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Cicada tymbals: sound-producing organs and musculature.
  1. Body of male Cicada from below, showing cover-plates of sound-producing organs
  2. From above showing tymbals (drums), natural size
  3. Section showing muscles which vibrate tymbals (magnified)
  4. A tymbal at rest
  5. A tymbal thrown into vibration (as when cicada is singing), more highly magnified

The tymbal (or timbal) is the corrugated exoskeletal structure used to produce sounds in insects. In male cicadas, the tymbals are membranes in the abdomen, responsible for the characteristic sound produced by the insect. In tiger moths, the tymbals are modified regions of the thorax and produce high-frequency clicks. In lesser wax moths the left and right tymbals emit high-frequency pulses that are used as mating calls.[1]

The paired tymbals of a cicada are located on the sides of the abdominal base. The "singing" of a cicada is not stridulation as in many other familiar sound-producing insects like crickets (where one structure is rubbed against another): the tymbals are regions of the exoskeleton that are modified to form a complex membrane with thin, membranous portions and thickened "ribs". These membranes vibrate rapidly, and enlarged chambers derived from the tracheae enable the cicada's body to be a resonance chamber, greatly amplifying the sound. Some cicadas produce sounds louder than 106 dB (SPL), among the loudest of all insect-produced sounds.[2] They modulate their noise by positioning their abdomens toward or away from the substrate.

  • The sound of an Amphipsalta zelandica cicada in Lower Hutt, New Zealand, recorded in mid-February, 2006
  • Magicicada cassini singing

The tymbals of a tiger moth are specialized regions on the metathoracic episterna, normally corrugated such that sound is produced when the entire tymbal surface is buckled by muscular contraction and then released, producing a series of extremely rapid "clicks" as the corrugations flex back into place.[3] These sounds are only occasionally audible to humans, and are used in both acoustic aposematism (the moths are advertising to bats that they are toxic[4]), and as mating signals. A recent study [5] demonstrates that these sounds are used by some moths to "jam" the sonar of moth-eating bats.[6]

References

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Tymbal

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A tymbal (or timbal) is a specialized, ribbed in the of certain , most notably cicadas, that serves as a primary -producing organ by under the rapid contraction of an attached tymbal muscle to generate sharp clicks and characteristic songs. Located on the dorsolateral surfaces of the first segment in male cicadas, the tymbal consists of a thin, corrugated chitinous plate that distorts inward during muscle contraction—producing an audible "in-click"—and rebounds outward for an "out-click," with each cycle creating frequencies up to several kilohertz and intensities reaching 100–120 decibels at close range. These sounds are amplified and resonated by large air-filled sacs in the , allowing calls to travel over long distances for purposes, while females lack functional tymbals but respond with flicks or substrate drumming. Tymbals differ from stridulatory mechanisms in other , as sound arises from rather than between body parts, and this organ is also present—though less prominently—in some hemipterans like leafhoppers and for similar acoustic signaling. The efficiency of tymbal-based production has evolved ultrastructural adaptations in the muscle, resembling asynchronous flight muscles with high-frequency oscillations up to 500 Hz, enabling sustained calling without fatigue.

Overview

Definition

The tymbal is a corrugated exoskeletal structure composed of , featuring thin membranous portions reinforced by thickened ribs, that enables sound production in certain through a of and snapping. This mechanism involves rapid inward distortion of the driven by muscular contraction, followed by elastic rebound, generating discrete clicks that form pulsed sounds when repeated quickly. Tymbals are primarily associated with male , where they facilitate the production of loud, species-specific calls for or territorial purposes, often amplified by adjacent air-filled cavities to reach intensities exceeding 100 dB. Unlike organs in other , such as those in that rely on frictional rubbing of body parts like a against a file, tymbals produce sound without direct contact between moving elements, relying instead on the membrane's inherent elasticity and rigidity. This structure is most prominently found in the order , particularly among cicadas, where paired tymbals on the serve as the core of their acoustic signaling system.

