Disparity between Feeding Performance and Predicted Muscle Strength in the Pharyngeal Musculature of Black Drum, Pogonias cromis (Sciaenidae)

Synopsis Pogonias cromis, black drum, is the largest durophagous sciaenid and feeds almost exclusively on hard-shelled bivalves and gastropods using powerful pharyngeal jaws. I estimated pharyngeal jaw bite forces used to crush live molluscs during feeding trials from juvenile and young adult Pogonias cromis, and they are the highest yet documented for bony fishes. Crushing ability in P. cromis scaled with strong positive allometry suggesting large adult fish may have one of the strongest bites among vertebrates. Physiological estimates of pharyngeal muscle strength derived from muscle cross sectional area accounted for only half of the force generated during actual feeding performance trials. The significant disparity between feeding performance and pharyngeal muscle strength in P. cromis indicates the presence of novel biomechanical linkages that enhance crushing ability for feeding on hard-shelled molluscs. I present a biomechanical model in which the lower pharyngeal jaw architecture of P. cromis emulates a second class lever mechanism that can amplify muscle forces transmitted to the shell of the prey.     

Stiffening the stingray skeleton - an investigation of durophagy in myliobatid stingrays (Chondrichthyes, batoidea, myliobatidae)

The stingray family Myliobatidae contains five durophagous (hard prey specialist) genera and two planktivorous genera. A suite of morphological features makes it possible for the hard prey specialists to crush mollusks and crustaceans in their cartilaginous jaws. These include: 1) flat, pavement-like tooth plates set in an elastic dental ligament; 2) multiple layers of calcified cartilage on the surface of the jaws; 3) calcified struts running through the jaws; and 4) a lever system that amplifies the force of the jaw adductors. Examination of a range of taxa reveals that the presence of multiple layers of calcified cartilage, previously described from just a few species, is a plesiomorphy of Chondrichthyes. Calcified struts within the jaw, called "trabecular cartilage," are found only in the myliobatid genera, including the planktivorous Manta birostris. In the durophagous taxa, the struts are concentrated under the area where prey is crushed, thereby preventing local buckling of the jaws. Trabecular cartilage develops early in ontogeny, and does not appear to develop as a direct result of the stresses associated with feeding on hard prey. A "nutcracker" model of jaw function is proposed. In this model, the restricted gape, fused mandibular and palatoquadrate symphyses, and asynchronous contraction of the jaw adductors function to amplify the closing force by 2-4 times.     

Scaling of feeding biomechanics in the horn shark Heterodontus francisci: ontogenetic constraints on durophagy

Organismal performance changes over ontogeny as the musculoskeletal systems underlying animal behavior grow in relative size and shape. As performance is a determinant of feeding ecology, ontogenetic changes in the former can influence the latter. The horn shark Heterodontus francisci consumes hard-shelled benthic invertebrates, which may be problematic for younger animals with lower performance capacities. Scaling of feeding biomechanics was investigated in H. francisci (n=16, 19–59 cm standard length (SL)) to determine the biomechanical basis of allometric changes in feeding performance and whether this performance capacity constrains hard-prey consumption over ontogeny. Positive allometry of anterior (8–163 N) and posterior (15–382 N) theoretical bite force was attributed to positive allometry of cross-sectional area in two jaw adducting muscles and mechanical advantage at the posterior bite point (0.79–1.26). Mechanical advantage for anterior biting scaled isometrically (0.52). Fracture forces for purple sea urchins Strongylocentrotus purpuratus consumed by H. francisci ranged from 24 to 430 N. Comparison of these fracture forces to the bite force of H. francisci suggests that H. francisci is unable to consume hard prey early in its life history, but can consume the majority of S. purpuratus by the time it reaches maximum size. Despite this constraint, positive allometry of biting performance appears to facilitate an earlier entry into the durophagous niche than would an isometric ontogenetic trajectory. The posterior gape of H. francisci is significantly smaller than the urchins capable of being crushed by its posterior bite force. Thus, the high posterior bite forces of H. francisci cannot be fully utilized while consuming prey of similar toughness and size to S. purpuratus, and its potential trophic niche is primarily determined by anterior biting capacity.     

