Zooplankton capture by a coral reef fish: an adaptive response to evasive prey

Synopsis High-speed cinematography and video using modified Schlieren optics and laser illumination helped elicit details of prey capture mechanisms used by Chromis viridis while feeding on calanoid copepods and Artemia. Chromis viridis is capable of a ram-jaw, low-suction feeding, as well as a typical suction feeding behavior described for other species of planktivores. By adjusting the degree of jaw protrusion and amount of suction used during a feeding strike, this fish can modulate its feeding strikes according to the prey type being encountered. The ram-jaw feeding mode enables C. viridis to capture highly evasive calanoid copepods within 6 to 10 msec. The use of specialized feeding behavior for evasive prey and the ability to vary feeding behavior are adaptations for feeding on evasive prey.     

Functional morphology of prey capture in the sturgeon,Scaphirhynchus albus

Acipenseriformes (sturgeon and paddlefish) are basal actinopterygians with a highly derived cranial morphology that is characterized by an anatomical independence of the jaws from the neurocranium. We examined the morphological and kinematic basis of prey capture in the Acipenseriform fish Scaphirhynchus albus, the pallid sturgeon. Feeding pallid sturgeon were filmed in lateral and ventral views and movement of cranial elements was measured from video sequences. Sturgeon feed by creating an anterior to posterior wave of cranial expansion resulting in prey movement through the mouth. The kinematics of S. albus resemble those of other aquatic vertebrates: maximum hyoid depression follows maximum gape by an average of 15 ms and maximum opercular abduction follows maximum hyoid depression by an average of 57 ms. Neurocranial rotation was not a part of prey capture kinematics in S. albus, but was observed in another sturgeon species, Acipenser medirostris. Acipenseriformes have a novel jaw protrusion mechanism, which converts rostral rotation of the hyomandibula into ventral protrusion of the jaw joint. The relationship between jaw protrusion and jaw opening in sturgeon typically resembles that of elasmobranchs, with peak upper jaw protrusion occurring after peak gape.     

Linking cranial kinematics,buccal pressure,and suction feeding performance in largemouth bass

The rate and magnitude of buccal expansion are thought to determine the pattern of water flow and the change in buccal pressure during suction feeding. Feeding events that generate higher flow rates should induce stronger suction pressure and allow predators to draw prey from further away. We tested these expectations by measuring the effects of prey capture kinematics on suction pressure and the effects of the latter on the distance from which prey were drawn-termed suction distance. We simultaneously, but not synchronously, recorded 500-Hz video and buccal pressure from 199 sequences of four largemouth bass, Micropterus salmoides, feeding on goldfish. From the video, we quantified several kinematic variables associated with the head and jaws of the feeding bass that were hypothesized to affect pressure. In a multiple regression, kinematic data accounted for 79.7% of the variation among strikes in minimum pressure. Faster mouth opening and hyoid depression were correlated with lower pressures, a larger area under the pressure curve, and a faster rate of pressure reduction. In contrast, buccal pressure variables explained only 16.5% of the variation in suction distance, and no single pressure variable had a significant relationship with suction distance. Thus, although expected relationships between head kinematics and buccal pressure were confirmed, suction distance was only weakly related to buccal pressure. Three explanations are considered. First, bass may not attempt to maximize the distance from which prey are drawn. Second, the response of prey items to suction-induced flow depends on prey behavior and orientation and is, therefore, subject to considerable variation. Third, previous theoretical work indicates that water velocity decays exponentially with distance from the predator's mouth, indicating that variation among strikes in flow at the mouth opening is compressed away from the mouth. These findings are consistent with other recent data and suggest that suction distance is a poor metric of suction feeding performance.     

