Reconstruction of cranial and hyobranchial muscles in the triassic temnospondyl Gerrothorax provides evidence for akinetic suction feeding

The cranial and hyobranchial muscles of the Triassic temnospondyl Gerrothorax have been reconstructed based on direct evidence (spatial limitations, ossified muscle insertion sites on skull, mandible, and hyobranchium) and on phylogenetic reasoning (with extant basal actinopterygians and caudates as bracketing taxa). The skeletal and soft‐anatomical data allow the reconstruction of the feeding strike of this bottom‐dwelling, aquatic temnospondyl. The orientation of the muscle scars on the postglenoid area of the mandible indicates that the depressor mandibulae was indeed used for lowering the mandible and not to raise the skull as supposed previously and implies that the skull including the mandible must have been lifted off the ground during prey capture. It can thus be assumed that Gerrothorax raised the head toward the prey with the jaws still closed. Analogous to the bracketing taxa, subsequent mouth opening was caused by action of the strong epaxial muscles (further elevation of the head) and the depressor mandibulae and rectus cervicis (lowering of the mandible). During mouth opening, the action of the rectus cervicis muscle also rotated the hyobranchial apparatus ventrally and caudally, thus expanding the buccal cavity and causing the inflow of water with the prey through the mouth opening. The strongly developed depressor mandibulae and rectus cervicis, and the well ossified, large quadrate‐articular joint suggest that this action occurred rapidly and that powerful suction was generated. Also, the jaw adductors were well developed and enabled a rapid mouth closure. In contrast to extant caudate larvae and most extant actinopterygians (teleosts), no cranial kinesis was possible in the Gerrothorax skull, and therefore suction feeding was not as elaborate as in these extant forms. This reconstruction may guide future studies of feeding in extinct aquatic tetrapods with ossified hyobranchial apparatus. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Functional morphology of the feeding mechanism in aquatic ambystomatid salamanders

This study addresses four questions in vertebrate functional morphology through a study of aquatic prey capture in ambystomatid salamanders: (1) How does the feeding mechanism of aquatic salamanders function as a biomechanical system? (2) How similar are the biomechanics of suction feeding in aquatic salamanders and ray-finned fishes? (3) What quantitative relationship does information extracted from electromyograms of striated muscles bear to kinematic patterns and animal performance? and (4) What are the major structural and functional patterns in the evolution of the lower vertebrate skull? During prey capture, larval ambystomatid salamanders display a kinematic pattern similar to that of other lower vertebrates, with peak gape occurring prior to both peak hyoid depression and peak cranial elevation. The depressor mandibulae, rectus cervicis, epaxialis, hypaxialis, and branchiohyoideus muscles are all active for 40–60 msec during the strike and overlap considerably in activity. The two divisions of the adductor mandibulae are active in a continuous burst for 110–130 msec, and the intermandibularis posterior and coracomandibularis are active in a double burst pattern. The antagonistic depressor mandibulae and adductor mandibulae internus become active within 0.2 msec of each other, but the two muscles show very different spike and amplitude patterns during their respective activity periods. Coefficients of variation for kinematic and most electromyographic recordings reach a minimum within a 10 msec time period, just after the mouth starts to open. Pressure within the buccal cavity during the strike reaches a minimum of ?25 mmHg, and minimum pressure occurs synchronously with maximum gill bar adduction. The gill bars (bearing gill rakers that interlock with rakers of adjacent arches) clearly function as a resistance within the oral cavity and restrict posterior water influx during mouth opening, creating a unidirectional flow during feeding. Durations of electromyographic activity alone are poor predictors of kinematic patterns. Analyses of spike amplitude explain an additional fraction of the variance in jaw kinematics, whereas the product of spike number and amplitude is the best statistical predictor of kinematic response variables. Larval ambystomatid salamanders retain the two primitive biomechanical systems for opening and closing the mouth present in nontetrapod vertebrates: elevation of the head by the epaxialis and depression of the mandible by the hyoid apparatus.     