Ecomorphology: Experimental Functional Anatomy for Ecological Problems

It is generally believed that the functional design of an organismrelates to its ecology, yet this ecomorphological paradigm hashistorically suffered from the lack of a rigorous frameworkfor its implementation. I present a methodology for experimentallyexploring the ecological consequences of variation in morphology.The central idea is that morphology influences ecology by limitingthe ability of the individual to perform key tasks in its dailylife. Inthis scheme the effect of morphological variation onbehavioral performance is first tested in laboratory experiments.As the behavioral capability of an individual defines the rangeof ecological resources that it can potentially make use of(the potential niche), the second step in the scheme involvescomparing the potential niche of an individual to actual patternsof resource use (the realized niche). This permits a quantitativeassessment of the significance of an organism's maximal capabilitiesin determining actual patterns of resource use. An example is presented from work on the feeding biology offishes in the family Labridae (wrasses and parrotfishes). Mostlabrids feed by crushing shelled prey in their powerful pharyngealjaws. This example explores the dietary consequences of variationin crushing strength amongand within species. Crushing strengthwas estimated from biomechanical analyses of the crushingapparatusin several species, and these predictions of relative strengthwere tested in laboratory feeding experiments with hard-shelledprey. Morphology accurately predicted relative crushing ability,and the final section of the study explored the effect of variationin crushing ability on diet. Within each of three species crushingstrength appears to underlie a major ontogentic dietary switchfrom soft-bodied prey to a diet dominated by hard-shelled prey.In each species this switch occurred at about the same crushingstrength, around 5 Newtons (N), in spite of the fact that thiscrushing strength is achieved by the three species at differentbody sizes. Diet breadth increases during ontogeny in each species,until a crushing strength of 5 N is achieved, when diet breadthbegins to decline. The strongest fishes specialized almost entirelyon molluscs and sea urchins. Thus, these labrids take advantageof ontogenetic and interspecific differences in crushing strengthby including harder and harder prey in their diet, and ultimatelyspecializing on hard prey types. The specialized organizationof the labrid pharyngeal jaws can be viewed as a key innovationthat has permitted this lineage of fishes to invade the mollusceating niche, a relatively empty trophic niche within the highlyspeciose and diverse communities of coral reef fishes.     

Eating with a saw for a jaw: Functional morphology of the jaws and tooth‐whorl in Helicoprion davisii

The recent reexamination of a tooth‐whorl fossil of Helicoprion containing intact jaws shows that the symphyseal tooth‐whorl occupies the entire length of Meckel's cartilage. Here, we use the morphology of the jaws and tooth‐whorl to reconstruct the jaw musculature and develop a biomechanical model of the feeding mechanism in these early Permian predators. The jaw muscles may have generated large bite‐forces; however, the mechanics of the jaws and whorl suggest that Helicoprion was better equipped for feeding on soft‐bodied prey. Hard shelled prey would tend to slip anteriorly from the closing jaws due to the curvature of the tooth‐whorl, lack of cuspate teeth on the palatoquadrate (PQ), and resistance of the prey. When feeding on soft‐bodied prey, deformation of the prey traps prey tissue between the two halves of the PQ and the whorl. The curvature of the tooth‐whorl and position of the exposed teeth relative to the jaw joint results in multiple tooth functions from anterior to posterior tooth that aid in feeding on soft‐bodied prey. Posterior teeth cut and push prey deeper into the oral cavity, while middle teeth pierce and cut, and anterior teeth hook and drag more of the prey into the mouth. Furthermore, the anterior‐posterior edges of the teeth facilitate prey cutting with jaw closure and jaw depression. The paths traveled by each tooth during jaw depression are reminiscent of curved pathways used with slashing weaponry such as swords and knifes. Thus, the jaws and tooth‐whorl may have formed a multifunctional tool for capturing, processing, and transporting prey by cyclic opening and closing of the lower jaw in a sawing fashion. J. Morphol. 276:47–64, 2015. © 2014 Wiley Periodicals, Inc.     

