Feeding mechanics of teleost fishes (Labridae; Perciformes): A test of four-bar linkage models

The feeding mechanisms of two labrid fishes (Cheilinus chlorurus and C. diagrammus: Labridae: Perciformes) are modeled using four-bar linkage theory from mechanical engineering. The actions of the feeding mechanisms are simulated by a computer program that uses morphometric data to calculate the geometry of mechanism structure. The predictions of three different four-bar linkages regarding the kinematics of feeding are compared to the movements observed through hign speed (200 fps) cinematography. A previously unidentified four-bar chain was found to be an accurate model of the mechanism by which upper jaw protrusion, maxillary rotation, and gape increase occur in Cheilinus. This mechanism involves the anterior jaws including the mandible, maxilla, premaxilla, palatine, and suspensorium. The accuracy of two previously described four-bar linkages was also tested by comparison of model predictions and film results. The opercular linkage proposed by Anker ('74) as a mechanism of jaw depression via opercular levation was found to be a poor predictor of feeding movements. This four-bar chain involves the opercle, suspensorium, interopercle, and mandible. Muller ('87) proposed a mechanism of hyoid depression involving cranial elevation due to epaxial muscle contraction as input motion The links in this mechanism include the neurocranium and hyomandibula, hyoid, sternohyoideus muscle, and pectoral girdle. This model was an accurate predictor of hyoid depression in Cheilinus when simultaneous cranial elevation and sternohyoideus contraction were simulated. Quantitative kinematic models involve simplifying assumptions when applied to complex musculoskeletal systems, but such models have a wide range of applications to vertebrate functional morphology.     

Using linkage models to explore skull kinematic diversity and functional convergence in arthrodire placoderms

Biomechanical models offer a powerful set of tools for quantifying the diversity of function across fossil taxa. A computer‐based four‐bar linkage model previously developed to describe the potential feeding kinematics of Dunkleosteus terrelli is applied here to several other arthrodire placoderm taxa from different lineages. Arthrodire placoderms are a group of basal gnathostomes showing one of the earliest diversifications of jaw structures. The linkage model allows biomechanical variation to be compared across taxa, identify trends in skull morphology among arthrodires that potentially influence function and explore the role of linkage systems in the early evolution of jaw structures. The linkage model calculates various kinematic metrics including gape angle, effective mechanical advantage, and kinematic transmission coefficients. Results indicate that the arthrodire feeding system may be more diverse and complex than previously thought. A range of potential kinematic profiles among arthrodire taxa illustrate a diversity of feeding function comparable with modern teleost fishes. Previous estimates of bite force in Dunkleosteus are revised based on new morphological data. High levels of kinematic transmission among arthrodires suggest the potential for rapid gape expansion and possible suction feeding. Morphological comparisons indicate that there were several morphological solutions for obtaining these fast kinematics, which allowed different taxa to achieve similar kinematic profiles while varying other aspects of the feeding apparatus. Mapping of key morphological components of the linkage system on a general placoderm phylogeny illustrates the potential importance of four‐bar systems to the early evolution of jaw structures. J. Morphol. 271:990–1005, 2010. © 2010 Wiley‐Liss, Inc.     

Do Changes in Morphology and Prey-Capture Movements Facilitate a Dietary Transition in Juvenile Colorado pikeminnow, Ptychocheilus lucius?

