenetically studied species, number of individuals, cells, the percentage of their alterations and Somatic index rearrangements, a Somatic index (S) was calculated (Sella et al 2004) for each species.…”