No description available.

No description available.

Stalk-eyed flies of the family Diopsidae have their eyes laterally displaced on the end of head extensions called “eye-stalks”. Diopsids vary in their degree of sexual dimorphism for eyespan (distance between the eyes). In some dimorphic species it has been well established that females preferentially mate with males possessing exaggerated eyespan. With over 150 members, the family Diopsidae is an ideal model system for analysing the evolution and development of exaggerated sexual traits. Progress towards understanding the mechanisms underlying the development of exaggerated eyespan has been significantly hampered by the lack of modern molecular genetic technology in stalk-eyed flies. I have developed a transgenic protocol in Teleopsis dalmanni, a highly dimorphic diopsid species. I selected and tested embryo microinjection procedures. I used excision assays to compare the activity of three potential transposable element vector systems. Minos and piggyBac demonstrated suitable activity in T. dalmanni embryos but mariner did not. Using Minos and the transgene construct Px3-eGFP, I successfully achieved stable germline transformation in T. dalmanni. A number of transgenic lines were created. In one, a single copy of the insertion was seen to segregate with the X chromosome. I used a histological approach to investigate the relative contributions of cell size and cell number to variation in eyespan. I compared estimates of cell size in the eye-stalks of newly eclosed flies among fully fed and nutritionally stressed individuals. For comparison, I assessed cell size in a non-sexually dimorphic organ, the wing. I found that variation in eyespan was explained, at least in part, by variation in cell size. No inherent difference in eye-stalk cell size was detected between the sexes. The implications of the cell size findings and of the future studies made possible by transgenic technology are discussed.

Dietary restriction (DR) extends lifespan in many organisms, through unknown mechanisms that may or may not be evolutionarily conserved. Currently, different diets and techniques exist in different laboratories to implement DR in the fruit fly, Drosophila melanogaster. Furthermore, DR is often implemented by food dilution, a technique that potentially enables flies to compensate for reduced nutrition by increasing their food intake. Thus, findings from DR experiments may not be strictly comparable because of these methodological differences and uncertainties. In this thesis, I examined the ability of DR to extend life in D. melanogaster with different genotypes and on different diet compositions. I demonstrate that many of the different diets used in different laboratories are inappropriate for DR and propose an optimised protocol to insure that DR studies are standardised. I also demonstrate, by combining two available feeding assays, that D. melanogaster do not compensate their food intake when exposed to DR by food dilution. The optimised feeding assay in this thesis provides a useful tool for researchers to measure fly total feeding, which is fundamental to studies involving their behaviour, nutrition and/ or drug administration. I demonstrate with this method that food intake is not altered in the lifespan extending mutation chico, the receptor substrate of the insulin/insulin-like signaling (IIS) pathway. IIS is a highly conserved pathway responsible for growth, development, stress resistance, metabolic homeostasis, reproduction, and recently, single gene mutations in the pathway have been shown to extend lifespan. One component of the pathway, dAkt, has yet to be established as a regulator of lifespan and fecundity in D. melanogaster. Although there is sufficient literature regarding its role in growth and development in fly larvae, it is much less understood in adults. Using viable dAkt mutants, I establish that for lifespan benefits to occur, the appropriate level of IIS reduction is required.

No description available.

No description available.

No description available.

No description available.

The morphology of the rays of the primary fans, the main food collecting organ, of 25 species of black-fly larvae (Diptera: Slmuliidae) were studied using the scanning electron microscope. The form, arrangement, spacing and dimensions of the microtrichia on the rays of these species was recorded. The flicking action of the primary fan was found to be frequent and irregular. The actions of the primary fan and mandible were also studied and their mode of action outlined. Experiments on black-fly larvae of four species (Simulium omatim Mg., S. variegatum Mg., S. monticola Fried, and S. reptans (L. ) ) were conducted in an artificial environment in which current velocity, food concentration and light level could be controlled. Each species was found to differ from the others in its rate of food intake over a range of current velocities. Species with similar patterns of miorotrichia on their head fans had comparable rates of food Intake at the same current velocities. Experiments were done, using a dye-tracer technique, on S. omatum, S. variegatum, S. reptans, S. venustum and S. pictipes- longistylatim in the natural stream habitat of these larvae to determine the rate of intake of natural food. Intake rates varied widely from species to species and within a species depending on current velocity and probably the amount of suspended matter in the stream Larvae of P. ferruglneum (Wahlb.) from Eastern Norway were found to predate on other aquatic arthropods including other species of black-fly larvae. Experiments were conducted on the space requirements of S. omatum larvae in an artificial environment. Densities of up to l4l larvae per sq. cm. were obtained. These densities were much higher than those found in nature. Densities in nature varied widely. Analysis was made of the movements of larvae on an attachment site of limited area.

A fast and powerful gaze stabilization reflex supports self-motion es- timation and flight control in flies. Changes in body posture are conveyed by a variety of sensory modalities and compensated for by fast and accurate head movements. This thesis aims to further our understanding of the behavioural basis of compensatory head move- ments, and presents a first foray into the in vivo imaging of the motor systems that actuate these control reflexes. Major sensors that contribute to gaze stabilisation are the visual ocelli and compound eyes on the head, and the mechanosensory halteres on the thorax. The integration of visual feedback and mechanosensory feedforward control gives rise to a two-degree-of-freedom controller, a design which is extensively used in engineering applications. I per- formed a linear systems analysis of compensatory head roll in response to forced thorax oscillations in the fly. The feedforward pathway ex- hibited a high bandwidth and constant gain and reduced the response delay of the reflex. Large stability margins in the feedback pathway supplied by the compound eyes guaranteed stable behaviour in the face of response variability. The occlusion of the ocelli did not change the gain of the feedback pathway, but significantly reduced the la- tency. I investigated the use of iodine-enhanced computed x-ray microto- mography (microCT) to perform fast three-dimensional imaging of the neck and flight motor systems. Virtual dissections of major func- tional units illustrate the possibilities and limitations of microCT. To observe the configuration of motor systems in behaving flies I per- formed gated microtomography using hard x-rays at the TOMCAT beamline of the Swiss Light Source, a third generation synchrotron. While 3D tomograms of the neck motor system proved elusive, this thesis presents the first in vivo tomograms of the flight motor and wing hinge during tethered flight.