Gert Stange

The ocellar component of flight equilibrium control in dragonflies

SummaryThis paper describes the dynamics of light-evoked head reflexes in the dragonflyHemicordulia tau under light conditions which were selected to optimally address the ocelli.1.The responses occur only during flight.2.Stimulation by a light positioned to address the median ocellus evokes a head movement around the pitch axis. The threshold is in the order of 107 photons · cm−2 · s−1. With increasing intensity, the responses become progressively faster but do not increase in amplitude.3.Stimulation by lights positioned to address the lateral ocelli evokes head movements around the roll axis with a similar threshold and similar dynamics as in the pitch responses. The responses are strongest when two sources at either side of the animal are switched in alternation.4.No evidence is found for interactions between the lateral and the median inputs.5.During sustained illumination from the median source, the head is tilted towards it indefinitely, and increasing the intensity causes only a small additional change of head position. Decreasing the intensity causes a large movement of the head away from the source, and then the system readapts rapidly and the head returns to the on-position (high pass filtering). If increment pulses are superimposed on a steady background, the magnitude of their effect is a function of both their duration and amplitude.6.If the median source is modulated by a square wave of a frequency above the high pass cut-off, the amplitudes of the responses are proportional to modulation depths and independent of average intensity over 4 log units.7.At intensities below 1011 photons cm−2s−1, the spectral sensitivity has a maximum in the green, exceeding the UV-sensitivity by a factor of 5; at higher intensities the responses become more sensitive to UV than to green (reverse Purkinje shift). It is suggested that the reverse Purkinje shift is a functional adaptation to optimize the detectability of the contrast between sky and ground both in dim light and in direct sunlight.8.The dynamics of the behavioural responses can be largely accounted for by known properties of the neuronal elements of ocellar systems.

Carbon-Dioxide Sensing Structures in Terrestrial Arthropods

Sensory structures that detect atmospheric carbon dioxide have been identified and described to the subcellular level in adults of Lepidoptera, Diptera, Hymenoptera, Isoptera, Chilopoda, and Ixodidae, as well as in lepidopteran larvae. The structures are usually composed of clusters of wall‐pore type sensilla that may form distinct sensory organs, often recessed in pits or capsules. In insects, they are located on either the palps or the antennae, in chilopods on the head capsule, and in ixodids on the forelegs. In the two cases where the central projections have been examined (Lepidoptera and mosquitoes), the clustering is preserved to the level of second order neurons, which are located in the deutocerebrum. Individual sensilla usually contain a single receptor neuron that is sensitive to CO2; it may be accompanied by other neurons that respond to other olfactory qualities. The distal dendritic processes of CO2‐sensitive neurons invariably show an increased surface area, dividing into many cylindrical branches or into lamellar structures. Lamellar membranes are often closely linked to arrays of microtubules. Fine pore canal tubules are usually associated with the cuticular pores. Microsc. Res. Tech. 47:416–427, 1999.

Anisotropic imaging in the dragonfly median ocellus: a matched filter for horizon detection

Abstract. It is suggested that the dragonfly median ocellus is specifically adapted to detect horizontally extended features rather than merely changes in overall intensity. Evidence is presented from the optics, tapetal reflections and retinal ultrastructure. The underfocused ocelli of adult insects are generally incapable of resolving images. However, in the dragonfly median ocellus the geometry of the lens indicates that some image detail is present at the retina in the vertical dimension. Details in the horizontal dimension are blurred by the strongly astigmatic lens. In the excised eye the image of a point source forms a horizontal streak at the level of the retina. Tapetal reflections from the intact eye show that the field of view is not circular as in most other insects but elliptical with the major axis horizontal, and that resolution in the vertical direction is better than in the horizontal. Measurements of tapetal reflections in locust ocelli confirm their visual fields are wide and circular and their optics strongly underfocused. The ultrastructure suggests adaptation for resolution, sensitivity and a high metabolic rate, with long, widely separated rhabdoms, retinulae cupped by reflecting pigment, abundant tracheoles and mitochondria, and convoluted, amplified retinula cell plasma membranes.

