Joseph C. Jackson

Nonlinear auditory mechanism enhances female sounds for male mosquitoes

Sound plays an important role in the life history of mosquitoes. Male mosquitoes detect females by the sound generated by their wingbeat. Because female wings are weak acoustic radiators, males have been driven by sexual selection to evolve sensitive acoustic sensors. Mosquito antennae are very sensitive acoustic receivers, featuring up to 16,000 sensory cells, a number comparable with that contained in the human cochlea. The antennal sound receiver exhibits frequency selectivity, input amplification, and self-generated oscillations, features that parallel the functional sophistication of the cochlear amplifier. Although arguably the male antenna is well suited to receiving weak female sounds, the role of active mechanisms in mosquito hearing is far from understood. Previous mechanical studies on mosquito hearing largely focused on the steady-state antennal response to harmonic sounds, mostly evaluating the data through conventional Fourier transforms. Here, we report on the time-resolved mechanical behavior of the male antenna in response to female sounds. Crucially, stimuli were designed to reflect the temporal acoustic profile of a female flying by. With these stimuli, several previously unreported nonlinear features were unveiled, involving amplification, compression, and hysteresis. The time-resolved analysis reveals that, through the active participation of the sensory neurons, the antenna mechanically responds to enlarge its own range of detection. This behavior augments the capacity of the antennal receiver to detect female sounds, enhancing the males chance to successfully pursue a passing female.

Holographic assembly workstation for optical manipulation

We report a holographic assembler workstation for optical trapping and micro-manipulation. The workstation is based on a titanium sapphire laser, making it particularly suited for biomaterials and incorporates a choice of user interfaces for different applications. The system is designed around a commercial inverted microscope and is configured such that it can be easily used by the non-specialist. We demonstrate the bio-capabilities of our system by manipulating a group of yeast cells, a single red blood cell and a single cell of the green algae colony Volvox.

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.

Time-of-flight measurement techniques for airborne ultrasonic ranging

Airborne ultrasonic ranging is used in a variety of different engineering applications for which other positional metrology techniques cannot be used, for example in closed-cell locations, when optical line of sight is limited, and when multipath effects preclude electromagnetic-based wireless systems. Although subject to fundamental physical limitations, e.g., because of the temperature dependence of acoustic velocity in air, these acoustic techniques often provide a cost-effective solution for applications in mobile robotics, structural inspection, and biomedical imaging. In this article, the different techniques and limitations of a range of airborne ultrasonic ranging approaches are reviewed, with an emphasis on the accuracy and repeatability of the measurements. Simple time-domain approaches are compared with their frequency-domain equivalents, and the use of hybrid models and biologically inspired approaches are discussed.

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.

Mathematical modelling of the active hearing process in mosquitoes

Insects have evolved diverse and delicate morphological structures in order to capture the inherently low energy of a propagating sound wave. In mosquitoes, the capture of acoustic energy and its transduction into neuronal signals are assisted by the active mechanical participation of the scolopidia. We propose a simple microscopic mechanistic model of the active amplification in the mosquito species Toxorhynchites brevipalpis. The model is based on the description of the antenna as a forced-damped oscillator coupled to a set of active threads (ensembles of scolopidia) that provide an impulsive force when they twitch. This twitching is in turn controlled by channels that are opened and closed if the antennal oscillation reaches a critical amplitude. The model matches both qualitatively and quantitatively with recent experiments: spontaneous oscillations, nonlinear amplification, hysteresis, 2 : 1 resonances, frequency response and gain loss owing to hypoxia. The numerical simulations presented here also generate new hypotheses. In particular, the model seems to indicate that scolopidia located towards the tip of Johnstons organ are responsible for the entrainment of the other scolopidia and that they give the largest contribution to the mechanical amplification.

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.

No evidence for DPOAEs in the mechanical motion of the locust tympanum

SUMMARY Distortion-product otoacoustic emissions (DPOAEs) are present in non-linear hearing organs, and for low-intensity sounds are a by-product of active processes. In vertebrate ears they are considered to be due to hair cell amplification of sound in the cochlea; however, certain animals lacking a cochlea and hair cells are also reported to be capable of DPOAEs. In the Insecta, DPOAEs have been recorded from the locust auditory organ. However, the site of generation of these DPOAEs and the physiological mechanisms causing their presence in the locust ear are not yet understood, despite there being a number of potential places in the tympanal organ that could be capable of generating DPOAEs. This study aimed to record locust tympanal membrane vibration using a laser Doppler vibrometer in order to identify a distinct place of DPOAE generation on the membrane. Two species of locust were investigated over a range of frequencies and levels of acoustic stimulus, mirroring earlier acoustic recording studies; however, the current experiments were carried out in an open acoustic system. The laser measurements did not find any evidence of mechanical motion on the tympanal membrane related to the expected DPOAE frequencies. The results of the current study therefore could not confirm the presence of DPOAEs in the locust ear through the mechanics of the tympanal membrane. Experiments were also carried out to test how membrane behaviour altered when the animals were in a state of hypoxia, as this was previously found to decrease DPOAE magnitude, suggesting a metabolic sensitivity. However, hypoxia did not have any significant effect on the membrane mechanics. The location of the mechanical generation of DPOAEs in the locusts ear, and therefore the basis for the related physiological mechanisms, thus remains unknown.

Features in geometric receiver shapes modelling bat-like directivity patterns

The directional properties of bat ears as receivers is a current area of interest in ultrasound research. This paper presents a new approach to analyse the relationship between morphological features and acoustical properties of the external ear of bat species. The beam pattern of Rousettus leschenaultiis right ear is measured and compared to that of receiver structures whose design is inspired by the bat ear itself and made of appropriate geometric shapes. The regular shape of these receivers makes it possible to control the key reception parameters and thus to understand the effect on the associated beam pattern of the parameters themselves. Measurements show one receiver structure has a beam pattern very similar to that of R. leschenaultiis ear, thus explaining the function of individual parts constituting its ear. As it is applicable to all bat species, this approach can provide a useful tool to investigate acoustics in bats, and possibly other mammals.