Functional morphology of durophagy in black carp,Mylopharyngodon piceus

The black carp, Mylopharyngodon piceus (Osteichthyes: Cyprinidae), crushes its snail and other molluscan prey with robust pharyngeal jaws and strong bite forces. Using gross morphology, histological sectioning, and X‐ray reconstruction of moving morphology (XROMM), we investigated structural, behavioral, and mechanical aspects of pharyngeal jaw function in black carp. Strut‐like trabeculae in their pharyngeal jaws support large, molariform teeth. The teeth occlude with a hypertrophied basioccipital process that is also reinforced with stout trabeculae. A keratinous chewing pad is firmly connected to the basioccipital process by a series of small bony projections from the base of the pedestal. The pharyngeal jaws have no bony articulations with the skull, and their position is controlled by five paired muscles and one unpaired median muscle. Black carp can crush large molluscs, so we used XROMM to compare pharyngeal jaw postures as fish crushed ceramic tubes of increasing sizes. We found that black carp increase pharyngeal jaw gape primarily by ventral translation of the jaws, with ventral rotation and lateral flaring of the jaws also increasing the space available to accommodate large prey items. A stout, robust ligament connects left and right jaws together firmly, but allows some rotation of the jaws relative to each other. Contrasting with the pharyngeal jaw mechanism of durophagous perciforms with fused left and right lower pharyngeal jaws, we hypothesize that this ligamentous connection may serve to decouple tensile and compressive forces, with the tensile forces borne by the ligament and the compressive forces transferred to the prey. J. Morphol. 276:1422–1432, 2015. © 2015 Wiley Periodicals, Inc.     

Morphology and mechanics of the teeth and jaws of white-spotted bamboo sharks (Chiloscyllium plagiosum)

The teeth of white-spotted bamboo sharks (Chiloscyllium plagiosum) are used to clutch soft-bodied prey and crush hard prey; however, the dual function is not evident from tooth morphology alone. Teeth exhibit characteristics that are in agreement with a clutching-type tooth morphology that is well suited for grasping and holding soft-bodied prey, but not for crushing hard prey. The dual role of this single tooth morphology is facilitated by features of the dental ligament and jaw joint. Tooth attachment is flexible and elastic, allowing movement in both sagittal and frontal planes. During prey capture spike-like tooth cusps pierce the flesh of soft prey, thereby preventing escape. When processing prey harder than the teeth can pierce the teeth passively depress, rotating inward towards the oral cavity such that the broader labial faces of the teeth are nearly parallel to the surface of the jaws and form a crushing surface. Movement into the depressed position increases the tooth surface area contacting prey and decreases the total stress applied to the tooth, thereby decreasing the risk of structural failure. This action is aided by a jaw joint that is ventrally offset from the occlusal planes of the jaws. The offset joint position allows many teeth to contact prey simultaneously and orients force vectors at contact points between the jaws and prey in a manner that shears or rolls prey between the jaws during a bite, thus, aiding in processing while reducing forward slip of hard prey from the mouth. Together the teeth, dental ligament, and jaws form an integrated system that may be beneficial to the feeding ecology of C. plagiosum, allowing for a diet that includes prey of varying hardness and elusiveness.     

Morphological convergence of pharyngeal jaw structure in durophagous perciform fish

This study investigated the ecomorphology of pharyngeal jaw structure and durophagy in three families of marine teleosts: the Sciaenidae, Haemulidae and Carangidae. Regressions of the bone and muscle mass of pharyngeal jaws were generated to elucidate the differences associated with eating hard-bodied and soft-bodied prey; within-family comparisons revealed significant differences in masses of bones and muscles involved with processing the former. Generally, the durophagous species − Trachinotus carolinus (Carangidae), Pogonias cromis (Sciaenidae) and Anisotremus surinamensis (Haemulidae) − had heavier and stronger pharyngeal toothplates and larger protractor pectoralis muscles, with masses of these musculoskeletal elements ranging from five times to nearly an order of magnitude larger than those of their soft-prey feeding relatives. Pogonias cromis and T. carolinus demonstrate convergence in the ontogeny and morphological modification of the pharyngeal toothplates and protractor pectoralis muscles that enhance crushing ability. In the Haemulidae, moderate size increases in a few pharyngeal jaw elements (and larger overall body size in A. surinamensis ) are sufficient for durophagy. Morphospace analysis of six species from the three families illustrates the strong functional association between the biomechanical properties of prey and the relative sizes of biting and transport mechanisms.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80 , 147−165.     

