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Chromosomal characterization of a tropical midge

  • Savitribai Phule Pune University Pune India


Cytogenetic studies were carried out with Chironomus ramosus, which is a widespread species among the tropical midges (Diptera: Chironomidae). This work is a first attempt to examine the salivary gland polytene chromosomes as well as the ganglionic mitotic chromosomes of this species. A detailed cytophotomap for each chromosome (n = 4) was prepared. Distinctive features of all the chromosomes are described. The results have been compared with other known species of tropical chironomids.
Chromosomal characterization of a tropical midge
B. B. Nath* and N. N. Godbole
Department of Zoology, University of Pune, Pune 411 007, India (*Reprint address)
Key words: karyology, Chironomus ramosus, polytene chromosome, tropical midge
Cytogenetic studies were carried out with Chironomus ramosus, which is a
widespread species among the tropical midges (Diptera: Chironomidae). This
work is a first attempt to examine the salivary gland polytene chromosomes as
well as the ganglionic mitotic chromosomes of this species. A detailed cyto-
photomap for each chromosome (n =4) was prepared. Distinctive features of all
the chromosomesare described. The results have been compared with other .
known species of tropical.chironomids.
Chironomid midges are. dipteran insects. They abound in most
freshwater environments and seem to have a remarkably wide range
of tolerance for different ecosystems (Oliver, 19:z.1;Pinder, 1986). The
ease with which cytogenetic work can be carried out with these insects
is largely due to the high degree of polyteny in larval tissues
(Grossbach, 1977).
Polytene chromosomes provide a very important tool in evolu-
tionary cytogenetics, and Chironomus ramosus is a useful model
(Martin, 1979). The Chironomus genus belongs to an ancient group
of dipteran insects (Suborder Nematocera), and it is separated
from Drosophila melanogasterby approximately 200 million years of
evolution (Curtis et al., 1995).
Several papers on karyotypic evolution in the genus Chironomus
have been published, mainly on temperate species (Keyl, 1962;
Martin et ai., 1974; Martin, 1979; Wulker, 1980). Unfortunately,
tropical species of Chironomus have not attracted much attention.
However, in recent years, chromosomes of several species of tropical
midges have been described from the Indian subcontinent (Saxena
et al., 1985; Nath and Lakhotia, 1989; Kumar and Gupta, 1990;
Gupta and Kumar, 1991; De and Gupta, 1994).
Chironomus ramosus is a new species described by Chaudhuri et al.
(1992). The current study is an attempt to characterize the chromo-
somes of C. ramosus and prepare a reference cytophotomap of salivary
gland polytene chromosomes for future cytogenetic studies.
25 Cytobios 91 25-31 1997 Published and @ 1997 by The Faculty Press
88 Regent Street, Cambridge, Great Britain
... Larvae collected from the Mula river were validated for taxonomic identification using morphological and cytotaxonomic keys [26,27] and reared in non-toxic plastic tubs (Ø = 35 cm) containing sterilized beach sand at the bottom (S2A Fig). The rearing procedure was described previously [28,29]. ...
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Vibrio cholerae causes the fatal cholera diarrhea. Chironomids (Diptera; Chironomidae) are abundant in freshwater aquatic habitats and estuaries and are natural reservoirs of V. cho-lerae. Until now, only the non-O1/O139 serogroups of V. cholerae were identified in chirono-mids. Here, we explored whether chironomids are natural reservoirs of V. cholerae O1/ O139 serogroups, which are associated with cholera endemics and pandemics. All four life stages of chironomids were sampled from two rivers, and a laboratory culture in Pune, India, and from a pond in Israel. In total, we analyzed 223 chironomid samples. The presence of V. cholerae O1/O139 serogroups was verified using molecular tools. Nine chironomid species were identified; of them, Chironomus circumdatus was the most abundant. The presence of V. cholerae serogroup O1 and the cholera toxin genes were detected in samples from all chironomid species. However, serogroup O139 was detected in only two chironomid species. Besides PCR to detect specific genes, a metagenomic analysis that was performed in three selected C. ramosus larvae, identified a list of virulence genes associated with V. cho-lerae. The findings provide evidence that chironomids are natural reservoirs of toxigenic V. cholerae O1/O139. Chironomid populations and V. cholerae show biannual peak patterns.