Prey location,biomechanical constraints,and motor program choice during prey capture in the tomato frog, <Emphasis Type="Italic">Dyscophus guineti</Emphasis>

This study investigated how visual information about prey location and biomechanical constraints of the feeding apparatus influence the feeding behavior of the tomato frog, Dyscophus guineti. When feeding on prey at small azimuths (less than ± 40°), frogs aimed their heads toward the prey but did not aim their tongues relative to their heads. Frogs projected their tongues rapidly by transferring momentum from the lower jaw to the tongue. Storage and recovery of elastic energy by the mouth opening muscles amplified the velocities of mouth opening and tongue projection. This behavior can only occur when the lower jaw and tongue are aligned (i.e., within the range of motion of the neck). When feeding on prey at large azimuths (greater than ± 40°), frogs aimed both the head and tongue toward the prey and used a muscular hydrostatic mechanism to project the tongue. Hydrostatic elongation allows for frogs to capture prey at greater azimuthal locations. Because the tongue moves independently of the lower jaw, frogs can no longer take advantage of momentum transfer to amplify the speed of tongue projection. To feed on prey at different azimuthal locations, tomato frogs switch between alternative strategies to circumvent these biomechanical constraints.     

Morphological and functional bases of durophagy in the queen triggerfish,Balistes vetula (Pisces,tetraodontiformes)

Tetraodontiform fishes are characterized by jaws specialized for powerful biting and a diet dominated by hard-shelled prey. Strong biting by the oral jaws is an unusual feature among teleosts. We present a functional morphological analysis of the feeding mechanism of a representative tetraodontiform, Balistes vetula. As is typical for the order, long, sharp, strong teeth are mounted on the short, robust jaw bones of B. vetula. The neurocranium and suspensorium are enlarged and strengthened to serve as sites of attachment for the greatly hypertrophied adductor mandibulae muscles. Electromyographic recordings made from 11 cranial muscles during feeding revealed four distinct behaviors in the feeding repertoire of B. vetula. Suction is used effectively to capture soft prey and is associated with a motor pattern similar to that reported for many other teleosts. However, when feeding on hard prey, B. vetula directly bit the prey, exhibiting a motor pattern very different from that of suction feeding. During buccal manipulation, repeated cycles of jaw opening and closing (biting) were coupled with rapid movement of the prey in and out of the mouth. Muscle activity during buccal manipulation was similar to that seen during bite-captures. A blowing behavior was periodically employed during prey handling, as prey were forcefully “spit out” from the mouth, either to reposition them or to separate unwanted material from flesh. The motor pattern used during blowing was distinct from similar behaviors described for other fishes, indicating that this behaviors may be unique to tetraodontiforms. Thus B. vetula combines primitive behaviors and motor patterns (suction feeding and buccal manipulation) with specialized morphology (strong teeth, robust jaws, and hypertrophied adductor muscles) and a novel behavior (blowing) to exploit armored prey such as sea urchins molluscs, and crabs. © 1993 Wiley-Liss, Inc.     

Kinetics of tongue projection in Ambystoma tigrinum: Quantitative kinematics,muscle function,and evolutionary hypotheses

The projectile tongue of caudate amphibians has been studied from many perspectives, yet a quantitative kinetic model of tongue function has not yet been presented for generalized (nonplethodontid) terrestrial salamanders. The purposes of this paper are to describe quantitatively the kinnematics of the feeding mechanism and to present a kinetic model for the function of the tongue in the ambystomatid salamander Ambystoma tigrinum. Six kinematic variables were quantified from high-speed films of adult A. tigrinum feeding on land and in the water. Tongue protrusion reaches its maximum during peak gape, while peak tongue height is reached earlier, 15 ms after the mouth starts to open. Tongue kinematics change considerably during feeding in the water, and the tongue is not protruded past the plane of the gape. Electrical stimulation of the major tongue muscles showed that tongue projection in A. tigrinum is the combined result of activity in four muscles: the geniohyoideus, Subarcualis rectus 1, intermandibularis posterior, and interhyoideus. Stimulation of the Subarcualis rectus 1 alone does not cause tongue projection. The kinetic model produced from the kinematic and stimulation data involves both a dorsal vector (the resultant of the Subarcualis rectus 1, intermandibularis posterior, and interhyoideus) and a ventral vector (the geniohyoideus muscle), which sum to produce a resultant anterior vector that directs tongue motion out of the mouth and toward the prey. This model generates numerous testable predictions about tongue function and provides a mechanistic basis for the hypothesis that tongue projection in salamanders evolved from primitive intraoral manipulative action of the hyobranchial apparatus.     

