No description available.

No description available.

Twenty-five different iso-chromosomal III lines of Drosophila melanogaster, with known haplotypes, were mixed and selected on malaoxon over twelve generations in order to find the importance of variants already present in the Drosophila genome relative to new mutations in the evolution of insecticide resistance. Measurements of mixed function oxidase and acetylcholinesterase activities, as well as insecticide resistance, were made over the twelve generations of selection and on the the iso-chromasomal III lines extracted after the selection was completed. These measurements were compared to those made of the twenty-five lines before selection. This comparison indicated that 52A, one of the origional twenty-five lines, may have been selected during this experiment. Comparisons of a possible cytochrome P-450 produced by a previously selected line of Drosophila called D23, and the DNA which is probably responsible for the production of this P-450, with the microsomal proteins and total genomic DNA of the selected lines were made using the techniques of Western and Southern blotting. The results of these procedures suggested that the mechanism of resistance used by the selected lines was not the same mechanism of resistance used by the D23 line. / Thesis / Master of Science (MSc)

<p> The relationship between the mixed-function oxidase (MFO) system and resistance of Drosophila melanoqaster to phosmet (ImidanR) an organophosphorus insecticide has been studied. The MFO activity was assayed by 7-ethoxycoumarin-O-deethylase (7-ECD) activity and resistance levels were determined by either adult LC- 50 or percent adult survival at 150 uM of Imidan. Two groups of isofemale lines sampled from Vineland, Ontario and a laboratory selected population were used to study variability of the MFO system and its relationship to variability in resistance. </p> <p> A significant positive correlation was found between 7-ECD specific activity and an antigenic determinant assayed by western blotting. The antiserum used to detect this determinant was prepared against a cytochrome P-450-enriched fraction from a malathion-resistant Drosophila melanoqaster strain by J. Pursey (1989). The antigenic determinant was contained on polypeptide P2, believed to be a cytochrome P-450 by its molecular weight and heme content. </p> <p> Laboratory selection on Imidan resulted in over 2 .1-fold increase in resistance. Two MFO activity groups were identified among isofemale lines established from nature. A siqnificant positive correlation was found between 7-ECD specific activity and resistance to Imidan among the Isofemale lines. The minimum number of genes controlling the difference in 7-ECD specific activity between two isofemale lines was estimated to be about 1. </p> <p> It was concluded that this natural Drosophila melanoqaster population has a major or few .genes on chromosome 3 affecting MFO activity and resistance but as well other factors on chromosomes 1 and 2 also contribute to variability in resistance. </p> / Thesis / Master of Science (MSc)

<p> This work incorporates information from two sources in order to examine the nature of natural selection acting on phenotypic characters in Drosophila melanogaster along a North South cline. Isofemale lines were established from flies collected along a North South cline extending from Winnipeg, Manitoba to Tampa Bay, Florida. Offspring from different lines within each position were then cultured under standardized conditions and used to examine phenotypic variation in 10 morphological characters along the cline. In a separate set of experiments, flies from Vineland, Ontario were mated in a half-sib design in order to estimate the genetic covariance of the set of 10 characters. The results from the clinal and heritability experiments were then combined using Lande's (1979) equation,&.= Gp-ls, to estimate the net selective differentials and net selection gradients for each adjacent set of populations. The study concluded that: 1) Clinal variation is non-linear, with larger flies in the middle latitudes and smaller flies in the north and south. 2) Selection appears to act primarily on body characters in the north (wing width and femur length) and head characters in the south (eye and face width). 3) Scutellum width and wing length generally moderate the prevalent trends in directional selection on the other characters through antagonistic correlated responses. 4) Clinal patterns of variation may not be at equilibrium, but instead dominated by seasonal responses to selection pressures. </p> / Thesis / Master of Science (MSc)

Thesis / Master of Science (MS)

