Thesis
A revised biomechanical model of frequency filtering and transmission in the field cricket (Gryllinae) ear and host–parasitoid interactions
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2026
- Thesis identifier
- T18059
- Person Identifier (Local)
- 202083622
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- The field cricket (subfamily Gryllinae) auditory pathway is characterised by its unique peripheral anatomy and well-characterised neurophysiological and behavioural organisation, establishing it as an important model in behavioural neuroscience, particularly neuroethology. Males produce a highly pure-toned calling song centred around 5 kHz, which females use for phonotactic localisation with exceptional directional sensitivity, resolving sound source position to within 1° of the frontal axis comparable to human hearing. This acuity arises from a distinct configuration of three sound inputs per ear: one external and two internal via the acoustic trachea. Gryllinae anatomy is further distinguished by asymmetric peripheral structures, comprising a large, thin posterior tympanal membrane (PTM), a smaller, thicker anterior tympanal membrane (ATM), and a cavity-like anterior tracheal branch (ATB) decoupled from the ATM. Auditory neurons are arranged tonotopically along the dorsal membrane of the ATB, enabling discrimination between calling and courtship song frequencies. While the neurophysiological and behavioural stages are well understood, the initial biomechanical stage remains unresolved. Two key questions persist: the mechanism underlying sharp frequency tuning and how PTM vibrations are transmitted to the auditory sensilla. Although the PTM is established as the primary acoustic input and has been extensively studied using laser Doppler vibrometry (LDV), reported frequency responses are inconsistent and often insufficient to explain sharp neuronal tuning near the calling song frequency. This has led to the longstanding hypothesis of an additional mechanical filter between the tympanum and sensilla. Competing explanations for transmission include mechanical coupling to internal tracheal structures, as well as airflow- and sound pressure–based mechanisms within the air-filled tracheal branches. Consequently, both filtering and transmission remain incompletely understood. To address these problems, this research employs an integrated experimental and computational approach combining three complementary techniques not previously applied to this system. Scanning LDV maps PTM vibration amplitude across the membrane and captures phase information beyond conventional single-point measurements. X-ray micro-computed tomography (micro-CT) provides non-invasive three-dimensional reconstructions of internal auditory structures, enabling 3D morphometric analysis and surpassing traditional 2D sectioning techniques. Finite element analysis (FEA), informed by micro-CT data, simulates the mechanical behaviour of internal components under acoustic stimulation. The results establish a revised biomechanical model of the Gryllinae peripheral auditory system. In contrast to recent single-point LDV studies, the PTM exhibits two vibrational optima at 6 kHz and 14 kHz. Phase analysis indicates that the higher frequency peak corresponds to the intrinsic resonance of the membrane, whereas the lower-frequency peak reflects a driven response arising from coupling with a second resonator, supporting the second filter hypothesis. X-ray micro-CT and FEA identify the dorsal membrane of the posterior tracheal branch (DM-PTB) as the probable 6 kHz resonator. In addition, a previously overlooked structure, termed here the dividing membrane (DivM), is identified; it possesses its own resonant frequency and amplifies vibrational energy. Simulations further suggest frequency-dependent, membrane driven ATB deformation. Together, both frequency filtering and sound transmission arise from a chain of mechanically coupled, successively tuned membranes extending from the PTM through the DM-PTB and DivM to the ATB supporting the auditory neurons. This framework reconciles discrepancies between tympanal and neuronal tuning and clarifies the mechanisms underlying filtering and transmission in the peripheral auditory pathway, emphasising that the PTM should not be considered in isolation but as part of a coupled system. It also indicates relevance to bioinspired applications, particularly in microelectromechanical systems (MEMS) diaphragm microphones used in smartphones and hearing aids. This relevance is underscored by the ear of the parasitoid fly Ormia ochracea, which is likewise tuned to the Gryllinae calling song and has already inspired multiple MEMS microphone patents. In addition to this biomechanical study, this research examines host–parasitoid interactions between field crickets and O. ochracea. By manipulating larval load and recording host cricket sex and size, this work shows that in-host resource competition determines developmental outcomes, influencing both fly offspring number and individual fitness. A protocol for maintaining laboratory colonies of O. ochracea is presented, recommending a one-larva regime and validating the commercially available field cricket Acheta domesticus, although not a natural host, as a viable model host.
- Advisor / supervisor
- Windmill, James
- Reid, Andrew
- Jackson, Joseph
- Resource Type
- DOI
- Date Created
- 2025
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