The purpose of this study is to evaluate the management and development of cricket in South Africa with particular reference to Natal. The objectives of this evaluation included Highlighting the period of cricket prior to unification; Describing the unification process and the conditions necessary for unity; and Evaluation of the development programmes at national and provincial levels. The extensive area of investigation and the vastness of the area of study, restricts this research to specific aspects that are pertinent to the topic. The objectives of the study therefore focus on the following : To provide a theoretical foundation and analysis of administration, organisation and structure, and development, in order to establish whether the current situation did in fact meet with the objectives of the unification process; To investigate the effects of the apartheid policy on sport in South Africa; and To provide a critical appraisal of existing development programmes in order to enhance the knowledge and literature-base of cricket administration in South Africa. Within the framework of this research, and the theoretical foundations of cricket administration and development, the effects of the government's policy of "Apartheid", the emergence of the non-racial sports struggle, the unification process, and the structure of cricket with particular emphasis on the development programmes both at national and provincial levels, are discussed. The conclusion, which draws inferences from each chapter, provides certain recommendations pertaining to the following: The establishment of a National Sports Coordinating Body; The development of a National Development Policy; The establishment of a National Development Fund; The Development of Talented Players; The Development of Officials; The Development of Clubs; The Provision of Facilities; The establishment of School Cricket Unification; and Control and Accountability. It is hoped that the recommendations and suggestions made address some aspects of the various issues raised about the unification process in cricket in South Africa. / Thesis (Ph.D.)-University of Durban-Westville, Durban, 1993.

Please read the summary in the front pages of the file named 00dissertation / Dissertation (LLM (Procedural Law))--University of Pretoria, 2007. / Procedural Law / unrestricted

Several animals, both vertebrate and invertebrate, communicate using sound and they do so in a non-ideal medium, the habitat in which they live. As acoustic signals pass through the habitat, they suffer loss of information due to signal degradation, which is often determined by the acoustic properties of the habitat. Understanding the influence of habitat-induced constraints on signaling is vital to the understanding of evolution of signal structure. Over time signals can evolve their temporal and/or spectral characteristics so as to resist or reduce degradation. Conversely, signalers may modify their behaviour so as to improve transmission for effective communication. The Acoustic Adaptation Hypothesis (AAH) predicts that given the properties of the habitat in which animals communicate, signals should evolve so as to maximize their broadcast range and the number of potential receivers. The prediction of the hypothesis is that signal transmission is best in the native habitat as compared to non-native habitats. Since its inception, the idea of acoustic adaptation has been tested in several vertebrate species including birds, mammals and frogs but rarely in invertebrates. Moreover, most of these studies have been carried out at the macrohabitat level, such as transmission in forests versus grasslands. For animals with limited mobility such as invertebrates, a finer level of investigation at the microhabitat level is more relevant. Only one study on cicadas has investigated the predictions of the AAH at the microhabitat level. Besides, investigations done at the community level are largely missing in the literature. The effect of height on signal transmission is well documented, however, only one study on birds has investigated the AAH with respect to vertical stratification of coexisting species. Among invertebrates, crickets are well known for their calling songs which males use to attract conspecific females over long distances. No study so far has tested the prediction of the AAH in these acoustically communicating invertebrates. The central focus of this study was to test the predictions of the AAH in a natural assemblage of ensiferan (cricket) species. I examined the prediction of the hypothesis at the microhabitat level with respect to the vertical stratification of co-existing ensiferan species. The study was carried out on an assemblage of crickets in the wet evergreen forests of Kudremukh National Park in the Western Ghats in Southern India. For this purpose, it was important to examine calling height and microhabitat selection in these animals because if the use of calling height and microhabitat was random, then there would not be any native height/microhabitat and the question of acoustic adaption would not arise. Therefore, I first standardized methods to characterize the habitat of the crickets. Using resource selection functions, I then quantified microhabitat selection in 13 ensiferan species. I also examined the calling heights of these species. My results suggest that these species are microhabitat specialists and also distribute vertically within the forest with respect to calling height. Based on the knowledge of the vertical distribution of these animals in the forest I then carried out playback experiments using natural calls of 12 species