Coordination of feeding, locomotor and visual systems in parrotfishes(Teleostei: Labridae)

Feeding kinematics of a surgeonfish reveal novel functions and relationships to reef substrata

Biting to obtain attached benthic prey characterizes a large number of fish species on coral reefs, and is a feeding mode that contributes to important ecosystem functions. We use high-speed video to reveal the mechanisms used by a surgeonfish, Acanthurus leucosternon, to detach algae. After gripping algae in its jaws, the species pulls it by ventrally rotating both the head and the closed jaws, in a novel use of the intra-mandibular joint. These motions remain in the plane of the fish, reducing the use of a lateral head flick to detach the algae. The novel ability to bite and pull algae off the substrate without bending the body laterally minimizes exposure to high water flows, and may be an adaptation to feeding in challenging reef habitats such as the crest and flat. Therefore, our results could potentially represent a key milestone in the evolutionary history of coral reef trophodynamics.

The Evolution of Feeding Mechanics in the Danioninae, or Why Giant Danios Don't Suck Like Zebrafish

By linking anatomical structure to mechanical performance we can improve our understanding of how selection shapes morphology. Here we examined the functional morphology of feeding in fishes of the subfamily Danioninae (order Cypriniformes) to determine aspects of cranial evolution connected with their trophic diversification. The Danioninae comprise three major lineages and each employs a different feeding strategy. We gathered data on skull form and function from species in each clade, then assessed their evolutionary dynamics using phylogenetic-comparative methods. Differences between clades are strongly associated with differences in jaw protrusion. The paedomorphic Danionella clade does not use jaw protrusion at all, members of the Danio clade use jaw protrusion for suction production and prey capture, and members of the sister clade to Danio (e.g., Devario and Microdevario) use jaw protrusion to retain prey after capture. The shape of the premaxillary bone is a major determinant of protrusion ability, and premaxilla morphology in each of these lineages is consistent with their protrusion strategies. Premaxilla shapes have evolved rapidly, which indicates that they have been subjected to strong selection. We compared premaxilla development in giant danio (Devario aequipinnatus) and zebrafish (Danio rerio) and discuss a developmental mechanism that could shift danionine fishes between the feeding strategies employed by these species and their respective clades. We also identified a highly integrated evolutionary module that has been an important factor in the evolution of trophic mechanics within the Danioninae.

Physiological oculo-auricular-facial-mandibular synkinesis elicited in humans by gaze deviations

Integrated motor behaviors involving ocular motion-associated movements of the head, neck, pinna, and parts of the face are commonly seen in animals orienting to a visual target. A number of coordinated movements have also been observed in humans making rapid gaze shifts to horizontal extremes, which may be vestiges of these. Since such integrated mechanisms point to a non-pathological co-activation of several anatomically separate cranial circuits in humans, it is important to see how the different pairs of integrative motor behaviors with a common trigger (i.e., ocular motion) manifest in relation to one another. Here, we systematically examined the pattern of eye movement-induced recruitment of multiple cranial muscles in humans. Simultaneous video-oculography and bilateral surface electromyograms of transverse auricular, temporalis, frontalis, and masseter muscles were recorded in 15 healthy subjects (8 females; 29.3±5.2 years) while they made head-fixed, horizontal saccadic, pursuit and optokinetic eye movements. Potential chin laterotrusion linked to contractions of masticator muscles was captured with a yaw-fixed accelerometer. Our findings objectively show an orchestrated aural-facial-masticatory muscle response to a range of horizontal eye movements (prevalence of 21-93%). These responses were most prominent during eccentric saccades. We further reveal distinctions between the various observed activation patterns in terms of their profile (transient or sustained), laterality (with respect to direction of gaze) and timing (with respect to saccade onset). Possible underlying neural substrates, their atavistic behavioral significance, and potential clinical applications for monitoring sensory attention and designing attention-directed hearing aids in the future are discussed.

Environmentally relevant concentrations of boscalid exposure affects the neurobehavioral response of zebrafish by disrupting visual and nervous systems

Boscalid is a persistent fungicide that is frequently detected in surface waters and may be neurotoxic to aquatic organisms. Herein, we evaluated the effects of environmentally relevant boscalid concentrations to zebrafish to explore its potentially neurotoxic mechanisms of effect. Behavioral responses (swimming, phototaxis, and predation), histopathology, transcriptomics, biochemical parameter analysis and gene expression of larval and adult zebrafish following boscalid treatment were assessed. We found that boscalid significantly inhibited the locomotor ability and phototactic response of larvae after an 8-d exposure, and altered the locomotor activity, predation trajectories and ability in adults after a 21-d exposure. It was noted that predation rates of zebrafish were significantly decreased by 30% and 100% after exposure to 0.1 and 1.0 mg/L boscalid, respectively. Adverse alterations in the cell differentiation of eyes and brain injury were also observed in both larvae and adults following boscalid exposure. The expression of genes related to neurodevelopment, neurotransmission, eye development, and visual function, in conjunction with RNA-Seq results, indicated that boscalid may impair visual phototransduction and nervous system processes in larval zebrafish. Conclusively, boscalid exposure may affect the neurobehavioral response of zebrafish by impairing proper visual and nervous system function.

