Showing papers on "Aquatic locomotion published in 2016"

“On the Fence” versus “All in”: Insights from Turtles for the Evolution of Aquatic Locomotor Specializations and Habitat Transitions in Tetrapod Vertebrates

Abstract: Though ultimately descended from terrestrial amniotes, turtles have deep roots as an aquatic lineage and are quite diverse in the extent of their aquatic specializations. Many taxa can be viewed as "on the fence" between aquatic and terrestrial realms, whereas others have independently hyperspecialized and moved "all in" to aquatic habitats. Such differences in specialization are reflected strongly in the locomotor system. We have conducted several studies to evaluate the performance consequences of such variation in design, as well as the mechanisms through which specialization for aquatic locomotion is facilitated in turtles. One path to aquatic hyperspecialization has involved the evolutionary transformation of the forelimbs from rowing, tubular limbs with distal paddles into flapping, flattened flippers, as in sea turtles. Prior to the advent of any hydrodynamic advantages, the evolution of such flippers may have been enabled by a reduction in twisting loads on proximal limb bones that accompanied swimming in rowing ancestors, facilitating a shift from tubular to flattened limbs. Moreover, the control of flapping movements appears related primarily to shifts in the activity of a single forelimb muscle, the deltoid. Despite some performance advantages, flapping may entail a locomotor cost in terms of decreased locomotor stability. However, other morphological specializations among rowing species may enhance swimming stability. For example, among highly aquatic pleurodiran turtles, fusion of the pelvis to the shell appears to dramatically reduce motions of the pelvis compared to freshwater cryptodiran species. This could contribute to advantageous increases in aquatic stability among predominantly aquatic pleurodires. Thus, even within the potential constraints of a body plan in which the body is encased by a shell, turtles exhibit diverse locomotor capacities that have enabled diversification into a wide range of aquatic habitats.

A bio-inspired swimming robot for marine aquaculture applications: From concept-design to simulation

Abstract: This paper presents the development of a bio-inspired swimming robot from concept design to simulation for marine aquaculture applications. Based on investigation of several fish motions, the Manta ray is found to be the most suitable mock object since the flapping pectoral fin features long-endurance, low noise, high payload capacity, good stability and maneuverability. Through a comprehensive analysis of the structure of Manta ray, the shape proportional relationship between the body and the pectoral fins is obtained. Even though the concept design simplifies the structure, major functional components are retained. By applying two degrees of freedoms to each segment of the pectoral fin, the propulsion mechanism allow the robotic fish to swim in 3D. In addition, a thrust analysis is performed for a good understanding of the fish's aquatic locomotion principle. The flapping motion is decomposed into two orthogonal waves and realized on the robotic fish, taking advantages of sine generators. Simulation experiments including motion comparison, speed and turning tests verify the correctness of the robotic fish's structure and its propulsion mechanisms.

Amphibious adaptations in a newly recognized amphibious fish: Terrestrial locomotion and the influences of body size and temperature

Abstract: Amphibious animals are adapted for both aquatic and terrestrial habitats. The conflicting requirements for dual habitats are perhaps most pronounced in the air-breathing fishes, which represent an intermediate stage between the totally aquatic habitat and terrestrial colonization. A key requirement for amphibious fishes is terrestrial locomotion. The different densities and compositions of air and water impose constraints for efficient terrestrial locomotion that differ from those required for aquatic locomotion. I investigated terrestrial locomotion in a small South African fish, Galaxias ‘nebula’, by exposing 60 individual fish to air in specially designed raceways and quantifying movement type and occurrence as a function of availability of water, fish size and environmental temperature. Nebula showed a sustained undulating form of terrestrial locomotion characteristic of amphibious fishes and also a transient ballistic locomotion (jumps) typical of fully aquatic species. Terrestrial movement was influenced by fish size, with medium-sized fish undertaking more jumps towards water, and fewer jumps away from water, than their smaller or larger conspecifics. In contrast, axial undulation was mainly influenced by temperature. However, there was no consistent pattern in temperature effects presumably because temperature is just one of a suit of environmental factors that may affect terrestrial locomotion. Nebula's amphibious adaptations allow it to cope with the unpredictability inherent in its natural environment.

Comparing submerged walking and swimming kinematics in epaulette sharks

Abstract: {Extract} The transition from swimming to walking was an important event in the evolution of tetrapods. To understand this transition, researchers have studied movement in many extinct and extant aquatic and semi-aquatic species. The epaulette shark Hemiscillum ocellatum uses slow-to-medium walking, fast walking, and swimming forms of aquatic locomotion. We described kinematic differences between the three gaits in neonate (n=6) and juvenile (n=6) sharks hatched and reared in the laboratory. Neonates retain nutrition from an internal yolk until they develop a consistent feeding schedule (~35d post-hatch). They are then classified as juveniles, foraging for worms, crustaceans, and small fish. We hypothesized that changes in diet and feeding habits would affect gait performance between neonates and juveniles. Using video tracking software and 13 anatomical landmarks along the fins, girdles, and body mid-line, whole body velocity, duty factor, fin frequency, girdle rotation, and body curvature were calculated to identify characteristic movements of the gaits for each shark. Velocity was greater in neonates when compared to juveniles across all gaits; however, both groups increased velocity from walking to swimming. Regardless of gait, pelvic girdles had a greater range of motion than pectoral girdles for both neonates and juveniles. In juveniles, regardless of gait, the contralateral sides of the pectoral and pelvic girdles were synchronized during lateral excursions. Neonates, however, exhibited overlapping of ipsilateral sides of the girdles. Understanding the transition from neonate to juvenile locomotory forms in this species could provide insight on the water to land transition of tetrapods.

A survival guide for feeble fish

Abstract: As avid anglers we were always interested in the survival chances of fish in turbulent oceans. This paper addresses this question mathematically. We show that a fish with bounded aquatic locomotion speed can reach any point in the ocean if the fluid velocity is incompressible, bounded, and has small mean drift.