of Ensifera in their natural habitat. The transmission experiments were carried out at five heights in the forest, including the ground, different parts of the understorey as well as in the canopy. The study aimed to examine whether vertical stratification in the ensiferan species of Kudremukh is driven by selection for maximizing transmission range. I examined the effect of different heights on signal degradation. The investigation was carried out with respect to three different measures of signal degradation, namely, total attenuation, signal to noise ratio as well as envelope distortion. The results indicate a lack of overall support for the AAH with respect to vertical stratification of crickets in Kudremukh. However, a strong, independent effect of height of calling on signal degradation was found, with the ground being the worst layer for transmission and the mid-understorey (2 m) emerging to be good for all species with respect to all three measures of signal degradation. I then analysed the transmission data from a different point of view, exploring the possibility of evolution of signal structures that may confer some advantages in terms of signal transmission, given the habitat-induced constrains on signal propagation. The idea was to examine why certain species perform better than others in terms of signal transmission. This investigation was aimed at characterizing the effect of call features on signal attenuation. I found that temporal features of calls did not have a strong effect on height-specific signal attenuation. While call duration had no effect on signal attenuation, duty cycle did influence attenuation profiles of the calls, with high duty cycle calls performing better than low duty cycle calls. However, there was no interaction of height with the temporal features of calls, eliminating the possibility of these features being shaped by microhabitat or height dependent transmission characteristics. Spectral features of calls, on the other hand, affected signal attenuation very strongly. As expected, low frequency calls performed better than high frequency calls and pure tone calls fared much better than the broadband calls, especially on the ground and the canopy. To the best of my knowledge, this is the first study to carry out a rigorous quantification of microhabitat selection in Ensifera. This is also the first detailed examination of the Acoustic Adaptation Hypothesis at the microhabitat level, tested in a natural assemblage of coexisting invertebrate species.

Among the different sensory modalities that play a role in sexual selection, acoustic communication plays an important one. Acoustic communication has been known to be used for male-male competition (territory maintenance, male aggression during mating),for advertisement to the opposite sex (mating status, body condition, genetic quality, nutritional status) and used by females to sample and choose conspecific preferred males. The use of acoustic communication for sexual display and information exchange has been extensively studied in multiple taxa, including insects, anurans, birds and mammals. Among insects, crickets have proven to be good model systems to study sexual selection based on acoustic communication as most species have an elaborate acoustic communication system, male advertisements, diverse types of mating incentives for females (such as glandular feeding) and a female dominated mating system. Generally, in crickets males produce species-specific calls which are used by females to localize conspecific males. Besides, calls show high levels of intraspecific variation and are energetically costly to produce. Moreover, as in crickets predominantly the females show phonotaxis towards male calls, calls also can play a role in mate sampling and choice by acting as indicators of preferred male quality. Despite being studied for many decades there are certain gaps in the studies examining mate choice in crickets. Some of them are, lack of understanding of the variation of male calling traits in nature and its role in signal evolution, lack of understanding regarding the ecological context of mate sampling and the evolution of alternative mating strategies. Hence, the tree cricket Oecanthus henryi was chosen as a study system to address these gaps in the understanding of female choice based on acoustic signals. In the tree cricket Oecanthus henryi, males call and females use calls to localize conspecific males and hence potentially females can choose males based on acoustic cues. To understand the evolution of female preference for male acoustic cues it is important to understand the variation in the calling songs in the field and identify repeatable call features that are reliable indicators of preferred male traits (morphological, developmental or genetic). I measured repeatability of male call traits in the field to understand their variation, reliability and consistency. Carrier frequency was the only call trait that was highly repeatable and hence was reliable and consistent. Following this I examined whether any of these call traits were indicators of male morphological traits (such as male size and fluctuating asymmetry) which are known to be preferred by females. It was found that carrier frequency was negatively correlated with body size; hence carrier frequency was both reliable and indicated male size. I also found that females preferred larger males during mating, as revealed by the longer mating durations and longer spermatophore retention time. Interestingly, though this study indicated that females could in principle use lower call carrier frequency to localize