Differences in locomotor behavior correspond to different patterns of morphological selection in two species of waterfall-climbing gobiid fishes

Behavior plays an important role in mediating relationships between morphology and performance in animals and, thus, can influence how selection operates. However, to what extent can the use of specific behaviors be associated with particular types of selection on morphological traits? Laboratory selection analyses on waterfall-climbing gobiid fishes were performed to investigate how behavioral variations in locomotion can affect patterns of linear and nonlinear morphological selection. Species from sister genera (Sicyopterus stimpsoni and Sicydium punctatum) that use different climbing behaviors were exposed to similar artificial waterfalls to simulate a controlled selective regime involving the climbing of a nearly vertical slope against flowing water. Juvenile S. stimpsoni “inch up” waterfalls by alternate attachment of oral and pelvic suckers with little axial or fin movement, leading to straightforward expectations that climbing selection should favor morphologies that improve drag reduction and substrate adhesion. In contrast, juvenile S. punctatum climb using substantial axial and fin movements, complicating expectations for selection patterns and potentially promoting correlational selection. Comparisons of directional, quadratic and correlational selection coefficients for various morphological traits and trait interactions indicated that these species showed different selection patterns that generally fit these predictions. Both directional and correlational selection patterns were different between the species, and on average were stronger in S. punctatum compared to S. stimpsoni. Stronger selection in S. punctatum may be related to its climbing style that requires more integrated movement of the fins and body axis than S. stimpsoni, promoting dynamic interactions among body regions within a complicated hydrodynamic environment.     

Feeding performance of the Hawaiian sleeper,Eleotris sandwicensis (Gobioidei: Eleotridae): correlations between predatory functional modulation and selection pressures on prey

The eleotrid fish Eleotris sandwicensis inhabits lower reaches of streams in the Hawaiian Archipelago, where it feeds on juveniles of native amphidromous gobiid fishes migrating upstream from the ocean. Using high‐speed video and geometric modelling, we evaluated the feeding kinematics and performance of E. sandwicensis on free swimming prey, including two species with juveniles of different characteristic sizes, and compared successful and unsuccessful strikes. With fast jaw movements and a highly expansive buccal cavity, E. sandwicensis achieves high suction performance that enables the capture of elusive prey. Our analyses indicated that the species with larger juveniles (Sicyopterus stimpsoni) could be captured from a distance of up to 18.6% of the predator's body length (BL), but capture of the smaller species (Awaous guamensis) required a closer distance (12.2% BL). Predator–prey distance appears to be the predominant factor determining strike outcome during feeding on juvenile A. guamensis. However, during feeding on juvenile S. stimpsoni, E. sandwicensis shows modulations of strike behaviour that correlate with capture success. Moreover, the ability of E. sandwicensis to capture larger prey fish from longer distances suggests a potential biomechanical basis underlying observations that predation by eleotrids imposes significant selection against large body size in juvenile gobies. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 359–374.     

Functional ecology of feeding in elasmobranchs

Feeding behavior in the species of captive chondrichthyans is studied to clarify the functional mechanisms responsible for feeding ecology. Kinematics and pressure in the buccal, hyoid and pharyngeal regions were quantified in Squalus acanthias, Chiloscyllium plagiosum and Leucoraja erinacea using sonomicrometry and pressure transducers. Means and coefficients of variation were analyzed by species and by behavior to test for stereotypy and flexibility in the feeding mechanism. Several instances of mechanical stereotypy as well as flexibility were found in the feeding kinematics and pressure of the three chondrichthyan species. In general, Squalus acanthias shows more stereotyped feeding behavior than C. plagiosum and L. erinacea. Different aspects of feeding behavior stand out among the three species. Chiloscyllium plagiosum generates lowest pressures, S. acanthias achieves the greatest area changes, and L. erinacea has longer durations for manipulating prey. Capture events are functionally and behaviorally stereotyped while processing events are functionally and behaviorally flexible with the ability to use suction or compression to process the same food item. Squalus acanthias is a functional specialist and C. plagiosum is functionally a generalist, with both species exhibiting behavioral flexibility. Leucoraja erinacea is a functional and behavioral generalist. Using functional morphology to explain mechanical stereotypy and flexibility in the feeding behavior of three suction feeding chondrichthyan species has allowed a better understanding of specialist and generalist trophic behaviors.     

