US-Austria Cooperative Research: Characterization of Air Currents in Relation to the Sensory Physiology and Behavior of Spiders

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This proposal on "Characterization of Air Currents in Relation to the Sensory Physiology and Behavior of Spiders" between Dr. Joseph A. Humphrey of the University of California at Berkeley and Dr. F.G. Barth of the University of Wien, Austria, is jointly approved by NSF and the FWF of Austria under the US-Austria Cooperative Science Program. The principal investigators propose a one-year program of research to investigate macroscopic fluid mechanic observables affecting prey capture and the "ballooning" phenomena in spiders and the relation of these to microscopic aspects of air motion-sensilla interactions. The highly interdisciplinary nature of this work combines the "zoological" expertise in Vienna and "engineering" expertise in Berkeley to advance knowledge in sensory physiology. Work in Berkeley will address the measurement and physico-mathema- tical modelling of the air motions relevant to behavior. The characteristics of the flows that stimulate and maintain the ballooning activity, as well as prey capture, will be experimentally determined in an especially constructed apparatus using laser-Doppler anemometry and flow visualization techniques. Time histories, averages and spectral frequency determinations of prescribed velocity fields will allow the investigators to elucidate the characteristics of the flows that elicit these activities. Theoretical work will focus on improving the fundamental under- standing, models and numerical predictability of the detailed distributions of velocity and pressure of such flows. In particular, various hypotheses advanced in a seminal paper by Humphrey ı1987! on the subject of ballooning will be rigorously checked. Closed form theoretical analysis will also be performed to model the response of the trichobothria sensilla, single or in groups, to natural fluctuations in the air flow. From this, estimates will be obtained of the forces that deflect the trichobothria, as well as the magnitudes and directions of the deflections themselves. Part of the experimental instrumentation (but not the apparatus) and the numerical procedures required to undertake this research are already available. With the necessary upgrades and adaptations they can both be applied to a range of problems of interest here and in related bio-fluid mechanics fields. The significance of this work lies in the impact that the experimental and theoretical findings will have in the fields of sensory physiology and biomechanics.