The Head and Neck Anatomy of Sea Turtles (Cryptodira: Chelonioidea) and Skull Shape in Testudines

Background

Sea turtles (Chelonoidea) are a charismatic group of marine reptiles that occupy a range of important ecological roles. However, the diversity and evolution of their feeding anatomy remain incompletely known.

Methodology/Principal Findings

Using computed tomography and classical comparative anatomy we describe the cranial anatomy in two sea turtles, the loggerhead (Caretta caretta) and Kemp’s ridley (Lepidochelys kempii), for a better understanding of sea turtle functional anatomy and morphological variation. In both taxa the temporal region of the skull is enclosed by bone and the jaw joint structure and muscle arrangement indicate that palinal jaw movement is possible. The tongue is relatively small, and the hyoid apparatus is not as conspicuous as in some freshwater aquatic turtles. We find several similarities between the muscles of C. caretta and L. kempii, but comparison with other turtles suggests only one of these characters may be derived: connection of the m. adductor mandibulae internus into the Pars intramandibularis via the Zwischensehne. The large fleshy origin of the m. adductor mandibulae externus Pars superficialis from the jugal seems to be a characteristic feature of sea turtles.

Conclusions/Significance

In C. caretta and L. kempii the ability to suction feed does not seem to be as well developed as that found in some freshwater aquatic turtles. Instead both have skulls suited to forceful biting. This is consistent with the observation that both taxa tend to feed on relatively slow moving but sometimes armoured prey. The broad fleshy origin of the m. adductor mandibulae externus Pars superficialis may be linked to thecheek region being almost fully enclosed in bone but the relationship is complex.     

Metamorphosis of the feeding mechanism in tiger salamanders (Ambystoma tigrinum): the ontogeny of cranial muscle mass

Most previous research on metamorphosis of the musculoskeletal system in vertebrates has focused on the transformation of the skeleton. In this paper we focus on the transformation of the muscles of the head during metamorphosis in tiger salamanders ( Ambystoma tigrinum ) in order (1) to provide new data on changes in myology during ontogeny, and (2) to aid in interpreting previous data on the metamorphosis of function in the head of salamanders.
The physiological cross-sectional area of nine head muscles was calculated by measuring fibre angles, fibre lengths, and muscle mass in two samples of tiger salamanders obtained just before and just after metamorphosis. The major mouth-opening muscles (rectus cervicis and depressor mandibulae) exhibit a significant decrease in estimated maximum tetanic tension (MTT) across metamorphosis of about 36%. The jaw-closing muscles (adductor mandibulae internus and externus) and the head-lifting muscles (epaxials) also decrease in MTT but not significantly. The muscles associated with tongue projection during feeding on land (the subarcualis rectus I, geniohyoideus, interhyoideus and intermandibularis) all show a slight increase in MTT at metamorphosis.
Metamorphic transformation of feeding behaviour in Ambystoma tigrinum involves changes in performance, the design of skeletal elements, changes in muscle force-generating capability, and changes in hydrodynamic design from unidirectional flow in larvae to bidirectional flow during aquatic feeding after metamorphosis. Although muscle activity patterns during aquatic feeding do not change across metamorphosis, tongue-based terrestrial feeding involves a suite of novel muscle activity patterns, morphological characters acquired at metamorphosis, and a metamorphic increase in the masses of muscles important in tongue projection.     

Form and function of the feeding apparatus of Alligator mississippiensis

The architecture of the jaw muscles and their tendons of Alligator mississippiensis is described and their function examined by electromyography. Alligator grabs its prey with forward lunges or rapid lateral movements of the head. It does not engage in regular masticatory cycles. Prey is manipulated by inertial movements and the tongue does not appear to play any role in transport. The Mm. adductor mandibulae externus, adductor mandibulae posterior, and pterygoideus activate bilaterally and simultaneously during rapid closing or crushing. The M. pterygoideus does not act during prey holding whereas the Mm. adductor mandibulae externus, adductor mandibulae posterior continue to be active. The Mm. depressor mandibulae and intramandibularis are variably active during both jaw opening and closing.     