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.

Weak Relationships Between Swimming Morphology and Water Depth in Wrasses and Parrotfish Belie Multiple Selective Demands on Form-Function Evolution

Mechanical tradeoffs in performance are predicted to sculpt macroevolutionary patterns of morphological diversity across environmental gradients. Water depth shapes the amount of wave energy organisms' experience, which should result in evolutionary tradeoffs between speed and maneuverability in fish swimming morphology. Here, we tested whether morphological evolution would reflect functional tradeoffs in swimming performance in 131 species of wrasses and parrotfish (Family: Labridae) across a water depth gradient. We found that maximum water depth predicts variation in pectoral fin aspect ratio (AR) in wrasses, but not in parrotfish. Shallow-water wrasses exhibit wing-like pectoral fins that help with "flapping," which allows more efficient swimming at faster speeds. Deeper water species, in contrast, exhibit more paddle-like pectoral fins associated with enhanced maneuverability at slower speeds. Functional morphology responds to a number of different, potentially contrasting selective pressures. Furthermore, many-to-one mapping may release some traits from selection on performance at the expense of others. As such, deciphering the signatures of mechanical tradeoffs on phenotypic evolution will require integrating multiple aspects of ecological and morphological variation. As the field of evolutionary biomechanics moves into the era of big data, we will be uniquely poised to disentangle the intrinsic and extrinsic predictors of functional diversity.

A Hierarchical View of Gecko Locomotion: Photic Environment, Physiological Optics, and Locomotor Performance

Terrestrial animals move in complex habitats that vary over space and time. The characteristics of these habitats are not only defined by the physical environment, but also by the photic environment, even though the latter has largely been overlooked. For example, numerous studies of have examined the role of habitat structure, such as incline, perch diameter, and compliance, on running performance. However, running performance likely depends heavily on light level. Geckos are an exceptional group for analyzing the role of the photic environment on locomotion as they exhibit several independent shifts to diurnality from a nocturnal ancestor, they are visually-guided predators, and they are extremely diverse. Our initial goal is to discuss the range of photic environments that can be encountered in terrestrial habitats, such as day versus night, canopy cover in a forest, fog, and clouds. We then review the physiological optics of gecko vision with some new information about retina structures, the role of vision in motor-driven behaviors, and what is known about gecko locomotion under different light conditions, before demonstrating the effect of light levels on gecko locomotor performance. Overall, we highlight the importance of integrating sensory and motor information and establish a conceptual framework as guide for future research. Several future directions, such as understanding the role of pupil dynamics, are dependent on an integrative framework. This general framework can be extended to any motor system that relies on sensory information, and can be used to explore the impact of performance features on diversification and evolution.

Morphology, Ecology, and Biogeography of Independent Origins of Cleaning Behavior Around the World

Members of an ecological guild may be anticipated to show morphological convergence, as similar functional demands exert similar selective pressures on phenotypes. Nature is rife with examples, however, where such taxa instead exhibit ‘incomplete’ convergence or even divergence. Incorporating factors such as character displacement by other guild members or variation in ecological specialization itself may therefore be necessary to gain a more complete understanding of what constrains or promotes diversity. Cleaning, a behavior in which species remove and consume ectoparasites from “clientele,” has been shown to exhibit variation in specialization and has evolved in a variety of marine habitats around the globe. To determine the extent to which specialization in this tropic strategy has affected phenotypic evolution, we examined the evolution of cleaning behavior in five marine fish families: Labridae, Gobiidae, Pomacanthidae, Pomacentridae, and Embiotocidae. We used a comparative framework to determine patterns of convergence and divergence in body shape and size across non-cleaning and cleaning members within these five clades. Highly specialized obligate cleaning, found in the Indo-Pacific and the Caribbean, evolved in the Labridae and Gobiidae at strikingly similar times. In these two regions, obligate cleaning evolves early, shows convergence on an elongate body shape, and is restricted to species of small body size. Facultative cleaning, shown either throughout ontogeny or predominately in the juvenile phase, exhibits a much more varied phenotype, especially in geographic regions where obligate cleaning occurs. Collectively, our results are consistent with varying extents of an ecological specialization constraining or spurring morphological evolution in recurrent ways across regions.

