James F. C. Windmill

Tympanal travelling waves in migratory locusts

SUMMARY Hearing animals, including many vertebrates and insects, have the capacity to analyse the frequency composition of sound. In mammals, frequency analysis relies on the mechanical response of the basilar membrane in the cochlear duct. These vibrations take the form of a slow vibrational wave propagating along the basilar membrane from base to apex. Known as von Békésys travelling wave, this wave displays amplitude maxima at frequency-specific locations along the basilar membrane, providing a spatial map of the frequency of sound - a tonotopy. In their structure, insect auditory systems may not be as sophisticated as those of mammals, yet some are known to perform sound frequency analysis. In the desert locust, this analysis arises from the mechanical properties of the tympanal membrane. In effect, the spatial decomposition of incident sound into discrete frequency components involves a tympanal travelling wave that funnels mechanical energy to specific tympanal locations, where distinct groups of mechanoreceptor neurones project. Notably, observed tympanal deflections differ from those predicted by drum theory. Although phenomenologically equivalent, von Békésys and the locusts waves differ in their physical implementation. von Békésys wave is born from interactions between the anisotropic basilar membrane and the surrounding incompressible fluids, whereas the locusts wave rides on an anisotropic membrane suspended in air. The locusts ear thus combines in one structure the functions of sound reception and frequency decomposition.

Keeping up with Bats: Dynamic Auditory Tuning in a Moth

Many night-flying insects evolved ultrasound sensitive ears in response to acoustic predation by echolocating bats . Noctuid moths are most sensitive to frequencies at 20-40 kHz , the lower range of bat ultrasound . This may disadvantage the moth because noctuid-hunting bats in particular echolocate at higher frequencies shortly before prey capture and thus improve their echolocation and reduce their acoustic conspicuousness . Yet, moth hearing is not simple; the ears nonlinear dynamic response shifts its mechanical sensitivity up to high frequencies. Dependent on incident sound intensity, the moths ear mechanically tunes up and anticipates the high frequencies used by hunting bats. Surprisingly, this tuning is hysteretic, keeping the ear tuned up for the bats possible return. A mathematical model is constructed for predicting a linear relationship between the ears mechanical stiffness and sound intensity. This nonlinear mechanical response is a parametric amplitude dependence that may constitute a feature common to other sensory systems. Adding another twist to the coevolutionary arms race between moths and bats, these results reveal unexpected sophistication in one of the simplest ears known and a novel perspective for interpreting bat echolocation calls.

Mechanical phase shifters for coherent acoustic radiation in the stridulating wings of crickets: the plectrum mechanism

SUMMARY Male crickets produce stridulatory songs using engaged tegmina (forewings): a plectrum on the left sweeps along a tooth row on the right. During stridulation, the plectrum moves across the teeth and vibrations are amplified by the surrounding cells and veins, resonating at the frequency of tooth impacts. The advance of the plectrum on the file is controlled by an escapement mechanism so that passing each single tooth generates one wave of a highly tonal signal. Both tegmina must oscillate in phase to avoid destructive interference. But as each plectrum-tooth contact begins, the right and left tegmina react in opposite oscillatory directions. A mechanical phase shifter is part of the left tegmen and compensates to achieve wing oscillation synchrony. We use a new technique to simulate plectrum-on-file interactions: in combination with laser vibrometry, this technique assessed plectrum mechanics in the cricket Gryllus bimaculatus. Using an excised teneral file, shaped like a partial gear and moved by a motor, and a microscan Doppler laser vibrometer, plectrum and left-tegmen mechanics were explored. The results show that plectrum and harp oscillate with a phase difference of ca. 156 deg., a shift rather than a complete phase inversion (180 deg.). This phase shift occurs at the site of a large wing vein (possibly A3). Plectrum and harp vibrate with similar fundamental frequency, therefore, plectrum torsion resonant frequency is important for maintaining vibration coherence. The mechanical aspects involved in this partial phase inversion are discussed with respect to the escapement mechanism. The plectrum mechanics and its implications in katydid stridulation are also considered.

Synchrony through twice-frequency forcing for sensitive and selective auditory processing.

Male mosquitoes detect flying females using antennal hearing organs sensitive to nanoscale mechanical displacements and that harbor motile mechanosensory neurons. The mechanisms supporting neuronal motility, and their function in peripheral sensory processing, remain, however, puzzling. The mechanical and neural responses reveal a transition that unmasks the onset of synchronization between sensory neurons. This synchronization constitutes an unconventional, mechanically driven, process of communication between sensory neurons. Enhancing auditory sensitivity and selectivity, synchronization between mechanosensors in the mosquito arises from entrainment to twice-frequency forcing and is formally analogous to injection-locking in high-power laser technology. This discovery opens up the enticing possibility that other sensory systems, even nonsensory cell ensembles, coordinate their actions through mechanical signaling.