Prey capture kinematics and four-bar linkages in the bay pipefish, Syngnathus leptorhynchus

Because of their modified cranial morphology, syngnathid pipefishes have been described as extreme suction feeders. The presumption is that these fishes use their elongate snout much like a pipette in capturing planktonic prey. In this study, we quantify the contribution of suction to the feeding strike and quantitatively describe the prey capture mechanics of the bay pipefish Syngnathus leptorhynchus, focusing specifically on the role of both cranial elevation and snout movement. We used high-speed video to capture feeding sequences from nine individuals feeding on live brine shrimp. Sequences were digitized in order to calculate kinematic variables that could be used to describe prey capture. Prey capture was very rapid, from 2 to 6 ms from the onset of cranial rotation. We found that suction contributed at most about one-eighth as much as ram to the reduction of the distance between predator and prey. This movement of the predator was due almost exclusively to movement of the snout and neurocranium rather than movement of the whole body. The body was positioned ventral and posterior to the prey and the snout was rotated dorsally by as much as 21 degrees, thereby placing the mouth immediately behind the prey for capture. The snout did not follow the identical trajectory as the neurocranium, however, and reached a maximum angle of only about 10 degrees. The snout consists, in part, of elongate suspensorial elements and the linkages among these elements are retained despite changes in shape. Thus, when the neurocranium is rotated, the four-bar linkage that connects this action with hyoid depression simultaneously acts to expand and straighten the snout relative to the neurocranium. We confirm the presence of a four-bar linkage that facilitates these kinematics by couplings between the pectoral girdle, urohyal, hyoid complex, and the neurocranium-suspensorium complex.     

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.     

The effects of intraspecific competition on the prey capture behavior and kinematics of the bluegill sunfish, Lepomis macrochirus

Competition has broad effects on fish and specifically the effects of competition on the prey capture kinematics and behavior are important for the assessment of future prey capture studies in bony fishes. Prey capture kinematics and behavior in bony fishes have been shown to be affected by temperature and satiation. The densities at which bony fish are kept have also been shown to affect their growth, behavior, prey selection, feeding and physiology. We investigated how density induced intraspecific competition for food affects the prey capture kinematics of juvenile bluegill sunfish, Lepomis macrochirus. High speed video was utilized to film five bold individuals feeding at three different densities representing different levels of intraspecific competition. We hypothesized that: (1) the feeding kinematics will be faster at higher levels of competition compared to lower levels of competition, and (2) bluegill should shift from more suction-based feeding towards more ram-based feeding with increasing levels of competition in order to outcompete conspecifics for a prey item. We found that, with increased intraspecific competition, prey capture became faster, involving more rapid jaw opening and therefore greater inertial suction, shorter mouth closing times, and shorter gape cycles. Furthermore, the attack velocity of the fish increased with increasing competition, however a shift towards primarily ram based feeding was not confirmed. Our study demonstrates that prey capture kinematics are affected by the presence of conspecifics and future studies need to consider the effects of competition on prey capture kinematics.     

A KINEMATIC STUDY OF SUCTION FEEDING AND ASSOCIATED BEHAVIOR IN THE LONG-FINNED PILOT WHALE, GLOBICEPHALA MELAS (TRAILL)

Analysis of videotaped feeding sequences provides novel documentation of suction feeding in captive juvenile long-finned pilot whales ( Globicephala melas ). Swimming and stationary whales were videotaped while feeding at the surface, mid-water, and bottom. The ingestion sequence includes a preparatory phase with partial gape followed by jaw opening and rapid hyoid depression to suck in prey at a mean distance of 14 cm (duration 90 msec), although prey were taken from much greater distances. Depression and retraction of the large, piston-like tongue generate negative intraoral pressures for prey capture and ingestion. Food was normally ingested without grasping by teeth yet was manipulated with lingual, hyoid, and mandibular movement for realignment; suction was then used to transport prey into the oropharynx. Whales frequently rolled or inverted before taking prey, presumably to avoid grasping and repositioning. Prey were sucked off the bottom or sides of the pool without direct contact; lateral suction was used to ingest items from the sides of the mouth.     