Oral shelling within an adaptive radiation of pupfishes: Testing the adaptive function of a novel nasal protrusion and behavioural preference

Dietary specialization on hard prey items, such as mollusks and crustaceans, is commonly observed in a diverse array of fish species. Many fish consume these types of prey by crushing the shell to consume the soft tissue within, but a few fishes extricate the soft tissue without breaking the shell using a method known as oral shelling. Oral shelling involves pulling a mollusc from its shell and it may be a way to subvert an otherwise insurmountable shell defence. However, the biomechanical requirements and potential adaptations for oral shelling are unknown. Here, we test the hypothesis that a novel nasal protrusion is an adaptation for oral shelling in the durophagous pupfish (Cyprinodon brontotheroides). We first demonstrate oral shelling in this species and then predict that a larger nasal protrusion would allow pupfish to consume larger snails. Durophagous pupfish are found within an endemic radiation of pupfish on San Salvador Island, Bahamas. We took advantage of closely related sympatric species and outgroups to test: (a) whether durophagous pupfish shell and consume more snails than other species, (b) if F1 and F2 durophagous hybrids consume similar amounts of snails as purebred durophagous pupfish, and (c) if nasal protrusion size in parental and hybrid populations increases the maximum size of consumed snails. We found that durophagous pupfish and their hybrids consumed the most snails, but did not find a strong association between nasal protrusion size and maximum snail size consumed within the parental or F2 hybrid population, suggesting that the size of their novel nasal protrusion does not provide a major benefit in oral shelling. Instead, we suggest that the nasal protrusion may increase feeding efficiency, act as a sensory organ, or is a sexually selected trait, and that a strong feeding preference may be most important for oral shelling.     

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.     

Structure and function of the horn shark (Heterodontus francisci) cranium through ontogeny: development of a hard prey specialist

The horn sharks (Heterodontidae: Chondrichthyes) represent one of four independent evolutions of durophagy in the cartilaginous fishes. We used high-resolution computed tomography (CT scanning) to visualize and quantify the mineralized tissue of an ontogenetic series of horn sharks. CT scanning of neonatal through adult California horn sharks (Heterodontus francisci) confirmed that this technique is effective for examining mineralized tissue in even small (<10 mm) specimens. The jaw joint is among the first areas to become mineralized and is the most heavily mineralized area in the cranium of a neonatal horn shark. The hyoid is also well mineralized, although the poorly mineralized molariform teeth indicate that the neonatal animal may be a suction feeder on softer prey. The symphysis of the jaws never mineralizes, in sharp contrast to the condition in the hard prey-crushing stingrays. Digitally reslicing the CT scans along the jaws allowed measurement of the second moment of area (Ina). Assuming that the jaws are made of the same material at all ages, Ina is an indicator of the flexural stiffness of the jaws. In all sizes of shark the lower jaws were stiffer than the upper and the stiffness increased in the area of the molariform teeth. The central region of the jaws, where the rami meet, support cuspidate grasping teeth and has the lowest Ina. The spotted eagle ray (Aetobatus narinari), a hard prey-crushing stingray, shows a different pattern of flexural stiffness, with the peak at the central part of the jaws where the prey is reduced between flattened tooth plates. Although the eagle ray jaws have a higher Ina than the horn shark, they are also far more heavily mineralized. When the relative amounts of mineralization are taken into account, horn sharks do better with what mineral they have than does the eagle ray. With a tight jaw joint and loose mandibular symphysis, as well as nearly opposite patterns of stiffness in the jaws, it is clear that two of the clades of hard prey specialists use very different methods for cracking the hard prey problem.     