Comments on the evolution of the jaw adductor musculature of snakes

The aim of this study is to provide a general view of the adductor musculature of the alethinophidian snakes. The aponeurotic system present in anilioid snakes is here described as being also present in colubroid and booid snakes. Although modified in various groups, this aponeurotic system retains the same topographical pattern in the anilioids, booids and colubroids, and is thus hypothesized to be homologous. An analysis of the aponeurotic system and related muscular bundles within the alethinophidian snakes is given. A new terminology is proposed for the jaw adductor muscles where the muscles levator anguli oris and adductor mandibulae externus superficialis (proper) of snakes (sensu Lakjer, 1926; Haas, 1962) retain these names even if this fails to reflect the presumed homologies with the bundles of the same name in lizards (see Rieppel, 1988b); the fibres originating from the temporal tendon in the Anilioidea, and presumed to form a bundle of composite nature (Rieppel, 1980b), are named the M. adductor mandibulae externus temporalis (lost by the Macrostomata); the M. adductor mandibulae externus medialis is a composite muscle in the Anilioidea (Rieppel, 1980b) which give rise to two different muscles in the ‘booids’, the M. adductor mandibulae externus medialis, pars anterior and the M. adductor mandibulae externus profundus, the former being secondarily lost by the Caenophidia which retains only fibres homologues of the 3b and 3c heads of the profundus layer of lizards; the so-called M. adductor mandibular externus profundus of snakes (sensu Lackjer, 1926; Haas, 1962) is also a composite muscle in the Anilioidea (Rieppel, 1980b), in the alethinophidians it is essentially made of fibres homologous with the posterior pinnate part of the medialis layer of lizards, and is here named the M. adductor mandibulae externus medialis, pars posterior. As a result from this analysis it follows that: (1) the Macrostomata are characterized by the downward extension of the fibres forming the M. adductor mandibulae externus medialis, pars anterior and the loss of the M. adductor mandibulae externus temporalis: (2) the Xenopeltidae are set apart from the remaining macrostomatan snakes by the retention of the M. levator anguli oris and of a well developed lateral sheet of the quadrate aponeurosis; (3) the ‘booids’ form a monophyletic group comprising only the Boidae and Bolyeriidae (with the exclusion of the Xenopeltidae and Tropidophiidae) which is characterized by a differentiated M. adductor mandibulae externus medialis, pars anterior inserting on the lateral surface of the compound bone via its own aponeurosis; (4) the Tropidophiidae are set apart from all other snakes by the peculiar course of their lateral head vein; however, they belong to the Caenophidia as they show a facial carotid artery which passes dorsally to the mandibular and maxillary branches of the trigeminus; (5) a possible additional character in favour of an Acrochordoidea + Colubroidea monophyletic unit may be given by the pattern of innervation of the jaw adductor muscles in these two taxa; (6) a new interpretation of the compressor glandulae muscular complex of Atractaspis resulted in a morphologically similar pattern to that of the viperids; the phylogenetic implications of such similarity are discussed in detail.     

Aspects of masticatory form and function in common tree shrews,Tupaia glis

Tree shrews have relatively primitive tribosphenic molars that are apparently similar to those of basal eutherians; thus, these animals have been used as a model to describe mastication in early mammals. In this study the gross morphology of the bony skull, joints, dentition, and muscles of mastication are related to potential jaw movements and cuspal relationships. Potential for complex mandibular movements is indicated by a mobile mandibular symphysis, shallow mandibular fossa that is large compared to its resident condyle, and relatively loose temporomandibular joint ligaments. Abrasive tooth wear is noticeable, and is most marked at the first molars and buccal aspects of the upper cheek teeth distal to P². Muscle morphology is basically similar to that previously described for Tupaia minor and Ptilocercus lowii. However, in T. glis, an intraorbital part of deep temporalis has the potential for inducing lingual translation of its dentary, and the large medial pterygoid has extended its origin anteriorly to the floor of the orbit, which would enhance protrusion. The importance of the tongue and hyoid muscles during mastication is suggested by broadly expanded anterior bellies of digastrics, which may assist mylohyoids in tensing the floor of the mouth during forceful tongue actions, and by preliminary electromyography, which suggests that masticatory muscles alone cannot fully account for jaw movements in this species.     