Integration between swim speed and mouth size evolves repeatedly in Trinidadian guppies and aligns with suction-feeding fishes

Well-supported correlations between swim speed and mouth size during prey capture suggest the broad existence of an integrated relationship between locomotion and feeding in suction-feeding fishes. However, the influence of specialization on this relationship is unclear. We used divergent populations of Trinidadian guppies (Poecilia reticulata) to test whether integration during suction is generalizable to a non-suction specialist and whether intraspecific specialization of component systems affects their integration. Guppies from replicate high- and low-predation streams were recorded capturing wild-type zooplankton using suction. Alternative general linear models supported a positive correlation between swim speed and mouth size in derived low-predation populations, suggesting that the relationship can be extended in some cases. High-predation populations lack this integration, which may be the result of direct selection or constraints imposed by selection on locomotion. As guppies invade new habitats they may be evolving a new, integrated performance phenotype from a non-integrated ancestor.

Ontogenetic Allometry in Shape and Flexibility Underlies Life History Patterns of Labrid Cleaning Behavior

Body shape plays a crucial role in the movement of organisms. In the aquatic environment, the shape of the body, fins, and the underlying axial skeleton reflect the ability of organisms to propel and maneuver through water. Ontogenetic changes in body shape and flexibility of the axial skeleton may coincide with shifts in ecology (e.g., changes in habitat or feeding mode). We use the evolution of cleaning behavior in the Labridae (wrasses and parrotfishes) as a case study. Cleaner fishes are species that remove and consume ectoparasites from other organisms. In many cases, cleaning involves a high degree of maneuverability, as cleaners on the hunt for parasites may continuously dart around the body of their clients. In labrids, at least 58 species are known to clean. Over two-thirds of these species, however, clean predominately as juveniles, exhibiting an ontogenetic shift away from cleaning as they enter adulthood. Using a phylogenetic comparative framework, we examined features of the axial skeleton, overall body shape, and pectoral fin shape in 31 species of labrids spread across four major clades to assess how scaling patterns in these systems are associated with the ontogeny of cleaning behavior. We find that across wrasses, the ontogeny of body shape shows evolutionary concordance with the degree of flexibility across the vertebral column. A key driver of this relationship is that species that shift away from cleaning over ontogeny show stronger positive allometry for body depth and vertebral moment of inertia than other taxa. Species that clean throughout their life histories show a more elongate body and vertebral column, and tend to maintain the combination of these characteristics over ontogeny. Cleaning behavior in labrid fishes is thus an excellent model with which to investigate morphological patterns as they relate to evolution, development, and ecology.

Patterns of variation in feeding strike kinematics of juvenile ghost praying mantis (Phyllocrania paradoxa): are components of the strike stereotypic?

Functional systems, such as feeding mechanics, often involve the evolution of several components of the musculoskeletal system that are moved in coordination to capture prey. Because these systems often involve the quick movement of several structures, some feeding systems have been hypothesized to be stereotypic. While the motor activity patterns are often stereotyped, the subsequent kinematics can be variable, many times in response to variation in prey stimulus (e.g., prey position). Patterns of feeding kinematics have been well studied among vertebrates, with less attention on invertebrate systems. The goal of this study was to examine the amount of stereotypy in the feeding strike kinematics of praying mantises. We filmed 8 juvenile ghost praying mantises (Phyllocrania paradox) at 1000 Hz, across several days within instar 7. We digitized several points that represent the movement of the coxa, trochanter-femur and tibia of the raptorial foreleg to obtain a set of kinematics including angles and angular velocities of the joint, as well as body lunge. Using the coefficient of variation, we found less stereotypy in the approach stage of the strike compared to the sweep. Using Bonferroni corrected Pearson's correlations of kinematics with prey position we found few traits related to prey position with the exception of some kinematics of the coxa joint and the amount of lunge used during the strike. Our results suggest that several components of the praying mantis strike are stereotypic, while others exhibit flexibility to ensure successful capture of the prey.

Feeding performance of king Mackerel, Scomberomorus cavalla

Feeding performance is an organism's ability to capture and handle prey. Although bite force is a commonly used metric of feeding performance, other factors such as bite pressure and strike speed are also likely to affect prey capture. Therefore, this study investigated static bite force, dynamic speeds, and predator and prey forces resulting from ram strikes, as well as bite pressure of the king mackerel, Scomberomorus cavalla, in order to examine their relative contributions to overall feeding performance. Theoretical posterior bite force ranged from 14.0-318.7 N. Ram speed, recorded with a rod and reel incorporated with a line counter and video camera, ranged from 3.3-15.8B L/s. Impact forces on the prey ranged from 0.1-1.9 N. Bite pressure, estimated using theoretical bite forces at three gape angles and tooth cross-sectional areas, ranged from 1.7-56.9 MPa. Mass-specific bite force for king mackerel is relatively low in comparison with other bony fishes and sharks, with relatively little impact force applied to the prey during the strike. This suggests that king mackerel rely on high velocity chases and high bite pressure generated via sharp, laterally compressed teeth to maximize feeding performance.

