Cytogenetic characteristics of a population of Chironomus riparius Meigen 1804 (Diptera, Chironomidae) from a polluted Po river station

A population of Chironomus riparius from a Po river station near Moncalieri (a trace-metal polluted station) was studied. In this population was established a great variability of band structure of polytene chromosomes as well as paracentric heterozygous inversions, deletions, deficiencies, partial breaks, diploid chromosome fragments, and changes in functional activity and appearance of heterochromatin. In arms A through F, some bands had an increased size compared to the standard chromosomic map. Some bands appeared in a heterozygous or normal homozygous state or were amplified. In all arms, many condensed stable bands appeared in the decondensed state when compared to the standard map. Asynaptic zones in arms E and G as well as heterozygous Balbiani rings and NORs were established. Very often the 4th chromosome was almost completely heteropycnotic and looded like a pompon chromosome. For the first time in this species, a high frequency of ectopic pairings of different arms was observed. Telomeric regions involved in ectopic pairings had a granular appearance, as did some centromeres. The hypothesis is advanced that such a high frequency of structural rearrangements could be correlated with genomic distribution of specific mobile elements.     

Comparative cytogenetic variability of polytene chromosomes from salivary glands of Chironomus riparius Mg., 1804 (Diptera, Chironomidae) from two polluted biotopes in Bulgaria and Russia

The structural-functional variation of Chironomus riparius salivary gland polytene chromosomes was studied in two geographically isolated Palearctic regions, Bulgaria (village Pancharevo) and Russia (St. Petersburg). The two biotopes, where larvae were collected, were polluted with various heavy metals from anthropogenic sources. Hereditary paracentric heterozygous inversions were characteristic of the Russian population, whereas somatic paracentric or pericentric heterozygous inversions were more common in the Bulgarian one. All inversions occurred at low frequencies. Other aberrations found in the two populations included somatic deletions resulting in a pompon structure of chromosome IVG, heterozygous translocation between chromosomes IVG and IIIF, enlargement of individual disks, and the appearance of a heterozygous block close to the centromere of chromosome IVG. In addition, changes in functional activity of the nucleolus organizer and Balbiani rings (BRc/BRb) were observed. Several aberration breakpoints proved to coincide with satellites of the Alu and Hinf families.     

Polymorphism and Divergence of Multilocus DNA Markers in Sibling Species Chironomus riparius Meigen and Chironomus piger Strenzke (Diptera,Chironomidae)

Intra- and interspecific variation and divergence of multilocus markers for genomic DNA of the sibling species from the thimmi group,Chironomus riparius and C. piger, were studied by PCR with arbitrary primers (RAPD). A high level of RAPD polymorphism was determined in both laboratory and natural populations of these species. The genetic distances were estimated between the C. riparius populations and between the sibling species C. riparius and C. piger. The genetic distance between C. riparius andC. piger was 4 to 5 times higher than that between the C. riparius populations. A comparison of the variation and divergence for the RAPD markers with those for other genomic markers—enzyme-coding genes and chromosomes (gene linkage groups)—showed that different components of the genome differed in their contribution to the genome divergence.     

The effect of mercury chloride on morphofunctional parameters in Chironomus riparius Meigen (Diptera, Chironomidae) larvae

The effects of various mercury chloride (HgCl₂) concentrations associated with bottom sediments on mercury accumulation in chironomid larvae and the modifications of morphofunctional parameters (mortality, growth, and structure of the mouth apparatus) have been studied. It was shown that, upon exposure, the larvae accumulated mercury in amounts exceeding its sediment concentrations. The mortality rate and metamorphosis duration increased with an increase in metal concentrations, while the animal size remained unaffected. Among all investigated morphological structures, the antennae were the most heavily effected.     