Jaw movement kinematics and jaw muscle (EMG) activity during drinking in the pigeon (Columba livia)

Summary Movements of the maxilla and mandible were recorded during drinking in the head-fixed pigeon and correlated with electromyographic activity in representative jaw muscle groups. During drinking, each jaw exhibits opening and closing movements along both the dorso-ventral and rostro-caudal axes which may be linked with or independent of each other. All subjects showed small but systematic increases in cycle duration over the course of individual drinking bouts. Cyclic jaw movements during drinking were correlated with nearly synchronous activity in the protractor (levator) of the upper jaw and in several jaw closer muscles, as well as with alternating activity in tongue protractor and retractor muscles. No EMG activity was ever recorded in the lower jaw opener muscle, suggesting that lower jaw opening in this preparation is produced, indirectly, by the contraction of other muscles. The results clarify the contribution of the individual jaws to the generation of gape variations during drinking in this species.Abbreviations AMEM adductor mandibulae externus muscle - DM depressor mandibulae muscle - EMG electromyographic - GENIO geniohyoideus muscle - LB lower beak - LED light-emitting diode - PQP protractor quadrati et pterygoidei muscle - PVL pterygoideus ventralis muscle, pars lateralis - SeH/StH serpihyoideus or stylohyoideus muscle - UB upper beak     

Morphology and function of the feeding apparatus of the lungfish, Lepidosiren paradoxa (Dipnoi)

The feeding mechanism of the South American lungfish, Lepidosiren paradoxa retains many primitive teleostome characteristics. In particular, the process of initial prey capture shares four salient functional features with other primitive vertebrates: 1) prey capture by suction feeding, 2) cranial elevation at the cranio-vertebral joint during the mouth opening phase of the strike, 3) the hyoid apparatus plays a major role in mediating expansion of the oral cavity and is one biomechanical pathway involved in depressing the mandible, and 4) peak hyoid excursion occurs after maximum gape is achieved. Lepidosiren also possesses four key morphological and functional specializations of the feeding mechanism: 1) tooth plates, 2) an enlarged cranial rib serving as a site for the origin of muscles depressing the hyoid apparatus, 3) a depressor mandibulae muscle, apparently not homologous to that of amphibians, and 4) a complex sequence of manipulation and chewing of prey in the oral cavity prior to swallowing. The depressor mandibulae is always active during mouth opening, in contrast to some previous suggestions. Chewing cycles include alternating adduction and transport phases. Between each adduction, food may be transported in or out of the buccal cavity to position it between the tooth plates. The depressor mandibulae muscle is active in a double-burst pattern during chewing, with the larger second burst serving to open the mouth during prey transport. Swallowing is characterized by prolonged activity in the hyoid constrictor musculature and the geniothoracicus. Lepidosiren uses hydraulic transport achieved by movements of the hyoid apparatus to position prey within the oral cavity. This function is analogous to that of the tongue in many tetrapods.     

Tongue evolution in the lungless salamanders, family plethodontidae. I. Introduction, theory and a general model of dynamics.

Plethodontid salamanders capture prey by projecting the tongue from the mouth. An analysis of theoretical mechanics of the hyobranchial skeleton is used to formulate a working hypothesis of tongue movements. Predictions that the skeletal elements of the tongue are included in the projectile and that the hyobranchial skeleton is folded during projection are central to the analysis. When decapitated in a particular way, salamanders project the tongue, and it is not retracted. When these heads are fixed and sectioned, examination confirms the predications. In turn, these observations are used to refine the working hypothesis and to generate a general model of tongue dynamics for plethodontids. Muscles performing the major roles of projection (subarcualis rectus I) and retraction (rectus cervicis profundus) are identified. The skeleton is folded passively along a morphological track having the form of a tractrix. Predictions concerning the shape of the track and the exact configuration of the folded skeleton are confirmed by study of sectioned material. The skeleton unfolds along the track during retraction and is spread into the resting state. The model developed herein will be used as a basis for predictions concerning selection patterns in the family and for analytical purposes in comparative and evolutionary studies.     