Eye movements are coordinated with pectoral fin beats during locomotion in a marine teleost fish

Animals must simultaneously engage multiple functional systems in order to navigate, feed, and survive in complex environments. Nearly all vertebrates perform rapid gaze-shifting eye movements called saccades, but we know little about the behaviour of saccades during rhythmic locomotion. This study examines how saccades are coordinated with locomotor movements in a pectoral-fin-propelled teleost fish, Cymatogaster aggregata, the shiner surfperch. Twelve individuals were filmed swimming in a flow tank at 10 cm s−1, and timing data were analyzed using circular statistics. Results reveal that Cymatogaster generates saccades non-uniformly throughout the pectoral fin cycle. Saccades primarily occur during fin abduction, when a large amount of thrust is produced, and rarely occur during the thrust-free refractory phase. Because vision is known to be impaired during saccades, we hypothesize that Cymatogaster synchronizes saccades with periods of high acceleration in order to stabilize retinal images during low-acceleration phases, which are nearly saccade-free.

Deficiency of zebrafish fgf20a results in aberrant skull remodeling that mimics both human cranial disease and evolutionarily important fish skull morphologies

The processes that direct skull remodeling are of interest to both human-oriented studies of cranial dysplasia and evolutionary studies of skull divergence. There is increasing awareness that these two fields can be mutually informative when natural variation mimics pathology. Here we describe a zebrafish mutant line, devoid of blastema (dob), which does not have a functional fgf20a protein, and which also presents cranial defects similar to both adaptive and clinical variation. We used geometric morphometric methods to provide quantitative descriptions of the effects of the dob mutation on skull morphogenesis. In combination with "whole-mount in situ hybridization" labeling of normal fgf20a expression and assays for osteoblast and osteoclast activity, the results of these analyses indicate that cranial dysmorphologies in dob zebrafish are generated by aberrations in post-embryonic skull remodeling via decreased osteoblasotgenesis and increased osteoclastogenesis. Mutational effects include altered skull vault geometries and midfacial hypoplasia that are consistent with key diagnostic signs for multiple human craniofacial syndromes. These phenotypic shifts also mimic changes in the functional morphology of fish skulls that have arisen repeatedly in several highly successful radiations (e.g., damselfishes and East-African rift-lake cichlids). Our results offer the dob/fgf20a mutant as an experimentally tractable model with which to examine post-embryonic skull development as it relates to human disease and vertebrate evolution.

Fusion of locomotor maneuvers, and improving sensory capabilities, give rise to the flexible homing strikes of juvenile zebrafish

At 5 days post-fertilization and 4 mm in length, zebrafish larvae are successful predators of mobile prey items. The tracking and capture of 200 μm long Paramecia requires efficient sensorimotor transformations and precise neural controls that activate axial musculature for orientation and propulsion, while coordinating jaw muscle activity to engulf them. Using high-speed imaging, we report striking changes across ontogeny in the kinematics, structure and efficacy of zebrafish feeding episodes. Most notably, the discrete tracking maneuvers used by larval fish (turns, forward swims) become fused with prey capture swims to form the continuous, fluid homing strikes of juvenile and adult zebrafish. Across this same developmental time frame, the duration of feeding episodes become much shorter, with strikes occurring at broader angles and from much greater distances than seen with larval zebrafish. Moreover, juveniles use a surprisingly diverse array of motor patterns that constitute a flexible predatory strategy. This enhances the ability of zebrafish to capture more mobile prey items such as Artemia. Visually-guided tracking is complemented by the mechanosensory lateral line system. Neomycin ablation of lateral line hair cells reduced the accuracy of strikes and overall feeding rates, especially when neomycin-treated larvae and juveniles were placed in the dark. Darkness by itself reduced the distance from which strikes were launched, as visualized by infrared imaging. Rapid growth and changing morphology, including ossification of skeletal elements and differentiation of control musculature, present challenges for sustaining and enhancing predatory capabilities. The concurrent expansion of the cerebellum and subpallium (an ancestral basal ganglia) may contribute to the emergence of juvenile homing strikes, whose ontogeny possibly mirrors a phylogenetic expansion of motor capabilities.

Flexibility in locomotor-feeding integration during prey capture in varanid lizards: effects of prey size and velocity

Feeding movements are adjusted in response to food properties, and this flexibility is essential for omnivorous predators as food properties vary routinely. In most lizards, prey capture is no longer considered to solely rely on the movements of the feeding structures (jaws, hyolingual apparatus), but instead is understood to require the integration of the feeding system with the locomotor system (i.e., coordination of movements). Here, we investigate flexibility in the coordination pattern between jaw, neck and forelimb movements in omnivorous varanid lizards feeding on four prey types varying in length and mobility: grasshoppers, live newborn mice, adult mice and dead adult mice. We test for bivariate correlations between 3D locomotor and feeding kinematics, and compare the jaw-neck-forelimb coordination patterns across prey types. Our results reveal that locomotor-feeding integration is essential for the capture of evasive prey, and that different jaw-neck-forelimb coordination patterns are used to capture different prey types. Jaw-neck-forelimb coordination is indeed significantly altered by the length and speed of the prey, indicating that a similar coordination pattern can be finely tuned in response to prey stimuli. These results suggest feed-forward as well as feedback modulation of the control of locomotor-feeding integration. As varanids are considered to be specialized in the capture of evasive prey (although they retain their ability to feed on a wide variety of prey items), flexibility in locomotor-feeding integration in response to prey mobility is proposed to be a key component in their dietary specialization.