Functional morphology of the feeding apparatus,feeding constraints,and suction performance in the nurse shark Ginglymostoma cirratum

The nurse shark, Ginglymostoma cirratum, is an obligate suction feeder that preys on benthic invertebrates and fish. Its cranial morphology exhibits a suite of structural and functional modifications that facilitate this mode of prey capture. During suction‐feeding, subambient pressure is generated by the ventral expansion of the hyoid apparatus and the floor of its buccopharyngeal cavity. As in suction‐feeding bony fishes, the nurse shark exhibits expansive, compressive, and recovery kinematic phases that produce posterior‐directed water flow through the buccopharyngeal cavity. However, there is generally neither a preparatory phase nor cranial elevation. Suction is generated by the rapid depression of the buccopharyngeal floor by the coracoarcualis, coracohyoideus, and coracobranchiales muscles. Because the hyoid arch of G. cirratum is loosely connected to the mandible, contraction of the rectus cervicis muscle group can greatly depress the floor of the buccopharyngeal cavity below the depressed mandible, resulting in large volumetric expansion. Suction pressures in the nurse shark vary greatly, but include the greatest subambient pressures reported for an aquatic‐feeding vertebrate. Maximum suction pressure does not appear to be related to shark size, but is correlated with the rate of buccopharyngeal expansion. As in suction‐feeding bony fishes, suction in the nurse shark is only effective within approximately 3 cm in front of the mouth. The foraging behavior of this shark is most likely constrained to ambushing or stalking due to the exponential decay of effective suction in front of the mouth. Prey capture may be facilitated by foraging within reef confines and close to the substrate, which can enhance the effective suction distance, or by foraging at night when it can more closely approach prey. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

The ontogeny of feeding kinematics in a giant salamander Cryptobranchus alleganiensis: Does current function or phylogenetic relatedness predict the scaling patterns of movement?

Studies of the scaling of feeding movements in vertebrates have included three species that display both near-geometric growth and isometry of kinematic variables. These scaling characteristics allow one to examine the “pure” relationship of growth and movement. Despite similar growth patterns, the feeding movements of toads (Bufo) slow down more with increasing body size than those of bass (Micropterus), and sharks (Ginglymostoma). This variation might be due to major differences in the mechanism of prey capture; the bass and sharks use suction to capture prey in water, while the toad uses tongue prehension to capture prey on land. To investigate whether or not these different scaling patterns are correlated with differences in feeding mechanics, we examined the ontogenetic scaling of prey capture movements in the hellbender salamander (Cryptobranchus alleganiensis), which also has near-geometric growth. The hellbender suction feeds in the same general manner as the teleosts and shark, but is much more closely related to the toad. The feeding movements of the hellbender scale more similarly to the feeding movements of toads than to those of fishes or sharks, indicating that phylogenetic relatedness rather than biomechanical similarity predicts ontogenetic scaling patterns of movement.     

Comparative anatomy and evolutionary history of suction feeding in cetaceans

Some odontocetes possess unique features of the hyolingual apparatus that are involved in suction feeding. The hyoid bone and associated musculature generates rapid, piston‐like retraction, and depression of the hyoid and tongue. “Capture” suction feeders (e.g., Globicephala) use suction for capturing and swallowing prey. “Combination” feeders (i.e., Lagenorhynchus) use both raptorial feeding (to capture prey) and suction (to ingest prey). In “capture” suction feeders, features of the hyoid and skull have been attributed to creating suction (i.e., large surface area and mandibular bluntness). In addition to odontocetes, a mysticete, the gray whale (Eschrichtius robustus), is considered a benthic suction feeder. However, anatomical studies of purported suction‐feeding structures of the gray whale are lacking. In addition, few studies have utilized evolutionary approaches to understand the history of suction feeding in cetaceans. This study incorporates quantitative and qualitative hyoid and cranial data from 35 extant and 14 extinct cetacean species into a multivariate principal component analysis and comparative phylogenetic analyses. Conclusions from these analyses are that some commonly attributed features (i.e., ventral throat grooves and mandibular bluntness) and one principal component are significantly correlated with suction feeding. Finally, ancestral state reconstructions indicate that suction feeding likely evolved once, early in cetacean evolutionary history.     