Functional morphology of the feeding system in the ruff — Gymnocephalus cernua (L. 1758) — (Teleostei,Percidae)

The ruff, Gymnocephalus cernua, is a European freshwater fish that feeds by sucking up small invertebrates from the bottom of ponds and slow flowing rivers. The feeding movements have been studied by simultaneous electromyography of seventeen muscles of the head and cinematographic techniques. A theoretical model of movements imposes the functional demands of suction upon an abstraction of the form of a teleost head. Three phases in the feeding act, a preparatory phase, a suction phase and a transport phase, could be correlated with the observed movements and EMGs. Differences between the predicted and the actual movement are discussed. Two different types of feeding occur. The direction, magnitude and duration of the suction forces during feeding are modified, according to the position of the prey. A mechanism preventing early mandibular depression allows sudden and strong suction. Retardation of the suspensorial abduction during the overall expansion of the buccal cavity is ascribed to kinetic interrelations with the hyoid arch. Protrusion of the upper jaws also permits an earlier closure of the mouth and directs the food-containing waterflow posteriorly. When the fish is feeding on sinking prey, protrusion occurs later in the sequence of movements than when it is feeding from the bottom. As the protruded jaws produce a downwardly pointed mouth this retardation aims the suction force.     

Stairway to Heaven: Evaluating Levels of Biological Organization Correlated with the Successful Ascent of Natural Waterfalls in the Hawaiian Stream Goby Sicyopterus stimpsoni

Selective pressures generated by locomotor challenges act at the level of the individual. However, phenotypic variation among individuals that might convey a selective advantage may occur across any of multiple levels of biological organization. In this study, we test for differences in external morphology, muscle mechanical advantage, muscle fiber type and protein expression among individuals of the waterfall climbing Hawaiian fish Sicyopterus stimpsoni collected from sequential pools increasing in elevation within a single freshwater stream. Despite predictions from previous laboratory studies of morphological selection, few directional morphometric changes in body shape were observed at successively higher elevations. Similarly, lever arm ratios associated with the main pelvic sucker, central to climbing ability in this species, did not differ between elevations. However, among climbing muscles, the adductor pelvicus complex (largely responsible for generating pelvic suction during climbing) contained a significantly greater red muscle fiber content at upstream sites. A proteomic analysis of the adductor pelvicus revealed two-fold increases in expression levels for two respiratory chain proteins (NADH:ubiquinone reductase and cytochrome b) that are essential for aerobic respiration among individuals from successively higher elevations. Assessed collectively, these evaluations reveal phenotypic differences at some, but not all levels of biological organization that are likely the result of selective pressures experienced during climbing.     

Feeding kinematics and performance of Hawaiian stream gobies,Awaous guamensis and Lentipes concolor: Linkage of functional morphology and ecology

Distributions of Hawaiian stream fishes are typically interrupted by waterfalls that divide streams into multiple segments. Larvae hatch upstream, are flushed into the ocean, and must climb these waterfalls to reach adult habitats when returning back to freshwater as part of an amphidromous life cycle. Stream surveys and studies of climbing performance show that Lentipes concolor Gill can reach fast‐flowing upper stream segments but that Awaous guamensis Valenciennes reaches only slower, lower stream segments. Gut content analyses for these two species indicate considerable overlap in diet, suggesting that feeding kinematics and performance of these two species might be comparable. Alternatively, feeding kinematics and performance of these species might be expected to differ in relation to the different flow regimes in their habitat (feeding in faster stream currents for L. concolor versus in slower currents for A. guamensis). To test these alternative hypotheses, we compared food capturing kinematics and performance during suction feeding behaviors of A. guamensis and L. concolor using morphological data and high‐speed video. Lentipes concolor showed both a significantly larger gape angle and faster jaw opening than A. guamensis. Geometric models calculated that despite the inverse relationship of gape size and suction pressure generation, the fast jaw motions of L. concolor allow it to achieve higher pressure differentials than A. guamensis. Such elevated suction pressure would enhance the ability of L. concolor to successfully capture food in the fast stream reaches it typically inhabits. Differences in jaw morphology may contribute to these differences in performance, as the lever ratio for jaw opening is about 10% lower in L. concolor compared with A. guamensis, suiting the jaws of L. concolor better for fast opening. J. Morphol. 2009. © 2008 Wiley‐Liss, Inc.     