Evolution of high trophic diversity based on limited functional disparity in the feeding apparatus of marine angelfishes (f. Pomacanthidae)

The use of biting to obtain food items attached to the substratum is an ecologically widespread and important mode of feeding among aquatic vertebrates, which rarely has been studied. We did the first evolutionary analyses of morphology and motion kinematics of the feeding apparatus in Indo-Pacific members of an iconic family of biters, the marine angelfishes (f. Pomacanthidae). We found clear interspecific differences in gut morphology that clearly reflected a wide range of trophic niches. In contrast, feeding apparatus morphology appeared to be conserved. A few unusual structural innovations enabled angelfishes to protrude their jaws, close them in the protruded state, and tear food items from the substratum at a high velocity. Only one clade, the speciose pygmy angelfishes, showed functional departure from the generalized and clade-defining grab-and-tearing feeding pattern. By comparing the feeding kinematics of angelfishes with wrasses and parrotfishes (f. Labridae) we showed that grab-and-tearing is based on low kinematics disparity. Regardless of its restricted disparity, the grab-and-tearing feeding apparatus has enabled angelfishes to negotiate ecological thresholds: Given their widely different body sizes, angelfishes can access many structurally complex benthic surfaces that other biters likely are unable to exploit. From these surfaces, angelfishes can dislodge sturdy food items from their tough attachments. Angelfishes thus provide an intriguing example of a successful group that appears to have evolved considerable trophic diversity based on an unusual yet conserved feeding apparatus configuration that is characterized by limited functional disparity.

The integration of locomotion and prey capture in divergent cottid fishes: functional disparity despite morphological similarity

Many mobile animals rely on the integration of locomotion and feeding to capture prey. Fishes commonly swim up to a prey item and utilize a combination of ram and suction feeding for prey capture. Marine cottids represent a diverse and abundant lineage of fishes that exhibit variation in feeding mode that is related to their mouth morphology. However, little is known regarding the integration of the locomotor and feeding systems during prey capture. We quantified the feeding kinematics, feeding performance and integration of locomotion and feeding in two species of divergent cottids: Blepsias cirrhosus (silver-spotted sculpin) and Oligocottus maculosus (tidepool sculpin). Individuals were caught from sympatric habitats near the Bamfield Marine Sciences Centre on Vancouver Island and filmed with a high-speed video camera (500 Hz) while feeding on amphipod prey. Two principal component axes summarize differences in integration and feeding mode despite similarity in attack velocity and feeding morphology (peak gape, peak cranial elevation and peak jaw protrusion). A greater number of correlations between locomotor and feeding variables in B. cirrhosus, compared with O. maculosus, indicate greater integration. We conclude that traditional measures of attack kinematics do not capture functionally and ecologically relevant differences between species. The mechanisms underlying differences in locomotor strategy likely result from unexplored morphological or ecological differences between species. In cottids, integration is apparent in more basal, subtidal species such as B. cirrhosus, and the need for integration may be superceded by demands from the habitat in more derived, shallow-water species such as O. maculosus.

The influence of an innovative locomotor strategy on the phenotypic diversification of triggerfish (family: Balistidae)

Innovations in locomotor morphology have been invoked as important drivers of vertebrate diversification, although the influence of novel locomotion strategies on marine fish diversification remains largely unexplored. Using triggerfish as a case study, we determine whether the evolution of the distinctive synchronization of enlarged dorsal and anal fins that triggerfish use to swim may have catalyzed the ecological diversification of the group. By adopting a comparative phylogenetic approach to quantify median fin and body shape integration and to assess the tempo of functional and morphological evolution in locomotor traits, we find that: (1) functional and morphological components of the locomotive system exhibit a strong signal of correlated evolution; (2) triggerfish partitioned locomotor morphological and functional spaces early in their history; and (3) there is no strong evidence that a pulse of lineage diversification accompanied the major episode of phenotypic diversification. Together these findings suggest that the acquisition of a distinctive mode of locomotion drove an early radiation of shape and function in triggerfish, but not an early radiation of species.