Temporal synchronization in the primary auditory response in the pigeon

Spike potentials were recorded from single fibres in the auditory nerve of the pigeon. In responses elicited by tonal stimuli, the timing of each spike relative to stimulus waveform was measured and period histograms were constructed. Phase locking of spikes was estimated in terms of a synchronicity index obtained by vector addition within the period histogram. A second measure of synchrony in the spike responses was obtained, that of temporal dispersion. For a population of fibres, vector strength of phase locking decreased for frequencies above 1 kHz, as reported for several other species. Temporal dispersion, however, also decreased with frequency, indicating enhanced temporal synchrony as frequency increased within the bandwidth of phase locking. The upper frequency limit of phase locking appears to depend on irreducible jitter of biological origin in the timing of spikes. For individual fibres, the bandwidth of synchronization of spikes consistently exceeds the response area, covering in addition the areas of suppression adjacent to the response area. Spike trains suppressed by a tonal stimulus become synchronized to that stimulus. Phase angles of synchronized responses systematically change as a function of tone level, when tone frequency is above or below CF, as reported for other avian species. Synchronicity and phase angle intensity functions are quite independent of spike rate intensity functions.

Bioinspired engineering of exploration systems: a horizon sensor/attitude reference system based on the dragonfly Ocelli for Mars exploration applications

Bioinspired engineering of exploration systems (BEES) is a fast emerging new discipline. It focuses on distilling the principles found in successful, nature-tested mechanisms of specific crucial functions that are hard to accomplish by conventional methods, but are accomplished rather deftly in nature by biological organisms. The intent is not just to mimic operational mechanisms found in a specific biological organism but to imbibe the salient principles from a variety of diverse organisms for the desired crucial function. Thereby, we can build exploration systems that have specific capabilities endowed beyond nature, as they will possess a mix of the best nature-tested mechanisms for each particular function. Insects (for example, honey bees and dragonflies) cope remarkably well with their world, despite possessing a brain that carries less than 0.01% as many neurons as ours does. Although most insects have immobile eyes, fixed focus optics, and lack stereo vision, they use a number of ingenious strategies for perceiving their world in three dimensions and navigating successfully in it. We are distilling some of these insect-inspired strategies for utilizing optical cues to obtain unique solutions to navigation, hazard avoidance, altitude hold, stable flight, terrain following, and smooth deployment of payload. Such functionality can enable access to otherwise unreachable exploration sites for much sought-after data. A BEES approach to developing autonomous dflight systems, particularly in small scale, can thus have a tremendous impact on autonomous airborne navigation of these biomorphic flyers particularly for planetary exploration missions, for example, to Mars which offer unique challenges due to its thin atmosphere, low gravity, and lack of magnetic field. Incorporating these success strategies of bioinspired navigation into biomorphic sensors such as the horizon sensor described herein fulfills for the first time the requirements of a variety of potential future Mars exploration applications described in this paper. Specifically we have obtained lightweight (similar to6 g), low power (<40 mW), and robust autonomous horizon sensing for flight stabilization based on distilling the principles of the dragonfly ocelli. Such levels of miniaturization of navigation sensors are essential to enable biomorphic microflyers (< 1 kg) that can be deployed in large numbers for distributed measurements. In this paper we present the first experimental test results of a biomorphic flyer platform with an embedded biomorphic ocellus (the dragonfly-inspired horizon sensor/attitude reference system). These results from the novel hardware implementation of a horizon sensor demonstrate the advantage of our approach in adapting principles proven successful in nature to accomplish navigation for Mars exploration

High resolution measurement of atmospheric carbon dioxide concentration changes by the labial palp organ of the moth Heliothis armigera (Lepidoptera : Noctuidae)

SummaryIn recordings of single unit action potentials, the responses of CO2-receptors in the labial palp organ of the moth Heliothis armigera to modulation of CO2-density around a background of 350 ppm were investigated. Modulation of CO2-density by square wave changes in concentration at constant barometric pressure evokes modulation of the spike rate. Modulation of CO2-density by square wave changes in barometric pressure at constant CO2-concentration evokes responses similar to those evoked by concentration modulation. For modulation depths of less than 1.5%, the output modulation depth is linearly related to the input; at higher modulation depths the gain decreases progressively.Using sinusoidal pressure modulation, the frequency dependence of both gain and output noise was determined over a range of 0.05 to 12.8 Hz. With increasing frequency the gain progressively increases at a rate of 2.4 dB/octave up to a maximum of 63 at 3 Hz; at higher frequencies, it decreases rapidly. The threshold sensitivity of the receptors, using input noise amplitude density as a criterion, is broadly tuned, with a minimum of 1 % contrast Hz-0.5 between 0.3 and 3 Hz. Using these figures, it is concluded that the sensory organ is capable of detecting fluctuations in CO2-density of 0.14% or 0.5 ppm. The results are related to the fluctuations in CO2-density which occur in a natural environment.

