Mechanisms of high-frequency song generation in brachypterous crickets and the role of ghost frequencies

Sound production in crickets relies on stridulation, the well-understood rubbing together of a pair of specialised wings. As the file of one wing slides over the scraper of the other, a series of rhythmic impacts cause harmonic oscillations, usually resulting in the radiation of pure tones delivered at low frequencies (2-8 kHz). In the short winged crickets of the Lebinthini tribe, acoustic communication relies on signals with remarkably high frequencies (> 8 kHz) and rich harmonic content. Using several species of the subfamily Eneopterinae, we characterise the morphological and mechanical specialisations supporting the production of high frequencies, and demonstrate that higher harmonics are exploited as dominant frequencies. These specialisations affect the structure of the stridulatory file, the motor control of stridulation and the resonance of the sound radiator. We place these specialisations in a phylogenetic framework and show that they serve to exploit high frequency vibrational modes pre-existing in the phylogenetic ancestor. In Eneopterinae, the lower frequency components are harmonically related to the dominant peak, suggesting they are relicts of ancestral carrier frequencies. Yet, such ghost frequencies still occur in the wings' free resonances, highlighting the fundamental mechanical constraints of sound radiation. These results support the hypothesis that such high frequency songs evolved stepwise, by a form of punctuated evolution which could be related to functional constraints, rather than by the progressive increase of the ancestral fundamental frequency

Distribution of sound pressure around a singing cricket: radiation pattern and asymmetry in the sound field

Male field crickets generate calls to attract distant females through tegminal stridulation: the rubbing together of the overlying right wing which bears a file of cuticular teeth against the underlying left wing which carries a sclerotised scraper. During stridulation, specialised areas of membrane on both wings are set into oscillating vibrations to produce acoustic radiation. The location of females is unknown to the calling males and thus increasing effective signal range in all directions will maximise transmission effectiveness. However, producing an omnidirectional sound field of high sound pressure levels may be problematic due to the mechanical asymmetry found in this sound generation system. Mechanical asymmetry occurs by the right wing coming to partially cover the left wing during the closing stroke phase of stridulation. As such, it is hypothesised that the sound field on the left-wing side of the animal will contain lower sound pressure components than on the right-wing side as a result of this coverage. This hypothesis was tested using a novel method to accurately record a high resolution, three dimensional mapping of sound pressure levels around restrained Gryllus bimaculatus field crickets singing under pharmacological stimulation. The results indicate that a bilateral asymmetry is present across individuals, with greater amplitude components present in the right wing side of the animal. Individual variation in sound pressure to either the right or left-wing side is also observed. However, statistically significant differences in bilateral sound field asymmetry as presented here may not affect signalling in the field

Functional morphology of tegmina-based stridulation in the relict species Cyphoderris monstrosa (Orthoptera: Ensifera: Prophalangopsidae)

Male grigs, bush-crickets and field crickets produce mating calls by tegminal stridulation: the scraping together of modified forewings functioning as sound generators. Bush- (Tettigoniidae) and field-crickets (Gryllinae) diverged some 240 million years ago, with each lineage developing unique characteristics in wing morphology and the associated mechanics of stridulation. The grigs (Prophalangopsidae), a relict lineage more closely related to bush crickets than to field-crickets, are believed to retain plesiomorphic features of wing morphology. The wing cells widely involved in sound production, such as the harp and mirror, are comparatively small, poorly delimited and/or partially filled with cross-veins. Such morphology is similarly observed in the earliest stridulating ensiferans, for which stridulatory mechanics remains poorly understood. The grigs, therefore, are of major importance to investigate the early evolutionary stages of tegminal stridulation, a critical innovation in the evolution of the Orthoptera. The aim of this study is to appreciate the degree of specialisation on grig forewings, through identification of sound radiating area areas and their properties. For well-grounded comparisons, homologies in wing venation (and associated areas) of grigs and bush-crickets are re-evaluated. Then, using direct evidence, this study confirms the mirror cell, in association with two other areas (termed ‘neck’ and ‘pre-mirror’), as the acoustic resonator in the grig Cyphoderris monstrosa. Despite the use of largely symmetrical resonators, as found in field-crickets, analogous features of stridulatory mechanics are observed between C. monstrosa and bush-crickets. Both morphology and function in grigs represents transitional stages between unspecialised forewings and derived conditions observed in modern species

The effects of temperature and body mass on jump performance of the locust Locusta migratoria