Ontogenetic diet shifts in juvenile fishes are sometimes associated with proportional changes to the feeding mechanism. In addition, many piscivorous teleosts transition from invertebrate-prey to fish-prey when the mouth attains a specific diameter. Allometric (disproportionate) growth of the jaws could accelerate a young fish’s ability to reach a critical gape diameter; alternately by opening the lower jaw to a greater degree, a fish might increase gape behaviorally. We investigated the ontogeny of feeding morphology and kinematics in an imperiled piscivore, the Colorado pikeminnow (Ptychocheilus lucius) in a size range of individuals across which a diet shift from invertebrate-prey to prey-fishes is known to occur. We predicted that: (1) the feeding apparatus of the fish would grow proportionally with the rest of the body (isometric growth), that (2) anatomical gape diameter at the known diet transition would be a similar gape diameter to that observed for other piscivorous juvenile fishes (15–20 mm) and (3) feeding kinematic variables would scale isometrically (that is, change in direct proportion to body length) as juvenile pikeminnow became larger. Furthermore, we also asked the question: if changes in feeding morphology and kinematics are present, do the changes in morphology appear to generate the observed changes in kinematics? For juvenile Colorado pikeminnow, the majority of the morphological variables associated with the skull and jaws scale isometrically (that is, proportionally), but seven of eight kinematic variables, including functional gape, scale with negative allometry (that is, they became disproportionately smaller in magnitude). In contrast with the overall trend of isometry, two key aspects of feeding morphology do change with size; the lower jaw of a young Colorado pikeminnow becomes longer (positive allometry), while the head becomes shallower (negative allometry). These findings do not support the hypothesis that morphological ontogenetic changes directly generate changes in feeding kinematics; in fact, allometric jaw growth would, a priori, be expected to generate a larger gape in older fish—which is the opposite of what was observed. We conclude that ontogenetic morphological changes produce a more streamlined cranium that may reduce drag during a rapid, anteriorly directed strike, while concomitant behavioral changes reduce the magnitude of jaw movements—behavioral changes that will facilitate a very rapid opening and closing of the jaws during the gape cycle. Thus, for juvenile pikeminnow, speed and stealth appear to be more important than mouth gape during prey capture.     

Micro- and macroevolutionary decoupling of cichlid jaws: a test of Liem's key innovation hypothesis

The extent to which elements of functional systems can change independently (modularity) likely influences the diversification of lineages. Major innovations in organismal design, like the pharyngeal jaw in cichlid fishes, may be key to a group's success when they relax constraints on diversification by increasing phenotypic modularity. In cichlid fishes, pharyngeal jaw modifications that enhanced the ability to breakdown prey may have freed their oral jaws from serving their ancestral dual role as a site of both prey capture and prey processing. This functional decoupling that allowed the oral jaws to become devoted solely to prey capture has been hypothesized to have permitted the two sets of cichlid jaws to evolve independently. We tested the hypothesis that oral and pharyngeal jaw mechanics are evolutionarily decoupled both within and among Neotropical Heroine cichlids. In the trophically polymorphic species Herichthys minckleyi, molariforms that exhibit enlarged molarlike pharyngeal jaw teeth were found to have approximately 400% greater lower jaw mass compared to H. minckleyi with the alternative papilliform pharyngeal morphology. However, oral jaw gape, lower jaw velocity ratios, anterior jaw linkage mechanics, and jaw protrusion did not differ between the morphotypes. In 40 other Heroine species, there was a weak correlation between oral jaw mechanics and pharyngeal jaw mass when phylogenetic history was ignored. Yet, after expansion of the cytochrome b phylogeny for Heroines, change in oral jaw mechanics was found to be independent of evolutionary change in pharyngeal jaw mass based on independent contrasts. Evolutionary decoupling of oral and pharyngeal jaw mechanics has likely played a critical role in the unparalleled trophic diversification of cichlid fishes.     

Evolution of levers and linkages in the feeding mechanisms of fishes

The evolution of feeding mechanisms in the ray-finned fishes(Actinopterygii) is a compelling example of transformation ina musculoskeletal complex involving multiple skeletal elementsand numerous muscles that power skull motion. Biomechanicalmodels of jaw force and skull kinetics aid our understandingof these complex systems and enable broad comparison of feedingmechanics across taxa. Mechanical models characterize how musclesmove skeletal elements by pulling bones around points of rotationin lever mechanisms, or by transmitting force through skeletalelements connected in a linkage. Previous work has focused onthe feeding biomechanics of several lineages of fishes, buta broader survey of skull function in the context of quantitativemodels has not been attempted. This study begins such a surveyby examining the diversity of mechanical design of the oraljaws in 35 species of ray-finned fishes with three main objectives:(1) analyze lower jaw lever models in a broad phylogenetic rangeof taxa, (2) identify the origin and evolutionary patterns ofchange in the linkage systems that power maxillary rotationand upper jaw protrusion, and (3) analyze patterns of changein feeding design in the context of actinopterygian phylogeny.The mandibular lever is present in virtually all actinopterygians,and the diversity in lower jaw closing force transmission capacity,with mechanical advantage ranging from 0.04 to 0.68, has importantfunctional consequences. A four-bar linkage for maxillary rotationarose in the Amiiformes and persists in various forms in manyteleost species. Novel mechanisms for upper jaw protrusion basedon this linkage for maxillary rotation have evolved independentlyat least five times in teleosts. The widespread anterior jawslinkage for jaw protrusion in percomorph fishes arose initiallyin Zeiformes and subsequently radiated into a wide range ofpremaxillary protrusion capabilities.     