Kinematics and functional morphology of aquatic feeding in Australian snake-necked turtles (Pleurodira; Chelodina)

Head kinematics during aquatic feeding of the Australian long-necked turtle (Chelodina) were studied by means of high speed video recordings. Buccal expansion was assessed by calculation of elliptical cross-sectional surfaces. Further, displacements of head, carapace, and prey in the earth bound frame, of the prey relative to the center of the gape, and of the head relative to the carapace were determined. Rates of change (velocities) of all these variables were calculated. These data are combined with information on the osteology and myology of the head. The robust development of the large hyobranchial apparatus, the massive intercornuatus muscle, and the presence of the branchiosquamosus muscle were related to aquatic feeding skills. Head kinematics are variable in amplitude and relative timing, but proceed always in a rostrocaudal sequence. According to their effect on the prey, two components are distinguished in the process of expansion. The first compensates for head/body movements (compensatory suction). The second causes distinct acceleration of water and prey (inertial suction). The latter component is mainly driven by the abduction of the second branchial arch. In spite of largely different structural solutions, optimal feeding conditions as deduced for suction in feeding fishes are also employed by Chelodina. This further promotes the assumption that hydrodynamics constrain evolutive solutions for aquatic feeding. J. Morphol. 233:113–125, 1997. © 1997 Wiley-Liss, Inc.     

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.     

Contrasting post-settlement selection results in many-to-one mapping of high performance phenotypes in the Hawaiian waterfall-climbing goby <Emphasis Type="Italic">Sicyopterus stimpsoni</Emphasis>

Natural selection drives adaptive evolution, but contrasting environmental pressures may lead to trade-offs between phenotypes that confer different performances. Such trade-offs may weaken the strength of selection and/or generate complex fitness surfaces with multiple local optima that correspond to different selection regimes. We evaluated how differences in patterns of phenotypic selection might promote morphological differences between subpopulations of the amphidromous Hawaiian waterfall-climbing goby, Sicyopterus stimpsoni. We conducted laboratory experiments on fish from the islands of Kaua‘i and Hawai‘i (the “Big Island”) to compare patterns of linear and nonlinear selection, and the opportunity for selection, that result from two contrasting pressures, predator evasion and waterfall climbing, which vary in intensity between islands. We found directional and nonlinear selection were strongest when individuals were exposed to their primary selective pressures (predator evasion on Kaua‘i, waterfall climbing on the Big Island). However, the opportunity for selection was greater for the non-primary pressure: climbing on Kaua‘i, predator evasion on the Big Island. Canonical rotation of the nonlinear gamma matrix demonstrated that individuals from Kaua‘i and the Big Island occupy regions near their local fitness peaks for some traits. Therefore, selection for predator evasion on Kaua‘i and climbing on the Big Island may be less effective in promoting morphological changes in this species, because variation of functionally important traits in their respective environments may have been reduced by directional or stabilizing selection. These results demonstrate that despite constraints on the opportunities for selection, population differences in phenotypic traits can arise due to differences in selective regimes. For S. stimpsoni, sufficient variation exists in other locomotor traits, allowing for necessary levels of performance in the contrasting selective regime (i.e., climbing on Kaua‘i and predator evasion on the Big Island) through many-to-one-mapping, which may be essential for the survival of local populations in an evanescent island environment.     