Occurrence in

Tymbals are predominantly distributed within the order , where they serve as specialized organs for generating mechanical signals such as sound and vibration, primarily in the suborders and , excluding . This distribution encompasses numerous families, with the organ enabling substrate-borne or airborne communication in diverse taxa. Within , the family (cicadas) exhibits the most widespread occurrence, with over 3,000 species worldwide featuring tymbals in males for producing loud courtship songs. Tymbals are also prevalent in other families, such as (planthoppers, including lanternflies), where they facilitate vibrational signaling, and Membracidae (treehoppers), which use them for alarm and courtship vibrations transmitted through plant substrates. In , tymbals appear in select families like Piesmatidae, contributing to defensive or communicative signals. Outside , tymbals or analogous buckling mechanisms are rare and typically limited to specific cases in other orders, such as certain (moths) where abdominal tymbal organs produce click sounds for defense. No verified tymbal structures occur in Coleoptera or , where sound production relies instead on or other mechanisms. In tymbal-bearing species, the organ is characteristically absent in females, which lack the associated musculature and instead rely on receptive hearing via tympanal organs to detect signals. This sexual dimorphism underscores the role of tymbals in -specific communication, though rare exceptions exist in primitive taxa where rudimentary forms may appear in both sexes.

Anatomy

Structure

The tymbal is a specialized structure in certain , primarily cicadas, consisting of a thin, chitinous that forms a flexible, often biconvex plate integrated into the abdominal . This is typically bowed outward and encircled by a rigid sclerotized ring for , with the entire organ located on either side of the first abdominal segment, near the junction with the . In many species, the tymbals are paired and partially concealed by overlying cuticular covers from adjacent segments. The features prominent vertical ribs, composed primarily of , which vary in number and arrangement across species to influence the organ's form. For instance, the bladder Cystosoma saundersii has seven long ribs spanning the membrane. These ribs alternate in length and are connected by thinner inter-rib regions, contributing to the overall corrugated morphology that enhances the tymbal's elasticity. Variations in rib count and membrane thickness are observed among genera, reflecting adaptations to specific body sizes and environmental pressures. At the microscopic level, the tymbal surface reveals a corrugated texture formed by a - composite, where forms protuberant ribs and a polygonal network, while resilin-rich regions at the interfaces provide inherent elasticity and resilience. This composite structure, with resilin autofluorescing under specific wavelengths, ensures the membrane's durability and flexibility, as seen in species like Dundubia rufivena. The tymbal connects to underlying muscles for activation, though its static morphology remains independent of muscular dynamics.

Associated Muscles and Organs

The tymbal muscles are highly specialized fibers that operate asynchronously, similar to muscles, allowing for rapid oscillations without direct neural synchronization to each contraction. In cicadas, these muscles feature short sarcomeres measuring 2-3 μm in length, which facilitate exceptionally high contraction frequencies reaching up to 500 Hz during sound production. These muscles originate on the first abdominal tergum and insert directly onto the ribs of the tymbal membrane, enabling precise control over the and rebound of the ribbed structure. At the histological level, tymbal muscles exhibit a high of mitochondria, occupying 34-42% of the fiber volume across various cicada species, which ensures efficient and rapid ATP regeneration to sustain the energetic demands of superfast contractions. Associated accessory organs enhance the functionality of the tymbal system. The operculum serves as a protective flap covering the tymbal and associated structures in male cicadas. Tympanal membranes, located nearby on the abdominal venter, function primarily in audition by detecting conspecific sounds. Tracheal within the act as resonators, amplifying the acoustic output by reflecting and prolonging vibrations from the tymbal.

Mechanism

Vibration Process

The vibration process of the tymbal begins with the rapid contraction of specialized tymbal muscles, which pull on the tymbal apodeme to initiate inward of the membrane's reinforced ribs. This contraction, generated by superfast muscles capable of high-frequency twitches, applies a force of approximately 0.25 N to deform the convex membrane inward, causing the ribs—typically four to seven in number depending on the —to collapse sequentially from posterior to anterior. Each sequential buckling event produces a distinct click as the rib snaps past its equilibrium point, storing elastic potential energy in the deformed structure. During a single muscle twitch, this buckling sequence generates multiple pulses, with each rib's collapse contributing one pulse; for example, in cicadas like , one contraction yields four inward pulses followed by a fifth from the collective rebound. The process operates at frequencies up to 1,000 Hz in species producing rapid songs, enabled by the muscles' ability to contract and relax in milliseconds, with each twitch driving the full cycle of inversion. Energy transfer occurs primarily through the elastic deformation of the ribs, where accumulated during inversion is rapidly released as during the subsequent eversion, propelling the membrane outward in a snap-like motion. The elastic rebound phase follows muscle relaxation, which requires only about 0.05 N to maintain the buckled state initially, allowing the stored energy to drive the back to their convex position and produce an additional . In some , such as bladder cicadas (Cystosoma saundersii), the first rib buckles independently for one , while subsequent (2–4) collapse together for a second, amplifying the mechanical impulse through coordinated . Rib plays a critical role in tuning the system's , with the mass, , and arrangement of the —often supported by pads—determining the natural vibration frequencies and ensuring efficient energy release during both inversion and eversion phases.