Ontogeny of cranial musculature in Clarias gariepinus (Siluroidei: Clariidae): The adductor mandibulae complex

The adductor mandibulae complex has been a subject of discussion and uncertainties due to a wide range of differentiations that have occurred in teleosts during evolution. In Siluroidei a specific modification of a part of the muscle complex has resulted in the formation of a retractor muscle of the maxillary barbel. The main part of the muscle complex, responsible for the closure of the mouth, has undergone some changes as well, which are at the base of the homology problems encountered by different authors. In this paper the muscles have been studied in three ontogenetic stages of the siluroid Clarias gariepinus (Clariidae); two of them have been described. Based on the ontogenetic evidence and the literature, the following muscles are recognized: 1) the very weakly differentiated adductor mandibulae A₂A'₃, where only little distinction can be made between the A₂ and the A'₃ muscle parts, and 2) the adductor mandibulae A“₃. Caudally, both muscles are separated from each other by the levator arcus palatini, but are fused together anteriorly, inserting onto the lower jaw. In juvenile C. gariepinus, a differentiation has occurred in the A”₃ muscle, thereby forming a distinct pars superficialis and a pars profunda. No A₁ nor an A_ω muscle is present. © 1996 Wiley-Liss, Inc.     

Functional morphology of the jaw muscles of two species of imperial pigeons, Ducula aenea nicobarica and Ducula badia insignis

1. The functional morphological study of the jaw muscles of 2 species of Imperial Pigeons, Ducula aenea nicobarica and Ducula badia insignis has revealed that the structural variations of the bill, osteological and connective tissue elements, and muscles of the jaw apparatus may be correlated to functional diversity in the fruit-eating adaptation of these birds. 2. Both the species of Ducula possess moderately long, thick and stout bill with flexion zones inside, elongated orbital process of the quadrate, stout pterygoid, broad palatine and wide mandibular ramus on either side with increased retroarticular space. Such skeletal modifications together with increased orbital space indicate wide attachment-sites for the muscles, aponeuroses, tendons, and ligaments. 3. The morphology of the quadrato-mandibular joints suggests possible 'coupled kinesis' of the upper jaw, along with depression of the lower jaw. However, in a rhynchokinetic upper jaw as possessed by these birds, the kinesis is just moderate. Hence the gape of the mouth is mainly effected by the depression of the lower jaw, rather less so by the protraction of the upper jaw. 4. Among the functional groups of muscles, M. depressor mandibulae, M. adductor mandibulae externus, M. pseudotemporalis profundus, and M. pterygoideus are especially well developed. The various components of these muscles are provided with stiff as well as wide aponeuroses and tendons (much stronger than those observed in Columba), indicating forceful opening and closure of the beaks for plucking off the fruit, grasping it hard and manipulating it with the help of the beaks before swallowing. 5. The fleshy insertion of the outer slip of M. pseudotemporalis profundus extends ventrally over the dorsolateral surface of the mandible much more than it does in Columba. Further, 2 short and stiff aponeuroses at the rostral insertion of the inner slip of the muscle increase the force of adduction on the mandible. 6. M. adductor mandibulae posterior has not only wider origin and insertion, but also greater mass of fibres than that observed in Columba. 7. M. adductor mandibulae externus and M. pterygoideus form muscle-complexes with the predominance of bipinnate and multipinnate arrangements of fibres and with occasional joining fibres between their components. Such arrangements of fibres indicate sustained force-production, rather than faster movements of the jaw apparatus. 8. M. pterygoideus ventralis lateralis has a well developed 'venter externus' slip which has its thick and fleshy insertion on the outer lateral angular and articular mandible.(ABSTRACT TRUNCATED AT 400 WORDS)     

The functional morphology of lingual prey capture in a scincid lizard,Tiliqua scincoides (Reptilia: Squamata)

