Sound and vibration: production and perception

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Many animals use sound and vibration to communicate with each other, to attract mates or to establish territories. They also use them to detect their predators and parasites, who inevitably make some sound or vibration even when they are trying to be stealthy. Since detecting these signals is often a matter of life-and-death, animals have evolved sensory systems that are exquisitely acute. On the other hand they have also developed different techniques of being very loud when they communicate with each other. The research that I am proposing seeks to understand the mechanical design and neurobiology of both the perception and production systems using insects and spiders as model systems. There are three main themes to my research programme. In the first theme, I will study a process called active auditory amplification. Active amplification is carried out by auditory sensory cells. The cells selectively amplify some signals over others by generating their own mechanical motion. There are different hypotheses about how this process works, and this project will provide evidence that will help us differentiate between these hypotheses. By illuminating the molecular mechanism, it will also help us develop hypothesis about the evolutionary origin of this process. I will use a new technique called optical coherence tomography (OCT) and measure cell motion inside the intact, and fully functioning auditory organs of different insects. In the second theme, I will study how spider vibration sensors work. Spiders use organs called slit sensilla for sensing vibrations. Slit sensilla appear like cracks in the exoskeleton and are concentrated around leg joints. When a spider experiences vibrations, its joints are bent by very small amounts and these forces are transmitted to the sensilla. How this transmission works, however is unknown. There are two hypotheses, one that structures inside the leg transmit the bending forces and the other that pressures changes inside the leg transmit the forces. But there is no direct evidence of either mechanism. Using the OCT system, we will be able to provide this evidence, by measuring the leg lumen for pressure and the joint structures for vibrations. In the last theme, I will study the singing behaviour of field crickets and katydids. Given their size, both are inefficient at producing sound, but they sing quite differently. Crickets sing with their wings raised and katydids with their wings held against the body. Katydid wings also look quite different, unlike crickets they are camouflaged to look like leaves. I will use vibration measurements and acoustic modelling to test whether the katydid mode of singing developed to improve their singing efficiency or their camouflage. The research I propose will answer important questions about the design and neurobiology of these miniature sensors that arthropods have perfected through evolution and will be very useful in providing biomimetic inspiration for sensor design.