Acoustic Properties

The tymbal produces sound pulses through rapid , resulting in a that begins with an initial followed by compression and decays nearly exponentially. In many species, these pulses exhibit dominant ranging from 2 to 5 kHz, with the spectral energy concentrated around the resonant frequency of the system. Amplification of these pulses occurs via the abdominal , which function as Helmholtz resonators tuned to the song's dominant , boosting sound pressure levels by approximately 10-20 dB compared to unamplified tymbal clicks. Sound pressure within the air sac can reach peaks of 155-159 dB SPL, while radiated output through the tympana averages around 148 dB SPL near the . This enhances the efficiency of sound projection, with individual songs achieving up to 100 dB SPL at 1 m. Cicada songs typically comprise pulse trains of 10-50 ms duration, repeated at rates of 1-5 per second to form modulated phrases. These trains create sustained tones when aggregated in choruses, where collective output can exceed 100 dB SPL. Species-specific acoustic signatures are evident in the ; for example, (Magicicada spp.) generate pulses with a 4-5 kHz dominant frequency, distinguishing their calls from other taxa.

Function

Sound Production in Communication

The primary function of tymbal sound production in is to facilitate communication, particularly in reproductive contexts where males generate calling songs to attract females. These songs often incorporate species-specific temporal patterns or phrases that enable mate recognition amid choruses of multiple , reducing the risk of hybridization. For instance, in cicadas, males produce distinct call sequences that females use to identify conspecifics, enhancing success. This sex-specific role is prevalent, with males typically serving as the sound producers while females exhibit phonotactic responses, orienting toward the calls to locate potential mates. Tymbal-generated songs vary by type to suit different interaction ranges and purposes. Advertisement calls, often long-range signals, are broadcast by males to advertise their presence and quality to distant females, as seen in choruses. Courtship songs, produced at close range during pair formation, may include softer, more intricate patterns to stimulate female receptivity. Additionally, distress signals can be emitted by males in response to predators, serving as acoustic aposematic warnings that deter attacks. Compared to , tymbal mechanisms allow for greater acoustic efficiency, producing louder sounds with less energy expenditure due to the rapid of the . In cicadas, these calls can reach intensities of up to 120 dB at the source, far exceeding typical stridulatory outputs and enabling propagation over several kilometers in some habitats. Moths employing abdominal tymbals, such as species in the Chloephorinae , generate clicks around 100 dB at close range, tuned to frequencies that align with female auditory sensitivities for effective mate attraction.

Behavioral Contexts

In cicadas, tymbal-based chorusing plays a key environmental role by facilitating the formation of large aggregations that contribute to , particularly in periodical species like Magicicada, where synchronized mass emergences overwhelm predators despite high initial mortality rates. These choruses self-organize through auditory interactions among males, achieving spatial synchrony over distances of tens to thousands of meters, which enhances group cohesion during breeding periods. For instance, in , males synchronize calls every 5 seconds in tree-based groups, responding to local sound cues to maintain chorus integrity. Defensive functions of tymbal sounds include the production of sudden, loud "stress" or disturbance calls that serve as startle responses to deter predators. In species such as Diceroprocta apache, these brief, high-intensity bursts disrupt predator attacks, reducing handling time and increasing escape success by startling avian or mammalian foes. Such sounds are elicited during physical disturbance, providing an immediate acoustic warning without physical harm to the cicada. Daily patterns of tymbal activity in cicadas are predominantly diurnal, with calling peaks occurring during when ambient temperatures reach optimal levels of 25–35°C, above a typical threshold of 24°C for initiation. This temperature dependence ensures metabolic efficiency for sound production, as lower temperatures inhibit tymbal vibration rates, while excessive heat may limit activity duration. Interspecies interactions involving tymbal sounds often manifest as acoustic interference within multi-species choruses, where overlapping calls can disrupt mate recognition and lead to reproductive costs. For example, in sympatric cicada communities, evolves to minimize such interference, with adjusting or timing to reduce cross-attraction. occasionally occurs, as seen in cases where predatory imitate cicada calls to exploit choruses, indirectly influencing cicada behavioral dynamics.

