This study represents the first of its kind to evaluate the importance of spatial and temporal co= incidence between parasitic insects and their insect hosts. Extensive and intensive field observations here demonstrate that lack of coincidence is possible between the European pine sawfly, Neodiprion sertifer Geoff. and its three most important parasites. In the ichneumonids, Exenterus canadensis Prov., spatial coincidence is nearly perfect, while temporal coincidence may be poor. The bombyliid, Villa sinuosa (Wd.) shows imperfect spatial coincidence, but good temporal coincidence. In the ichneumonid Pleolophus basizonus (Grav.) both spatial and temporal coincidence may be imperfect. The degress of coincidence are related to the physiology of development and the behaviour of the parasites and their host in their variable environmental contexts. The interrelations of host density, parasite density, time of contacts, number of eggs laid, and number of hosts attacked, were studied experimentally with P. basizonus. The results were more closely described by the predictions of the Holling than of the Watt equation. The distribution of eggs in hosts was more often adequately described by the negative binomial than the Poisson equation for probabilities. The effect of asynchrony in the species studied cannot be considered without reference to superparasitisms. At low host densities superparasitism largely buffers effects of decreased synchrony, but its buffering diminishes to an asymptote as host density increases. In any given generation, imperfect spatial coincidence has little effect where attack is asymptotic. Simulations of host-parasite interactions over 25 to 35 host generations showed that for P. basizonus and E. Canadensis, host and parasite populations would become stable after passing through one or more oscillations even when, temporal and spatial coincidence are reduced. Predictions for V. sinuosa indicate its inability to restrain host populations even at perfect coincidence. / Science, Faculty of / Zoology, Department of / Graduate

The saltwater mosquito larva, Aedes dorsal is, is one of the only organisms capable of inhabiting hypersaline lakes composed almost entirely of high concentrations of NaHC03 and Na2C03 salts. Under laboratory conditions larvae survived and developed normally in saline media with pH values up to 10.5, HC0₃⁻ concentrations up to 250 mM, or C0₃²- concentrations up to 100 mM. Despite ingestion of these alkaline media at rates equivalent to 130% of larval body weight per day, these insects regulated hemolymph pH (7.55-7.70) and HCO₃⁻ concentrations (8.0 - 18.5 mM) within narrow physiological limits. Micropuncture and microcannulation studies on the rectal salt gland demonstrated that this organ was an important site of pH and HC0₃⁻ regulation. Microcannulated salt glands secreted a strongly hyperosmotic fluid containing 402 mM HCO₃⁻ and 41 mM C0₃²⁻ at a rate of 38 nl-h⁻¹. Lumen-to-bath HC0₃⁻ and C0₃²⁻ gradients of 21:1 and 241:1, respectively, were generated by the salt gland epithelium against a transepithelial potential of -25 mV (lumen negative) demonstrating clearly the active nature of HCO₃⁻ secretion. To study the mechanisms of HCO₃⁻ transport, an in vitro microperfused rectal salt gland preparation was developed. Net total CO₂ transport (J[sup=JCo₂; sub=net]) as measured by microcalorimetry in perfused salt glands was unaffected by bilateral Na⁺ or K⁺ and serosal Cl⁻ substitutions, or by serosal addition of 1.0 mM ouabain, 2.0 mM amiloride or 0.5 mM SITS. Removal of luminal Cl⁻ inhibited (J[sup=JCo₂; sub=net] by 80%, while serosal addition of 1.0 mM acetazolamide or 0.5 mM DIDS inhibited by (J[sup=JCo₂; sub=net] 80% and 40%, respectively. Perfusion of the anterior and posterior rectal segments demonstrated clearly that the anterior rectum was the site of CO₂ secretion in the microperfused salt gland. Net Cl⁻ reabsorption in the anterior segment was measured by electron microprobe analysis and was equivalent to the rate of CO₂ secretion. In addition, Cl⁻ reabsorption in the anterior segment was completely inhibited by bilaterally replacing C0₂ and HC0₃⁻ with a phosphate or HEPES buffered saline. These data provide strong quantitative evidence for the presence of a 1:1 Cl⁻/HCO₃⁻ exchange mechanism located in the anterior rectal salt gland segment. Microcannulation studies on the individual salt gland segments demonstrated that both rectal segments are capable of secreting a hyperosmotic fluid containing Na⁻, Cl⁻ and HCO₃⁻. Based on these results and the results of studies in which the effects of serosal ion substitutions on salt gland fluid secretion were examined, it has been suggested tentatively that both segments secrete a NaCl-rich fluid and that fluid secretion is driven by coupled NaCl transport. It is further suggested that once this fluid enters the salt gland lumen its composition is modified by ion exchange and reabsorptive processes which are dependent upon the ionic regulatory needs of the animal. In larvae inhabiting low Cl⁻, NaHCO₃-CO₃ lakes, this modification involves a 1:1 exchange of luminal Cl⁻ for serosal HCO₃⁻. The cellular mechanisms of anterior salt gland HCO₃⁻ and Cl⁻ transport were examined using ion and voltage-selective microelectrodes in conjunction with a microperfused anterior segment preparation which allowed complete changes in serosal and mucosal saline composition to be made in <5-10 seconds. Addition of DIDS or acetazolamide to or removal of CO₂ and HCO₃⁻ from the serosal bath caused large, 20-50 mV hyperpolarizations of Va and had little effect on . Rapid changes in luminal Cl⁻ concentration altered Va in a rapid, step-wise manner. The slope of the relationship between Va and luminal Cl⁻ activity was 42.2 mV/decalog a[sup=l; sub=Cl⁻ (r = 0.992). Intracellular Cl⁻ activity was 23.5 mM and was approximately 10 mM lower than that predicted for a passive distribution at the apical membrane. Changes in serosal Cl⁻ concentration had no effect on indicating an electrically silent basolateral Cl⁻ exit step. Intracellular pH in anterior rectal cells was 7.67 and the calculated a[sup=C;sub=HCO₃] - was 14.4 mM. These results show that under control conditions HC0₃⁻ enters the anterior rectal cell by an active mechanism against an electrochemical gradient of 77.1 mV and exits the cell at the apical membrane down a favorable electrochemical gradient of 27.6 mV. Based on these results, a tentative cellular model has been proposed in which Cl⁻ enters the apical membrane of the anterior rectal cells by passive, electrodiffusive movement through a Cl⁻-selective channel, and HCO₃⁻ exits the cell by an active or passive electrogenic transport mechanism. The electrically silent nature of basolateral Cl⁻ exit and HC0₃⁻ entry, and the effects of serosal addition of Cl⁻/HCO₃⁻ exchange inhibitor DIDS on (J[sup=JCo₂; sub=net] and V[sub=te] suggest strongly that the basolateral membrane is the site of a direct coupling between Cl⁻ and HCO₃⁻ movements via a Cl⁻/HC0₃⁻ exchange mechanism. / Science, Faculty of / Zoology, Department of / Graduate