Jaw and hyolingual movements during prey transport in varanid lizards: effects of prey type

The ability to modulate feeding kinematics in response to prey items with different functional properties is likely a prerequisite for most organisms that feed on a variety of food items. Variation in prey properties is expected to reveal variation in feeding function and the functional role of the different phases in a transport cycle. Here we describe the kinematics of prey transport of two varanid species, Varanus niloticus and Varanus ornatus. These species were selected for analysis because of their highly specialised hyolingual system and food transport mechanism (inertial food transport). In these animals, tongue and hyoid movements are expected to make no, or only a minor, contribution to prey transport. We observed statistically significant prey type effects that could be associated with prey properties such as mass, size and mobility. These data show that both species are capable of modulating the kinematics of food transport in response to different prey types. Moreover, not only the kinematics of the jaws were modulated in response to prey characteristics but also the anterior/posterior movements of the tongue and hyoid. This suggests a more important role of the tongue and hyolingual movements in these animals than previously suspected. In contrast, head movements were rather stereotyped and were not modulated in response to changes in prey type.     

Prey capture by Luciocephalus pulcher: implications for models of jaw protrusion in teleost fishes

Synopsis Luciocephalus pulcher possesses one of the most protrusible jaws known among teleosts, the premaxillae extending anteriorly a distance of 33% of the head length during feeding. Jaw bone movement during feeding proceeds according to a stereotypical pattern and resembles that of other teleosts except for extreme cranial elevation and premaxillary protrusion. Anatomical specializations associated with cranial elevation include: a highly modified first vertebra with a separate neural spine, articular fossae on the posterior aspect, greatly enlarged zygapophyses on the second vertebra with complex articular condyles, and highly pinnate multi-layered epaxial musculature with multiple tendinous insertions on the skull. Luciocephalus, despite the extreme jaw protrusion, does not use suction during prey capture: rather, the prey is captured by a rapid lunge (peak velocity of about 150 cm per sec) and is surrounded by the open mouth. Previous hypotheses of the function of upper jaw protrusion are reviewed in relation to jaw movements inLuciocephalus. Protrusion is not obligatorily linked with suction feeding; behavioral aspects of the feeding process limit the possible range of biological roles of a given morphological specialization, and make prediction of role from structure risky.     

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.     

Musculoskeletal determinants of pelvic sucker function in hawaiian stream gobiid fishes: Interspecific comparisons and allometric scaling

Gobiid fishes possess a distinctive ventral sucker, formed from fusion of the pelvic fins. This sucker is used to adhere to a wide range of substrates including, in some species, the vertical cliffs of waterfalls that are climbed during upstream migrations. Previous studies of waterfall‐climbing goby species have found that pressure differentials and adhesive forces generated by the sucker increase with positive allometry as fish grow in size, despite isometry or negative allometry of sucker area. To produce such scaling patterns for pressure differential and adhesive force, waterfall‐climbing gobies might exhibit allometry for other muscular or skeletal components of the pelvic sucker that contribute to its adhesive function. In this study, we used anatomical dissections and modeling to evaluate the potential for allometric growth in the cross‐sectional area, effective mechanical advantage (EMA), and force generating capacity of major protractor and retractor muscles of the pelvic sucker (m. protractor ischii and m. retractor ischii) that help to expand the sealed volume of the sucker to produce pressure differentials and adhesive force. We compared patterns for three Hawaiian gobiid species: a nonclimber (Stenogobius hawaiiensis), an ontogenetically limited climber (Awaous guamensis), and a proficient climber (Sicyopterus stimpsoni). Scaling patterns were relatively similar for all three species, typically exhibiting isometric or negatively allometric scaling for the muscles and lever systems examined. Although these scaling patterns do not help to explain the positive allometry of pressure differentials and adhesive force as climbing gobies grow, the best climber among the species we compared, S. stimpsoni, does exhibit the highest calculated estimates of EMA, muscular input force, and output force for pelvic sucker retraction at any body size, potentially facilitating its adhesive ability. J. Morphol. 2013. © 2013 Wiley Periodicals, Inc.     