Largemouth bass (Micropterus salmoides) switch feeding modalities in response to sensory deprivation

Animals use a suite of sensory modalities to precisely locate and capture prey. While numerous studies have examined the effects of sensory deprivation on the behaviors leading to prey capture and while it is generally believed that information in the pre-strike period determines the way fish capture prey, this study is the first to examine the contribution of sensory information to jaw kinematics during capture. Largemouth bass were filmed using high-speed videography while capturing live mosquitofish. Bass were examined intact, with visual deprivation under infrared light, and with lateral line deprivation following treatment with cobalt chloride. Deprived of visual cues, this visual ram-feeding predator switches towards suction-based feeding to successfully capture prey. They approach prey slowly but open their mouths more rapidly, which has been shown to result in greater buccal pressure, causing their prey to move a greater distance at a more rapid velocity as they are being drawn into the predators' mouths. Deprived of lateral line cues, bass have higher forward velocities during capture and capture prey earlier in the gape cycle. This study demonstrates that sensory pre-strike information directly affects the capture modality employed by fishes and that fish can modulate between ram and suction not only by adjusting the amount of ram by increasing or decreasing their movements, but also by actively increasing the amount of suction used. These results suggest that the ability to modulate feeding behavior may allow animals to not only exploit a broader breadth of prey items, but also to be capable of doing so in a wider variety of environments.     

Feeding kinematics and morphology of the alligator gar (Atractosteus spatula,Lacépède, 1803)

Living gars are a small clade of seven species that occupy an important position on the actinopterygian phylogenetic tree as members of Holostei, sister-group to teleosts, and exhibit many plesiomorphic traits used to interpret and reconstruct early osteichthyan feeding mechanisms. Previous studies of gar feeding kinematics have focused on the ram-based, lateral-snapping mode of prey capture found in the narrow-snouted Lepisosteus genus, whereas this study focuses on a member of the broad-snouted Atractosteus sister-genus, the alligator gar (Atractosteus spatula, Lacépède, 1803). High-speed videography reveals that the feeding system of alligator gars is capable of rapid expansion from anterior to posterior, timed in a way to generate suction, counteract the effects of a bow-wave during ram-feeding, and direct a unidirectional flow of water through the feeding system. Reconstructed contrast-enhanced μCT-based cranial anatomy and three-dimensional modeling of linkage mechanics show that a lateral-sliding palatoquadrate, flexible intrasuspensorial joint, pivoting interhyal, and retractable pectoral girdle increase the range of motion and expansive capabilities of the alligator gar feeding mechanism. Reconstructions of muscular anatomy, inferences from in vivo kinematics, and in situ manipulations show that input from the hyoid constrictors and hypaxials play an important role in decoupling and modulating the dual roles of the sternohyoideus during feeding: hyoid retraction (jaw opening) and hyoid rotation (pharyngeal expansion). The alligator gar possesses an intricate feeding mechanism, capable of precise control with plesiomorphic muscles that represent one of the many ways the ancestral osteichthyan feeding mechanism has been modified for prey capture.     

Kinematics of prey capture and chewing in the lizard Agama agama (squamata: Agamidae)

High speed video recordings (200 fields per second) of prey capture and food processing in Agama agama permit the identification of strikes, chews and transport movements. Ten variables from strike movements and seven variables from chewing sequences are digitized; transport movements are inspected only. Univariate and multivariate statistical analyses disclose significant interindividual differences for three variables (maximum gape distance, maximum head angle, and maximum throat distance); but neither these nor principal components analysis show differences between strikes and chews for any of the gape change and hyoid depression variables. However, strikes and chews obviously differ in tongue protrusion and body movements. Chewing may be divided into four stages, comparable to those of transport cycles of other lizards and the generalized tetrapod model. Transport differs from chewing by having a shorter power stroke and relatively more cranial and less jaw movement. The kinematics of feeding in Agama agama are compared with those of other lizards studied previously.     