Locusts jump by rapidly releasing energy from cuticular springs built into the hind femur that deform when the femur muscle contracts. This study is the first to examine the effect of temperature on jump energy at each life stage of any orthopteran. Ballistics and high-speed cinematography were used to quantify the energy, distance, and take-off angle of the jump at 15, 25, and 35°C in the locust Locusta migratoria. Allometric analysis across the five juvenile stages at 35°C reveals that jump distance (D; m) scales with body mass (M; g) according to the power equation D = 0.35M0.17±0.08 (95% CI), jump take-off angle (A; degrees) scales as A = 52.5M0.00±0.06, and jump energy (E; mJ per jump) scales as E = 1.91M1.14±0.09. Temperature has no significant effect on the exponent of these relationships, and only a modest effect on the elevation, with an overall Q10 of 1.08 for jump distance and 1.09 for jump energy. On average, adults jump 87% farther and with 74% more energy than predicted based on juvenile scaling data. The positive allometric scaling of jump distance and jump energy across the juvenile life stages is likely facilitated by the concomitant relative increase in the total length (Lf+t; mm) of the femur and tibia of the hind leg, Lf+t = 34.9M0.37±0.02. The weak temperature-dependence of jump performance can be traced to the maximum tension of the hind femur muscle and the energy storage capacity of the femur's cuticular springs. The disproportionately greater jump energy and jump distance of adults is associated with relatively longer (12%) legs and a relatively larger (11%) femur muscle cross-sectional area, which could allow more strain loading into the femur's cuticular springs. Augmented jump performance in volant adult locusts achieves the take-off velocity required to initiate flight.Edward P. Snelling, Christie L. Becker, Roger S. Seymou

Fermion Condensation Quantum Phase Transition versus Conventional Quantum Phase Transitions

The main features of fermion condensation quantum phase transition (FCQPT), which are distinctive in several aspects from that of conventional quantum phase transition (CQPT), are considered. We show that in contrast to CQPT, whose physics in quantum critical region is dominated by thermal and quantum fluctuations and characterized by the absence of quasiparticles, the physics of a Fermi system near FCQPT or undergone FCQPT is controlled by the system of quasiparticles resembling the Landau quasiparticles. Contrary to the Landau quasiparticles, the effective mass of these quasiparticles strongly depends on the temperature, magnetic fields, density, etc. This system of quasiparticles having general properties determines the universal behavior of the Fermi system in question. As a result, the universal behavior persists up to relatively high temperatures comparatively to the case when such a behavior is determined by CQPT. We analyze striking recent measurements of specific heat, charge and heat transport used to study the nature of magnetic field-induced QCP in heavy-fermion metal CeCoIn$_5$ and show that the observed facts are in good agreement with our scenario based on FCQPT and certainly seem to rule out the critical fluctuations related with CQPT. Our general consideration suggests that FCQPT and the emergence of novel quasiparticles near and behind FCQPT and resembling the Landau quasiparticles are distinctive features intrinsic to strongly correlated substances.Comment: 10 pages, Revtex, new references and facts are adde

Digging the optimum pit: Antlions, spirals and spontaneous stratification

Most animal traps are constructed from self-secreted silk, so antlions are rare among trap builders because they use only materials found in the environment. We show how antlions exploit the properties of the substrate to produce very effective structures in the minimum amount of time. Our modelling demonstrates how antlions: (i) exploit self-stratification in granular media differentially to expose deleterious large grains at the bottom of the construction trench where they can be ejected preferentially, and (ii) minimize completion time by spiral rather than central digging. Both phenomena are confirmed by our experiments. Spiral digging saves time because it enables the antlion to eject material initially from the periphery of the pit where it is less likely to topple back into the centre. As a result, antlions can produce their pits—lined almost exclusively with small slippery grains to maximize powerful avalanches and hence prey capture—much more quickly than if they simply dig at the pit’s centre. Our demonstration, for the first time to our knowledge, of an animal using self-stratification in granular media exemplifies the sophistication of extended phenotypes even if they are only formed from material found in the animal’s environment

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

How male sound pressure level influences phonotaxis in virgin female Jamaican field crickets (Gryllus assimilis)

Understanding female mate preference is important for determining the strength and direction of sexual trait evolution. The sound pressure level (SPL) acoustic signalers use is often an important predictor of mating success because higher sound pressure levels are detectable at greater distances. If females are more attracted to signals produced at higher sound pressure levels, then the potential fitness impacts of signalling at higher sound pressure levels should be elevated beyond what would be expected from detection distance alone. Here we manipulated the sound pressure level of cricket mate attraction signals to determine how female phonotaxis was influenced. We examined female phonotaxis using two common experimental methods: spherical treadmills and open arenas. Both methods showed similar results, with females exhibiting greatest phonotaxis towards loud sound pressure levels relative to the standard signal (69 vs. 60 dB SPL) but showing reduced phonotaxis towards very loud sound pressure level signals relative to the standard (77 vs. 60 dB SPL). Reduced female phonotaxis towards supernormal stimuli may signify an acoustic startle response, an absence of other required sensory cues, or perceived increases in predation risk