Eliot G. Drucker

Bio: Eliot G. Drucker is an academic researcher from University of California, Irvine. The author has contributed to research in topics: Fish fin & Fin. The author has an hindex of 18, co-authored 19 publications receiving 2351 citations. Previous affiliations of Eliot G. Drucker include Harvard University.

Locomotor forces on a swimming fish: three-dimensional vortex wake dynamics quantified using digital particle image velocimetry.

Abstract: Quantifying the locomotor forces experienced by swimming fishes represents a significant challenge because direct measurements of force applied to the aquatic medium are not feasible. However, using the technique of digital particle image velocimetry (DPIV), it is possible to quantify the effect of fish fins on water movement and hence to estimate momentum transfer from the animal to the fluid. We used DPIV to visualize water flow in the wake of the pectoral fins of bluegill sunfish (Lepomis macrochirus) swimming at speeds of 0.5-1.5 L s(-)(1), where L is total body length. Velocity fields quantified in three perpendicular planes in the wake of the fins allowed three-dimensional reconstruction of downstream vortex structures. At low swimming speed (0.5 L s(-)(1)), vorticity is shed by each fin during the downstroke and stroke reversal to generate discrete, roughly symmetrical, vortex rings of near-uniform circulation with a central jet of high-velocity flow. At and above the maximum sustainable labriform swimming speed of 1.0 L s(-)(1), additional vorticity appears on the upstroke, indicating the production of linked pairs of rings by each fin. Fluid velocity measured in the vicinity of the fin indicates that substantial spanwise flow during the downstroke may occur as vortex rings are formed. The forces exerted by the fins on the water in three dimensions were calculated from vortex ring orientation and momentum. Mean wake-derived thrust (11.1 mN) and lift (3.2 mN) forces produced by both fins per stride at 0.5 L s(-)(1) were found to match closely empirically determined counter-forces of body drag and weight. Medially directed reaction forces were unexpectedly large, averaging 125 % of the thrust force for each fin. Such large inward forces and a deep body that isolates left- and right-side vortex rings are predicted to aid maneuverability. The observed force balance indicates that DPIV can be used to measure accurately large-scale vorticity in the wake of swimming fishes and is therefore a valuable means of studying unsteady flows produced by animals moving through fluids.

Morphology and experimental hydrodynamics of fish fin control surfaces

Abstract: Over the past 520 million years, the process of evolution has produced a diversity of nearly 25000 species of fish. This diversity includes thousands of different fin designs which are largely the product of natural selection for locomotor performance. Fish fins can be grouped into two major categories: median and paired fins. Fins are typically supported at their base by a series of segmentally arranged bony or cartilaginous elements, and fish have extensive muscular control over fin conformation. Recent experimental hydrodynamic investigation of fish fin function in a diversity of freely swimming fish (including sharks, sturgeon, trout, sunfish, and surfperch) has demonstrated the role of fins in propulsion and maneuvering. Fish pectoral fins generate either separate or linked vortex rings during propulsion, and the lateral forces generated by pectoral fins are of similar magnitudes to thrust force during slow swimming. Yawing maneuvers involve differentiation of hydrodynamic function between left and right fins via vortex ring reorientation. Low-aspect ratio pectoral fins in sharks function to alter body pitch and induce vertical maneuvers through conformational changes of the fin trailing edge. The dorsal fin of fish displays a diversity of hydrodynamic function, from a discrete thrust-generating propulsor acting independently from the body, to a stabilizer generating only side forces. Dorsal fins play an active role in generating off-axis forces during maneuvering. Locomotor efficiency may be enhanced when the caudal fin intercepts the dorsal fin wake. The caudal fin of fish moves in a complex three-dimensional manner and evidence for thrust vectoring of caudal fin forces is presented for sturgeon which appear to have active control of the angle of vortices shed from the tail. Fish are designed to be unstable and are constantly using their control surfaces to generate opposing and balancing forces in addition to thrust. Lessons from fish for autonomous underwater vehicle (AUV) design include: 1) location of multiple control surfaces distributed widely about the center of mass, 2) design of control surfaces that have a high degree of three-dimensional motion through a flexible articulation with the body, 3) the ability to modulate fin surface conformation, and 4) the simultaneous use of numerous control surfaces including locating some fin elements in the downstream wake generated by other fins. The ability to manufacture an AUV that takes advantage of these design features is currently limited by the nature of available materials and mechanical drive trains. But future developments in polymer artificial muscle technology will provide a new approach to propulsor design that will permit construction of biomimetic propulsors with conformational and articulational flexibility similar to that of fish fins.