Polyhomeotic (ph) is a developmentally important gene in Drosophila melanogaster which has been genetically characterized and recently cloned. ph is genetically and molecularly complex and has a strong maternal effect. Analysis of null or amorphic alleles reveal phenotypic effects that include embryonic lethality, cell death of the ventral epithelium, homeotic transformations, and alteration in the pattern of axon pathways. Two independent point mutations are required to produce a ph null allele. I have shown that the ph locus contains two, large, highly conserved, tandem repeats that are both transcribed. I have identified transcripts that are altered in ph mutants and that are developmentally regulated. Fourteen cDNA's have been isolated, and mapped. Northern and Southern blot analysis, and comparisons between cDNA and genomic restriction maps shows that the cDNAs represent at least 4 different transcripts that include distinct products of both repeats as well as non-repeated sequence. Both the genetic behavior and molecular organization of the ph locus are unique in Drosophila. / Science, Faculty of / Zoology, Department of / Graduate

Differences in progeny characteristics arising from differences in maternal age at time of birth are discussed as a possible source of ecologically important variation. The literature on effects of maternal age on progeny guality is reviewed. Experiments designed to document any effects of maternal age on two biological processes are described. The processes selected were production of alatae by an aphid, ASiSiioSiEiiOS. £isum , and incidence of diapause in a sawfly, Eriocamoa ovata . Maternal-age effects influenced the production of alatae by the aphid. Early-born progeny of wingless aphids were more likely to respond to a standard crowding stimulus by producing alatae than were late-born progeny. Early-born alata-producers also produced higher numbers of alatae than late-born ones. Maternal age affected the progeny of winged aphids, but in the opposite manner. Early-born progeny of this morph usually did not produce alatae at all, whereas late-born progeny did. The inhibition of alata-prcduction in the lineage of an alate aphid was satisfactorily explained by maternal age effects alone. A timing mechanism such as the "interval timer" proposed by Lees (1966) did not apply. Ho significant effects of maternal age on the incidence of diapause in the sawfly could be found. However, diapause was shown to be influenced by at least two factors. More animals diapaused at low humidities. Seven-instar larvae diapaused more frequently than did six-instar larvae. Larval developmental times varied with the number of instars, the occurrence of diapause, and the date of egg-laying. Length of the cccocn stage of ncn-diapausing individuals varied with the date of egg-laying. It is concluded that maternal age effects, although not universal, are a common biological phenomenon, and probably of ecological significance as a source of variation. / Land and Food Systems, Faculty of / Graduate

