Thesis (doctoral)--Ludwig-Maximilians-Universitat zu Munchen, 1906.

Call number: LD2668 .T4 1956 O32 / Master of Science

Call number: LD2668 .T4 1965 L332 / Master of Science

Escape behavior is the critical output of rapid sensorimotor processing in the brain that allows animals to sense danger and avoid it. The circuit structures and mechanisms that underlie escape are still under investigation. Drosophila larvae are an advantageous system for studying the neuromuscular circuitry of escape behavior. When threatened with harmful mechanical touch, heat, or light, larvae perform C-shaped bending and lateral rolling, followed by rapid forward crawling. The sensory input and neural circuitry that promotes escape in the larva have been extensively characterized, but we do not understand how bending and rolling motor programs are generated by the larval neuromuscular system. This work identifies the movement patterns, muscle activities, and motor circuit features that drive escape behavior. High-speed imaging approaches reveal that larvae select between four distinct, interchangeable patterns of escape rolling, and that each pattern consists of synchronous rotations of every segment as the larva rotates. Investigating electron microscopic reconstructions of premotor and motor neurons elucidates premotor to motor connectivity patterns that could underlie sequential muscle activity that circumnavigates the larva and propels synchronous rotation along the whole body. Volumetric Swept Confocally-Aligned Planar Excitation (SCAPE) microscopy uncovers that, unlike larval crawling, a well-studied form of larval locomotion that is driven by bilaterally symmetric peristaltic waves of muscle activity, the muscle activity during bending and rolling occurs in a circumferential sequence that is synchronous along the larva’s segments. Muscles neighboring the dorsal and ventral midlines of the larva demonstrate left-right symmetric activity during rolling, and ventral muscles appear to drive the propulsion. Shifts in magnitude of left-right symmetric activity in midline muscles allow the larva to transition from initial escape bending into escape rolling. Preliminary computational predictions of PMN activities confirm the likely necessity of strong ventral muscle coactivity for driving escape. Probing specific PMNs during rolling demonstrates robustness of circuits controlling escape and requires further investigation, alongside the role that sensory feedback could play in this behavior. Altogether, these data reveal a new circuit organization and motor activity pattern that underlie the coordination of muscles during an escape sequence. Future work could reveal circuit components necessary for escape, including the mechanistic basis for action selection, behavioral maintenance, and behavioral flexibility.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

The citrus industry is subject to a number of serious insect pests. Of these, the most important is a sedentary group known as the Armoured Scale Insects (Diaspididae). Ebeling (1950) states that they are of greater economic importance to the industry than all the other pests put together. A great deal has been published on various aspects of the biology, ecology and control of the Diaspididae, much of the work appearing in the books of Quayle (1938), Ebeling (1950) and Bodenheimer (1951). It is very noticeable, however, that the study of the active larvae, or "crawlers", of these insects has been relatively neglected. This lack of work on crawlers is surprising, since they are the only distributive stage in the life cycle of the species. The adult male is also free-living during its brief life span, but takes no part in the actual distribution of the species. It is the position of the female Scale Insect which is important in determining the further spread of the species, since this is the point from which subsequent crawlers will start out on their wanderings. The stage in the life cycle responsible for the position of the female is, of course, the crawler. The crawler is also responsible for the parallel distribution of the male Scales, so that the female can be fertilised. The role of the adult male is confined to the maintenance of the gene flow. From an economic point of view it seems desirable that a complete study be made of the biology of this distributive stage of these important pests.

Internal sensory neurons monitor the chemical and physical state of the body, providing critical information to the nervous system for maintaining homeostasis and survival. Across species, such neurons innervate visceral organs to detect and relay information about their chemical and physical state to the central nervous system (CNS). While electrophysiology experiments over several decades have revealed a wide of range of stimuli that can activate internal sensory neurons, how stimuli are detected at the cellular and molecular level is only beginning to be elucidated. To elucidate the cellular and molecular basis of chemosensation by internal neurons, I used a population of larval Drosophila sensory neurons, tracheal dendrite (td) neurons, as the model system for my thesis work.I first presented a detailed characterization of the morphology of td neurons and their association with the tracheal system. I found that td dendrites extend along tracheal epithelial cells across their whole length. I further described that td dendrites extend to tracheal fusion sites, and can be observed terminating as enlarged bulbs adjacent to the tube enlargements. This specialized structure formed by td dendrites in relation to the nearby tracheal tissues may serve as an end organ for td sensory functions. I then proceeded to test the sensory functions of the td neurons. I found that td neurons respond to respiratory gases, namely decreases in O2 levels and increases in CO2 levels. Furthermore, I assessed the roles of atypical soluble guanylyl cyclases (Gycs) and a gustatory receptor (Gr) in mediating these responses. I found that Gyc88E/Gyc89Db are necessary for td responses to hypoxia, and that Gr28b is necessary for td responses to CO₂. Rescue of Gr28b isoform c rescued the mutant phenotype and also generalized the response to CO₂ in the td network. Additionally, I presented data suggesting carbonic anhydrases from surrounding tissues are required for td responses to CO₂, further elucidating the sensory transduction pathway of internal CO₂ detection. I further showed that gas-sensitive td neurons are activated when larvae burrow for a prolonged duration, demonstrating a natural-like feeding condition in which td neurons are activated. I also found that Drosophila larvae tend to avoid their td neurons being activated, suggesting td activation is aversive to the animals. Together, my work identified two stimuli that are detected by partially overlapping subsets of internal sensory neurons, and established roles for Gyc88E/Gyc89Db in the detection of hypoxia, and Gr28b together with carbonic anhydrases in the detection of CO₂. Combined with our previous understanding, different td neurons express various combinations of chemosensory receptors and have distinct functions, some of which remain to be discovered, indicating that this is a multifunctional internal sensory system. In conclusion, the results I presented in my thesis established new sensory detection pathways of Drosophila larval internal sensory neurons, which may be generalized across species and facilitate understanding of internal sensory systems.

This thesis describes an investigation into the effects of habitat composition, principally the composition of algae in a wrack bed, on the life history of the seaweed fly, Coelopa frigida. The mating system of C. frigida is dominated by intense sexual conflict characterised by frequent harassment by males leading to a vigorous pre-mating struggle. This response leads to sexual selection for large male size and sexual dimorphism. The mating behaviour of C. frigida is affected by their environment, with exposure to brown algae inducing harassment in males and oviposition in females. Despite more than two decades of research into coelopid reproduction little is known about how habitat composition alters the patterns and processes of sexual conflict. Studies contained in this thesis consider environmental influences that both directly and indirectly influence sexual conflict. Direct effects of the environment are measured by conducting mating trials following culture of C. frigida on different species of algae and by exposing males to different species of algae. This work is accompanied by studies of larval development and adult survival on different algae. In recent years it has been observed that the distribution of European coelopids has undergone a northward range shift. An investigation into the current distribution of European coelopid species and a discussion of the effects of climate change that may have caused this change is included. Finally, the use of stable isotope analysis to determine the diet of wild coelopids and alternative statistical methods to analyse mating trials are described.