Malathion-resistance in Drosophila Melanogster was studied in susceptible laboratory strains (CS and OR), a heterogeneous intermediate-resistant strain (C1-39), and a more resistant, artificially selected (with malathion). strain (MH19) by comparing the in vitro metabolism of [¹⁴c]-malathion and [¹⁴c]-malaoxon in crude enzyme preparations made from adult flies. Extracts from all strains were found to contain two enzymatic activities that metabolized malathion and/or malaoxon. One activity degraded malathion to its α- and β-monocarboxylic acids and was designated as malathion-carboxylesterase activity (ME-activity). ME-activity was progressively lost in CS-extracts during reaction with [¹⁴c]-malathion due to inhibition of the enzyme(s) by a tightly bound [¹⁴c]-labeled molecule (not identified) that could not be removed by chromatography on Sephadex G-25. ME-activity, based on initial (0-1 min) rates with or without metyrapone present was similar in all strains and furthermore, the carboxylesterase inhibitors TPP and DEF did not synergize malathion toxicity in either resistant or susceptible strains. It was concluded that carboxylesterase-mediated degradation of malathion was not a factor in the resistance of the C1-39 and MH19 strains. A second enzyme system, microsomal mixed-function oxidases (MFO), converted malathion to malaoxon (activation) and degraded malaoxon to at least two products that were tentatively identified (malaoxon α-and β-monoacids and demethyl-malaoxon). The rate of conversion of malathion to malaoxon was highest in crude extracts of the most resistant MH19 flies, intermediate in C1-39 and could not be detected in the susceptible CS flies while the rate of malaoxon degradation was similar between MH19 and C1-39, but higher than that in the susceptible OR flies. Furthermore, malaoxon (but not malathion) toxicity was most strongly synergized by the MFO-inhibitor MTP in the more resistant strains (MH19 and C1-39) . These results were used along with a previous result that MH19 strain possesses a less sensitive form of the target enzyme, acetylcholinesterase (R.A. Morton, personal communication), to propose a biochemical mechanism that accounts for the increased malathion-resistance of the C1-39 and MH19 strains. / Thesis / Master of Science (MS)

Thesis / Master of Science (MS)

The period gene determines biological rhythmicity in Drosophila melanogaster. The X-linked gene is 7.4kb, containing 8 exons and 7 introns from which a 4.5kb message is translated. A striking feature of the protein encoded by per is a series of alternating threonine-glycine residues in the fifth exon. Moreover, this string of residues is polymorphic for length variation in natural populations, the most frequent variants having 17, 20 or 23 Thr-Gly pairs. In the present study, a geographic analysis of this polymorphism within North American populations was conducted, the results of which indicate significant variation of allele frequency with latitude. The use of spatial autocorrelation analysis and Mantel tests clearly show that the most common variant, encoding 17 Thr-Gly pairs, exhibits a clinal pattern in its distribution along a north-south axis. Furthermore, DNA sequence analysis of several variants has uncovered a novel new variant which encodes 22 Thr-Gly pairs whose nucleotide sequence differs from any published data. Similar statistical analysis conducted on seven allozymes for populations collected along the same transect shows that several have monotonic clinal patterns in their allele frequency distributions which also show correlation with latitude. A previous study of morphological traits on the same populations showed the existence of a non-monotonic clinal pattern. Comparison of the results observed for the molecular and morphological markers indicates that they are subject to different evolutionary forces. The results highlight the importance of comparing patterns of geographic variation using different genetic elements. / Thesis / Master of Science (MS)

Insects accumulate various xenobiotics and toxic molecules through feeding and environmental exposure. This study examines the toxicology and regulation of a class of toxic molecules, organic cations, in Drosophila melanogaster. The results of this thesis demonstrate that transepithelial tetraethylammonium (TEA) secretion across the main segment of the Malpighian tubules is increased in response to diuretic factors. Both cAMP and cGMP, which increase transepithelial potential (TEP), as well as tyramine and LK-1, which decrease TEP, all enhanced TEA secretion. Both inc~eases and decreases ofTEP may enhance proton transport into the lumen of the tubule thus increasing the rate of organic cation/proton exchange across the apical membrane. These findings suggest that factors previously referred to as diuretic factors may in fact :let primarily or secondarily as stimulants of organic cation excretion. Haemolymrh concentrations of TEA increased linearly with the concentration of TEA in the diet and declined rapidly upon transfer of the larvae to TEA-free diet. The rate of decline was reduced by slowing the metabolic rate or by the addition of cimetidine to a diet containing TEA. Although larvae tolerated high levels of TEA in the diet, mortality increased when TEA was combined with either quinidine or cimetidine. It is suggested that inhibition of TEA transport by cimetidine or quinidine results in prolonged exposure to higher levels of TEA in the haemolymph and a consequent increase in toxicity. Surprisingly, TEA flux and fluid secretion rate were both reduced in Malpighian tubules isolated from adult flies raised on TEA-enriched diet. This suggests that the high concentration of TEA in the diet produced a non-lethal yet deleterious effect on the Malpighian tubules of Drosophila. / Thesis / Master of Science (MS)