Illusionary self-motion perception in zebrafish

Zebrafish mutant belladonna (bel) carries a mutation in the lhx2 gene (encoding a Lim domain homeobox transcription factor) that results in a defect in retinotectal axon pathfinding, which can lead to uncrossed optic nerves failing to form an optic chiasm. Here, we report on a novel swimming behavior of the bel mutants, best described as looping. Together with two previously reported oculomotor instabilities that have been related to achiasmatic bel mutants, reversed optokinetic response (OKR) and congenital nystagmus (CN, involuntary conjugate oscillations of both eyes), looping opens a door to study the influence of visual input and eye movements on postural balance. Our result shows that looping correlates perfectly with reversed OKR and CN and is vision-dependent and contrast sensitive. CN precedes looping and the direction of the CN slow phase is predictive of the looping direction, but is absent during looping. Therefore, looping may be triggered by CN in bel. Moreover, looping in wild-type fish can also be evoked by whole-field motion, suggesting that looping in a bel mutant larvae is a result of self-motion perception. In contrary to previous hypotheses, our findings indicate that postural control in vertebrates relies on both direct visual input (afference signal) and eye-movement-related signals (efference copy or reafference signal).

Prey location, biomechanical constraints, and motor program choice during prey capture in the tomato frog, Dyscophus guineti

This study investigated how visual information about prey location and biomechanical constraints of the feeding apparatus influence the feeding behavior of the tomato frog, Dyscophus guineti. When feeding on prey at small azimuths (less than +/- 40 degrees), frogs aimed their heads toward the prey but did not aim their tongues relative to their heads. Frogs projected their tongues rapidly by transferring momentum from the lower jaw to the tongue. Storage and recovery of elastic energy by the mouth opening muscles amplified the velocities of mouth opening and tongue projection. This behavior can only occur when the lower jaw and tongue are aligned (i.e., within the range of motion of the neck). When feeding on prey at large azimuths (greater than +/- 40 degrees), frogs aimed both the head and tongue toward the prey and used a muscular hydrostatic mechanism to project the tongue. Hydrostatic elongation allows for frogs to capture prey at greater azimuthal locations. Because the tongue moves independently of the lower jaw, frogs can no longer take advantage of momentum transfer to amplify the speed of tongue projection. To feed on prey at different azimuthal locations, tomato frogs switch between alternative strategies to circumvent these biomechanical constraints.

Stereotypy, flexibility and coordination: key concepts in behavioral functional morphology

Animal movement and its muscular control are central topics in functional morphology. As experimentalists we often manipulate stimuli in a controlled setting or compare species to observe the degree of variation in movement and motor control of particular behaviors. Understanding and communicating the biological significance of these sources of variability requires a universal terminology that is presently lacking in the functional morphology literature. We suggest that `stereotypy' be used to refer to the degree of variability observed in a behavior across trials under a given set of conditions. The ability of an organism to alter its behavior across experimental treatments is referred to as `flexibility'. We discuss how there has been a tendency to confound the phenomenon of a behavior exhibiting low variability, which we refer to as stereotyped, with inflexibility, or the inability to alter the behavior in response to a change in stimulus. The degree of stereotypy and flexibility in a behavior need not be correlated, nor need they have a common underlying basis. Coordination, a term used to describe the relationship between different body parts during movement, can be stereotyped and can show flexibility. Stereotypy of coordination can be assessed by the strength of correlations between movements of two body parts. The influence of coordination coherence on behavioral performance has rarely been considered,and could shed light on how taxa differ in their ability to perform behaviors. We suggest definitions of the terms stereotypy, flexibility and coordination,and provide examples of how and when these terms could be used when discussing behavioral changes in functional morphology.

Visual fields of four batoid fishes: a comparative study

The visual fields of elasmobranch fishes are not well characterized even though this is a fundamental element of the visual system. The batoid fishes (skates, rays) form a monophyletic clade within the subclass Elasmobranchii and exhibit a broad range of morphologies and corresponding ecologies. We hypothesized that their visual field characteristics would reflect their diverse morphology and ecology. This was tested by quantifying the monocular, binocular and cyclopean horizontal and vertical visual fields of four batoid species (Raja eglanteria, Urobatis jamaicensis, Dasyatis sabina and Rhinoptera bonasus) that encompassed a range from a basal skate to a more derived ray. The horizontal and vertical visual fields differed significantly among species; however, all species possessed horizontal anterior and dorsal binocular overlaps. Urobatis jamaicensis, a small reef-associated stingray, demonstrated a 360 degrees panoramic visual field in the horizontal plane, and R. bonasus, a schooling benthopelagic ray, a 360 degrees panoramic view in the vertical plane. Large anterior binocular overlaps were measured in D. sabina (72 degrees ) and R. bonasus (46 degrees ) but came at the expense of large posterior blind areas. The anterior binocular overlaps in R. eglanteria (28 degrees ) and U. jamaicensis (34 degrees ) were smaller but were coupled with large monocular fields that provided expansive peripheral views. The most phylogenetically basal species, the clearnose skate (Raja eglanteria), had the most reduced visual field in contrast to the more derived ray species. To our knowledge, this study represents the first comparative assessment of visual fields in basal vertebrates.

