Trap‐jaws revisited: the mandible mechanism of the ant Acanthognathus

Abstract.Ants of the genus Acanthognathus stalk small insects and catch their prey by a strike with their long, thin mandibles. The mandibles close in less than 2.5 ms and this movement is controlled by a specialized closer muscle. In Acanthognathus , unlike other insects, the mandible closer muscle is subdivided into two distinct parts: as in a catapult, a large slow closer muscle contracts in advance and provides the power for the strike while the mandibles are locked open. When the prey touches specialized trigger hairs, a small fast closer muscle rapidly unlocks the mandibles and thus releases the strike. The fast movement is steadied by large specialized surfaces in the mandible joint and the sensory‐motor reflex is controlled by neurones with particularly large, and thus fast‐conducting, axons.     

Jaws that snap: control of mandible movements in the ant Mystrium

Ants of the genus Mystrium employ a peculiar snap-jaw mechanism in which the closed mandibles cross over to deliver a stunning blow to an adversary within about 0.5 ms. The mandible snapping is preceded by antennation and antennal withdrawal. The strike is initiated by contact of the adversary with mechanosensory hairs at the side of the mandible, and is powered by large yet slow closer muscles whose energy is stored by a catapult mechanism. Recording of closer muscle activity indicates that the mandibles are not triggered by any fast muscle. Instead, we suppose that activity differences between the left and right mandible muscles imbalance a pivot at the mandible tip and release the strike. The likelihood for the strike to occur can be modulated by an alarm pheromone. The presence of specialized sensilla and of a complex muscle receptor organ shows that the mandibles are also adapted to functions other than snapping and suggests that the force of the mandible can be finely adjusted for other tasks.     

The control of mandible movements in the ant Odontomachus

Ants use their mandibles to manipulate many different objects including food, brood and nestmates. Different tasks require the modification of mandibular force and speed. Besides normal mandible movements the trap-jaw ant Odontomachus features a particularly fast mandible reflex during which both mandibles close synchronously within 3 ms. The mandibular muscles that govern mandible performance are controlled by four opener and eight closer motor neurons. During slow mandible movements different motor units can be activated successively, and fine tuning is assisted by co-activation of the antagonistic muscles. Fast and powerful movements are generated by the additional activation of two particular motor units which also contribute to the mandible strike. The trap-jaw reflex is triggered by a fast trigger muscle which is derived from the mandible closer. Intracellular recording reveals that trigger motor neurons can generate regular as well as particularly large postsynaptic potentials, which might be passively propagated over the short distance to the trigger muscle. The trigger motor neurons are dye-coupled and receive input from both sides of the body without delay, which ensures the synchronous release of both mandibles.     

The sensory basis for the trap-jaw mechanism in the ant Odontomachus bauri

Ants of the ponerine genus Odontomachus have evolved a mechanism that allows them to instantaneously close their long mandibles to catch prey or defend themselves. This trap-jaw action is triggered by contact of trigger hairs with a potential prey item. Two of these long mechanosensory hair sensilla reside proximally on each mandible and are supplied by giant sensory cells.Extracellular recordings demonstrate that the sensory cells respond to tactile stimulation. Their phasic responses encode amplitude and velocity of hair-deflection away from the midline, but not hair position. The discharge of action potentials follows stimulus frequencies of more than 300 Hz. During sinusoidal stimulation, the cells adapt very little, sustain discharge rates of more than 200 Hz for more than 20 s, and reach peak spike rates of about 450 Hz.The afferent axons of these sensory cells give rise to huge axon terminals within the suboesophageal ganglion. One of the afferents has a prominent contralateral branch, the other is confined to ipsilateral neuropil. Anatomical data indicate that the 4 afferents may be coupled and may serve as the substrate for a very fast reflex.Abbreviations HRP horseradish peroxidase - LGS lateral giant sensillum - MGS median giant sensillum - SEM scanning electron microscopy - SOG suboesophageal ganglion     

Sensory feedback in the control of mouthpart movements in the desert locust Schistocerca gregaria

ABSTRACT. When imposed movements were applied to one or both mandibles of the desert locust, Schistocerca gregaria , the other mouthparts moved in synchrony with the mandibles. This occurred in the presence or absence of food, and when the mandibles were driven at a higher or lower frequency than that seen during normal feeding. Electromyogram recordings from the mandibular closer muscles revealed bursts of activity at the same frequency as the imposed movement. This activity occurred during mandibular closing. Burst length was a function of driving wavelength. At low driving frequencies (less than 0.5 Hz), smaller bursts were seen prior to the longer closing burst; a series of similar small bursts was seen when the mandibles were held in the open position. When one mandible was driven, closer muscle activity was largely confined to that side. In the presence of food, however, activity was seen in both closer muscles. A possible mechanism for this is described. After destruction of the campaniform sensilla on the ventral surface of the mandibles, the bursts of activity in the mandibular closers, seen when the mandibles were held open, were replaced by continuous activity. This suggests that the function of these sensilla is to inhibit motor output to the closer muscles when the tension becomes high. When feeding on relatively incompressible food the closer muscle burst length increased, although chewing frequency did not alter. This effect was also produced by loading the mandibles artificially. A model for the feedback control of this behaviour is proposed.     