... The tanks were constructed of clay bricks reinforced with concrete columns. To begin with, egg masses collected from the field were reared and developmental stages were validated for taxonomic identification using morphological and cytotaxonomic keys (Chaudhuri et al. 1992, Nath and Godbole 1997). To initiate rearing, ≈100 late fourth instar larvae each were transferred to rearing tubs (Ø=35 cm) placed in a net cage under laboratory conditions (Fig. 1d), which were maintained exactly as described by Nath and Godbole (1998). ...
... While related to C. incertipenis and C. ramosus, they do not appear to be either of those species. C. ramosus characteristically has a nucleolus in arm B, and not in arm G (Nath and Godbole 1997), while C. incertipenis is present in Jammu and Kashmir, but differs in the mtCOI sequence (unpublished data). ...
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Chironomus samoensis, as currently recognised, is not a single species but a complex of more or less closely related species. C. samoensis Edwards 1928 is redescribed from additional material, and considered to occur only in the Pacific region. Reasons for excluding material from other areas are given. C. flaviplumus Tokunaga 1940 is confirmed as the correct name for the Japanese material, the Indian material described by Chattopadhyay et al. (1991) is given the new name C. indiaensis, and new names are required for material from Australia and additional species from India.
... Radiation tolerance in C. ramosus larvae was demonstrated by us in SGC in earlier studies (Datkhile et al. 2011), hence the current investigation was focused on the same tissue. Also, DNA content is higher in SGC compared to other diploid tissues of the midge larvae (Daneholt and Edstr ö m 1967, Macgregar and Varley 1988, Nath and Godbole 1997. Detailed dosimetry studies of C. ramosus had established that 2200 Gy dose was well tolerated by 80% larvae over a period of 24 h observation, hence this LD 20 dose was chosen for studying eff ect on DNA. ...
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Chironomus ramosus is one of the recently reported radio-tolerant insects. Salivary gland cells of fourth instar larvae respond to ionizing radiations with increases in the levels of antioxidant enzymes and chaperone proteins. Here we made an attempt to study the state of nuclear DNA after exposure of larvae to a Lethal Dose for 20 percent of the population (LD20) of gamma radiation (2,200 Gy, at a dose rate 5.5 Gy/min). Genomic DNA preparations were subjected to competitive ELISA (Enzyme Linked Immuno-Sorbant Assay) for detection of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and dynamic light scattering (DLS) to monitor any radiation induced damage. Single salivary gland cells were subjected to alkaline single cell gel electrophoresis, (ASCGE) comet assay and pulsed field gel electrophoresis (PFGE) to check for DNA double strand breaks. Results from all four experimental procedures confirmed damage of nucleobases and fragmentation of nuclear DNA immediately after radiation. Forty-eight h after radiation exposure, modified 8-oxodG residues returned to basal level, homodispersity of genomic DNA reappeared, the length of comet tail regressed significantly (ASCGE) and PFGE pattern matched with that of high molecular weight unirradited DNA. Chironomus ramosus larvae showed control of DNA damage as observed over 48 h in post irradiation recovery which could be attributed to their ability to tolerate gamma radiation stress.
... Some points can be made by reference to the map of Nath & Godbole (1997): ramA1: 1 -2c, 10 -12, 3-2d, 9 -4, 13 -19 Larva, pupa and adult described by Chaudhuri, Das & Sublette (1992). Chromosomes described by Nath & Godbole (1997). In their map, chromosome I is comprised of arms D and C, chromosome II of arms F and B; chromosome III of arms A and E, and chromosome IV is arm G. ...