Tuning the drum: the mechanical basis for frequency discrimination in a Mediterranean cicada

SUMMARY Cicadas are known to use sound to find a mate. While the mechanism employed by male cicadas to generate loud calling songs has been described in detail, little information exists to explain how their ears work. Using microscanning laser Doppler vibrometry, the tympanal vibrations in the cicada Cicadatra atra are measured in response to acoustic playbacks. The topographically accurate optical measurements reveal the vibrational behaviour of the anatomically complex tympanal membrane. Notably, the tympanal ridge, a distinct structural element of the tympanum that is a link to the receptor cells, undergoes mechanical vibrations reminiscent of a travelling wave. In effect, the frequency for which the maximum deflection amplitude is observed regularly decreases from the apex to the base of the ridge. It is also shown that whilst female ears are mechanically tuned to the males song, the males tympanum is only partially tuned to its own song. This study establishes the presence of a peripheral auditory mechanism that can potentially process auditory frequency analysis. In view of the importance of acoustic signalling in cicadas, this unconventional tympanal mechanism may be employed in the context of species recognition and sexual selection.

Design for remanufacturing in China: a case study of electrical and electronic equipment

As global demand for consumer goods continues to rise, the problem of waste electrical and electronic equipment (or e-waste) increases. E-waste is of particular concern to the world’s governments and environmentalists alike, not just because of the sheer quantity that is being produced annually, but also because e-waste often contains both hazardous materials and scarce or valuable materials. Much research is now focused upon how this waste can be treated safely, economically, and in an environmentally sound manner. This paper presents the findings from a literature review and case study research conducted as a small part of the Globally Recoverable and Eco-friendly E-equipment Network with Distributed Information Service Management (GREENet) project. The GREENet project aims to share knowledge and expertise in e-waste treatment across Europe (in this case, the UK) and China. The focus of this particular study was upon ‘design for remanufacture’ and e-waste in China: as a remanufacturing industry begins to emerge, are Chinese original equipment manufacturers (OEMs) prepared to design more remanufacturable products and could electrical and electronic products become a part of this industry? Findings presented in this paper suggest that design for remanufacture could become more relevant to Chinese OEMs in the near future, as environmental legislation becomes increasingly stringent and a government remanufacturing pilot scheme expands. However, findings from case studies of Chinese e-waste recyclers would suggest that electrical and electronic products are not presently highly suited to the remanufacturing process.

The Speed of Sound in Silk: Linking Material Performance to Biological Function

Sonic properties of spider silks are measured independent of the web using laser vibrometry and ballistic impact providing insights into Natures design of functionalized high-performance materials. Through comparison to cocoon silk and other industrial fibers, we find that major ampullate silk has the largest wavespeed range of any known material.

So small, so loud: extremely high sound pressure level from a pygmy aquatic insect (corixidae, micronectinae)

To communicate at long range, animals have to produce intense but intelligible signals. This task might be difficult to achieve due to mechanical constraints, in particular relating to body size. Whilst the acoustic behaviour of large marine and terrestrial animals has been thoroughly studied, very little is known about the sound produced by small arthropods living in freshwater habitats. Here we analyse for the first time the calling song produced by the male of a small insect, the water boatman Micronecta scholtzi. The song is made of three distinct parts differing in their temporal and amplitude parameters, but not in their frequency content. Sound is produced at 78.9 (63.6-82.2) SPL rms re 2.10(-5) Pa with a peak at 99.2 (85.7-104.6) SPL re 2.10(-5) Pa estimated at a distance of one metre. This energy output is significant considering the small size of the insect. When scaled to body length and compared to 227 other acoustic species, the acoustic energy produced by M. scholtzi appears as an extreme value, outperforming marine and terrestrial mammal vocalisations. Such an extreme display may be interpreted as an exaggerated secondary sexual trait resulting from a runaway sexual selection without predation pressure.

Extremely high frequency sensitivity in a 'simple' ear

An evolutionary war is being played out between the bat, which uses ultrasonic calls to locate insect prey, and the moth, which uses microscale ears to listen for the approaching bat. While the highest known frequency of bat echolocation calls is 212 kHz, the upper limit of moth hearing is considered much lower. Here, we show that the greater wax moth, Galleria mellonella, is capable of hearing ultrasonic frequencies approaching 300 kHz; the highest frequency sensitivity of any animal. With auditory frequency sensitivity that is unprecedented in the animal kingdom, the greater wax moth is ready and armed for any echolocation call adaptations made by the bat in the on-going bat–moth evolutionary war.

Shrinking wings for ultrasonic pitch production: hyperintense ultra-short-wavelength calls in a new genus of neotropical katydids (Orthoptera: Tettigoniidae)

This article reports the discovery of a new genus and three species of predaceous katydid (Insecta: Orthoptera) from Colombia and Ecuador in which males produce the highest frequency ultrasonic calling songs so far recorded from an arthropod. Male katydids sing by rubbing their wings together to attract distant females. Their song frequencies usually range from audio (5 kHz) to low ultrasonic (30 kHz). However, males of Supersonus spp. call females at 115 kHz, 125 kHz, and 150 kHz. Exceeding the human hearing range (50 Hz–20 kHz) by an order of magnitude, these insects also emit their ultrasound at unusually elevated sound pressure levels (SPL). In all three species these calls exceed 110 dB SPL rms re 20 µPa (at 15 cm). Males of Supersonus spp. have unusually reduced forewings (<0.5 mm2). Only the right wing radiates appreciable sound, the left bears the file and does not show a particular resonance. In contrast to most katydids, males of Supersonus spp. position and move their wings during sound production so that the concave aspect of the right wing, underlain by the insect dorsum, forms a contained cavity with sharp resonance. The observed high SPL at extreme carrier frequencies can be explained by wing anatomy, a resonant cavity with a membrane, and cuticle deformation.