The biophysics and biochemistry of a cochlea-like organ in the ear of Neotropical bush-crickets (Insecta: Tettigonidae)

There has been an increasing interest in the study of complex auditory processes in the mammalian cochlea (e.g. frequency resolution, frequency discrimination and active amplification). These processes depend on the propagation of frequency information in the form of travelling waves (of the type exemplified in a tsunami) along the tonotopically arranged auditory sensilla. The physiological and biophysical bases of traveling waves in the mammalian cochlea remain elusive, yet vital to understanding tonotopy (the mapping of sound frequency across space) and active amplification. In vertebrates, both location and osseous protective material make the inner ear difficult to access without altering its integrity. While conventional methods for hearing research in vertebrates have improved notably in recent years, these still require surgical procedures to gain physical access to the inner ear, compromising the natural conditions of the hearing system. Indeed, measurement of auditory activity in-vivo has only been done through small surgical openings or other isolated places. Remarkably, complex auditory processes are not unique to vertebrates, and similar mechanisms for sound filtering, amplification, and frequency analysis have also been found in the ears of insects. Hearing organs in insects are unusually small, highly sensitive, and easily accessible by means of non-destructive methods. Among insects, bushcrickets (Insecta: Orthoptera) have a unique hearing system which consists of minute tympanal ears located in the forelegs, and inner ears with tonotopically organised auditory sensilla within a fluid-filled cavity. Unlike in vertebrates, the bush-cricket inner ear is not coiled, but stretched. Critically, the assessment of auditory processes in this small-scale ear is proposed to be possible in a non- vi invasive manner. The purpose of this thesis was to further the knowledge of acoustic perception in bush-crickets by providing new data on the travelling wave phenomenon, the suitability of bush-crickets for non-invasive experimentation, and the elemental composition of the liquid contained in the bush-cricket inner ear. It was demonstrated that transparency is the cuticle property that allows the observation and measurement of travelling waves and tonotopy in bush-crickets through the use of light measurement techniques, specifically laser Doppler vibrometry. This approach provides a non-invasive alternative for measuring the natural motion of the sensillia-bearing surface embedded in the intact inner ear’s fluid. Subsequently, this experimental technique was used to generate novel data on inner ear mechanics from a number of bush-cricket species. Finally, in the form of a chemical analysis, I established that the inner ear’s liquid differs from the hemolymph based on the variation of their ion concentration values. From a biomechanical perspective, the presence of a liquid-filled cavity along with a species-specific ion concentration, likely contributes to an optimal functioning of the hearing organ just as it occurs in vertebrates. These results highlight the importance of considering analogous models of vertebrate hearing systems for advanced studies of auditory function. Such models can be used to effectively observe, collect, and measure auditory data otherwise impossible to attain noninvasively in vertebrates, and specifically mammalian species

Psocoptera (Insecta: Psocodea) from the National Natural Park Gorgona, Cauca, Colombia

The Psocoptera fauna of Gorgona National Natural Park, Colombian pacific, consists of 75 species in 42 genera and 21 families. 1 730 specimens were collected in the period November 2007-June 2011. Five families, 20 genera and nine species are new records for Colombia, and two genera and ten species are new to science. The psocid fauna of the island constitutes an extension of the continental fauna

Three new species of Loneura (Psocodea:’Psocoptera’:Ptiloneuridae) from Gorgona Island, Cauca, Colombia, with a new infrageneric classification

Three related species of Loneura Navás, from Gorgona Island (Cauca, Colombia), are here described and illustrated. The types are deposited in the Entomological Museum of the Universidad del Valle (MUSENUV). A set of infrageneric groups within Loneura is proposed based on the structure of the male hypandrium and phallosome. The species of the genus are assigned to the groups recognized in this classification

Lack of correlation between vertical distribution and carrier frequency, and preference for open spaces in arboreal katydids that use extreme ultrasound, in Gorgona, Colombia (Orthoptera: Tettigoniidae)