Transmission of force and velocity in the feeding mechanisms of labrid fishes (Teleostei,Perciformes)

Summary The feeding mechanisms of four species of the teleostean family Labridae (Cheilinus fasciatus, C. trilobatus, Oxycheilinus bimaculatus, and O. unifasciatus) were modeled using four-bar linkage theory from mechanical engineering. The predictions of four-bar linkage models regarding the kinematics of feeding were compared to the movements observed with high speed cinematography (200 frames/s). A four-bar linkage was an accurate model of the mechanism by which upper jaw protrusion, maxillary rotation, and gape increase occur in each species. A four-bar mechanism of hyoid depression was an accurate predictor of hyoid depression when simultaneous cranial elevation and sternohyoideus contraction were simulated. Morphometrics of the linkage systems of the jaws and hyoid were collected for 12 labrid species. These data were used to calculate the transmission of force and motion through the musculoskeletal linkages. Several measures of mechanical advantage and displacement advantage were compared, including both traditional lever ratios and transmission coefficients of four-bar linkages. Alternative designs of the feeding mechanisms maximize force or velocity for the capture of different prey types. High velocity transmission of both the jaw and hyoid systems is characteristic of those species that feed on evasive prey, whereas species that feed on benthic invertebrates favor increased force transmission in both systems. Quantitative models of biomechanical systems supply criteria for functionally relevant morphometrics, and aid in calculating the capacity for transmission of force and velocity in musculoskeletal systems.     

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.     

Muscle fiber types and functional demands in feeding mechanisms of fishes

Profiles of muscle fiber types and pharyngeal jaw dentition vary in accordance with trophic demands and skeletal organization in teleost fishes. Carnivorous, omnivorous, and molluscivorous members of the ecologically analogous Cichlidae and Centrarchidae were compared in terms of their pharyngeal jaw anatomy and branchial muscle histochemistry. The two families differed greatly in patterns of tooth form, wear, and replacement. Four muscle fiber type patterns were discoverd: (1) single fiber, (2) zoned, (3) mosaic, and (4) zoned-mosaic. Multiple fiber type muscles were more prevalent in fishes that masticate tough foods with their pharyngeal jaws. Such muscles were also more prevalent in cichlids than in centrarchids. It appears that muscles with multiple fiber types in lower vertebrates are, as a rule, compartmentalized, whereas in higher vertebrates, multiple fiber type muscles are a musaic matrix. The occurrence of mosaic patterns in some fish branchial muscles, however, suggests that mosaic muscles are initially single fiber type muscles exposed to complex functional demands, such as food preparation. Furthermore, it is plausible that the evolutionary replacement of the lower vertebrate zoning pattern by the higher vertebrate mosaic matrix is directly related to the effects of gravity, a force more influential on terrestrial than on aquatic organisms.     

Premaxillary movements in cyprinodontiform fishes: an unusual protrusion mechanism facilitates "picking" prey capture

Premaxillary protrusion is hypothesized to confer a number of feeding advantages to teleost fishes; however, most proposed advantages relate to enhanced stealth or suction production during prey capture. Cyprinodontiformes exhibit an unusual form of premaxillary protrusion where the descending process of the premaxilla does not rotate anteriorly to occlude the sides of the open mouth during prey capture. Instead, the premaxilla is protruded such that it gives the impression of a beak during prey capture. We quantified premaxillary kinematics during feeding in four cyprinodontiform taxa and compared them with three percomorph taxa to identify any performance consequences of this protrusion mechanism. Individual prey capture events were recorded using digital high-speed video at 250-500 frames per second (n4 individuals, 4 strikes per individual). Species differed in the timing of movement and the maximum displacement of the premaxilla during the gape cycle and in the contribution of the premaxilla to jaw closing. Cyprinodontiform taxa produced less premaxillary protrusion than the percomorph taxa, and were consistently slower in the time to maximum gape. Further, it appears cyprinodontiforms can alter the contribution of the premaxilla to mouth closure on an event-specific basis. We were able to demonstrate that, within at least one species, this variability is associated with the location of the prey (bottom vs. water column). Cyprinodontiform upper jaw movements likely reflect increased dexterity associated with a foraging ecology where prey items are "picked" from a variety of locations: the bottom, water column, or surface. We postulate that dexterity requires slow, precisely controlled jaw movements; thus, may be traded off for some aspects of suction-feeding performance, such as protrusion distance and speed.     