preferred larger males, simultaneous choice experiments done in the laboratory revealed that the females do not use this cue. These contrasting results may be because females are incapable of discriminating small differences in frequency or because they use non-acoustic cues for mate choice. However, whichever cues the females use to discriminate between males in the laboratory conditions, often these preferences are not realized in the field. The main reason behind this is that searching for preferred mates in the field can be costly and this might force females to choose sub-optimal males. Theoretical models predict that male movement and spacing in the field should influence female sampling tactics and in turn, females should drive the evolution of male movement and spacing to sample them optimally. Moreover, simultaneous sampling of males using the best-of-n or comparative Bayes strategy should yield maximum mating benefits to females. Many of the theoretical mate sampling strategies involves recall of the quality and location of individual males, which in turn requires male positions to be stable within a night. Calling males of O. henryi showed high site fidelity within a night, potentially enabling female sampling strategies that require recall. To examine the possibility of simultaneous acoustic sampling of males, I estimated male acoustic active spaces using information on male spacing, call transmission and female phonotactic threshold. Males were found to be spaced far apart and active space overlap was rare. I then examined female sampling scenarios by studying female spacing relative to male acoustic active spaces. Only 15% of sampled females could hear multiple males, suggesting that simultaneous mate sampling is rare in the field. Moreover, the relatively large distances between calling males suggest high search costs, which may favor threshold strategies that do not require memory. Using the insights gathered from these two studies I examined a unique calling behaviour from leaf holes, baffling, observed in this species. Baffling behaviour has been found in multiple species of the genus Oecanthus where the males call from selfmade holes in leaves rather than calling from leaf edges (their natural calling surface) thus increasing their loudness many fold. I started by examining the natural history of baffling and found that baffling is an extremely rare behaviour in the field. However field observations and laboratory experiments revealed that many males can baffle and hence it is not an obligatory behaviour shown only by a few males. It was hypothesized that one reason for the rarity of baffling could be resource limitation. It was found that baffling males prefer larger leaves possibly due to higher SPL gains achieved by baffling on the larger leaves, which is a limited resource in the field. However this alone was insufficient to explain extreme rarity of bafflers in the field. Hence I examined which males were using this behaviour in the field. Using field observations and laboratory experiments it was found that less preferred males (smaller and quieter) baffled more which provided them with higher calling SPL and greater sound-field volume and thus a higher number of potential mates. Moreover, baffling also increased the mating duration for the less preferred males thus providing more time to these males for sperm transfer. The females could not differentiate between an inherently loud caller and a caller whose SPL was increased artificially (as if it was baffling). Hence I concluded that baffling is probably a cheater strategy used by the less preferred males to fool the females into approaching them and mating for longer durations. To my knowledge, this is the first study that has estimated male call variation in the field to understand its role in female choice in tree crickets. Moreover this is also the first study to examine the ecological context of mate choice in tree crickets. This is also the first study to examine the advantages of baffling behaviour and its potential evolutionary implications. the different sensory modalities that play a role in sexual selection, acoustic communication plays an important one. Acoustic communication has been known to be used for male-male competition (territory maintenance, male aggression during mating),for advertisement to the opposite sex (mating status, body condition, genetic quality, nutritional status) and used by females to sample and choose conspecific preferred males. The use of acoustic communication for sexual display and information exchange has been extensively studied in multiple taxa, including insects, anurans, birds and mammals. Among insects, crickets have proven to be good model systems to study sexual selection based on acoustic communication as most species have an elaborate acoustic communication system, male advertisements, diverse types of mating incentives for females (such as glandular feeding) and a female dominated mating system. Generally, in crickets males produce species-specific calls which are used by females to localize conspecific males. Besides, calls show high levels of intraspecific variation and are energetically costly to produce. Moreover, as in crickets predominantly the females show phonotaxis towards male calls, calls also can play a role in mate sampling and choice by acting as indicators of preferred male quality. Despite being studied for many decades there are certain gaps in the studies examining mate choice in crickets. Some of them are, lack of understanding of the variation of male calling traits in nature and its role in signal evolution, lack