Modulation in the feeding prey capture of the ant-lion, Myrmeleon crudelis

Ant-lions are pit-building larvae (Neuroptera: Myrmeleontidae), which possess relatively large mandibles used for catching and consuming prey. Few studies involving terrestrial arthropod larva have investigated prey capture behavior and kinematics and no study has shown modulation of strike kinematics. We examined feeding kinematics of the ant-lion, Myrmeleon crudelis, using high-speed video to investigate whether larvae modulate strike behavior based on prey location relative to the mandible. Based on seven capture events from five M. crudelis, the strike took 17.60 ± 2.92?msec and was characterized by near-simultaneous contact of both mandibles with the prey. Modulation of the angular velocity of the mandibles based on prey location was clearly demonstrated. M. crudelis larvae attempted to simultaneously contact prey with both mandibles by increasing mean angular velocity of the far mandible (65 ± 21?rad?sec(-1) ) compared with the near mandible (35 ± 14?rad?sec(-1) ). Furthermore, kinematic results showed a significant difference for mean angular velocity between the two mandibles (P<0.005). Given the lengthy strike duration compared with other fast-striking arthropods, these data suggest that there is a tradeoff between the ability to modulate strike behavior for accurate simultaneous mandible contact and the overall velocity of the strike. The ability to modulate prey capture behavior may increase dietary breadth and capture success rate in these predatory larvae by allowing responsive adjustment to small-scale variations in prey size, presentation, and escape response.     

Mandible movements in ants.

Ants use their mandibles for almost any task, including prey-catching, fighting, leaf-cutting, brood care and communication. The key to the versatility of mandible functions is the mandible closer muscle. In ants, this muscle is generally composed of distinct muscle fiber types that differ in morphology and contractile properties. Fast contracting fibers have short sarcomeres (2-3 microm) and attach directly to the closer apodeme, that conveys the muscle power to the mandible joint. Slow but forceful contracting fibers have long sarcomeres (5-6 microm) and attach to the apodeme either directly or via thin thread-like filaments. Volume proportions of the fiber types are species-specific and correlate with feeding habits. Two biomechanical models explain why species that rely on fast mandible strikes, such as predatory ants, have elongated head capsules that accommodate long muscle fibers directly attached to the apodeme at small angles, whereas species that depend on forceful movements, like leaf-cutting ants, have broader heads and many filament-attached fibers. Trap-jaw ants feature highly specialized catapult mechanisms. Their mandible closing is known as one of the fastest movements in the animal kingdom. The relatively large number of motor neurons that control the mandible closer reflects the importance of this muscle for the behavior of ants as well as other insects.     

Fast and Powerful: Biomechanics and Bite Forces of the Mandibles in the American Cockroach Periplaneta americana

Knowing the functionality and capabilities of masticatory apparatuses is essential for the ecological classification of jawed organisms. Nevertheless insects, especially with their outstanding high species number providing an overwhelming morphological diversity, are notoriously underexplored with respect to maximum bite forces and their dependency on the mandible opening angles. Aiming for a general understanding of insect biting, we examined the generalist feeding cockroach Periplaneta americana, characterized by its primitive chewing mouth parts. We measured active isometric bite forces and passive forces caused by joint resistance over the entire mandibular range with a custom-built 2D force transducer. The opening angle of the mandibles was quantified by using a video system. With respect to the effective mechanical advantage of the mandibles and the cross-section areas, we calculated the forces exerted by the mandible closer muscles and the corresponding muscle stress values. Comparisons with the scarce data available revealed close similarities of the cockroaches’ mandible closer stress values (58 N/cm2) to that of smaller specialist carnivorous ground beetles, but strikingly higher values than in larger stag beetles. In contrast to available datasets our results imply the activity of faster and slower muscle fibres, with the latter becoming active only when the animals chew on tough material which requires repetitive, hard biting. Under such circumstances the coactivity of fast and slow fibres provides a force boost which is not available during short-term activities, since long latencies prevent a specific effective employment of the slow fibres in this case.     