Functional design and prey capture dynamics in an ecologically generalized surfperch (Embiotocidae)

Kinematic and electromyographic analyses of prey capture in two species of surfperch (Embiotocidae) reveal differing abilities to modulate strike activity in response to different prey types. Both the black perch, Embiotoca jacksoni, and the shiner perch, Cymatogaster aggregata, demonstrate stereotyped and conserved neuromuscular and kinematic activity in suction feeding. A distinguishing anatomical trait in this family, the interopercular shelf, enhances the coupling of hyoid movement with mandibular depression. Analyses of variance suggest a preprogrammed motor output that is ballistically launched for suction generation, with the possibility of more plasticity in latter phases of the strike. While the trophically limited shiner perch displays a stereotyped repertoire of this one strike pattern, very small prey, larger conglomerates of these, and large distinct prey elicit three modulated patterns in the black perch. Functional characteristics that enable the ecologically generalized black perch to exploit a variety of prey types include energy–conserving modulatory ability, behavioural flexibility in utilizing a conserved suction–generating programme, and the addition of specialized winnowing and spitting activity.     

Functional morphology of extreme jaw protrusion in Neotropical cichlids

The New World cichlids Petenia splendida and Caquetaia spp. possess extraordinarily protrusible jaws. We investigated the feeding behavior of extreme (here defined as greater than 30% head length) and modest jaw-protruding Neotropical cichlids by comparing feeding kinematics, cranial morphology, and feeding performance. Digital high-speed video (500 fps) of P. splendida, C. spectabile, and Astronotus ocellatus feeding on live guppy prey was analyzed to generate kinematic and performance variables. All three cichlid taxa utilized cranial elevation, lower jaw depression, and rotation of the suspensorium to protrude the jaws during feeding experiments. Extreme anterior jaw protrusion in P. splendida and C. spectabile resulted from augmented lower jaw depression and anterior rotation of the suspensorium. Morphological comparisons among eight cichlid species revealed novel anterior and posterior points of flexion within the suspensorium of P. splendida and Caquetaia spp. The combination of anterior and posterior loosening within the suspensorium in P. splendida and Caquetaia spp. permitted considerable anterior rotation of the suspensorium and contributed to protrusion of the jaws. Petenia splendida and C. spectabile exhibited greater ram distance and higher ram velocities than did A. ocellatus, resulting primarily from increased jaw protrusion. Petenia splendida and C. spectabile exhibited lower suction feeding performance than A. ocellatus, as indicated by lower suction-induced prey movements and velocities. Thus, extreme jaw protrusion in these cichlids may represent an adaptation for capturing elusive prey by enhancing the ram velocity of the predator but does not enhance suction feeding performance.     

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.     

Piscivorous cyprinid fish modulates suction feeding kinematics to capture elusive prey

Previous studies have shown that evasive prey generally elicit a different kinematical pattern of prey capture from suction feeding fish compared to non-evasive types of prey. However, no evidence exists that predatory fish can modulate their prey capture kinematics in response to whether or not an elusive prey performs an escape response. Here, we analyse prey capture kinematics of a specialist piscivore (asp, Aspius aspius) during feeding on untethered, live goldfish, which regularly displayed escape attempts when attacked by the asp. Significant modulation occurred in function of the escape attempts of prey: mouth opening was prolonged and increased in magnitude, and one individual also showed an increased hyoid depression when feeding on prey trying to escape. As the orientation of the prey with respect to the predator prior to the start of mouth opening was related to the probability of observing an escape attempt, asp could theoretically perform this type of modulation by a priori choosing a pre-programmed motor pattern. However, since contact between the prey and the asp's mouth appeared to be a factor improving the timing of mouth closing, this fine-tuning of prey capture kinematics is more likely to be caused by reflexive neural feedback control.     