This is a preliminary listing of the species of the genus Chironomus found in India, South East Asia, China and Japan, particularly those for which cytological confirmation exists. I am very much indebted to numerous people who have provided me with material from these areas.
... A laboratory-reared inbred line of Chironomus ramosus was used which originated from a natural population of tropical midge [9]. This line has been routinely maintained for the last 10 yr under laboratory conditions. ...
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Chironomid midges are the most commonly found dipteran insects in all types of aquatic ecosystems. Cuticular extract was bio-assayed, and it exhibited enhanced attraction to the larvae. Therefore, it was subsequently analysed by gas chromatography–mass spectrometry. Two compounds were identified as farnesol and farnesene. Bioassay of farnesol indicated its attractive properties. The components present in the cuticular extract can, therefore, be considered as pheromone-like compounds.
... The embryonic developmental stages of Chironomus have been studied (264,265). Also its chromosomes have been characterised (266). Also effects of stresses on Chironomus like heat shock (267) have been studied. ...
... Cytological analysis was carried out using the salivary gland polytene chromosome band map of Nath and Godbole (1997). Acetic acid:methanol (1:3) fixed, 2% aceto-carmine-stained squash preparations of salivary gland polytene chromosomes were analysed for specific banding patterns in chromosome IV. ...
A natural population of a tropical midge, Chironomus ramosus (Diptera: Chironomidae), was found to be polymorphic for a paracentric inversion (IV: 18C-19D). Based on the characteristic banding pattern of the fourth chromosome in the larval salivary gland polytene nuclei, individuals were classified as either structural homozygotes or heterozygotes. Isofemale lines were obtained and subsequently standard (S/S) and inversion (I/I) homozygotes were characterised by careful progeny testing in the laboratory. While exploring various biotic and abiotic factors that might be responsible for the maintenance of inversion polymorphism, we detected nematode (Family: Mermithidae) infections among the larval population. A detailed study indicated that the inversion polymorphism in the natural population of C. ramosus was apparently being maintained as a result of the selective pressure exerted by the nematode parasite. The corresponding pattern of increase and decrease in genotype frequencies and the relative fitness values indicated a selective advantage of inversion heterozygotes (S/I) over both homozygous types (S/S and I/I). Both empirical and experimental data suggest the strong heterotic nature of adaptation in this C. ramosus population towards nematode infection. This is the first report of its kind where inversion polymorphism has been shown to be associated with nematode parasitism.
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Pesticide has an ample application on account of its efficiency against a wide variety of insect pest. its entry affect aquatic flora and fauna. The present study deals with the acute toxicity testing of endosulfan to IVth instar larvae of Chironomus stratipennis, a most common and widely occuring Indian species. The information on the biology, band maps and puffing activity of species inhabiting in Maharashtra and especially Nasik region is meager. Hence the present study was undertaken to study normal puffing of fourth instar larvae and induction of puffs after pesticide treatment in vivo and in vitro in Chironomus striatipennis from Nasik region. A result was endosulfan-induced puff in 13A and 14C region of III chromosome arm in vivo and in 14C region of III chromosome arm in vitro. KEY WORDS: Chironomus stratipennis, endosulfan, IV th instar, in vivo. INTRODUCTION Polytene chromosomes have been reported from many Dipterans like Chironomous. These are present in the nuclei by successive chromosomal duplication inside the intact cell nucleus without cell division. The cells of salivary glands; Malpighian tubule tracheae, fat body, midgut and hindgut of dipteran larvae show the presence of polytene chromosomes.Chironomous adults are commonly known as midges. They look like mosquito except proboscis. Midges belong to the suborder Nematocera of order Diptera. These are all non biting midges. Chironomid midges exhibit unique life cycle. The adults have short lifespan of 3-4 days swarming of adults occur near water bodies & female lays eggs in gelatinous mass numbering 650-700. They are found in fresh water bodies. Larvae feed on diatoms, algae and organic detritus material. The red color of larvae is because of presence of hemoglobin like respiratory pigment hence known as " blood worm " .These larvae are mostly predated by fishes. Polytene chromosome occurs in tissues which are engaged in vigorous metabolic activities these cells may be secretory or nonsecretory in function. The nuclear membrane & nucleoli remain intact throughout replication cycle. Thus, the nucleus containing the haploid number of giant chromosome each composed of 1000-2000 DNA strands giving multistranded cable like appearance. The peculiar characteristic feature of polytene chromosome is presence of puffs, bulbs and balbiani rings, which are formed at certain loci and are formed at certain loci and are transient features.