Shape analysis of the jaws between two minnow species over ontogeny

This study compares sand shiner (Notropis stramineus ) and silverjaw (Ericymba buccata ) minnows, in terms of the morphological shape changes of the upper, lower, and pharyngeal jaws over ontogeny. These two species of minnows initially feed on midge larvae and undergo an ontogenic prey shift. The traditional morphometrics measured—total length, snout‐to‐vent length, eye diameter, premaxilla length, lower jaw length, gape—were regressed onto total length to test for allometry. Digital pictures were processed with tpsDig and further analyzed with MorphoJ utilizing a regular geometric morphometrics procedure using principle component analyses. We examined gut contents for 16 fish of each species. For the silverjaw minnows, we found all jaw variables to exhibit positive allometric growth with increasing total length, while most of the jaw variables for the sand shiner exhibited negative allometric growth with increasing total length. This correlates with an ontogenic prey shift for both species. Sand shiner minnows have been found to be more omnivorous, feeding on algae later in life, while silverjaw minnows undergo a prey shift to larger invertebrates. These species lack oral dentition causing an increased reliance on the pharyngeal apparatus. Principle component analyses revealed elongation of pharyngeal jaw elements in the silverjaw minnows and a relative shortening and bulking of pharyngeal jaws in the sand shiner minnows. The ontogenic dietary shifts observed in these two species provide possible explanation for the morphological changes over ontogeny in jaw elements, which are likely enabling these species to occupy the same habitat with little niche overlap.     

Functional morphology of jaw trabeculation in the lesser electric ray Narcine brasiliensis, with comments on the evolution of structural support in the Batoidea

The design of minimum-weight structures that retain their integrity under dynamic loading regimes has long challenged engineers. One solution to this problem found in both human and biological design is the optimization of weight and strength by hollowing a structure and replacing its inner core with supportive struts. In animals, this design is observed in sand dollar test, avian beak, and the cancellous bone of tetrapod limbs. Additionally, within the elasmobranch fishes, mineralized trabeculae (struts) have been reported in the jaws of durophagous myliobatid stingrays (Elasmobranchii: Batoidea), but were believed to be absent in basal members of the batoid clade. This study, however, presents an additional case of batoid trabeculation in the lesser electric ray, Narcine brasiliensis (Torpediniformes). The trabeculae in these species likely play different functional roles. Stingrays use their reinforced jaws to crush bivalves, yet N. brasiliensis feeds by ballistically protruding its jaws into the sediment to capture polychaetes. In N. brasiliensis, trabeculae are localized to areas likely to experience the highest load: the quadratomandibular jaw joints, hyomandibular-cranial joint, and the thinnest sections of the jaws immediately lateral to the symphyses. However, the supports perform different functions dependent on location. In regions where the jaws are loaded transversely (as in durophagous rays), "load leading" trabeculae distribute compressive forces from the cortex through the lumen of the jaws. In the parasymphyseal regions of the jaws, "truss" trabeculae form cross-braces perpendicular to the long axes of the jaws. At peak protrusion, the jaw arch is medially compressed and the jaw loaded axially such that these trabeculae are positioned to resist buckling associated with excavation forces. "Truss" trabeculae function to maintain the second moment of area in the thinnest regions of the jaws, illustrating a novel function for batoid trabeculation. Thus, this method of structural support appears to have arisen twice independently in batoids and performs strikingly different ecological functions associated with the distribution of extreme loading environments.     

Feeding biomechanics of five demersal Antarctic fishes

There is scant information available on the ecomorphology of Antarctic fishes, and especially on their feeding capabilities. We measured interspecific variation in mechanical advantage (MA), force-producing capability, and suction index for the jaws of the five dominant taxa of high-Antarctic fishes: the nototheniid Trematomus bernacchii; the zoarcids Pachycara brachycephalum, Lycodichthys dearborni, and Ophthalmolycus amberensis; and the liparid Paraliparis devriesi. Analysis of variance indicated significant differences in jaw metrics, and ordinations of morphological traits identified three loosely defined groups reflecting their family-level taxonomy. Principal component analyses showed distinct segregation between the nototheniid and the liparid, indicating that they are at the extremes of the feeding performance continuum. The zoarcids fell in the middle, suggesting that they utilize a combination of feeding modes to capture prey. The liparid had the lowest MA and bite force, but a large epaxialis implied a ram-suction-feeding mode. The large adductor mandibulae in the zoarcids P. brachycephalum and L. dearborni suggest that they are capable of grasping mobile prey and manipulating sedentary, hard-shelled macroinvertebrates. The zoarcids had a smaller epaxialis than the liparid and may not be as efficient as suction-feeders. Values for mechanical advantage ratios and suction indices in Antarctic fishes were within the range known for non-Antarctic fishes. The five Antarctic species do not possess dentition specialized for durophagous feeding; however, the high mechanical advantage ratio in the nototheniid and, to a lesser extent, in the zoarcids, suggests that durophagy may be possible.     

