Drosophila TRPN( = NOMPC) Channel Localizes to the Distal End of Mechanosensory Cilia

BACKGROUND: A TRPN channel protein is essential for sensory transduction in insect mechanosensory neurons and in vertebrate hair cells. The Drosophila TRPN homolog, NOMPC, is required to generate mechanoreceptor potentials and currents in tactile bristles. NOMPC is also required, together with a TRPV channel, for transduction by chordotonal neurons of the fly's antennal ear, but the TRPN or TRPV channels have distinct roles in transduction and in regulating active antennal mechanics. The evidence suggests that NOMPC is a primary mechanotransducer channel, but its subcellular location-key for understanding its exact role in transduction-has not yet been established. METHODOLOGY/PRINCIPAL FINDINGS: Here, by immunostaining, we locate NOMPC at the tips of mechanosensory cilia in both external and chordotonal sensory neurons, as predicted for a mechanotransducer channel. In chordotonal neurons, the TRPN and TRPV channels are respectively segregated into distal and proximal ciliary zones. This zonal separation is demarcated by and requires the ciliary dilation, an intraciliary assembly of intraflagellar transport (IFT) proteins. CONCLUSIONS: Our results provide a strong evidence for NOMPC as a primary transduction channel in Drosophila mechansensory organs. The data also reveals a structural basis for the model of auditory chordotonal transduction in which the TRPN and TRPV channels play sequential roles in generating and amplifying the receptor potential, but have opposing roles in regulating active ciliary motility

Tonotopically Arranged Traveling Waves in the Miniature Hearing Organ of Bushcrickets

Place based frequency discrimination (tonotopy) is a fundamental property of the coiled mammalian cochlea. Sound vibrations mechanically conducted to the hearing organ manifest themselves into slow moving waves that travel along the length of the organ, also referred to as traveling waves. These traveling waves form the basis of the tonotopic frequency representation in the inner ear of mammals. However, so far, due to the secure housing of the inner ear, these waves only could be measured partially over small accessible regions of the inner ear in a living animal. Here, we demonstrate the existence of tonotopically ordered traveling waves covering most of the length of a miniature hearing organ in the leg of bushcrickets in vivo using laser Doppler vibrometery. The organ is only 1 mm long and its geometry allowed us to investigate almost the entire length with a wide range of stimuli (6 to 60 kHz). The tonotopic location of the traveling wave peak was exponentially related to stimulus frequency. The traveling wave propagated along the hearing organ from the distal (high frequency) to the proximal (low frequency) part of the leg, which is opposite to the propagation direction of incoming sound waves. In addition, we observed a non-linear compression of the velocity response to varying sound pressure levels. The waves are based on the delicate micromechanics of cellular structures different to those of mammals. Hence place based frequency discrimination by traveling waves is a physical phenomenon that presumably evolved in mammals and bushcrickets independently

Deliberation, Unjust Exclusion, and the Rhetorical Turn

Theories of deliberative democracy have faced the charge of leading to the unjust exclusion of voices from public deliberation. The recent rhetorical turn in deliberative theory aims to respond to this charge. I distinguish between two variants of this response: the supplementing approach and the systemic approach. On the supplementing approach, rhetorical modes of political speech may legitimately supplement the deliberative process, for the sake of those excluded from the latter. On the systemic approach, rhetorical modes of political speech are legitimate within public deliberation, just so long as they result in net benefits to the deliberative system. I argue that neither of these two approaches adequately meets the unjust exclusion charge. Whereas the supplementing approach does not go far enough to incorporate rhetorical speech into public deliberation, the systemic approach goes too far by legitimizing forms of rhetoric that risk only exacerbating the problem of unjust exclusion. More constructively, I draw on Aristotle’s conception of rhetoric, as an art (technē) that is a counterpart to dialectic, to argue for a constitutive approach to rhetoric. I show how this approach provides a more expansive notion of deliberation that remains normatively orientated

Hearing in hooktip moths (Drepanidae: Lepidoptera)

This study presents anatomical and physiological evidence for a sense of hearing in hooktip moths (Drepanoidea). Two example species, Drepana arcuata and Watsonalla uncinula, were examined. The abdominal ears of drepanids are structurally unique compared to those of other Lepidoptera and other insects, by having an internal tympanal membrane, and auditory sensilla embedded within the membrane. The tympanum is formed by two thin tracheal walls that stretch across a teardrop-shaped opening between dorsal and ventral air chambers in the first abdominal segment. There are four sensory organs (scolopidia) embedded separately between the tympanal membrane layers: two larger lateral scolopidia within the tympanal area, and two smaller scolopidia at the medial margin of the tympanal frame. Sound is thought to reach the tympanal membrane through two external membranes that connect indirectly to the dorsal chamber. Summary The ear is tuned to ultrasonic frequencies between 30 and 65·kHz, with a best threshold of around 52·dB·SPL at 40·kHz, and no apparent difference between genders. Thus, drepanid hearing resembles that of other moths, indicating that the main function is bat detection. Two sensory cells are excited by sound stimuli. Those two cells differ in threshold by approximately 19·dB. The morphology of the ear suggests that the two larger scolopidia function as auditory sensilla; the two smaller scolopidia, located near the tympanal frame, were not excited by sound. We present a biophysical model to explain the possible functional organization of this unique tympanal ear

What does a butterfly hear? Physiological characterization of auditory afferents in Morpho peleides (Nymphalidae)

Many Nymphalidae butterflies possess ears, but little is known about their hearing. The tympanal membrane of butterflies typically comprises distinct inner and outer regions innervated by auditory nerve branches NII and NIII and their respective sensory organs. Using the Blue Morpho butterfly (Morpho peleides) as a model, we characterized threshold and suprathreshold responses of NII and NIII. Both are broadly tuned to 1–20 kHz with best frequencies at 1–3 kHz, but NIII is significantly more sensitive than NII. The compound action potentials (CAPs) of both branches increase their first peak amplitudes and areas in response to higher sound levels. NII and NIII differed in their suprathreshold CAP responses to sound frequencies, with stronger responses to 1–3 and 4–6 kHz, for NIII and NII respectively; results that are consistent with tympanal membrane mechanics. These results indicate that butterflies are capable of amplitude and frequency discrimination. Both auditory branches responded to playbacks of the flight and calls of predatory birds. We propose that the ears of butterflies, like those of many vertebrate prey such as some rabbits and lizards, function primarily in predator risk assessment

Caterpillar talk: Acoustically mediated territoriality in larval Lepidoptera

We provide evidence for conspecific acoustic communication in caterpillars. Larvae of the common hook-tip moth, Drepana arcuata (Drepanoidea), defend silk nest sites from conspecifics by using ritualized acoustic displays. Sounds are produced by drumming the mandibles and scraping the mandibles and specialized anal “oars” against the leaf surface. Staged interactions between a resident and intruder resulted in escalated acoustic “duels” that were typically resolved within minutes, but sometimes extended for several hours. Resident caterpillars generally won territorial disputes, regardless of whether they had built the nest, but relatively large intruders occasionally displaced residents from their nests. All evidence is consistent with acoustic signaling serving a territorial function. As with many vertebrates, ritualized signaling appears to allow contestants to resolve contests without physical harm. Comparative evidence indicates that larval acoustic signaling may be widespread throughout the Lepidoptera, meriting consideration as a principal mode of communication for this important group of insects