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Session Schedule & Abstracts

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Sunday 3rd July, 2016

Feeding 2

Room: Salon C   9:30 am–11:00 am

Moderator(s): Ferry LA, Moran CJ
FED2-1  9:30 am  XROMM and VROMM studies of suction feeding in fishes. Brainerd E.L.*, Brown University; Camp A.L., Brown University; Wilga C.D., University of Alaska Anchorage; Scott B.R., University of Rhode Island; Olsen A.M., University of Chicago; Jimenez Y.E., Brown University; Laurence-Chasen J.D., Brown University; Knörlein B.J., Brown University
Abstract: Suction feeding in actinopterygian and chondrichthyan fishes relies on coordinated and highly three-dimensional motion of skeletal elements. We can now quantify these motions by using X-ray Reconstruction of Moving Morphology (XROMM) to produce accurate animations of 3-D skeletal shape and in vivo movement. In bamboo sharks we used marker-based XROMM (with conical carbide markers) to track the motions of the cranial cartilages. Long-axis rotation (LAR) cannot be detected from markers alone, but rigid-body animation in XROMM yields full 6 degree-of-freedom motion, including LAR. For Meckel's cartilage we found 10-15° LAR in one direction (supination) prior to peak gape, and then 20-25° of fast pronation after peak gape. The ceratohyal also showed slow LAR of 10-20° before peak, and rapid counter-rotation of 10-40° after peak gape. The hyomandibula showed 10-50° of rapid LAR in just one direction. In ray-finned fishes we used spherical tantalum markers for XROMM animation of cranium, maxilla, mandible, suspensorium, operculum, hyoid bar, urohyal and pectoral girdle. We generated a dynamic digital endocast from the XROMM skeletal animations to measure the instantaneous rate of buccal volume expansion and instantaneous suction power. We mapped cranial muscles onto the XROMM skeletal animations to measure muscle strain, and measured body muscle strain with fluoromicrometry. In largemouth bass we found that the cranial muscles generate a negligible amount of power, and instead more than 95% of the power for high-performance strikes comes from axial muscles. Additionally, by combining XROMM with kinematic modeling we find that a 3-D, 4-bar model provides a good representation of opercular linkage kinematics in largemouth bass and significantly outperforms a planar, 4-bar model. A new method, Video Reconstruction of Moving Morphology (VROMM), shows promise for XROMM without X-rays, particularly for superficial bones such as the cranial bones of actinopterygians.

FED2-2  9:45 am  Comparative biomechanics of biting vs. suction feeding in fish. Brocklehurst RJ*, School of Earth Sciences, University of Bristol, Bristol, UK; Porro LB, Structure and Motion Laboratory, Department of Comparative Biomedical Sciences, Royal Veterinary College, Hatfield, UK; Herrel A, Département Écologie et Gestion de la Biodiversité, Muséum National d’Histoire Naturelle, Paris, France; Adriaens D, Research Group Evolutionary Morphology of Vertebrates, Ghent University, Ghent, Belgium; Standen EM, Department of Biology, University of Ottawa, Ottawa, Canada; Rayfield EJ, School of Earth Sciences, University of Bristol, Bristol, UK
Abstract: Suction feeding and biting are the two most common feeding modes in living aquatic and terrestrial vertebrates respectively. However, the evolution of biting for terrestrial feeding in tetrapods from their aquatic suction feeding ancestors remains poorly understood. This is partly due to a lack of comparative data from living functional analogues of fossil taxa. Here, we use comprehensive three dimensional finite element analysis to investigate the mechanical performance of the lower jaw in three extant fishes: Esox lucius (Actinopterygii: Teleostei), Anguilla anguilla (Actinopterygii: Teleostei) and Polypterus senegalus (Actinopterygii: Polypteriformes). High speed video footage demonstrates that Esox is primarily a suction feeder, whereas Anguilla is a known biter. Polypterus is the most basal living ray-finned fish and a widely used extant analogue of early tetrapods. We use stress metrics to compare mandibular structural strength, and strain energy to determine the mechanical efficiency of the lower jaw. The jaws of Anguilla are stronger and more efficient than those of Esox; we interpret these differences as a result of selection for increased bite force production in Anguilla and the need for the lower jaw to withstand these higher forces, suggesting clear differences in jaw mechanics between a biter and suction feeder. Whilst broader studies are needed, functional data from extant taxa could help elucidate feeding function in fossils. Polypterus is intermediate between Esox and Anguilla in terms of both jaw strength and efficiency. This suggests that Polypterus is capable of using a mixture of biting and suction feeding for prey capture, which implies that stem tetrapods may have functioned in a similar manner. The capacity for biting and terrestrial-style feeding likely evolved early on in the tetrapodomorph lineage while the ancestors of tetrapods were still aquatic.

FED2-3  10:00 am  Feeding behavior variation in polyphenic bluegill. Moran CJ*, Fairfield University; Neubauer DL, Fairfield University; Rzucidlo CL, Fairfield University; Gerry SP, Fairfield University
Abstract: Polyphenic populations are a valuable resource for understanding the relationship between form and function. Morphological variation within a population can have dramatic impacts on performance and subsequently fitness. In Lake Waban (Wellesley, MA) bluegill (Lepomis macrochirus) have diverged into two ecomorphs which occupy pelagic and littoral habitats. Based on morphological variation of the oral jaws and diet studies, we hypothesized that littoral individuals would use more suction during feeding than pelagic fish. To address this hypothesis we measured pressure and kinematics during prey capture on earthworms, mealworms and brine shrimp. We found that littoral fish used more suction when feeding on all prey types and varied their feeding behaviors dependent on prey type. Similarly, the littoral ecomorph traveled a greater distance during feeding, suggesting that they use more ram than the pelagic fish. Pelagic bluegill exhibited a stereotyped feeding behavior for all prey types, which suggests that they have reduced modularity during feeding. These results give further credence to the divergence in behavior and morphology that is seen when comparing two phenotypes of bluegill. Future studies will investigate differences in muscle morphology and mechanics between these phenotypes.