Male Tettigoniidae emit sound to attract conspecific females. The sound is produced by stridulation. During stridulation the forewings open and close, but it is during the closing stroke that the scraper contacts the file teeth to generate the predominant sound components, which are amplified by adjacent wing cells specialized in sound radiation. The sounds usually exceed the sonic boundary and might occur above 40 kHz, reaching extreme ultrasonic frequencies of 150kHz in some species. Here we test the hypothesis that Tettigoniidae species should prefer microhabitats that favour efficient signal transmission, i.e. that there is a relationship of sound frequency with the vertical distribution of the species (from ground to canopy) at Gorgona National Natural Park, Colombia. We sampled 16 trees and four different altitudinal levels between 1 and 20m above the understory vegetation. We placed collecting blankets separated by vertical distances of 5m, and knocked insects down using the technique known as fogging. We found no correlation between vertical distribution and carrier frequency, but there was a preference for open spaces (below the canopy and above the understory) in species using extreme ultrasound. This is the first quantitative description of the vertical distribution in neotropical species of the family Tettigoniidae and its relationship to the calling song frequency

Wing resonances in a new dead-leaf-mimic katydid (Tettigoniidae: Pterochrozinae) from the Andean cloud forests

Day-camouflaged leaf-mimic katydids Typophyllum spp. have a remarkable way of evading predators as male and female forewings appear as bite-damaged leaves complete with necrotic spots. As in all other katydids, males produce sound signals to attract females by rubbing their forewings together. The biophysical properties of these special leaf-like forewings remain obscure. Here we study the wing mechanics and resonances of Typophyllum spurioculis, a new species of leaf-mimic katydid with a broad distribution in the Andes from Western Ecuador to the middle Central Cordillera in Colombia. This species performs an unusual laterally directed aposematic display, showing orange spots that simulate eyes at the leg base. At night, males are conspicuous by their loud, audible calling songs, which exhibit two spectral peaks at ca. 7 and 12 kHz. Using micro-scanning laser Doppler vibrometry we find the effective sound radiators of the wings (speculae) vibrate with three modes of vibration, two of which include the frequencies observed in the calling song. Remarkably, this resonance is preserved in the parts of the wings mimicking necrotic leaves, which are in theory not specialised for sound production. The eyespot function is discussed

Chamber music: an unusual Helmholtz resonator for song amplification in a Neotropical bush-cricket (Orthoptera, Tettigoniidae)

Animals use sound for communication, with high-amplitude signals being selected for attracting mates or deterring rivals. High amplitudes are attained by employing primary resonators in sound producing structures to amplify the signal (e.g., avian syrinx). Some species actively exploit acoustic properties of natural structures to enhance signal transmission by using these as secondary resonators (e.g., tree-hole frogs). Male bush-crickets produce sound by tegminal stridulation and often use specialised wing areas as primary resonators. Interestingly, Acanthacara acuta, a Neotropical bush-cricket, exhibits an unusual pronotal inflation, forming a chamber covering the wings. It has been suggested that such pronotal chambers enhance amplitude and tuning of the signal by constituting a (secondary) Helmholtz resonator. If true, the intact system – when stimulated sympathetically with broadband sound – should show clear resonance around the song carrier frequency which should be largely independent of pronotum material, and change when the system is destroyed. Using laser Doppler vibrometry on living and preserved specimens, micro computed tomography, 3D printed models, and finite element modelling, we show that the pronotal chamber not only functions as a Helmholtz resonator due to its intact morphology but also resonates at frequencies of the calling song on itself, making song production a three-resonator system

Wing mechanics, vibrational and acoustic communication in a new bush-cricket species of the genus Copiphora (Orthoptera: Tettigoniidae) from Colombia

Male bush-crickets produce acoustic signals by wing stridulation to call females. Several species also alternate vibratory signals with acoustic calls for intraspecific communication, a way to reduce risk of detection by eavesdropping predators. Both modes of communication have been documented mostly in neotropical species, for example in the genus Copiphora. In this article, we studied vibratory and acoustic signals and the biophysics of wing resonance in C. vigorosa, a new species from the rainforest of Colombia. Different from other Copiphora species in which the acoustic signals have been properly documented as pure tones, C. vigorosa males produce a complex modulated broadband call peaking at ca. 30 kHz. Such a broadband spectrum results from several wing resonances activated simultaneously during stridulation. Since males of this species do rarely sing, we also report that substratum vibrations have been adopted in this species as a persistent communication channel. Wing resonances and substratum vibrations were measured using a μ-scanning Laser Doppler Vibrometry. We found that the stridulatory areas of both wings exhibit a relatively broad-frequency response and the combined vibration outputs fits with the calling song spectrum breadth. Under laboratory conditions the calling song duty cycle is very low and males spend more time tremulating than singing