of understanding regarding the ecological context of mate sampling and the evolution of alternative mating strategies. Hence, the tree cricket Oecanthus henryi was chosen as a study system to address these gaps in the understanding of female choice based on acoustic signals. In the tree cricket Oecanthus henryi, males call and females use calls to localize conspecific males and hence potentially females can choose males based on acoustic cues. To understand the evolution of female preference for male acoustic cues it is important to understand the variation in the calling songs in the field and identify repeatable call features that are reliable indicators of preferred male traits (morphological, developmental or genetic). I measured repeatability of male call traits in the field to understand their variation, reliability and consistency. Carrier frequency was the only call trait that was highly repeatable and hence was reliable and consistent. Following this I examined whether any of these call traits were indicators of male morphological traits (such as male size and fluctuating asymmetry) which are known to be preferred by females. It was found that carrier frequency was negatively correlated with body size; hence carrier frequency was both reliable and indicated male size. I also found that females preferred larger males during mating, as revealed by the longer mating durations and longer spermatophore retention time. Interestingly, though this study indicated that females could in principle use lower call carrier frequency to localize preferred larger males, simultaneous choice experiments done in the laboratory revealed that the females do not use this cue. These contrasting results may be because females are incapable of discriminating small differences in frequency or because they use non-acoustic cues for mate choice. However, whichever cues the females use to discriminate between males in the laboratory conditions, often these preferences are not realized in the field. The main reason behind this is that searching for preferred mates in the field can be costly and this might force females to choose sub-optimal males. Theoretical models predict that male movement and spacing in the field should influence female sampling tactics and in turn, females should drive the evolution of male movement and spacing to sample them optimally. Moreover, simultaneous sampling of males using the best-of-n or comparative Bayes strategy should yield maximum mating benefits to females. Many of the theoretical mate sampling strategies involves recall of the quality and location of individual males, which in turn requires male positions to be stable within a night. Calling males of O. henryi showed high site fidelity within a night, potentially enabling female sampling strategies that require recall. To examine the possibility of simultaneous acoustic sampling of males, I estimated male acoustic active spaces using information on male spacing, call transmission and female phonotactic threshold. Males were found to be spaced far apart and active space overlap was rare. I then examined female sampling scenarios by studying female spacing relative to male acoustic active spaces. Only 15% of sampled females could hear multiple males, suggesting that simultaneous mate sampling is rare in the field. Moreover, the relatively large distances between calling males suggest high search costs, which may favor threshold strategies that do not require memory. Using the insights gathered from these two studies I examined a unique calling behaviour from leaf holes, baffling, observed in this species. Baffling behaviour has been found in multiple species of the genus Oecanthus where the males call from self- made holes in leaves rather than calling from leaf edges (their natural calling surface) thus increasing their loudness many fold. I started by examining the natural history of baffling and found that baffling is an extremely rare behaviour in the field. However field observations and laboratory experiments revealed that many males can baffle and hence it is not an obligatory behaviour shown only by a few males. It was hypothesized that one reason for the rarity of baffling could be resource limitation. It was found that baffling males prefer larger leaves possibly due to higher SPL gains achieved by baffling on the larger leaves, which is a limited resource in the field. However this alone was insufficient to explain extreme rarity of bafflers in the field. Hence I examined which males were using this behaviour in the field. Using field observations and laboratory experiments it was found that less preferred males (smaller and quieter) baffled more which provided them with higher calling SPL and greater sound-field volume and thus a higher number of potential mates. Moreover, baffling also increased the mating duration for the less preferred males thus providing more time to these males for sperm transfer. The females could not differentiate between an inherently loud caller and a caller whose SPL was increased artificially (as if it was baffling). Hence I concluded that baffling is probably a cheater strategy used by the less preferred males to fool the females into approaching them and mating for longer durations. To my knowledge, this is the first study that has estimated male call variation in the field to understand its role in female choice in tree crickets. Moreover this is also the first study to examine the ecological context of mate choice in tree crickets. This is also the first study to examine the advantages of baffling behaviour and its potential evolutionary implications.