The in vitro, short-circuited locust rectum actively transports chloride. This electrogenic transport is energized by aerobic metabolism, based primarily upon proline oxidation. Isolated rectal mito-chondrialoxidize a variety of substrates, but the highest state 3 rate of 0₂ consumption occurs when proline is the stubstrate. An enzyme profile of the rectal tissue indicates that the rectum can oxidize amino acids and carbohydrates but has a limited capacity for lipid oxidation. Analysis of the two fluids which bathe the rectum in vivo, the hemolymph and the Malpighian tubule fluid, reveals that proline is present in bothethe hemolymph (12-15 mM) and tubule fluid (38-43 mM). Although glycine is also found in high concentration in the hemolymph (13-17 mM), far lower concentrations of this and other amino acids are found in the Malpighian tubule fluid. Glucose is also found in the hemolymph (2 mM) and Malpighian tubule fluid (4 mM). The high concentraion of proline in the tubule fluid indicated that this amino acid may be actively transported by tubules. This prediction was confirmed by experiments with in vitro tubules. This is the first evidence of aetive secretion of a metabolically useful compound by insect Malpighian tubules. Experiments involving the measurement of short-circuit current (Isc) across the locust rectum were also performed. The results of these experiments indicate that high levels (50 mM) of proline stimulate the Isc of substrate-depleted recta better than high levels of any other substrate tested. Physiological levels of proline also cause a large increase in the Isc of substrate-depleted recta, while physiological levels of glucose produce a much smaller stimulation. Over 90% of the Isc stimulation can be produced by adding proline (15 mM) solely to the lumen side of the tissue. Other studies were performed to estimate the metabolic cost of actively transporting chloride. The oxygen consumption of chloride-depleted recta were measured before and after reintroduction of chloride. From these data a Cl⁻/ATP ratio of 3-4 was obtained. Further calculations indicated that tissue proline oxidation is sufficient to energize active chloride transport. The results outlined here suggest that in vivo, the rectal lumen is bathed with a high concentration of proline which can be readily oxidized by the rectal mitochondria to support the work of actively transporting chloride. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

Insectivorous bats have been found to have unusually high levels of mercury. While broad geographic scale studies have investigated factors contributing to mercury bioaccumulation in bats across Canada, studies investigating differences in regional scale bioaccumulation and the contributing factors remain scarce. Here, I comprehensively investigate the bioaccumulation of mercury in two insectivorous bats, the big brown bat (Eptesicus fuscus) and the little brown bat (Myotis lucifugus), collected over a period of ~20 years along the St. Lawrence River in Eastern Ontario, parts of which are historical hotspots of mercury, to address two objectives: First the determination of biological and environmental factors, including dietary sources, contributing to reported patterns of fur total mercury bioaccumulation, and second the investigation of DNA-based biomarkers as potential tools to assess internal tissue-responsiveness to mercury exposure, specifically global DNA methylation and expression levels of mitochondrial DNA. With regard to factors determining fur total mercury concentration in Eastern Ontario bats, significant differences between species exist, as higher concentrations were found in big brown bats compared to little brown bats. Sex contributed to differences in fur total mercury, however in a species-specific manner. Male fur contained higher total mercury concentrations compared to females in big brown bats, but not little brown bats. Female reproductive status differentially affected fur mercury concentrations between both species, reducing concentrations in pregnant little brown bats, while significantly increasing concentrations during lactation in big brown bats. Finally, fur total mercury concentration in adults was higher than that of juvenile bats (< 1 yr). To address the hypothesis that aquatic emerging and terrestrial insect diets differentially contribute to Eastern Ontario bat mercury concentration, I used stable isotope analysis and telemetry approaches and caught aquatic and terrestrial insects. While higher total mercury was identified in aquatic compared to terrestrial insects, a high degree of variability in the isotope signature in insects and bats in Eastern Ontario did not allow to fully address this hypothesis. However, data pointed to a more specialized diet in big brown bats compared to a more generalist diet in little brown bats as well as a sex-specific correlation between dietary source and fur total mercury concentration in little and big brown bats. The evaluation of potential epigenetic and mitochondrial DNA-level molecular biomarkers in kidney, brain and liver (DNA methylation and assessment of relative mitochondrial DNA copy number) did not reveal significant correlations with fur total mercury concentrations. This may suggest that the mercury concentrations measured in this study were not high enough to elicit these specific DNA level responses or they do not represent relevant biomarkers of environmental methylmercury exposure, at least in big brown bats. Overall, this thesis contributes to our understanding of regional variability in fur total mercury concentration within and between Eastern Ontario bat species. These findings provide important insights for future targeted investigations of the contribution of aquatic emerging and terrestrial insect dietary sources on the one hand and underline the importance of accounting for regional variability in more global scale comparisons of bat mercury bioaccumulation on the other.

No description available.

No description available.

No description available.