Locomotor function of the dorsal fin in teleost fishes: experimental analysis of wake forces in sunfish

Abstract: A key evolutionary transformation of the locomotor system of ray-finned fishes is the morphological elaboration of the dorsal fin. Within Teleostei, the dorsal fin primitively is a single midline structure supported by soft, flexible fin rays. In its derived condition, the fin is made up of two anatomically distinct portions: an anterior section supported by spines, and a posterior section that is soft-rayed. We have a very limited understanding of the functional significance of this evolutionary variation in dorsal fin design. To initiate empirical hydrodynamic study of dorsal fin function in teleost fishes, we analyzed the wake created by the soft dorsal fin of bluegill sunfish (Lepomis macrochirus) during both steady swimming and unsteady turning maneuvers. Digital particle image velocimetry was used to visualize wake structures and to calculate in vivo locomotor forces. Study of the vortices generated simultaneously by the soft dorsal and caudal fins during locomotion allowed experimental characterization of median-fin wake interactions. During high-speed swimming (i.e. above the gait transition from pectoral- to median-fin locomotion), the soft dorsal fin undergoes regular oscillatory motion which, in comparison with analogous movement by the tail, is phase-advanced (by 30% of the cycle period) and of lower sweep amplitude (by 1.0 cm). Undulations of the soft dorsal fin during steady swimming at 1.1 bodylength s(-1) generate a reverse von Karman vortex street wake that contributes 12% of total thrust. During low-speed turns, the soft dorsal fin produces discrete pairs of counterrotating vortices with a central region of high-velocity jet flow. This vortex wake, generated in the latter stage of the turn and posterior to the center of mass of the body, counteracts torque generated earlier in the turn by the anteriorly positioned pectoral fins and thereby corrects the heading of the fish as it begins to translate forward away from the turning stimulus. One-third of the laterally directed fluid force measured during turning is developed by the soft dorsal fin. For steady swimming, we present empirical evidence that vortex structures generated by the soft dorsal fin upstream can constructively interact with those produced by the caudal fin downstream. Reinforcement of circulation around the tail through interception of the dorsal fin's vortices is proposed as a mechanism for augmenting wake energy and enhancing thrust. Swimming in fishes involves the partitioning of locomotor force among several independent fin systems. Coordinated use of the pectoral fins, caudal fin and soft dorsal fin to increase wake momentum, as documented for L. macrochirus, highlights the ability of teleost fishes to employ multiple propulsors simultaneously for controlling complex swimming behaviors.

A hydrodynamic analysis of fish swimming speed: wake structure and locomotor force in slow and fast labriform swimmers