Polymorphism and divergence of multilocus DNA markers in sibling species Chironomus riparius Meigen and Chironomus piger Strenzke (Diptera, Chironomidae)

Intra- and interspecific variation and divergence of multilocus markers for genomic DNA of the sibling species from the thimmi group, Chironomus riparius and C. piger, were studied by PCR with arbitrary primers (RAPD). A high level of RAPD polymorphism was determined in both laboratory and natural populations of these species. The genetic distances were estimated between the C. riparius populations and between the sibling species C. riparius and C. piger. The genetic distance between C. riparius and C. piger was 4 to 5 times higher than that between the C. riparius populations. A comparison of the variation and divergence for the RAPD markers with those for other genomic markers--enzyme-coding genes and chromosomes (linked gene groups)--showed that different components of the genome differed in their contribution to the genome divergence.     

Chromosomal variability in natural populations of Chironomus cingulatus meigen (Diptera, Chironomidae)

Chromosomal polymorphism has been studied in seven natural populations of Chironomus cingulatus from Western Europe, Western Siberia, and the Republic of Sakha (Yakutia). The banding sequences pool of the species includes 15 banding sequences. Chromosomal polymorphism was revealed in five out of seven chromosomal arms. Arm B is the most polymorphic with four banding sequences. There are three banding sequences in arm A. Arms D, E, and G have two banding sequences. None of the chromosome rearrangements were revealed in arms C and F. The populations of C. cingulatus differ clearly in their number and frequency of banding sequences, which indicates that different gene sequences are adaptive in different populations.     

A structural study of the anal papillae of the midge Chironomus riparius Meigen (Diptera: Chironomidae)

Larvae of the midge, Chironomus riparius Mg., have four anal papillae arranged as two pairs, one dorsal to and the other ventral to the anus. Structural study with light and electron microscopes has revealed that their integument consists of a thin cuticle overlaying a thick, syncytial epidermis which is specialised to facilitate ion transport. There is a distinct neck or collar region at the junction of each papilla with the rest of the body wall. Although in many respects these structures resemble those in mosquitoes, there are both morphological and physiological features which suggest that differences exist in the means by which ion exchange with the environment is controlled and effected in the two families.     

A new method for establishing a permanent laboratory culture of Chironomus riparius Meigen (Diptera: Chironomidae)

A new technique for the establishment of a permanent laboratory culture of Chirono-mus riparius is described. Larvae and pupae were reared in plastic tanks containing tap water, filamentous algae and a commercially prepared fishfood. The tanks were aerated, maintained at a constant temperature of 24°C and subjected to a constant lighting regime of 13 h of light followed by 11 h of darkness. Adults flew freely in a modified handling box, mated, and oviposited on strips of filter paper placed in the plastic tanks containing the aquatic stages. It has proved unnecessary to change the water or medium, which has saved both time and effort. Moreover, larvae established themselves in ail parts ofthe alga, and therefore more could be kept in each tank than when, as in previous methods, they are provided only with a substratum on the floor of the container.     

Water quality and the occurrence of Chironomus riparius Meigen (Diptera: Chironomidae) in a stream receiving sewage effluent

SUMMARY. The effects of a sewage effluent in Moat Brook, Staffordshire, were determined from regular collections of water and biological samples from directly comparable stations above and below the sewage outfall.
The eutrophic conditions below the outfall result in the replacement of Polypedilum laetum by Chironomus riparius (except in the spring) as the dominant member of the Chironominae. Continuous recruitment of first instar larvae to the population of C. riparius in summer and autumn results in much overlap of generations, but emergence trap captures suggest at least five generations in the year.
The usefulness of C. riparius as an indicator of enriched conditions in lotic ecosystems should be considered in relation to oviposition behaviour and the occurrence and seasonal variation in density of the adults and aquatic stages (including the more conspicuous third and fourth instar larvae).     