Integrated diversification of locomotion and feeding in labrid fishes

An organism's performance of any ecological task involves coordination of multiple functional systems. Feeding performance is influenced by locomotor abilities which are used during search and capture of prey, as well as cranial mechanics, which affect prey capture and processing. But, does this integration of functional systems manifest itself during evolution? We asked whether the locomotor and feeding systems evolved in association in one of the most prominent and diverse reef fish radiations, the Labridae. We examined features of the pectoral fins that affect swimming performance and aspects of the skull that describe force and motion of the jaws. We applied a recent phylogeny, calculated independent contrasts for 60 nodes and performed principal components analyses separately on contrasts for fin and skull traits. The major axes of fin and skull diversification are highly correlated; modifications of the skull to amplify the speed of jaw movements are correlated with changes in the pectoral fins that increase swimming speed, and increases in force capacity of the skull are associated with changes towards fins that produce high thrust at slow speeds. These results indicate that the labrid radiation involved a strong connection between locomotion and feeding abilities.

Neural development of the zebrafish (Danio rerio) pectoral fin

The innervation and actuation of limbs have been major areas of research in motor control. Here we describe the innervation of the pectoral fins of the larval zebrafish (Danio rerio) and its ontogeny. Imaging and genetic tools available in this species provide opportunities to add new perspectives to the growing body of work on limbs. We used immunocytological and gross histological techniques with confocal microscopy to characterize the pattern of pectoral fin nerves. We retrogradely labeled fin neurons to describe the distributions of the pectoral fin motor pool in the spinal cord. At 5 days postfertilization, four nerves innervate the pectoral fins. We found that the rostral three nerves enter the fin from the dorsal side of the fin base and service the dorsal and middle fin regions. The fourth nerve enters the fin from the ventral fin base and innervates the ventral region. We found no mediolateral spatial segregation between adductor and abductor cell bodies in the spinal cord. During the larval stage pectoral fins have one adductor and one abductor muscle with an endoskeletal disc between them. As the skeleton and muscles expand and differentiate through postlarval development, there are major changes in fin innervation including extensive elaboration to the developing muscles and concentration of innervation to specific nerves and fin regions. The pattern of larval fin innervation recorded is associated with later muscle subdivision, suggesting that fin muscles may be functionally subdivided before they are morphologically subdivided.

Tectal control of locomotion, steering, and eye movements in lamprey

The intrinsic function of the brain stem-spinal cord networks eliciting the locomotor synergy is well described in the lamprey-a vertebrate model system. This study addresses the role of tectum in integrating eye, body orientation, and locomotor movements as in steering and goal-directed behavior. Electrical stimuli were applied to different areas within the optic tectum in head-restrained semi-intact lampreys (n = 40). Motions of the eyes and body were recorded simultaneously (videotaped). Brief pulse trains (<0.5 s) elicited only eye movements, but with longer stimuli (>0.5 s) lateral bending movements of the body (orientation movements) were added, and with even longer stimuli locomotor movements were initiated. Depending on the tectal area stimulated, four characteristic response patterns were observed. In a lateral area conjugate horizontal eye movements combined with lateral bending movements of the body and locomotor movements were elicited, depending on stimulus duration. The amplitude of the eye movement and bending movements was site specific within this region. In a rostromedial area, bilateral downward vertical eye movements occurred. In a caudomedial tectal area, large-amplitude undulatory body movements akin to struggling behavior were elicited, combined with large-amplitude eye movements that were antiphasic to the body movements. The alternating eye movements were not dependent on vestibuloocular reflexes. Finally, in a caudolateral area locomotor movements without eye or bending movements could be elicited. These results show that tectum can provide integrated motor responses of eye, body orientation, and locomotion of the type that would be required in goal-directed locomotion.

Biting releases constraints on moray eel feeding kinematics

We present an analysis of prey capture functional morphology in eels by comparing two species of moray eels, Muraena retifera and Echidna nebulosa (Family Muraenidae), to the American eel Anguilla rostrata (Family Anguillidae). The skulls of both moray species exhibited extreme reductions of several prominent components of the suction-feeding mechanism, including the hyoid bar, the sternohyoideus muscle and the pectoral girdle. Associated with these anatomical modifications, morays showed no evidence of using suction during prey capture. From 59 video sequences of morays feeding on pieces of cut squid we saw no hyoid depression and no movement of prey toward the mouth aperture during the strike, a widely used indicator of suction-induced water flow. This was in contrast to A. rostrata, which exhibited a robust hyoid, sternohyoideus muscle and pectoral girdle, and used suction to draw prey into its mouth. Average prey capture time in morays, about 500 ms, was roughly 10 times longer than in A. rostrata, and morays frequently reversed the direction of jaw and head rotation in the midst of the strike. We tested whether the absence of suction feeding reduces temporal constraints on feeding kinematics, permitting greater variance in traits that characterize timing and the extent of motion in the neurocranium, by comparing moray eel species with A. rostrata,two Centrarchids and a cichlid. Kinematic variance was roughly 5 times higher in morays than the suction-feeding species. Prey capture by suction demands a rapid, highly coordinated series of cranial movements and the loss of this mechanism appears to have permitted slower, more variable prey capture kinematics in morays. The alternative prey capture strategy in morays, biting,may be tied to their success as predators in the confined spaces of reef crevices where they hunt for cephalopods, crustaceans and fish.