Effects of changes in atmospheric carbon dioxide on the location of hosts by the moth, Cactoblastis cactorum

Abstract Sensory organs that detect CO2 are common in herbivorous moths and butterflies, but their function has been unclear until now. As the CO2 gradients in the vicinity of a host plant depend on its physiological condition, CO2 could provide a sensory cue for the suitability of the plant as a larval food source. This study investigated whether changing the atmospheric CO2 concentration affected oviposition by Cactoblastis cactorum on its host, the cactus Opuntia stricta. On host plants exposed to rapid fluctuations in CO2 concentration, the frequency of oviposition was reduced by a factor of 3.2 compared to the control. As the fluctuations mask the much smaller CO2 signals generated by the plants, this suggests that those signals constitute an important component of the host identification process. On host plants exposed to a constant background of doubled CO2, oviposition was also reduced, by a factor of 1.8. An increased background reduces host signal detectability, partially as a consequence of a general principle of sensory physiology (Weber-Fechners law), and partially due to other factors specific to CO2-receptor neurons.

The CO2 sense of the moth Cactoblastis cactorum and its probable role in the biological control of the CAM plant Opuntia stricta

The interaction between the moth, Cactoblastis cactorum, and the cactus, Opuntia stricta, is used as a model to examine the question of whether the CO2 sense of a herbivorous insect can detect the CO2 gradients associated with a plants metabolic activity. Both the anatomical and the electrophysiological characteristics of CO2-sensitive receptor neurons in C. cactorum indicate an adaptation to the detection of small fluctuations around the atmospheric background. Evidence is provided that further rises in background will impair the function of the sensory organ. In the habitat of the plant, during the diurnal window of the moths activity, two types of CO2 gradients occur that are detectable by the moths sensors. The first gradient, associated with soil respiration, is vertical and extends from the soil surface to an altitude of approximately 1 m. Its magnitude is well above the detectability limit of the sensors. The notion that this gradient provides, to a flying insect, a cue for the maintenance of a flight altitude favourable for host detection is supported by field observations of behaviour. The second gradient, associated with CO2 fixation by the plant, extends from the surfaces of photosynthetic organs (cladodes) over a boundary layer distance of approximately 5 mm. Again, its magnitude is well above the detectability limit. The notion that this gradient provides, to a walking insect, a cue to the physiological condition of the plant is supported by the observation that females of C. cactorum, prior to oviposition, actively probe the plant surface with their CO2 sensors. In a simulation of probing, pronounced responses of the sensors to the CO2-fixing capacity of O. stricta are observed. We propose that by probing the boundary layer, females of C. cactorum can detect the healthiest, most active O. stricta cladodes, accounting for earlier observations that the most vigorous plants attract the greatest density of egg sticks.

An overview of insect-inspired guidance for application in ground and airborne platforms

Abstract Flying insects provide a clear demonstration that living organisms can display surprisingly competent mechanisms of guidance and navigation, despite possessing relatively small brains and simple nervous systems. Consequently, they are proving to be excellent organisms in which to investigate how visual information is exploited to guide locomotion and navigation. Four illustrative examples are described here, in the context of navigation to a destination. Bees negotiate narrow gaps by balancing the speeds of the images in the two eyes. Flight speed is regulated by holding constant the average image velocity as seen by the two eyes. This automatically ensures that flight speed is reduced to a safe level when the passage narrows. Smooth landings on a horizontal surface are achieved by holding image velocity constant as the surface is approached, thus automatically ensuring that flight speed is close to zero at touchdown. Roll and pitch are stabilized by balancing the signals registered by three visual organs, the ocelli, that view the horizon in the left, right and forward directions respectively. Tests of the feasibility of these navigational strategies, by implementation in robots, are described.

The mapping of visual space by identified large second-order neurons in the dragonfly median ocellus

In adult dragonflies, the compound eyes are augmented by three simple eyes known as the dorsal ocelli. The outputs of ocellar photoreceptors converge on relatively few second-order neurons with large axonal diameters (L-neurons). We determine L-neuron morphology by iontophoretic dye injection combined with three-dimensional reconstructions. Using intracellular recording and white noise analysis, we also determine the physiological receptive fields of the L-neurons, in order to identify the extent to which they preserve spatial information. We find a total of 11 median ocellar L-neurons, consisting of five symmetrical pairs and one unpaired neuron. L-neurons are distinguishable by the extent and location of their terminations within the ocellar plexus and brain. In the horizontal dimension, L-neurons project to different regions of the ocellar plexus, in close correlation with their receptive fields. In the vertical dimension, dendritic arborizations overlap widely, paralleled by receptive fields that are narrow and do not differ between different neurons. These results provide the first evidence for the preservation of spatial information by the second-order neurons of any dorsal ocellus. The system essentially forms a one-dimensional image of the equator over a wide azimuthal area, possibly forming an internal representation of the horizon. Potential behavioural roles for the system are discussed.