Succession of Chironomus Meigen Species (Diptera,Chironomidae) in Newly Filled Ponds

The colonization by Chironomus spp. of two ponds filled after a dry period was investigated. Field data were collected by means of quantitative benthic samples and emergence traps. C. melanescens. C. annularius, C. riparius, C. piger, C. luridus, C. obtusidens, C. plumosus, C. dorsalis and Camptochironomus tentans were determined cytotaxonomically in ponds investigated. C. melanescens and C. annularius appear to be the most characteristic species colonizing in high numbers in newly filled ponds. Larvae of C. annularius grew more slowly in ponds compared with the former one which resulted in a characteristic succession of both larval types. Most species mentioned disappeared completely from the ponds investigated after the metamorphosis of a single cohort. They were replaced by C. plumosus which was often attended by C. annularius in smaller ponds.     

Karyofunds of Chironomus plumosus (L.) (Diptera, Chironomidae). V. terminal and interstitial populations

The study of polytene chromosomes of Chironomus plumosus from Rybinsk reservoir, its inflows and surrounding water bodies allow to mark out two type's of population. Terminal populations--presented by karyoforms with concrete limited composition of genotype combinations and zygotic arm combinations, which adapted to specific complex of the habitat factors. The immediate exchange of genes between different terminal populations is absent (even they placed in nearness) from allochronie of life cycles and impossibility of larvae-immigrants to finish ontogenesis in unfit for they habitat conditions. Interstitial populations inhabit the biotopes, where the karyoforms of two or more terminal populations can to finish ontogenesis and to reproduce. The genetic exchange between terminal population implement through interstitial populations.     

Site specific differentiation in metal tolerance in the midge Chironomus riparius (Diptera,Chironomidae)

Metal tolerance in Chironomus riparius (Diptera) populations from contaminated streams was studied by comparing the effects of cadmium, zinc and iron on first generation laboratory reared midges. First instar larvae were exposed for four days, after which surviving larvae were counted and their length measured. Larvae from two highly polluted sites, kept under control conditions, grew substantially slower than those from other populations. All populations showed the same growth responses to increased zinc concentrations, but differences were found in the responses to both cadmium and iron. Since population differentiation was demonstrated in first generation laboratory animals, it is suggested that the differences between populations of C. riparius have a genetic basis.     

Gytogenetics of Chironomus riparius L. from the fishpond in Borok village (Diptera, Chironomidae)

We have found three inherited inversions in Chironomus riparius populations from the Borok fishpond, namely: (A3d-B1a) in the arm A (C5a-C6a) in the arm D and (B3b-4d/e) in the arm F. Increase of heterochromatin in some bands of chromosome F (B3h, B3h + B3c--C1a) and puffs appearance in the arms C, D and E have been observed. We saw also changes in functional activity of nucleolar organizer (N) and Balbiani rings (BRe/BRb). It has been found that some of inversion breakpoints coincide with the Alu and Hinf satellite DNA localization sites.     

Mechanical,sensory and glandular structures in the tarsal unguitractor apparatus of Chironomus riparius (Diptera,Chironomidae)

Summary The legs of chironomid midges from a laboratory colony were examined in the region of the joint between the fifth tarsal segment and the pretarsus, especially the surface of the unguitractor and the manner in which the unguitractor fits into a ventromedian groove in the edge of the tarsus when the joint is flexed. The region was reconstructed from serial sections to clarify the spatial relations of the internal structures to one another and to the external structures. Ultrastructural characteristics of the cells and cuticle suggest a secretory function of the unguitractor. An amphinematic scoloparium is suspended between the point at which the unguitractor attaches to its tendon and the transverse diaphragm within the tarsus. This mechanoreceptor could serve as a proprioceptive sensor of the position of unguitractor and tarsus; it could also be an exteroceptor, sensing vibration in the substrate and/or the air. In the context of functional morphology, the clamping of the unguitractor in the ventral hollow in the tarsus could have the effect of resetting the sensitivity of the sensor. On the other hand, this arrangement could also simply act as an energy-saving means of fixing the claws in the grasping position for long periods.Abbreviations aj adhering junction - bl basal labyrinth - bm basement membrane - cc cuticular cap - cd cellular diaphragm - cth cuticular thickening - dp matrix with dense particles - ec enveloping cells - f filaments - fot funnel-like opening of tendon - ic intracellular canaliculi - lp lateral process of ec - pAc process of A cell - pv pulvillus - r rootlets of cilia - sc scolopale cell - sco scoloparium - sd septate desmosomes - t tendon - tb tubular body - tu tubules - u unguis, or claw - upl unguitractor plate     

