School of BioSciences - Research Publications
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ItemCopy Number Variation and Transposable Elements Feature in Recent, Ongoing Adaptation at the Cyp6g1 Locus(PUBLIC LIBRARY SCIENCE, 2010-06)The increased transcription of the Cyp6g1 gene of Drosophila melanogaster, and consequent resistance to insecticides such as DDT, is a widely cited example of adaptation mediated by cis-regulatory change. A fragment of an Accord transposable element inserted upstream of the Cyp6g1 gene is causally associated with resistance and has spread to high frequencies in populations around the world since the 1940s. Here we report the existence of a natural allelic series at this locus of D. melanogaster, involving copy number variation of Cyp6g1, and two additional transposable element insertions (a P and an HMS-Beagle). We provide evidence that this genetic variation underpins phenotypic variation, as the more derived the allele, the greater the level of DDT resistance. Tracking the spatial and temporal patterns of allele frequency changes indicates that the multiple steps of the allelic series are adaptive. Further, a DDT association study shows that the most resistant allele, Cyp6g1-[BP], is greatly enriched in the top 5% of the phenotypic distribution and accounts for approximately 16% of the underlying phenotypic variation in resistance to DDT. In contrast, copy number variation for another candidate resistance gene, Cyp12d1, is not associated with resistance. Thus the Cyp6g1 locus is a major contributor to DDT resistance in field populations, and evolution at this locus features multiple adaptive steps occurring in rapid succession.
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ItemCytogenetics of a parthenogenetic Arctic species of Micropsectra (Diptera, Chironomidae)(ZOOLOGICAL INST, 2011)Micropsectra sedna (Oliver, 1976) is a parthenogenetic midge from the Canadian Arctic. The parthenogenetic mechanism is apomictic thelytoky, with a restitutional division during oogenesis, as found in other parthenogenetic Chironomidae. It is triploid, with two similar chromosome sets, and the third is relatively dissimilar, pairing little with the diploid set. Two karyotypes were observed: a single individual with eight polytene elements in the salivary glands (3n=12), considered standard, while the majority of larvae showed only seven polytene chromosomes (3n=11). Hybrid speciation is considered likely, although chromosomal recombination following the origin of thelytoky has played some part in karyotype evolution. A single morphologically distinct larva was also found, which might be the donor of the haploid chromosome set. The apomictic restitutional system is compared to that of the other, independently derived, parthenogenetic Chironomids to assess the extent of similarity between species.
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ItemChironomus columbiensis (Diptera : Chironomidae) new to the fauna of the United States(FLORIDA ENTOMOLOGICAL SOC, 2008-09-01)We document the first records of Chironomus columbiensis in the United States. It is one of a number of Neotropical Chironomidae recently detected in the United States.
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ItemCytogenetic differentiation between Palearctic and Nearctic populations of Chironomus plumosus L-(Diptera, Chironomidae)(NRC Research Press, 1999-10-01)Macrogeographic patterns of chromosomal banding sequences were studied in natural populations of the Holarctic species Chironomus plumosus. Of the 31 inversion sequences now known, 16 are endemic to the Palearctic, 7 are endemic to the Nearctic, and 8 are Holarctic sequences common to both zoogeographic zones. Differences in the sets of inversion sequences found on each continent, plus differing frequencies of Holarctic sequences, result in great overall divergence of karyotypes on the two continents. The karyotype of Nearctic C. plumosus differs from that of Palearctic populations primarily by the presence of a homozygous Nearctic sequence in arm A (n'plu A9), along with fixation (h'plu C2, h'plu E2, and h'plu F1), or high frequency (h'plu D2), of Holarctic sequences which are present but less frequent in the Palearctic. Although long continental isolation has led to great divergence of karyotypes on opposite sides of the Atlantic Ocean, all populations of C. plumosus show sufficient cytogenetic similarity to constitute a single Holarctic species.
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ItemReview of the genus Chironomus (Diptera: Chironomidae). VI. Cytology of the Chironomus maturus complex.(Natural Sciences Research Institute, Eastern New Mexico University, 1974)Two species, Chironomus maturus Johannsen and Chiron- omus whitsell Sublette and Sublette, having the chromosome arm combination AF, BE, CD, and G, are described. An evolutionary relationship to an ancestral group of the thummi- and pseudothummi- complexes as well as the parathummi-complex is postulated.
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ItemYama tahitiensis n.gen., n.sp. from Tahiti (Diptera: Chironomidae).(California Academy of Sciences, 1980)Describes the morphology of the adult male and female, pupa, larva and polytene chromosomes of a new species and genus of chironomid from Tahiti
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ItemChromosomes and continents(Springer US, 2008-12-01)
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ItemNo Preview AvailableA variable intron distribution in globin genes of Chironomus:: evidence for recent intron gain(ELSEVIER SCIENCE BV, 1997-12-31)The intron positions found in globin genes of plants, protozoa and invertebrates have been interpreted as evidence for a three-intron-four-exon structure of the ancestral globin gene. In particular, the so-called 'central' introns, which are not found in vertebrate globin genes but are present in a variety of invertebrate and plant species, have been used as an argument for an ancestral gene structure featuring three introns. We have analyzed the presence or absence of central introns in the Gb genes 2beta, 9 and 7A of various European and Australasian species of the insect Chironomus. We find unrelated central introns at different positions in some of the species investigated, while other species completely lack introns in these genes. This variable distribution of introns is parsimoniously explained by independent intron additions. Such a gain of introns may occur convergently at identical positions in unrelated taxa. Insertion by gene conversion may be a viable mechanism to explain intron gain.
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ItemNo Preview AvailableExtraordinary conservation of cysteines among homologous Chironomus silk proteins sp185 and sp220(SPRINGER VERLAG, 1997-04)Aquatic larvae of the midge, Chironomus tentans, synthesize a 185-kDa silk protein (sp185) with the cysteine-containing motif Cys-X-Cys-X-Cys (where X is any residue) every 20-28 residues. We report here the cloning and full-length sequence of cDNAs encoding homologous silk proteins from Chironomus pallidivittatus (sp185) and Chironomus thummi (sp220). Deduced amino acid sequences reveal proteins of nearly identical mass composed of 72 blocks of 20-28 residues, 61% of which can be described by the motif X5-8-Cys-X5-(Trp/Phe/Tyr)-X4-Cys-X-Cys-X-Cys. Spatial arrangement of these residues is preserved more than surrounding sequences. cDNA clones enabled us to map the genes on polytene chromosomes and identify for the first time the homolog of the Camptochironomus Balbiani ring 3 locus in Chironomus thummi. The apparent molecular weight difference between these proteins (185 vs 220 kDa) is not attributable to primary structure and may be due to differential N-linked glycosylation. DNA distances and codon substitutions indicate that the C. tentans and C. pallidivittatus genes are more related to each other than either is to C. thummi; however, substitution rates for the 5'- and 3'-halves of these genes are different. Blockwise sequence comparisons suggest intragenic variation in that some regions evolved slower or faster than the mean and may have been subjected to different selective pressures.