Ontogeny of the jaw apparatus and suspensorium of the Tetraodontiformes

Konstantinidis, P. and Johnson, G. David 2012. Ontogeny of the jaw apparatus and suspensorium of the Tetraodontiformes. —Acta Zoologica (Stockholm) 93 : 351–366. The jaw apparatus and suspensorium of adult Tetraodontiformes are well adapted to a durophagous feeding habit. Anatomical indicators are the short, stout jaws and a suspensorium in which the quadrate lies in the same vertical plane as the autopalatine. In contrast, the palatoquadrate of larval Tetraodontiformes generally resembles that of larval percomorphs – a more posteriorly positioned quadrate and a slender and long Meckelian cartilage. Among Tetraodontiformes, the Triacanthodidae retain a protrusible upper jaw and a versatile suspensorium. The jaws of the Balistoidei have greater mobility achieved by a reduced autopalatine that has lost its bony contact with the suspensorium. In contrast to the Balistoidei, the beak‐like jaws of the Tetraodontoidei lack individual teeth in the biting part of the jaws. The autopalatine is enlarged, which results in immobilization of the ethmopalatine articulation. The Ostraciidae are exceptional in having the distal part of the autopalatine reduced, while the proximal part remains attached to the suspensorium.     

Morphological and digestive adjustments buffer performance: How staging shorebirds cope with severe food declines

Organisms cope with environmental stressors by behavioral, morphological, and physiological adjustments. Documentation of such adjustments in the wild provides information on the response space in nature and the extent to which behavioral and bodily adjustments lead to appropriate performance effects. Here we studied the morphological and digestive adjustments in a staging population of migrating Great Knots Calidris tenuirostris in response to stark declines in food abundance and quality at the Yalu Jiang estuarine wetland (northern Yellow Sea, China). At Yalu Jiang, from 2011 to 2017 the densities of intertidal mollusks, the food of Great Knots, declined 15‐fold. The staple prey of Great Knots shifted from the relatively soft‐shelled bivalve Potamocorbula laevis in 2011–2012 to harder‐shelled mollusks such as the gastropod Umbonium thomasi in 2016–2017. The crushing of the mollusks in the gizzard would require a threefold to 11‐fold increase in break force. This was partially resolved by a 15% increase in gizzard mass which would yield a 32% increase in shell processing capacity. The consumption of harder‐shelled mollusks was also accompanied by reliance on regurgitates to excrete unbreakable parts of prey, rather than the usual intestinal voidance of shell fragments as feces. Despite the changes in digestive morphology and strategy, there was still an 85% reduction in intake rate in 2016–2017 compared with 2011–2012. With these morphological and digestive adjustments, the Great Knots remaining faithful to the staging site to a certain extent buffered the disadvantageous effects of dramatic food declines. However, compensation was not complete. Locally, birds will have had to extend foraging time and use a greater daily foraging range. This study offers a perspective on how individual animals may mitigate the effects of environmental change by morphological and digestive strategies and the limits to the response space of long‐distance migrating shorebirds in the wild.     

Jaw morphology and ontogeny in five species of Ophryotrocha

Detailed scanning electron microscopy of jaws within the genus Ophryotrocha (Dorvilleidae, Annelida) was performed on 871 jaw parts. The investigations resulted in new understandings of the ontogeny and jaw morphology and have systematic implications for the family. Five species in the genus (Ophryotrocha alborana, O. diadema, O. gracilis, O. hartmanni, and O. labronica pacifica) were kept in culture, and the development of the jaws was studied by sampling throughout their life history. Ophryotrocha species have mandibular plates that remain the same throughout ontogeny, whereas the posterior shafts elongate. Both mandibular plate morphology and shaft ontogeny have species‐specific distinctions. In Ophryotrocha, the maxillae can be assigned to three to four distinct types, which are replaced by moulting. The maxillary morphology and developmental stages at which moults occur are species specific, although with broad intervals. A redefinition is given for some of the basic jaw elements, and new homologies are proposed for structures that are also present across other dorvilleid taxa. J. Morphol. 2010. © 2009 Wiley‐Liss, Inc.     