Cortisol response to acute stress in jundiá Rhamdia quelen acutely exposed to sub-lethal concentrations of agrichemicals

Exposure to agrichemicals can have deleterious effects on fish, such as disruption of the hypothalamus-pituitary-inter-renal axis (HPI) that could impair the ability of fish to respond to stressors. In this study, fingerlings of the teleost jundiá (Rhamdia quelen) were used to investigate the effects of the commonly used agrichemicals on the fish response to stress. Five common agrichemicals were tested: the fungicide - tebuconazole, the insecticide - methyl-parathion, and the herbicides - atrazine, atrazine+simazine, and glyphosate. Control fishes were not exposed to agrichemicals and standard stressors. In treatments 2-4, the fishes were exposed to sub-lethal concentrations (16.6%, 33.3%, and 50% of the LC(50)) of each agrichemical for 96 h, and at the end of this period, were subjected to an acute stress-handling stimulus by chasing them with a pen net. In treatments 5-7 (16.6%, 33.3%, and 50% of the LC(50)), the fishes were exposed to the same concentrations of the agrichemicals without stress stimulus. Treatment 8 consisted of jundiás not exposed to agrichemicals, but was subjected to an acute stress-handling stimulus. Jundiás exposed to methyl-parathion, atrazine+simazine, and glyphosate presented a decreased capacity in exhibiting an adequate response to cope with stress and in maintaining the homeostasis, with cortisol level lower than that in the control fish (P<0.01). In conclusion, the results of this study clearly demonstrate that the acute exposure to sub-lethal concentrations of methyl-parathion, atrazine+simazine, and glyphosate exert a deleterious effect on the cortisol response to an additional acute stressor in the jundiá fingerlings.     

Unusual kinematics and jaw morphology associated with piscivory in the poeciliid,Belonesox belizanus

Piscivory in fishes is often associated with the evolution of highly elongate jaws that achieve a large mouth opening, or gape. Belonesox belizanus, the pike killifish, has independently evolved this morphology, which is derived from short-jawed poeciliids within the Cyprinodontiformes. Using kinematic analysis of high-speed video footage, we observed a novel aspect of the elongate jaws of Belonesox; the premaxilla rotates dorsally during mouth opening, while the lower jaw rotates ventrally. Anatomical study revealed that this unusual motion is facilitated by the architecture of the premaxillomandibular ligament, prominent within cyprinodontiforms. In Belonesox, it allows force to be transferred from the lower jaw directly to the premaxilla, thereby causing it to rotate dorsally. This dorsal rotation of the premaxilla appears to be assisted by a mediolateral twisting of the maxilla during jaw opening. Twisting maxillae are found in members of the group such as Fundulus, but are lost in Gambusia. Models revealed that elongate jaws partially account for the enlarged gape, but enhanced rotation at the quadrato-mandibular joint was equally important. The large gape is therefore created by: (i) the convergent evolution of elongate jaws; (ii) enhanced jaw rotation, facilitated by loss of a characteristic cyprinodontiform trait, the lip membrane; and (iii) premaxilla rotation in a novel direction, facilitated by the retention and co-option of additional cyprinodontiform traits, the premaxillomandibular ligament and a twisting maxilla.     