Raising the Sugar Content – Orchid Bees Overcome the Constraints of Suction Feeding through Manipulation of Nectar and Pollen Provisions

Unlike most other bees, the long-tongued orchid bees ingest nectar using suction feeding. Although long tongues allow exploitation of flowers with deep spurs, the energy intake rate is optimal at 10–20% lower nectar sugar concentrations compared to that of lapping bees. This constraint might be compensated by a higher digestive throughput. Additionally, orchid bees might evaporate water from regurgitated droplets of crop contents. We found male Euglossa championi (n = 10) and Euglossa dodsoni (n = 12) to regularly regurgitate droplets of crop content to the base of their proboscis, generating a fluid film between the proximal parts of the galeae, glossa and labial palps. Rhythmic movements of the proboscis may help to increase convection. There was a significant change in sugar concentration between the initially imbibed solution and the resulting crop content (P<0.05) and the time individual bees had engaged in this liquid exposure behavior was positively correlated with the resulting crop sugar concentration. Female Euglossa townsendi and Euglossa viridissima showed the same behavior. Additionally, they manipulated their nectar-enriched pollen provisions for extensive periods of time before deposition in brood cells. The deposited pollen loads (n = 14) showed a significantly higher sugar concentration than the sugar-water available to the bees (P<0.001). Thus, both male and female euglossines show behaviors that promote evaporative water loss from nectar. We suggest that the behaviors have evolved in concert with suction feeding on dilute nectar from deep floral tubes.     

Work that body: fin and body movements determine herbivore feeding performance within the natural reef environment

Herbivorous fishes form a keystone component of reef ecosystems, yet the functional mechanisms underlying their feeding performance are poorly understood. In water, gravity is counter-balanced by buoyancy, hence fish are recoiled backwards after every bite they take from the substrate. To overcome this recoil and maintain contact with the algae covered substrate, fish need to generate thrust while feeding. However, the locomotory performance of reef herbivores in the context of feeding has hitherto been ignored. We used a three-dimensional high-speed video system to track mouth and body kinematics during in situ feeding strikes of fishes in the genus Zebrasoma, while synchronously recording the forces exerted on the substrate. These herbivores committed stereotypic and coordinated body and fin movements when feeding off the substrate and these movements determined algal biomass removed. Specifically, the speed of rapidly backing away from the substrate was associated with the magnitude of the pull force and the biomass of algae removed from the substrate per feeding bout. Our new framework for measuring biting performance in situ demonstrates that coordinated movements of the body and fins play a crucial role in herbivore foraging performance and may explain major axes of body and fin shape diversification across reef herbivore guilds.     

Feeding mechanism of Epibulus insidiator (Labridae; Teleostei): Evolution of a novel functional system

The feeding mechanism of Epibulus insidiator is unique among fishes, exhibiting the highest degree of jaw protrusion ever described (65% of head length). The functional morphology of the jaw mechanism in Epibulus is analyzed as a case study in the evolution of novel functional systems. The feeding mechanism appears to be driven by unspecialized muscle activity patterns and input forces, that combine with drastically changed bone and ligament morphology to produce extreme jaw protrusion. The primary derived osteological features are the form of the quadrate, interopercle, and elongate premaxilla and lower jaw. Epibulus has a unique vomero-interopercular ligament and enlarged interoperculo-mandibular and premaxilla-maxilla ligaments. The structures of the opercle, maxilla, and much of the neurocranium retain a primitive labrid condition. Many cranial muscles in Epibulus also retain a primitive structural condition, including the levator operculi, expaxialis, sternohyoideus, and adductor mandibulae. The generalized perciform suction feeding pattern of simultaneous peak cranial elevation, gape, and jaw protrusion followed by hyoid depression is retained in Epibulus. Electromyography and high-speed cinematography indicate that patterns of muscle activity during feeding and the kinematic movements of opercular rotation and cranial elevation produce a primitive pattern of force and motion input. Extreme jaw protrusion is produced from this primitive input pattern by several derived kinematic patterns of modified bones and ligaments. The interopercle, quadrate, and maxilla rotate through angles of about 100 degrees, pushing the lower jaw into a protruded position. Analysis of primitive and derived characters at multiple levels of structural and functional organization allows conclusions about the level of design at which change has occurred to produce functional novelties.     