Tooth reorientation affects tooth function during prey processing and tooth ontogeny in the lesser electric ray, Narcine brasiliensis

The dental anatomy of elasmobranch fishes (sharks, rays and relatives) creates a functional system that is more dynamic than that of mammalian dentition. Continuous dental replacement (where new teeth are moved rostrally to replace older ones) and indirect fibrous attachment of the dentition to the jaw allow teeth to reorient relative to the jaw over both long- and short-term scales, respectively. In this study, we examine the processing behavior and dental anatomy of the lesser electric ray Narcine brasiliensis (Olfers, 1831) to illustrate that the freedom of movement of elasmobranch dentition allows a functional flexibility that can be important for complex prey processing behaviors. From static manipulations of dissected jaws and observations of feeding events in live animals, we show that the teeth rotate during jaw protrusion, resulting in a secondary grasping mechanism that likely serves to hold prey while the buccal cavity is flushed free of sediment. The function of teeth is not always readily apparent from morphology; in addition to short-term reorientation, the long-term dental reorientation during replacement allows a given tooth to serve multiple functions during tooth ontogeny. Unlike teeth inside the mouth, the cusps of external teeth (on the portion of the tooth pad that extends past the occlusal plane) lay flat, such that the labial faces act as a functional battering surface, protecting the jaws during prey excavation.     

Prey capture behavior and kinematics of the Atlantic cownose ray, Rhinoptera bonasus

The structurally reinforced jaws of the cownose ray, Rhinoptera bonasus testify to this species' durophagous diet of mollusks, but seem ill-suited to the behaviors necessary for excavating such prey. This study explores this discordance by investigating the prey excavation and capture kinematics of R. bonasus. Based on the basal suction feeding mechanism in this group of fishes, we hypothesized a hydraulic method of excavation. As expected, prey capture kinematics of R. bonasus show marked differences relative to other elasmobranchs, relating to prey excavation and use of the cephalic lobes (modified anterior pectoral fin extensions unique to derived myliobatiform rays). Prey are excavated by repeated opening and closing of the jaws to fluidize surrounding sand. The food item is then enclosed laterally by the depressed cephalic lobes, which transport it toward the mouth for ingestion by inertial suction. Unlike in most sharks, upper jaw protrusion and mandibular depression are simultaneous. During food capture, the ray's spiracle, mouth, and gill slit movements are timed such that water enters only the mouth (e.g., the spiracle closes prior to prey capture and reopens immediately following). Indigestible parts are then hydraulically winnowed from edible prey portions, by mouth movements similar to those used in excavation, and ejected through the mouth. The unique sensory/manipulatory capabilities of the cephalic lobes, as well as the cownose ray's hydraulic excavation/winnowing behaviors and suction feeding, make this species an effective benthic predator, despite its epibenthic lifestyle.     

Prey selection by molluscivorous cichlids foraging on a schistosomiasis vector snail,Biomphalaria glabrata

Summary This paper considers prey size selection by four molluscivorous cichlids feeding on the intermediate host snail of Schistosoma parasites, Biomphalaria glabrata. Haplochromis ishmaeli obtains its prey by crushing the snails between the pharyngeal jaws, whereas H. xenognathus, H. sauvagei and Macropleurodus bicolor apply both pharyngeal crushing and oral shelling. The fishes crushed significantly more snails with the highest reward in biomass per second of crushing. Oral shelling occurred far less often than pharyngeal crushing. Encounter rates with prey showed significant variations between different size classes of prey. The fish have no overall knowledge of snail availability in a tank. The probability that a snail will be eaten at encounter, calculated from the number encountered and the number eaten, reflects the prey size preference of the fish. Those snails with the highest biomass/crushing-time ratio had the highest probability of being crushed; observed and predicted prey size preferences corresponded well. Although for oral shelling the potential reward in biomass per second is of the same magnitude as for crushing, the probability of successful shelling is very low. Apparently the fish prefer prey with lowest risks.