Motor control of the mandible closer muscle in ants

Despite their simple design, ant mandible movements cover a wide range of forces, velocities and amplitudes. The mandible is controlled by the mandible closer muscle, which is composed of two functionally distinct subpopulations of muscle fiber types: fast fibers (short sarcomeres) and slow ones (long sarcomeres). The entire muscle is controlled by 10-12 motor neurons, 4-5 of which exclusively supply fast muscle fibers. Slow muscle fibers comprise a posterior and an antero-lateral group, each of which is controlled by 1-2 motor neurons. In addition, 3-4 motor neurons control all muscle fibers together. Simultaneous recordings of muscle activity and mandible movement reveal that fast movements require rapid contractions of fast muscle fibers. Slow and subtle movements result from the activation of slow muscle fibers. Forceful movements are generated by simultaneous co-activation of all muscle fiber types. Retrograde tracing shows that most dendritic arborizations of the different sets of motor neurons share the same neuropil in the subesophageal ganglion. In addition, fast motor neurons and neurons supplying the lateral group of slow closer muscle fibers each invade specific parts of the neuropil that is not shared by the other motor neuron groups. Some bilateral overlap between the dendrites of left and right motor neurons exists, particularly in fast motor neurons. The results explain how a single muscle is able to control the different movement parameters required for the proper function of ant mandibles.     

Carnivorous Utricularia: The buckling scenario

We review recent results about the functioning of aquatic carnivorous traps from the genus Utricularia. The use of high speed cameras has helped to elucidate the mechanism at the origin of the ultra fast capture process of Utricularia, at a millisecond time scale. As water is pumped out of the trap, pressure decreases inside the trap and elastic energy is stored due to the change of shape of the trap body. This energy is suddenly released when the trap is fired: the trap door undergoes an elastical instability: buckling, which allows its fast and passive opening and closure. This mechanism is used by Utricularia both to catch preys touching its trigger hairs and to fire spontaneously at regular time intervals. The results leading to this interpretation are reviewed and discussed and suggestions for further work are briefly presented.     

Free body analysis,beam mechanics,and finite element modeling of the mandible of Alligator mississippiensis

The mechanical behavior of mammalian mandibles is well‐studied, but a comprehensive biomechanical analysis (incorporating detailed muscle architecture, accurate material properties, and three‐dimensional mechanical behavior) of an extant archosaur mandible has never been carried out. This makes it unclear how closely models of extant and extinct archosaur mandibles reflect reality and prevents comparisons of structure–function relationships in mammalian and archosaur mandibles. We tested hypotheses regarding the mechanical behavior of the mandible of Alligator mississippiensis by analyzing reaction forces and bending, shear, and torsional stress regimes in six models of varying complexity. Models included free body analysis using basic lever arm mechanics, 2D and 3D beam models, and three high‐resolution finite element models of the Alligator mandible, incorporating, respectively, isotropic bone without sutures, anisotropic bone with sutures, and anisotropic bone with sutures and contact between the mandible and the pterygoid flange. Compared with the beam models, the Alligator finite element models exhibited less spatial variability in dorsoventral bending and sagittal shear stress, as well as lower peak values for these stresses, suggesting that Alligator mandibular morphology is in part designed to reduce these stresses during biting. However, the Alligator models exhibited greater variability in the distribution of mediolateral and torsional stresses than the beam models. Incorporating anisotropic bone material properties and sutures into the model reduced dorsoventral and torsional stresses within the mandible, but led to elevated mediolateral stresses. These mediolateral stresses were mitigated by the addition of a pterygoid‐mandibular contact, suggesting important contributions from, and trade‐offs between, material properties and external constraints in Alligator mandible design. Our results suggest that beam modeling does not accurately represent the mechanical behavior of the Alligator mandible, including important performance metrics such as magnitude and orientation of reaction forces, and mediolateral bending and torsional stress distributions. J.Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Variation in mandible shape and body size of house mice Mus musculus in five separate New Zealand forest habitats

This study investigates variation in house mouse Mus musculus body size and mandible shape across New Zealand, using geometric morphometrics and biomechanical advantage analyses. The Mus phylogroups currently known in New Zealand include Mus musculus domesticus, M. m. musculus and M. m. castaneus. We examined samples of house mice inhabiting five different podocarp and beech forest environments across the North and South Islands (Pureora Forest, Zealandia Wildlife Sanctuary, Craigieburn Forest Park, Eglinton Valley and Hollyford Valley). Significant variation in mandible shape and body size was found between all five forest populations. South Island mice had larger bodies and greater mechanical advantage in the temporalis muscle compared with their North Island counterparts. Zealandia Sanctuary mouse mandibles were broader and shorter than South Island mouse mandibles, and had greater masseter muscle advantage. Centroid size and body weight, but not head-body length, varied significantly with two distinct genetic haplotypes. Finally, annual rainfall was the most significant covariate with mandible shape. Higher rainfall locations were generally associated with soft-food related mandible shapes, while lower rainfall correlated with hard-food mandible shapes. This preliminary investigation provides the framework for further research into mandible shape and body size variation in New Zealand house mice.     