Abstract: Past study of interspecific variation in the swimming speed of fishes has focused on internal physiological mechanisms that may limit the ability of locomotor muscle to generate power. In this paper, we approach the question of why some fishes are able to swim faster than others from a hydrodynamic perspective, using the technique of digital particle image velocimetry which allows measurement of fluid velocity and estimation of wake momentum and mechanical forces for locomotion. We investigate the structure and strength of the wake in three dimensions to determine how hydrodynamic force varies in two species that differ markedly in maximum swimming speed. Black surfperch (Embiotoca jacksoni) and bluegill sunfish (Lepomis macrochirus) swim at low speeds using their pectoral fins exclusively, and at higher speeds switch to combined pectoral and caudal fin locomotion. E. jacksoni can swim twice as fast as similarly sized L. macrochirus using the pectoral fins alone. The pectoral fin wake of black surfperch at all speeds consists of two distinct vortex rings linked ventrally. As speed increases from 1.0 to 3.0 L s(−)(1), where L is total body length, the vortex ring formed on the fin downstroke reorients to direct force increasingly downstream, parallel to the direction of locomotion. The ratio of laterally to downstream-directed force declines from 0.93 to 0.07 as speed increases. In contrast, the sunfish pectoral fin generates a single vortex ring per fin beat at low swimming speeds and a pair of linked vortex rings (with one ring only partially complete and attached to the body) at maximal labriform speeds. Across a biologically relevant range of swimming speeds, bluegill sunfish generate relatively large lateral forces with the paired fins: the ratio of lateral to downstream force remains at or above 1.0 at all speeds. By increasing wake momentum and by orienting this momentum in a direction more favorable for thrust than for lateral force, black surfperch are able to swim at twice the speed of bluegill sunfish using the pectoral fins. In sunfish, without a reorientation of shed vortices, increases in power output of pectoral fin muscle would have little effect on maximum locomotor speed. We present two hypotheses relating locomotor stability, maneuverability and the structure of the vortex wake. First, at low speeds, the large lateral forces exhibited by both species may be necessary for stability. Second, we propose a potential hydrodynamic trade-off between speed and maneuverability that arises as a geometric consequence of the orientation of vortex rings shed by the pectoral fins. Bluegill sunfish may be more maneuverable because of their ability to generate large mediolateral force asymmetries between the left- and right-side fins.

Function of pectoral fins in rainbow trout: behavioral repertoire and hydrodynamic forces

Abstract: Salmonid fishes (trout, salmon and relatives) have served as a model system for study of the mechanics of aquatic animal locomotion, yet little is known about the function of non-axial propulsors in this major taxonomic group. In this study we examine the behavioral and hydromechanical repertoire of the paired pectoral fins of rainbow trout Oncorhynchus mykiss, performing both steady rectilinear swimming and unsteady maneuvering locomotion. A combination of kinematic analysis and quantitative flow visualization (using digital particle image velocimetry) enables identification of the propulsive roles played by pectoral fin motions. During constant-speed swimming (0.5 and 1.0 body length s(-1)), the pectoral fins remain adducted against the body. These fins are actively recruited, however, for a variety of maneuvering behaviors, including station holding in still water (hovering), low-speed (i.e. non-fast-start) turning, and rapid deceleration of the body during braking. Despite having a shallow pectoral-fin base orientation (the plesiomorphic teleost condition), trout are capable of rotating the fin base over 30 degrees during maneuvering, which affords the fin an impressive degree of kinematic versatility. When hovering, the pectoral fins are depressed beneath the body and twisted along their long axes to allow anteroposterior sculling. During turning and braking, the fins undergo spanwise rotation in the opposite direction and exhibit mediolateral and dorsoventral excursions. Water velocity fields and calculated momentum flows in the wake of the pectoral fins reveal that positive thrust is not generated during maneuvering, except during the retraction half-stroke of hovering. Relatively large laterally directed fluid force (mean 2.7 mN) is developed during turning, whose reaction powers yawing rotation of the body (4-41 degrees s(-1)). During deceleration, the wake-force line of action falls below the center of mass of the body, and this result supports a long-standing mechanical model of braking by fishes with ventrally positioned paired fins. Despite its traditional categorization as a propulsor of limited functional importance, the salmoniform pectoral fin exhibits a diverse locomotor repertoire comparable to that of higher teleostean fishes.

How Animals Move: An Integrative View

Abstract: Recent advances in integrative studies of locomotion have revealed several general principles. Energy storage and exchange mechanisms discovered in walking and running bipeds apply to multilegged locomotion and even to flying and swimming. Nonpropulsive lateral forces can be sizable, but they may benefit stability, maneuverability, or other criteria that become apparent in natural environments. Locomotor control systems combine rapid mechanical preflexes with multimodal sensory feedback and feedforward commands. Muscles have a surprising variety of functions in locomotion, serving as motors, brakes, springs, and struts. Integrative approaches reveal not only how each component within a locomotor system operates but how they function as a collective whole.