FED2-4  10:15 am  Where does the vertebral column bend during suction feeding in fishes? A comparative study of axial bending during cranial elevation. Jimenez YE*, Brown University; Camp AL, Brown University; Brainerd EL, Brown University
Abstract: During suction feeding, many fishes use their epaxial muscles to generate a substantial amount of power to produce cranial elevation. When the muscles contract they reduce the angle between the head and body, causing the axial skeleton to bend dorsoventrally. Axial bending increases cranial elevation and improves feeding performance, but is not well studied. The goal of this study is to locate where the vertebral column bends during suction feeding and relate it to the axial morphology of different species. We collected and analyzed live feeding data from three species (largemouth bass, pacific staghorn sculpin, and striped surfperch) using XROMM and VROMM. We used joint coordinate systems to measure relative motion between the neurocranium and body plane to determine the degree of cranial elevation and the location of the axis of rotation (AOR). We also analyzed the morphology of the axial skeleton. We found that largemouth bass had AORs centered around vertebral joints 2 and 3 (42 and 58% of strikes, respectively). Striped surfperch had AORs centered around joints 1, 2, and 3 (25, 56, and 19%). Finally, AORs of staghorn sculpin were located in joints 3 through 7. Surfperch and bass AORs were associated with spaces between the neural spines and epineural bones. Moreover, surfperch and sculpin AORs were in the anterior vertebrae where the zygapophyses articulate. Despite the similar locations of the AORs of largemouth bass and striped surfperch, there were significant differences in the amount of cranial elevation they produced. As such, more posterior AORs are not necessarily associated with greater cranial elevation. This is particularly evident in staghorn sculpin, in which the same AOR (joint 6) produced some of the highest and lowest cranial elevations (35° and 12°). Given the great deal of interspecific variation of the axial skeleton, it is important to investigate the role of these different morphologies in suction feeding.

FED2-5  10:30 am  Built to bite? Bite performance based on 3D-reconstructions in European glass eels (Teleostei: Anguilliformes). De Meyer J.*, Ghent University; Bouilliart M., Ghent University; Dhaene J., Centre for X-ray Tomography of Ghent University; Adriaens D., Ghent University
Abstract: In the yellow eel stage of both the European and Japanese eel (Anguilla anguilla and A. japonica respectively), two phenotypes can be found: narrow- and broad-heads. This dimorphism has been linked to dietary differences, with the broad-headed phenotypes feeding on hard prey and the narrow-headed ones feeding on soft prey. The broad heads are therefore associated with larger adductor mandibulae muscles, which increase their bite force. Next to this, they exhibit an elongated lower jaw with a larger coronoid process, providing a larger surface to which the adductor mandibulae can attach. Interestingly, recent research showed that broad- and narrow-headed phenotypes are already present in the non-feeding glass eel stage of the European eel, the predecessor of the yellow eel stage. It was then hypothesized that broad-headed glass eels might be better suited to start feeding on hard prey. Here, we wanted to test this hypothesis by studying the morphology of broad- and narrow-headed glass eels. To study the morphology of the glass eels, heads of 5 narrow- and broad-heads were CT-scanned. These scans were then used to make 3D-reconstructions of the cranial musculoskeletal system. Next to this, a newly developed 3D-bite model was used to assess the bite force of the glass eels based on these reconstructions. We found that broad-headed glass eels are already characterized by larger adductor mandibulae muscles, which were associated with higher bite forces compared to the narrow-headed ones. The measured bite forces were still very low, which could be expected since the glass eels are not actively feeding yet. Nevertheless, these results imply that broad-headed glass eels would be indeed better suited to start feeding on hard prey, which could eventually result in the dimorphism observed in the yellow eel stage.

FED2-6  10:45 am  Premaxillary protrusion in Lampriformes: innovations and radiations. Ferry LA*, Arizona State University; Paig-Tran EW, California State University Fullerton; Summers AP, University of Washington
Abstract: Jaw (premaxillary) protrusion is thought to be a key innovation correlated with the subsequent radiation and diversification of fishes. Extreme amounts of protrusion are associated with suction prey capture, often on highly elusive prey. Notable examples of this are the sling-jaw wrasse Epibulus insinuator and the cichlid Petunia splendid; wrasses and cichlids both being extremely speciose clades of fishes. Interestingly, king-of-the-salmon or ribbonfish, Trachipterus altivelis (Lampriformes), also are capable of extreme jaw protrusion. The Lampriformes as a group are not terribly species-rich, yet multiple members appear to show the capacity for impressive jaw protrusion. Here we present findings regarding the anatomy of ribbonfish and their relatives, as well as the implications for jaw protrusion and prey capture in a group of fishes not easily studied via traditional functional morphological tools. Using a predictive model based upon morphological metrics, we compare protrusion ability within Lampriformes and across the Acanthomorpha, highlighting (extant) species and clades with particularly impressive premaxillae. Based upon available data, the ribbonfish may be the capable of the most extreme protrusion recorded to date. However, the link between premaxillary protrusion and subsequent species radiations is less clear.

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