Comparative Cytogenetic Variation of the Salivary Gland Polytene Chromosomes in Chironomus riparius Mg., 1804 (Diptera, Chironomidae) from Two Polluted Biotopes of Bulgaria and Russia

The structural–functional variation ofChironomus riparius salivary gland polytene chromosomes was studied in two geographically isolated Palearctic regions, Bulgaria (village Pancharevo) and Russia (St. Petersburg). The two biotopes, where larvae were collected, were polluted with various heavy metals from anthropogenic sources. Hereditary paracentric heterozygous inversions were characteristic of the Russian population, whereas somatic paracentric or pericentric heterozygous inversions were more common in the Bulgarian one. All inversions occurred at low frequencies. Other aberrations found in the two populations included somatic deletions resulting in a pompon structure of chromosome IVG, heterozygous translocation between chromosomes IVG and IIIF, enlargement of individual disks, and the appearance of a heterozygous block close to the centromere of chromosome IVG. In addition, changes in functional activity of the nucleolus organizer and Balbiani rings (BRc/BRb) were observed. Several aberration breakpoints proved to coincide with satellites of the Alu and Hinf families.     

Development and localization of microsatellite markers for the sibling species Chironomus riparius and Chironomus piger (Diptera: Chironomidae)

Five variable microsatellite loci are reported for the nonbiting midge species Chironomus riparius and Chironomus piger. All loci show considerable intraspecific variation and species‐specific alleles, which allow to discriminate among the two closely related species and their interspecific hybrids, and to estimate genetic diversity within and between populations. Additionally, the loci were localized on C. riparius polytene chromosomes to verify their single copy status and investigate possible chromosomal linkage. The described markers are used in different studies with regard to population and ecological genetics and evolutionary ecotoxicology of Chironomus.     

A new species of Chironomus Meigen, 1803 (Diptera,Chironomidae) from the southeast of Brazil

The article describes the larva, pupa, adults and karyotype of Chironomus reissi, sp. n., which live on leaf detritus beds of small temporary waters in the southeast of Brazil. The species belongs to the pseudothummi cytocomplex with the chromosome arm combination AE, BF, CD, G.     

Cadmium,zinc, lead and copper inChironomus riparius (Meigen) larvae (Diptera,Chironomidae): uptake and effects

Cadmium, Zn, Pb and Cu uptake and effects in larvae ofChironomus riparius (Meigen) were studied in an integrated laboratory investigation, in which metal analyses in different instar stages, uptake kinetics and effects on development and growth were considered in three separate experiments.In short-term experiments with fourth instar larvae, it was demonstrated that only a minor portion of metals was adsorbed on the larval exoskeletons. No conclusive evidence on the uptake mechanism was found, but active uptake of trace metals seemed highly unlikely.In partial life cycle experiments, all four metals studied were readily accumulated in chironomid larvae. Uptake could be described satisfactorily utilizing a first-order one-compartment uptake model which incorporated growth. In all cases steady state conditions were approached and high uptake and elimination rate constants were estimated. Distinct differences between essential (Zn and Cu) and non-essential (Cd and Pb) metals were noted. Larval growth was significantly impaired upon exposure.Finally, long-term exposure experiments with low Cd concentrations (0.010 and 0.025 mg 1^{–1) resulted initially in growth impairment and high mortality in first instar stages, but surviving larvae restored growth and adults emerged even before control adults. In similar experiments with Zn (0.1 and 1.0 mg 1–1}), development of larvae was significantly retarded. High Zn concentrations in larvae were noted and almost no adult midges emerged.