Artificial light at night (ALAN), or ecological light pollution, is increasingly prevalent worldwide. Exposure to ALAN tends to negatively impact animals—particularly, nocturnal animals—but life-history strategies may mitigate these costs. Animals in many regions are also increasingly exposed to climate-related stressors, such as heat and drought. Yet, interactions among ALAN, life-history strategy, and stress tolerance are unknown. Therefore, I determined if developmental ALAN exposure (1) affects development, (2) affects adult phenotype, including heat and desiccation tolerance, and (3) affects and/or interacts with life-history strategy. To address my aims, I used the variable field cricket (Gryllus lineaticeps) because its geographic range is increasingly exposed to ALAN, heat, and drought conditions; it exhibits different life-history strategies (flight-capability vs. flight-incapability); and it is mainly nocturnal. Although developmental duration and success were not impacted by ALAN exposure, ALAN affected adult phenotype, with a positive effect on body mass, body size, and reproductive investment, and a negative effect on heat tolerance. Life-history strategy also affected stress tolerance—flight-incapable females had greater heat tolerance, and their desiccation tolerance was improved by ALAN exposure. Thus, key features of environmental change (i.e., exposure to ALAN, heat, and drought) may favor some life-history strategies over others.

Stressful experiences in early life can have profound and lasting impacts on phenotypic development. In anthropogenic environments, organisms are increasingly exposed to evolutionarily novel stressors that may play a major role in shaping the phenotypic variation upon which natural selection acts. For instance, ionizing radiation persists in areas affected by nuclear reactor accidents, nuclear weapons testing, and the nuclear power production process. This thesis explored the dose-response effects of early life ionizing radiation exposure on life- history traits in the cricket (Acheta domesticus L.). Specifically, this work had two goals: (1) to examine the effects of early life radiation stress on the potential tradeoff between growth and self-maintenance, and (2) to explore the dose-dependent effects of juvenile radiation exposure on adult trait expression (particularly fecundity, offspring investment, and offspring fitness). It was found that exposure to moderate doses of radiation in early development resulted in a slower juvenile growth rate but increased survival in early adulthood, suggesting that self- maintenance was prioritized over growth. Despite the strong inhibitory effects of early life radiation on adult female body mass, age-specific fecundity was negatively impacted only at relatively high radiation doses. Crickets exposed to moderate radiation doses in early development laid larger eggs in adulthood relative to controls and these eggs had a greater hatching success, suggesting that radiation exposure had transgenerational effects on offspring performance. No noticeable effects of early life radiation exposure were detected on total and non-enzymatic antioxidant capacity or hydrogen peroxide levels in adult females. Together, this research indicates that a single, acute exposure to ionizing radiation in early life can affect phenotypic development in a complex, dose-dependent manner and that rather than being purely negative, phenotypic responses can be sustained or even enhanced. / Thesis / Master of Science (MSc) / Stressful experiences in early life can have lasting impacts on organismal development, but the extent to which early life stress is harmful is unclear. In human-dominated environments, pollutants such as ionizing radiation can be a significant form of developmental stress. This thesis explores the fitness-related effects of early life ionizing radiation exposure in the cricket, Acheta domesticus. Impacts on growth, longevity, fecundity, and offspring fitness are explored. This research indicates that early life stress can affect phenotypic development in a complex, dose-dependent manner and that rather than being purely negative, responses can be sustained or even enhanced.

Insects maintain blood (haemolymph) Ca2+ concentrations within a narrow range in order to support the health of internal tissues and organs. The Malpighian (renal) tubules play a primary role in haemolymph Ca2+ homeostasis by sequestering excess Ca2+ within calcified biomineral deposits (Ca-rich granules) often located within type I (principal) tubule cells. Using the classic Ramsay assay, the scanning ion-selective microelectrode technique (SIET), and modifications of these two electrophysiological techniques, this thesis begins to unravel the sites and mechanisms of Ca2+ transport by the Malpighian tubules isolated from eight insects, representing seven orders. A segment-specific pattern of Ca2+ flux was observed along the length of the Malpighian tubules isolated from D. melanogaster, A. aegypti and A. domesticus and was uniform along the