The evolution of the premaxillary protrusion system in some teleostean fish groups

Changes in the acanthopteran (acanthopterygian) system of premaxillary protrusion are traced from its incipient representation in the iniomous (myctophiform) genus Aulopus to its fully evolved form in the percoids. Two complementary components of the system are differentiated. One is the protrusion of the premaxillary, brought about primarily by the anteroventral movement of a ligament attached to the rostral cartilage. The second, which distinguishes the acanthopteran system from other types of jaw protrusion, is the emplacement of a bony maxillary wedge between the skull and the protruded premaxillary.
The acanthopteran type of protrusion appears to have evolved in large-mouthed fishes, with the lateral expansion of the gape that occurs in such forms a fundamental element of this system's mechanics. The modifications that occur in small-mouthed fishes with little or no lateral expansion of the gape are discussed.
Premaxillary protrusion was investigated in available fish groups sometimes placed between the iniomous fishes and the percoids in classifications. Of these groups, the beloniform and cyprinodont fishes have developed protrusion systems of non-acanthopteran types.     

Ecological redundancy between coral reef sharks and predatory teleosts

Reef sharks may be ecologically redundant, such that other mesopredatory fishes compensate for their functions when they decline in number, preventing trophic cascades. Oral jaw gape, hereafter referred to as gape, determines maximum prey size in many piscivores and therefore affects the size structure of prey assemblages. Here, we examine whether gape and maximum prey size differ between five species of reef shark and 21 species of teleost (n?=?754) using data collected from 38 reefs in the Indo-Pacific. Sharks displayed relatively small gape dimensions compared to most teleost species and, at smaller sizes, the giant trevally Caranx ignobilis and other teleosts may be able to consume larger prey than similar-sized sharks. However, ecological redundancy between reef sharks and teleosts appears to decline at larger sizes, such that the grey reef shark Carcharhinus amblyrhynchos, for example, may be capable of consuming larger prey than any other reef predator at its largest sizes, regardless of prey body shape. Moreover, sharks may be able to consume proportionally larger prey as they grow, in contrast to reef teleosts, which may largely be limited by their gapes to ever-smaller prey as a proportion of their body size. Our results also suggest that reef sharks may be unable to swallow whole prey that are >?36% of their length, consistent with gut-content studies. Conservation of reef ecological function may therefore depend not only on the protection of sharks but also particular size classes and key components of the mesopredatory guild.

     

The phylogenetic significance of bone types in euteleost fishes

The paradentary is a small, sometimes dentigerous element in the lower jaw of some atherinomorph neoteleost fishes. Identification of the paradentary as a neomorphic, perichondrally ossified bone prompted re-examination of theories of the association of bone and teeth in teleost fishes. Teeth on a chondral lower jaw bone might be explained simply by epidermal-mesodermal interactions. Since the work of Kolliker in 1859, it has been known that there are two basic types of bone in teleost fishes: cellular bone, characterized by a matrix that has enclosed osteoblasts or osteocytes; and acellular bone, characterized by a relatively featureless matrix that lacks these bone-forming cells. Cellular bone is typical of lower teleosts, whereas acellular bone is typical of higher teleosts. Ontogenetic data indicate that acellular bone is derived relative to cellular bone. Even though identification of cellular and acellular bone can be made readily with histological preparations, acellular bone has been used infrequently as a character in analyses of teleost phylogeny. Acellular bone is considered here to be a derived character within teleost fishes. It is found in all Neoteleostei as well as some, but not all Salmoniformes. Independent of studies of bone, derived types of teeth in teleosts have been described in terms of their failure to become completely mineralized. Acellular bone and teeth of higher teleosts share several properties, including a large fraction of collagen. Teleosts lack a parathyroid gland; bone type is critical to the mechanism of calcium regulation. It is proposed that the character of acellular bone be incorporated into phylogenetic analyses of teleost fishes by correlating it with derived types of tooth structure.     

Intraspecific variation in Gape–prey size Relationships and Feeding Success During Early Ontogeny in Red Drum, Sciaenops Ocellatus