Evolution

Origins and Development

The tymbal organ originated in the late period, over 300 million years ago, within the common ancestor of the Tymbalia clade, comprising excluding . This evolution began with simple cuticular vibrations generated by modified dorsoventral muscles of the first abdominal segment, which were homologous across the clade and likely derived from ancestral contact signals during copulation. Over time, these primitive mechanisms developed into more complex ribbed tymbal plates, enhancing vibration amplification and signal complexity, as evidenced by comparative morphology in extant groups. A pivotal was the of asynchronous muscles for tymbal function, enabling rapid oscillations and high-frequency sounds up to 25 kHz, particularly in advanced forms like cicadas. This asynchronous mechanism, characterized by stretch activation and ultrastructural features such as hexagonal myofilaments, likely arose from modifications of thoracic flight muscles, facilitated by the absence of powerful metathoracic flight muscles in early Tymbalia ancestors. Such developments, dated phylogenetically to around 300 million years ago, provided a selective advantage for vibroacoustic communication in terrestrial environments. Phylogenetically, the tymbal is basal and synapomorphic for the Tymbalia, present in (including and Fulgoromorpha), , and , but entirely absent in , supporting its evolution as an autapomorphy of this . of tymbal-like organs has occurred rarely outside , notably in certain such as arctiid and geometrid moths, where prothoracic or abdominal tymbals produce ultrasonic clicks for bat defense. Studies in model insects, such as , demonstrate how Abd-B gradients control abdominal diversification, providing a framework for understanding abdominal development in hemipterans.

Fossil Evidence

The fossil record provides direct evidence of tymbal structures primarily from the era, supporting their ancient origins within the Cicadoidea superfamily of Hemipteran . The earliest Cicadoidea fossils date to the period (approximately 252–201 million years ago), marking the initial diversification of cicadomorphans capable of vibrational signaling, though soft-tissue preservation limits confirmation of tymbals in these specimens. Definitive tymbal fossils, identified through micro-CT imaging, appear in mid-Cretaceous amber deposits from the Hukawng Valley in northern , dated to about 99 million years ago. These inclusions reveal tymbal organs as paired, chitinous membranous structures on the first and second abdominal terga, often accompanied by associated muscles, tracheae, and resonant cavities. Key specimens include Eunotalia emeryi, Cretotettigarcta problematica, Cretotettigarcta shcherbakovi, and Pranwanna xiai, all preserved in and representing stem-group cicadoids. In Pranwanna xiai, both male and female adults exhibit well-developed tymbal muscles and an enlarged abdominal cavity, indicating potential for louder aerial sound production akin to modern , while other species show simpler configurations suited to substrate-borne vibrations similar to extant . These structures were present across sexes, suggesting roles in non-sexual communication such as predator avoidance or aggregation. The ubiquity of tymbals in cicadoid fossils implies they were a plesiomorphic trait, evolving early in the lineage for vibroacoustic signaling. Earlier records of , such as the late (Moscovian, 315–307 million years ago) fossil Aviorrhyncha magnifica from the Commentry locality in , represent the oldest known Tymbalia ( excluding ), the broader encompassing tymbal-bearing . While direct tymbal preservation is absent due to compression fossils lacking soft tissues, phylogenetic analyses infer the organ's origin as an autapomorphy of Tymbalia over 300 million years ago, linked to modifications of thoracic flight muscles for buckling the membrane. Post-Mesozoic fossils, including Eocene lagerstätten like the 47-million-year-old Eoplatypleura messelensis from Germany's Messel Pit, confirm continuity of tymbal morphology into crown-group cicadas with enhanced vocal capabilities. This sparse but revealing record underscores tymbals' role in the of acoustic communication in .

References

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