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Examination of heat shock induced transcriptional activity in salivary gland polytene nuclei of a tropical Chironomus, C. striatipennis, revealed nine heat-shock puffs. In 24 °C-reared larvae optimal heat-shock response was seen at 39 °C, while a 41 °C shock was nearly lethal. In a population grown under natural conditions of seasonal variations, the heat-shock response was dependent upon the current ambient temperature. In summer months, response to 39 °C was variable, from complete to no induction of heat-shock puffs in different cells. In control glands from larvae growing at 33–36 °C in summer, heat-shock genes were not active, although in 24 °C-reared larvae, 33 °C already caused partial induction. Unlike the 24 °C-reared population, a 41 °C shock to summer larvae was not lethal. [ ³⁵ S]Methionine-labelled protein synthesis pattern in the summer larvae revealed appreciable accumulation of heat-shock polypeptides in control glands, which possibly autoregulates their further induction and also explains the better thermotolerance of these larvae. In a developmental study of a 24 °C-reared population, some heat-shock polypeptides were found to be commonly synthesized at 39 °C in all the tissues (salivary glands of larvae; Malpighian tubules of larvae, pupae, and adult; adult ovaries), while other heat-shock polypeptides showed apparent tissue and (or) developmental stage specificity. Heat shock protein 70 was most abundantly synthesized in all the tissues examined.Key words: temperature shock, thermotolerance, heat-shock polypeptides, polytene chromosomes, puffs.
The karyotype of the neotropical Chironomus columbiensis n.sp., as observed in the salivary gland chromosomes, has the unusual chromosome arm combination AG, BF, CD, E (columbiensis‐complex). The chromosomal banding pattern is closely related to that of Chironomus anonymus (arm combination AE, BF, CD, G, pseudothummi‐complex) in the southwest part of the United States and the Antilles. The reasons for describing C. columbiensis as a new species and for associating the second species with C. anonymus is discussed. The pupa of C. anonymus is described and adults are redescribed. It can be assumed that more relationships between North and South American Chironomus species will be found.
The polytene chromosomes of the salivary glands of Nilodorum biroi (Kieffer) comprise three long metacentric or submetacentric chromosomes. It is considered that this is a derived condition from a diploid number of 8, by the tandem fusion of a small acrocentric element (C) to a metacentric chromosome (AB). A standard chromosome map for the genus is provided and the chromosomal polymorphism of Indian and Australian populations is described.
Chironomus circumdatus is one of the most common and wide-spread species in India. Cytogenetic studies pertaining to the mitotic and polytene chromosomes, nucleolar organizer regions, C-banding and naturally occurring chromosomal polymorphism have been carried out for the first time in this Indian species. Altogether seven inversions comprising six paracentric and one pericentric are detected in the Indian populations. The distribution of inversions in relation to different environmental conditions is discussed.
Among the various types of differentiated insect tissues, Chironomid salivary glands provide an especially fortunate combination of features. The glands consist of a limited number of very large cells that are committed to the continuous synthesis of specific proteins. Extensive polytenization renders their chromosomes visible in unChapaulleled detail during interphase so that units of genetic function can be studied at the level of the light-microscope. A gland comprises two or more related cell types that exhibit minor differences in terms of cell morphology, chromomere activity and protein synthesis and thus provide excellent tools for comChapautive studies of differentiated states in the same tissue.