On the reflex coactivation of ankle flexor and extensor muscles induced by a sudden drop of support surface during walking in humans.

Recent studies have revealed that the stretch reflex responses of both ankle flexor and extensor muscles are coaugmented in the early stance phase of human walking, suggesting that these coaugmented reflex responses contribute to secure foot stabilization around the heel strike. To test whether the reflex responses mediated by the stretch reflex pathway are actually induced in both the ankle flexor and extensor muscles when the supportive surface is suddenly destabilized, we investigated the electromyographic (EMG) responses induced after a sudden drop of the supportive surface at the early stance phase of human walking. While subjects walked on a walkway, the specially designed movable supportive surface was unexpectedly dropped 10 mm during the early stance phase. The results showed that short-latency reflex EMG responses after the impact of the drop (<50 ms) were consistently observed in both the ankle flexor and extensor muscles in the perturbed leg. Of particular interest was that a distinct response appeared in the tibialis anterior muscle, although this muscle showed little background EMG activity during the stance phase. These results indicated that the reflex activities in the ankle muscles certainly acted when the supportive surface was unexpectedly destabilized just after the heel strike during walking. These reflex responses were most probably mediated by the facilitated stretch reflex pathways of the ankle muscles at the early stance phase and were suggested to be relevant to secure stabilization around the ankle joint during human walking.     

Vision and the foraging technique of skimmers (Rynchopidae)

In birds, the position and extent of the region of binocular vision appears to be determined primarily by feeding ecology. Of prime importance is the degree to which vision is used for the precise control of bill position when foraging. Skimmers (Rynchops, Rynchopidae, Charadriiformes) exhibit a unique foraging behaviour and associated structural adaptations. When foraging they fly low and straight over water with the mouth open and the mandible partially submerged. Items that are hit by the lower mandible are grasped by a rapid reflex bill closure. It is believed that this unique ‘skimming’ foraging technique is guided by tactile rather than visual cues. It is predicted therefore that the visual fields of skimmers will have similar topography to those of other tactile feeding birds. We determined retinal visual fields in Black Skimmers Rynchops niger using an ophthalmoscopic reflex technique. Contrary to expectation the visual fields of Black Skimmers are not like those of other tactile feeders. They show high similarity with those of birds that feed by precision‐pecking. The projection of the bill tip when the mouth is closed and when open (as in skimming) falls within the frontal binocular field and there is an extensive blind area above and behind the head. We argue that this visual field topography functions to achieve accurate bill positioning with respect to the water surface when skimming and, because foraging skimmers cannot determine the identity of what they are seizing as they skim, to permit the visual identification of prey items held between the mandibles after they have been taken from the water surface. When skimming, only a small portion of the binocular field, approximately 5° wide and extending 5° above the horizontal, looks in the direction of travel. The small size of this forward‐facing region of binocularity in skimmers suggests that control of locomotion in birds does not necessarily require extensive binocularity in the direction of travel.     

Additional mandibles of Rangwapithecus gordoni,an early Miocene catarrhine from the Tinderet localities of Western Kenya

Two catarrhine mandibles and five isolated teeth have been discovered from Early Miocene localities in Western Kenya. One mandible comes from the well‐known locality of Songhor whereas the other is from a newly discovered locality, Lower Kapurtay, located near Songhor. The mandibles both can clearly be assigned to the species Rangwapithecus gordoni based on molar morphology, which is unique among Early Miocene catarrhines. The isolated specimens can be assigned to Rangwapithecus based on their similarities in morphology to the homologues preserved in the two mandibles. These specimens provide important new information about the dentognathic morphology of Rangwapithecus, which is described in detail. The mandible from Songhor (KNM‐SO 22228) represents the first definitive female mandible of Rangwapithecus. The Lower Kapurtay mandible (KNM‐KT 31234) appears to be male but is much smaller than another recently described male mandible of this species (KNM‐SO 17500) and the type maxilla (KNM‐SO 700). These specimens enable a reassessment of the attributions of all other mandibles and isolated lower teeth of Rangwapithecus, and we present a complete hypodigm of the mandibular and lower dental material for the species. Finally, we provide some additions to the diagnosis of Rangwapithecus gordoni based on previously unknown morphology. Am J Phys Anthropol 153:341–352, 2014. © 2013 Wiley Periodicals, Inc.     