A functional morphospace for the skull of labrid fishes: patterns of diversity in a complex biomechanical system

The Labridae (including wrasses, the Odacidae and the Scaridae) is a species‐rich group of perciform fishes whose members are prominent inhabitants of warm‐temperate and tropical reefs worldwide. We analyse functionally relevant morphometrics for the feeding apparatus of 130 labrid species found on the Great Barrier Reef and use these data to explore the morphological and mechanical basis of trophic diversity found in this assemblage. Morphological measurements were made that characterize the functional and mechanical properties of the oral jaws that are used in prey capture and handling, the hyoid apparatus that is used in expanding the buccal cavity during suction feeding, and the pharyngeal jaw apparatus that is used in breaking through the defences of shelled prey, winnowing edible matter from sand and other debris, and pulverizing the algae, detritus and rock mixture eaten by scarids (parrotfishes). A Principal Components Analysis on the correlation matrix of a reduced set of ten variables revealed complete separation of scarids from wrasses on the basis of the former having a small mouth with limited jaw protrusion, high mechanical advantage in jaw closing, and a small sternohyoideus muscle and high kinematic transmission in the hyoid four‐bar linkage. Some scarids also exhibit a novel four‐bar linkage conformation in the oral jaw apparatus. Within wrasses a striking lack of strong associations was found among the mechanical elements of the feeding apparatus. These weak associations resulted in a highly diverse system in which functional properties occur in many different combinations and reflect variation in feeding ecology. Among putatively monophyletic groups of labrids, the cheilines showed the highest functional diversity and scarids were moderately diverse, in spite of their reputation for being trophically monomorphic and specialized. We hypothesize that the functional and ecological diversity of labrids is due in part to a history of decoupled evolution of major components of the feeding system (i.e. oral jaws, hyoid and pharyngeal jaw apparatus) as well as among the muscular and skeletal elements of each component. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82 , 1–25.     

Aerial and aquatic feeding in the silver arawana,Osteoglossum bicirrhosum

Synopsis The silver arawana, Osteoglossum bicirrhosum, hunts along shorelines and within flooded forests in the Amazon River basin and supplements its limited consumption of aquatic vertebrates by leaping from the water to obtain terrestrial and arboreal prey. We offered O. bicirrhosum prey both suspended above and submerged below the surface of the water. From high-speed digital recordings, we measured kinematic variables associated with the jaws, cranium, pectoral fins, and body during orientation and prey capture. Aquatic and aerial feeding events were kinematically distinct, with aerial events generally involving faster, larger movements and a distinct delay in the onset of lower jaw depression until the head had left the water. The comparatively large gape during leaping may facilitate prey capture by overcoming variability in the apparent position of the prey due to refraction, while the delayed onset of mouth opening may serve to reduce the effects of drag. This distinctive leaping behaviour allows exploitation of the terrestrial prey base, especially during seasonal inundation of the Amazon River basin when the aquatic food base is widely dispersed.     

PATTERNS OF VARIATION IN AQUATIC AMBYSTOMATID SALAMANDERS: KINEMATICS OF THE FEEDING MECHANISM

Patterns of variation in the feeding mechanism of three species of ambystomatid salamanders (Ambystoma dumerilii, A. mexicanum, and A. ordinarium) were studied to provide insight into the nature of variation in kinematic parameters of the jaw mechanism associated with prey capture. A nested analysis of variance design provided an assessment of the amount of variation in six kinematic variables (measured from 200 frames/sec films of feeding behavior) both among species and among individuals within species. For all six variables, a highly significant proportion of the variance was explained at the intraspecific level. Among species, the most robust discriminators were variables associated with movement of the hyoid. The variables reflecting gape and lifting of the head provided no significant discrimination among species and had large error variances. The hyoid apparatus is the most phylogenetically conservative component of the feeding mechanism in lower vertebrates and was the most stereotyped component of feeding behavior within the salamander species studied here.