We investigated the functional morphology of lingual prey capture in the blue‐tongued skink, Tiliqua scincoides, a lingual‐feeding lizard nested deep within the family Scincidae, which is presumed to be dominated by jaw‐feeding. We used kinematic analysis of high‐speed video to characterize jaw and tongue movements during prey capture. Phylogenetically informed principal components analysis of tongue morphology showed that, compared to jaw‐feeding scincids and lacertids, T. scincoides and another tongue‐feeding scincid, Corucia zebrata, are distinct in ways suggesting an enhanced ability for hydrostatic shape change. Lingual feeding kinematics show substantial quantitative and qualitative variation among T. scincoides individuals. High‐speed video analysis showed that T. scincoides uses significant hydrostatic elongation and deformation during protrusion, tongue‐prey contact, and retraction. A key feature of lingual prey capture in T. scincoides is extensive hydrostatic deformation to increase the area of tongue‐prey contact, presumably to maximize wet adhesion of the prey item. Adhesion is mechanically reinforced during tongue retraction through formation of a distinctive “saddle” in the foretongue that supports the prey item, reducing the risk of prey loss during retraction.     

The roles of visual and proprioceptive information during motor program choice in frogs

Previous studies have shown that leopard frogs, Rana pipiens, use tongue prehension to capture small prey and jaw prehension to capture large prey. After hypoglossal nerve transection, the frogs fail to open their mouths when attempting to feed on small prey, but open their mouths and capture large prey. Here, we investigate how visual information about the prey and proprioceptive information from the tongue interact to influence the motor program choice. Using pieces of earthworm of various sizes, we found that Rana exhibits two different behavior patterns based on prey size. The frogs captured the 1.5-cm prey using tongue prehension, whereas 2.0-cm and larger prey were captured using jaw prehension. After hypoglossal transection, the frogs never opened their mouths when they tried to feed on 1.5-cm prey. When feeding on 3.0-cm and larger prey after transection, they always opened their mouths and captured the prey using jaw prehension. When offered 2.0-cm prey, they alternated randomly between opening and not opening the mouth. Therefore, deafferentation changed the pattern of motor program choice at the behavioral border. This implies that afferents from the tongue interact with visual input to influence motor program choice.     

Rhythmic electromyographic activities of trunk muscles characterize the sexual behavior in the Himé salmon (landlocked sockeye salmon,Oncorhynchus nerka)

Summary In order to describe precisely the fixed action patterns of salmon sexual behavior, we recorded the electromyographic (EMG) activities of trunk and jaw muscles from freely behaving male and female Himé salmon (landlocked sockeye salmon,Oncorhynchus nerka). A series of action patterns (quivering and spawning act in males, digging, covering, prespawning act and spawning act in females, and the swimming and turning movements in both sexes) were characterized by rhythmic activities of the trunk muscles. Each of these activity patterns is quantitatively distinct from the others in such parameters as frequency, bout duration, duty value, intersegmental phase delay, and spatial distribution of rhythmic activities. However, all of these rhythms share a qualitatively homologous pattern with the forward swimming movement: rhythmic activities alternate on both sides of the body (bilateral coupling) and are posteriorly propagated (intersegmental coupling). In addition, a 31 intersegmental phase coupling occurs in the most anterior trunk muscles during the spawning act in some males. Based on these observations, we discussed the biomechanics for these motor patterns (oviposition, ejaculation, body vibration, and mouth opening), and the neural mechanisms for the pattern generation. A possibility was pointed out that the locomotor pattern generator in the spinal cord may be modulated by descending supraspinal signals and recruited to generate such diverse forms of action patterns in sexual behavior.Abbreviations CPG central pattern generator - EMG electromyography - AC adductor mandibulae (cephalic portion) - AM adductor mandibulae (mandibular portion) - DO dilator operculi - GH geniohyoideus - LAP levator arcus palatitni - LPe musculus lateralis profundus (epaxial portion) - LPh musculus lateralis profundus (hypaxial portion) - LS musculus lateralis superficialis - PD protractor dorsalis - PI protractor ischii - RD retractor dorsalis - RI retractor ischii