Shape analysis of symmetric structures: quantifying variation among individuals and asymmetry.

Abstract: Morphometric studies often consider parts with internal left-right symmetry, for instance, the vertebrate skull. This type of symmetry is called object symmetry and is distinguished from matching symmetry, in which two separate structures exist as mirror images of each other, one on each body side. We explain a method for partitioning the total shape variation of landmark configurations with object symmetry into components of symmetric variation among individuals and asymmetry. This method is based on the Procrustes superimposition of the original and a reflected copy of each landmark configuration and is compatible with the two-factor ANOVA model customary in studies of fluctuating asymmetry. We show a fully multivariate framework for testing the effects in the two-factor model with MANOVA statistics, which also applies to shapes with matching symmetry. We apply the new methods in a small case study of pharyngeal jaws of the Neotropical cichlid fish Amphilophus citrinellus. The analysis revealed that the symmetric component of variation in the pharyngeal jaws is dominated by the contrast between two alternative trophic morphs in this species and that there is subtle but statistically significant directional asymmetry. Finally, we provide some general recommendations for morphometric studies of symmetric shapes.

Hydrodynamics of Fishlike Swimming

Abstract: Interest in novel forms of marine propulsion and maneuvering has sparked a number of studies on unsteadily operating propulsors. We review recent experimental and theoretical work identifying the principal mechanism for producing propulsive and transient forces in oscillating flexible bodies and fins in water, the formation and control of large-scale vortices. Connection with studies on live fish is made, explaining the observed outstanding fish agility.

Fish exploiting vortices decrease muscle activity.

Abstract: Fishes moving through turbulent flows or in formation are regularly exposed to vortices. Although animals living in fluid environments commonly capture energy from vortices, experimental data on the hydrodynamics and neural control of interactions between fish and vortices are lacking. We used quantitative flow visualization and electromyography to show that trout will adopt a novel mode of locomotion to slalom in between experimentally generated vortices by activating only their anterior axial muscles. Reduced muscle activity during vortex exploitation compared with the activity of fishes engaged in undulatory swimming suggests a decrease in the cost of locomotion and provides a mechanism to understand the patterns of fish distributions in schools and riverine environments.

African cichlid fish: a model system in adaptive radiation research

Abstract: The African cichlid fish radiations are the most diverse extant animal radiations and provide a unique system to test predictions of speciation and adaptive radiation theory. The past few years have seen major advances in the phylogenetics, evolutionary biogeography and ecology of cichlid fish. Most of this work has concentrated on the most diverse radiations. Unfortunately, a large number of small radiations and 'non-radiations' have been overlooked, potentially limiting the contribution of the cichlid system to our understanding of speciation and adaptive radiation. I have reviewed the literature to identify 33 intralacustrine radiations and 76 failed radiations. For as many as possible I collected information on lake size, age and phylogenetic relationships. I use these data to address two questions: (i) whether the rate of speciation and the resulting species richness are related to temporal and spatial variation in ecological opportunity and (ii) whether the likelihood of undergoing adaptive radiation is similar for different African cichlid lineages. The former is a key prediction of the ecological theory of adaptive radiation that has been presumed true but remains untested for cichlid radiations. The second is based on the hypothesis that the propensity of cichlids to radiate is due to a key evolutionary innovation shared by all African cichlids. The evidence suggests that speciation rate declines through time as niches get filled up during adaptive radiation: young radiations and early stages of old radiations are characterized by high rates of speciation, whereas at least 0.5 Myr into a radiation speciation becomes a lot less frequent. The number of species in cichlid radiations increases with lake size, supporting the prediction that species diversity increases with habitat heterogeneity, but also with opportunity for isolation by distance. Finally, the data suggest that the propensity to radiate within lakes is a derived property that evolved during the evolutionary history of some African cichlids, and the appearance of which does not coincide with the appearance of proposed key innovations in morphology and life history.