Feeding Kinematics,Suction, and Hydraulic Jetting Performance of Harbor Seals (Phoca vitulina)

The feeding kinematics, suction and hydraulic jetting capabilities of captive harbor seals (Phoca vitulina) were characterized during controlled feeding trials. Feeding trials were conducted using a feeding apparatus that allowed a choice between biting and suction, but also presented food that could be ingested only by suction. Subambient pressure exerted during suction feeding behaviors was directly measured using pressure transducers. The mean feeding cycle duration for suction-feeding events was significantly shorter (0.15±0.09 s; P<0.01) than biting feeding events (0.18±0.08 s). Subjects feeding in-water used both a suction and a biting feeding mode. Suction was the favored feeding mode (84% of all feeding events) compared to biting, but biting comprised 16% of feeding events. In addition, seals occasionally alternated suction with hydraulic jetting, or used hydraulic jetting independently, to remove fish from the apparatus. Suction and biting feeding modes were kinematically distinct regardless of feeding location (in-water vs. on-land). Suction was characterized by a significantly smaller gape (1.3±0.23 cm; P<0.001) and gape angle (12.9±2.02°), pursing of the rostral lips to form a circular aperture, and pursing of the lateral lips to occlude lateral gape. Biting was characterized by a large gape (3.63±0.21 cm) and gape angle (28.8±1.80°; P<0.001) and lip curling to expose teeth. The maximum subambient pressure recorded was 48.8 kPa. In addition, harbor seals were able to jet water at food items using suprambient pressure, also known as hydraulic jetting. The maximum hydraulic jetting force recorded was 53.9 kPa. Suction and hydraulic jetting where employed 90.5% and 9.5%, respectively, during underwater feeding events. Harbor seals displayed a wide repertoire of behaviorally flexible feeding strategies to ingest fish from the feeding apparatus. Such flexibility of feeding strategies and biomechanics likely forms the basis of their opportunistic, generalized feeding ecology and concomitant breadth of diet.     

Do Movement Patterns Differ Between Laboratory and Field Suction Feeding Behaviors in a Mexican Cichlid?

Synopsis We analyzed feeding behavior of individuals of Herichthys minckleyi, the Cuatro Ciénegas cichlid, under laboratory conditions and freely behaving in their natural environment using high-speed video imaging. In a multivariate analysis of suction feeding behaviors there was no clear grouping of feeding events based on the environment, which suggests that most of the variability in the data was unrelated to differences between lab and field behaviors. In fact, the variability within an environment was far greater than the variability between the two environments. These results suggest that laboratory studies can accurately describe the kinematics of behaviors seen in the field. However, although lab based studies can quantify behaviors seen in the field, natural habitats are complex and provide individuals with the opportunity to exploit a wide range of food types and microhabitats, which may elicit behaviors not observed in the laboratory. However, feeding behaviors observed in the lab are representative of frequently used feeding behaviors in the field, at least for this species. Thus, we suggest that laboratory studies of feeding behavior, particularly those that test biomechanical or performance-based hypotheses can be extrapolated to natural environments.     

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.     

Diet and food selection in the endemic Hawaiian amphidromous goby, Sicyopterus stimpsoni (Pisces: Gobiidae)

Synopsis The ecological role of Sicyopterus stimpsoni as a nearly exclusive algal grazer in Hawaiian streams is established through gut content analysis of 192 fish from Wainiha River on the northern island of Kaua'i. Algae in three phyla (Chlorophyta, Cyanophyta, and Chrysophyta) were found to be the primary components of the fish's diet (94.62% of dry biomass). Aquatic insect immatures (primarily Chironomidae) accounted for most of the remaining food biomass (5.37%). Poorly developed gill rakers and high gut-to-length ratios provide evidence for adaptation to herbivory and morphological separation of S. stimpsoni from sympatric gobiods. Interspecific competition for the green alga, Cladophora sp., is suggested as an important feature of biotic interactions among native stream fishes but is mitigated by interspecific differences in food preference and utilization. A Category V hurricane which devastated the island in September 1992 provided a fortuitous opportunity to study disturbance influences on benthic food resources in the stream. Disturbance regimes influenced food selection of S. stimpsoni by altering the abundance and composition of stream algae. Rapid adjustment of S. stimpsoni to changes occurring in algal resource abundance illustrates its superb adaptation to life in a swift-water environment subjected to periodic flood-induced disturbance.