length in the remaining species. The majority (≥ 90%) of Ca2+ entering the tubule cells is sequestered within intracellular calcium stores in Ca2+-transporting segments of D. melanogaster and A. domesticus tubules, consistent with the presence of Ca-rich storage granules in these tubule segments. In addition, this thesis provides the first measurements of basolateral Ca2+ flux across single principal and secondary tubule cells of T. ni, where Ca2+ uptake occurs only across principal cells. Perhaps the most important finding of this thesis is that increasing fluid secretion through manipulation of intracellular levels of cAMP or Ca2+ in isolated tubules of A. domesticus had opposite effects on tubule Ca2+ transport. The adenylyl cyclase-cAMP-PKA pathway promotes Ca2+ sequestration whereas both 5-hydroxytryptamine and thapsigargin inhibited sequestration. In contrast, tubules of the remaining species were generally insensitive to cAMP or thapsigargin and v rates of tubule Ca2+ transport were often very low. The presence of Ca-rich granules in the cells of the midgut in several of the species with low rates of tubule Ca2+ transport provide evidence for a putative role of the midgut in haemolymph Ca2+ homeostasis. Taken together, these results suggest that the principal cells of the Malpighian tubules contribute to haemolymph calcium homeostasis through neuroendocrine regulated sequestration of excess Ca2+ during periods of high dietary calcium intake. Sequestration of dietary Ca2+ by the midgut may reduce Ca2+ entry into the haemolymph and therefore Ca2+ sequestration by the Malpighian tubules need not be so rapid. Finally, reversible tubule Ca2+ transport may allow internal reserves of Ca2+ (Ca-rich granules) to be returned to the haemolymph allowing insects to survive prolong periods of Ca2+ deficiency (i.e. overwintering). / Thesis / Doctor of Philosophy (PhD) / This thesis contributes to our understanding of how insects regulate the calcium content of their blood (haemolymph). Using electrophysiological techniques with improved spatial resolution (from millimeters to micrometers) this thesis sought to determine the sites, mechanisms and regulation of Ca2+ transport by insect Malpighian (renal) tubules in order to gain insights into the role of Ca-rich granules (similar to those identified in early stages of human kidney stone formation i.e. nephrolithiasis) within these tissues. Using eight insect species this thesis demonstrates that the Malpighian tubules act as dynamic Ca2+ stores that appear to be under neuroendocrine control: actively taking up Ca2+ through calcium entry channels, where the majority (≥ 90%) of excess haemolymph Ca2+ is sequestered within intracellular stores (Ca-rich granules) during period of excess dietary calcium and passively releasing Ca2+ back to the haemolymph during periods of metamorphosis or calcium deficiency (i.e. overwintering).

Thesis (Ph. D.)--University of Technology, Sydney, 2000. / Sportsmen: Tarpot, Tom Wills, Mullagh, King Cole, Jellico, Peter, Red Cap, Harry Rose, Bullocky, Johnny Cuzens, Dick-a-Dick, Charley Dumas, Jim Crow, Sundown, Mosquito, Tiger and Twopenny. Bibliography: p. 431-485.

In vielen Kommunikationssytemen wird Information durch die zeitliche Struktur von Signalen kodiert. Ein neuronales System, welches rhythmische Signale verarbeitet, sollte davon profitieren, seine inhärenten Filtereigenschaften den Frequenzcharakteristika dieser Signale anzupassen. Die Grille Gryllus bimaculatus stellt ein einfaches biologisches System dar, für welches nur wenige, spezifische Modulationsfrequenzen verhaltensrelevant sind. Ich habe einzelne Neuronen im peripheren und höheren auditorischen System der Grille hinsichtlich einer möglichen Anpassung auf diese Frequenzen untersucht. Hierfür habe ich extrazelluläre Elektrophysiologie mit verschiedenen Stimulationsparadigmen kombiniert, welche auf amplitudenmodulierten Tönen basierten. Die Analyse der experimentellen Daten ergab, dass bereits in der auditorischen Peripherie einige der untersuchten Neurone Bandpasseigenschaften aufwiesen, da sie verhaltensrelevante Modulationsfrequenzen mit den höchsten Feuerraten beantworteten. Anhand einfacher mathematischer Modelle demonstriere ich, wie weitverbreitete, zellintrinsische und netzwerkbasierte Mechanismen die beobachteten Feuerratenresonanzen erklären könnten. Diese Mechanismen umfassen unterschwellige Resonanz von Membranströmen, aktivitätsabhängige Adaptation, sowie das Zusammenwirken von Exzitation und Inhibition. Ich zeige, wie eine serielle Kombination solcher elementarer Filter die deutliche Selektivität im Verhalten der Grille erklären könnte, ohne dabei auf ein dediziertes Filterelement zurückzugreifen. Allgegenwärtige neuronale Mechanismen könnten demnach eine dezentralisierte Filterkaskade in einem hochspezialisierten und größenbeschränkten neuronalen System begründen. / In many communication systems, information is encoded in the temporal pattern of signals. For rhythmic signals that carry information in specific frequency bands, a neuronal