The relationship between predator gape and prey consumption in laboratory-reared larva and field-caught early juvenile red drum, Sciaenops ocellatus, was investigated in light of the hypothesis that feeding success varies throughout the early life history intervals of marine fishes. We expected the feeding ability of red drum to be more strongly constrained by mouth gape in smaller fish and expected this ability to improve with gape size. To test this hypothesis, field-caught, early juvenile red drum were examined to determine the relationship between gape size and prey size consumed. In field-caught early juveniles, gape (height and width) and prey size consumed (length and width) increased linearly with standard length (SL); however, mean width of prey consumed was only 20–47% of gape width. Furthermore, when regressed on SL, gape width yielded a higher slope than prey width. To further test this hypothesis on less developed, pre-metamorphic fish, age-specific differences in gape, number of prey and size of prey consumed prior to metamorphosis were determined from laboratory-reared red drum larvae. Similar patterns were observed for gape height– and gape width–SL relationships in laboratory-reared red drum larvae. Size of consumed prey increased from three days from hatching (dfh) to 18dfh. The percentage of feeding larvae also increased from 3% at 3dfh to 97% at 18dfh. In both field-caught, early juvenile red drum and laboratory-reared larvae, there was little evidence that the size of prey consumed was constrained by mouth gape. It is hypothesized that besides gape size, the development of other features of the feeding mechanism (e.g., hyoid and opercular series) influences prey-capture performance prior to settlement in marine fishes.     

Eating without hands or tongue: specialization, elaboration and the evolution of prey processing mechanisms in cartilaginous fishes

The ability to separate edible from inedible portions of prey is integral to feeding. However, this is typically overlooked in favour of prey capture as a driving force in the evolution of vertebrate feeding mechanisms. In processing prey, cartilaginous fishes appear handicapped because they lack the pharyngeal jaws of most bony fishes and the muscular tongue and forelimbs of most tetrapods. We argue that the elaborate cranial muscles of some cartilaginous fishes allow complex prey processing in addition to their usual roles in prey capture. The ability to manipulate prey has evolved twice along different mechanical pathways. Batoid chondrichthyans (rays and relatives) use elaborate lower jaw muscles to process armored benthic prey, separating out energetically useless material. In contrast, megacarnivorous carcharhiniform and lamniform sharks use a diversity of upper jaw muscles to control the jaws while gouging, allowing for reduction of prey much larger than the gape. We suggest experimental methods to test these hypotheses empirically.     

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.     

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 quantitative theory of expected volume changes of the mouth during feeding in teleost fishes

The mechanism of mouth expansion in fish, consisting of jaws, suspensoria (j) and hyoids (h) has been modelled by a four-bar isosceles linkage. This model provides insight into limitations and demands of the expansion system used in feeding, as it can be optimized with regard to maximum mouth volume increase. The optimum length ratio of hyoids and jaws was found to be h/j = 0–7. This optimum is modified by mouth bottom depression, jaw protrusion and swimming.
To expand the mouth, at least two forces are required; one exerted by the sternohyoid and ventral body muscles, the other by the epaxial muscles through transmission in the quadrato-articular joints. (Data from EMG experiments confirm the synchronous activity of these muscle groups.) Force transmission and mouth volume increase are constraining quantities, which can be compromised. This leads to a model of the initial mouth shape which is actually found in many 'generalized' fishes, and to demands concerning volume and physiological cross-sectional area of the muscles involved.
Options for specific relative lengths of jaws and hyoids (h/j-ratios) are, for various fish species, compared with model predictions. The applicability of the model approach is shown by the obtained results.     

THE GENETIC BASIS OF A COMPLEX FUNCTIONAL SYSTEM

The relationship between form and function can have profound effects on evolutionary dynamics and such effects may differ for simple versus complex systems. In particular, functions produced by multiple structural configurations (many‐to‐one mapping, MTOM) may dampen constituent trade‐offs and promote diversification. Unfortunately, we lack information about the genetic architecture of MTOM functional systems. The skulls of teleost fishes contain both simple (lower jaw levers) as well as more complex (jaws modeled as 4‐bar linkages) functional systems within the same craniofacial unit. We examined the mapping of form to function and the genetic basis of these systems by identifying quantitative trait loci (QTL) in hybrids of two Lake Malawi cichlid species. Hybrid individuals exhibited novelty (transgressive segregation) in morphological components and function of the simple and complex jaw systems. Functional novelty was proportional to the prevalence of extreme morphologies in the simple levers; by contrast, recombination of parental morphologies produced transgression in the MTOM 4‐bar linkage. We found multiple loci of moderate effect and epistasis controlling jaw phenotypes in both the simple and complex systems, with less phenotypic variance explained by QTL for the 4‐bar. Genetic linkage between components of the simple and complex systems partly explains phenotypic correlations and may constrain functional evolution.