Mandible and Taxonomy of the Earliest European Homo

Although variability of the mandible makes it problematic for taxonomy, the holotypes of three of the oldest European species, Home georgicus, H. antecessor, H. heidelbergensis, are mandibles. Moreover, the distinctive validity of these three species cannot be established from these particular mandibles. The holotype of H. georgicus is pathological and similar to H. erectus in some important features, while others features are so widely spread that they are of little taxonomic value. H. antecessor shows juvenile mandibular features which are chronologically and geographically widespread, and similarities with H. pekinensis do not appear significant. The mandible from Mauer, H. heidelbergensis, is generally plesiomorphic, but similar to Neanderthals in a few important features. Neanderthals are a highly peculiar human group from the anatomical, geographical and chronological points of view. They are genetically different from H. sapiens and they seem to emerge in Europe during Middle Pleistocene. Mauer could be one of their earliest representatives.     

Contribution of muscle series elasticity to maximum performance in drop jumping

The contribution of muscle in-series compliance on maximum performance of the muscle tendon complex was investigated using a forward dynamic computer simulation. The model of the human body contains 8 Hill-type muscles of the lower extremities. Muscle activation is optimized as a function of time, so that maximum drop jump height is achieved by the model. It is shown that the muscle series elastic energy stored in the downward phase provides a considerable contribution (32%) to the total muscle energy in the push-off phase. Furthermore, by the return of stored elastic energy all muscle contractile elements can reduce their shortening velocity up to 63% during push-off to develop a higher force due to their force velocity properties. The additional stretch taken up by the muscle series elastic element allows only m. rectus femoris to work closer to its optimal length, due to its force length properties. Therefore the contribution of the series elastic element to muscle performance in maximum height drop jumping is to store and return energy, and at the same time to increase the force producing ability of the contractile elements during push-off.     

Cuticular microstructure of Australian ant mandibles confirms common appendage construction

Exoskeletons characterise Arthropoda and have allowed the morphological and taxonomic diversity of the phylum. Exoskeletal sclerotisation occurs in genetically designated regions, and mandibles represent one such area of high sclerotisation. Mandible morphology reflects dietary preferences and niche partitioning and has therefore been well documented. However, mandibular cuticular microstructure has been under-documented. Here we use scanning electron microscopy to explore mandible microstructure in four disparate Australian Formicidae taxa (ants) with different life modes and diets: Camponotus nigriceps, Iridomyrmex purpureus, Odontomachus simillimus and Rhytidoponera aciculata. We test the hypothesis that mandible construction is highly conserved across these species, as would be expected for arthropod cuticle. We show broadly similar mandible microstructure but report that pore canals and cuticular indentations are not ubiquitous among all studied taxa. Our preliminary results demonstrate that ant taxa have morphologically plastic mandibles with a highly conserved construction, potentially reflecting an interesting record of evolutionary stasis.     

Bone remodelling in Neanderthal mandibles from the El Sidrón site (Asturias, Spain)

Skull morphology results from the bone remodelling mechanism that underlies the specific bone growth dynamics. Histological study of the bone surface from Neanderthal mandible specimens of El Sidrón (Spain) provides information about the distribution of the remodelling fields (bone remodelling patterns or BRP) indicative of the bone growth directions. In comparison with other primate species, BRP shows that Neanderthal mandibles from the El Sidrón (Spain) sample present a specific BRP. The interpretation of this map allows inferences concerning the growth directions that explain specific morphological traits of the Neanderthal mandible, such as its quadrangular shape and the posterior location of the mental foramen.     

The juvenile mandible of<Emphasis Type="Italic">Lufengpithecus</Emphasis>

The juvenile mandible ofLufengpithecus lufengensis (PA869) discovered in 1980 at back to latest Miocene lignite rich deposit in Shihuiba Village, Lufeng County, Yunnan Province in southwest of China is described in this study. The specimen was compared with the juvenile mandibles ofSivapithecus, Australopithecus, earlyHomo and extant great apes. Some characteristics of the juvenile mandible ofLufengpithecus indicate that the proportional relation between the length, the height and the thickness of the mandibular corpus are very similar to those of the adult mandible of same species. This Lufeng juvenile mandible is of a 3–3.5 years old female individual.