system may profit from tuning its inherent filtering properties towards a peak sensitivity in the respective frequency range. The cricket Gryllus bimaculatus is a simple biological system for which only a narrow range of modulation frequencies is behaviorally relevant. I examined individual neurons in the peripheral and higher auditory system for tuning towards specific temporal parameters and modulation frequencies. To this end, I combined extracellular electrophysiology with different stimulation paradigms involving amplitude-modulated sounds. Analysis of the experimental data revealed that—even in the auditory periphery—some of the examined neurons acted as tuned band-pass filters, yielding highest firing-rates for behaviorally relevant modulation frequencies. Using simple computational models, I demonstrate how common, cell-intrinsic or network-based mechanisms could account for the experimentally observed firing-rate resonances. These mechanisms include subthreshold resonances, spike-triggered adaptation, as well as the interplay of excitation and inhibition. I present how a serial combination of such elementary filters could explain the strong selectivity evident in the cricket’s behavior—without the need for a dedicated filter element. Pervasive neuronal mechanisms could therefore constitute an efficient, distributed frequency filter in a highly specialized, size-constrained neuronal system.

This thesis describes work from both the University of Cambridge in the lab of Berthold Hedwig and from the HHMI Janelia Research Campus in the lab of Michael Reiser. At the University of Cambridge, my work involved the development and demonstration of a method for electrophoretically delivering dyes and tracers for anatomical and functional imaging into animals that are not amenable to genetic labelling techniques. Using this method in locusts and crickets - model systems of particular interest for their acoustic communication - I successfully delivered polar fluorescent dyes and tracers through the sheath covering the auditory nerve, simultaneously staining both the peripheral sensory structures and the central axonal projections without destroying the nerve's function. I could label neurons which extend far from the tracer delivery site on the nerve as well as local neuron populations through the brain's surface. I used the same method to deliver calcium indicators into central neuropils for in vivo optical imaging of sound-evoked activity, as well as calling song-evoked activity in the brain. The work completed at the Janelia Research Campus began with the development of a modern version of a modular LED display and virtual reality control system to enable research on the visual control of complex behaviors in head-fixed animals. The primary advantages of our newly developed LED-based display over other display technologies are its high-speed operation, brightness uniformity and control, precise synchronization with analog inputs and outputs, and its ability to be configured into a variety of display geometries. Utilizing the system's fast display refresh rates, I conducted the first accurate characterization of the upper limits of the speed sensitivity of Drosophila for apparent motion during flight. I also developed a flexible approach to presenting optic flow scenes for functional imaging of motion-sensitive neurons. Finally, through the on-line analysis of behavioral measures, image rendering, and display streaming with low latency to multi-color (UV/Green) LED panels, I demonstrated the ability to create more naturalistic stimuli and interactive virtual visual landscapes. Lastly, I used this new visual display system to explore a newly discovered cell-type that had been implicated in higher-order motion processing from a large genetic screen of visually-guided behavior deficits. Using genetic silencing and activation methods, and by designing stimuli that modeled the optic flow encountered during different types of self-motion, colleagues in the Reiser lab and I showed that this cell-type - named Lobula Plate Columnar 1 (LPC1) - is required for the stopping behavior of walking flies caused by back-to-front translation motion but is not involved in the rotational optomotor response. Using calcium imaging, I found that LPC1 was selectively excited by back-to-front motion on the eye ipsilateral to the neuron population and inhibited by front-to-back motion on the contralateral eye, demonstrating a simple mechanism for its selectivity to translation over rotation. I also examined an anatomically similar cell type - named Lobula-Lobula Plate Columnar type 1 (LLPC1) - and found that its selectivity results from a similar but opposite calculation for the detection of front-to-back translational motion. The detection of back-to-front motion had previously been hypothesized to be useful for collision avoidance, and this work provides a neural mechanism for how this detection could be accomplished, as well as providing a platform from which to explore the larger network for translation optic flow.