Feeding, fins and braking maneuvers: locomotion during prey capture in centrarchid fishes

Locomotion is an integral aspect of the prey capture strategy of almost every predatory animal. For fishes that employ suction to draw prey into their mouths, locomotor movements are vital for the correct positioning of the mouth relative to the prey item. Despite this, little is known regarding the relationships between locomotor movements and prey capture. To gain insights into how fishes move during prey capture and the mechanisms underlying deceleration during prey capture, I measured the fin and body movements of largemouth bass, Micropterus salmoides, and bluegill sunfish, Lepomis macrochirus. Using a high-speed video camera (500 frames s-1), I captured locomotor and feeding movements in lateral and ventral (via a mirror) view. Largemouth bass swam considerably faster than bluegill during the approach to the prey item, and both species decelerated substantially following prey capture. The mean magnitude of deceleration was significantly higher in largemouth bass (-1089 cm s-2) than bluegill (-235 cm s-2), and the timing of maximum deceleration was much later for largemouth bass (30.3 ms after maximum gape) than bluegill (6.7 ms after maximum gape). Both species employed their pectoral, anal and caudal fins in order to decelerate during prey capture. However, largemouth bass protracted their pectoral fins more and faster,likely contributing to the greater magnitude of deceleration in the species. The primary mechanism for increased deceleration was an increase in approach speed. The drag forces experienced by the fins and body are proportional to the velocity of the flow squared. Thus, the braking forces exerted by fins,without any change in kinematics, will increase exponentially with small increases in swimming speed, perhaps allowing these fishes to achieve higher braking forces at higher swimming speeds without altering body or fin kinematics. This result can likely be extended to other maneuvers such as turning.

Feeding with speed: prey capture evolution in cichilds

The diversity of both the locomotor and feeding systems in fish is extensive, although little is known about the integrated evolution of the two systems. Virtually, all fish swim to ingest prey and all open their buccal cavity during prey capture, but the relationship between these two ubiquitous components of fish feeding strikes is unknown. We predicted that there should be a positive correlation between ram speed (RS) and maximum gape (MG) because the accuracy of a predatory strike goes down with an increase in RS and fish with larger mouths eat larger, more evasive prey. For 18 species of neotropical cichlids, we used phylogenetic-independent contrasts to study the relationship between the predator closing speed (RS) and mouth size (MG) during prey capture. To provide a robust comparative framework, we augmented existing phylogenetic information available from the mitochondrial cytochrome b gene with sequences from the S7 nuclear ribosomal intron for these species. Then, we captured high-speed (500 images per second), lateral view feeding sequences of each species by using a digital video camera and measured both RS and MG. Uncorrected species values of MG and RS were positively and significantly correlated. When accounting for any of the set of phylogenetic relationships recovered, the independent contrasts of RS and MG remained significantly, and positively, correlated. This tight evolutionary coupling highlights what is likely a common relationship between locomotor behaviour and feeding kinematics in many organisms.

Biomimetic evolutionary analysis: testing the adaptive value of vertebrate tail stiffness in autonomous swimming robots

For early vertebrates, a long-standing hypothesis is that vertebrae evolved as a locomotor adaptation, stiffening the body axis and enhancing swimming performance. While supported by biomechanical data, this hypothesis has not been tested using an evolutionary approach. We did so by extending biomimetic evolutionary analysis (BEA), which builds physical simulations of extinct systems, to include use of autonomous robots as proxies of early vertebrates competing in a forage navigation task. Modeled after free-swimming larvae of sea squirts (Chordata, Urochordata), three robotic tadpoles (`Tadros'), each with a propulsive tail bearing a biomimetic notochord of variable spring stiffness, k (N m-1), searched for, oriented to, and orbited in two dimensions around a light source. Within each of ten generations, we selected for increased swimming speed, U (m s-1) and decreased time to the light source, t (s),average distance from the source, R (m) and wobble maneuvering, W (rad s-2). In software simulation, we coded two quantitative trait loci (QTL) that determine k: bending modulus, E (Nm-2) and length, L (m). Both QTL were mutated during replication, independently assorted during meiosis and, as haploid gametes, entered into the gene pool in proportion to parental fitness. After random mating created three new diploid genotypes, we fabricated three new offspring tails. In the presence of both selection and chance events(mutation, genetic drift), the phenotypic means of this small population evolved. The classic hypothesis was supported in that k was positively correlated (r2=0.40) with navigational prowess, NP, the dimensionless ratio of U to the product of R, t and W. However, the plausible adaptive scenario, even in this simplified system, is more complex, since the remaining variance in NP was correlated with the residuals of R and U taken with respect to k, suggesting that changes in k alone are insufficient to explain the evolution of NP.