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

Caracterización fisicoquímica de la zona de transición acuático terrestre de un humedal tropical (Ayapel-Colombia)

Contextualization: The aquatic-terrestrial transition zone (ZTAT) in the floodplain (alluvial plain) Ramsar Ayapel (Colombia) remains flooded for more than half of the year, and its coastal strip generates a strong influence on the ecosystem. An approach to the spatial and temporal characterization of this zone is crucial for further functional analysis, especially when tropical floodplains are little explored except for some Amazonian ecosystems.  Knowledge gap: Floodplain dynamics are mainly regulated by flood pulses, directly influencing he physical and chemical conditions of water and sediment. Therefore, the biota is adapted to the flooding and waterlogging conditions of the ecosystem. However, research has addressed the terrestrial and aquatic phases as separate systems, making it necessary to resort to methodologies that demonstrate connectivity in the system and facilitate the interpretation of key factors in the ecological functioning of tropical wetlands.  Purpose: The research analyzed the structure and functioning of the ZTAT through physical and chemical variables at different times of the flood pulse.  Methodology: In two wetlands of the muddy complex, sensitive to the flood pulse, three samplings were carried out: rising water (July/2021), high water (September/2021), and declining water (March/2022). The ZTAT was monitored by delimiting it into four subzones: water, sediments, floodable soil, and soil. Results and conclusions: Significant changes in time associated with water level and nitrogen concentrations were revealed; while in space, assisted by the contrast of the ZTAT at the two sites, differences were reflected through in situ variables and soil characteristics. It was detected that depth, transparency, and a higher concentration of nitrogen forms, and some ions such as aluminum and magnesium generated differences on a time level. On the contrary, conductivity, calcium concentration, and variables associated with soil characteristics expressed it at the spatial level due to exploring the ZTAT. Therefore, the physicochemical dynamics of moments and sites in a wetland require a sampling design that, using the ZTAT, facilitates the scale of physicochemical analysis.Contextualización: la zona de transición acuático terrestre (ZTAT) en la planicie de inundación (llanura aluvial) Ramsar Ayapel (Colombia), permanece inundada más de la mitad de un año y su franja litoral genera una fuerte influencia en el ecosistema. Una aproximación a la caracterización espacial y temporal de esta zona es fundamental para un posterior análisis funcional, especialmente cuando, a excepción de algunos ecosistemas amazónicos, las planicies de inundación tropical son poco exploradas.  Vacío de conocimiento: la dinámica de las planicies de inundación está regulada principalmente por los pulsos de inundación, que influyen directamente en las condiciones físicas y químicas del agua y el sedimento; por lo anterior, la biota presenta adaptaciones a las condiciones de inundación y anegamiento del ecosistema. Sin embargo, las investigaciones han abordado la fase terrestre y acuática como sistemas separados, haciéndose necesario acudir a metodologías que evidencien la conectividad en el sistema y faciliten la interpretación de factores clave en el funcionamiento ecológico en los humedales tropicales.  Propósito: la investigación analizó la estructura y el funcionamiento de la ZTAT a través de variables físicas y químicas en diferentes momentos del pulso de inundación.  Metodología: en dos humedales del complejo cenagoso, sensibles al pulso de inundación, se realizaron tres muestreos: aguas en ascenso (julio de 2021); aguas altas (septiembre de 2021); y aguas en descenso (marzo de 2022). Se monitoreó la ZTAT delimitándola en cuatro subzonas: agua, sedimentos, suelo inundable y suelo.  Resultados y conclusiones: se revelaron cambios significativos en el tiempo asociados al nivel del agua y a las concentraciones de nitrógeno; mientras en el espacio, asistido por el contraste de la ZTAT en los dos sitios, se reflejaron diferenciaciones a través de las variables in situ y las características del suelo. Se detectó que la profundidad, transparencia y una mayor concentración de formas de nitrógeno y algunos iones como aluminio y magnesio generaron diferencias a nivel temporal; mientras la conductividad, concentración del calcio y variables asociadas a las características del suelo lo expresaron a nivel espacial gracias a la exploración de la ZTAT; por tanto, la dinámica fisicoquímica de momentos y sitios en un humedal requiere un diseño de muestreo que por medio de la ZTAT facilita la escala de análisis fisicoquímico