Reverse Swimming Research Articles

Light-propelled self-sustained swimming of a liquid crystal elastomer torus at low Reynolds number

The well-known Purcell's toroidal swimmer can translate in low Reynolds number fluid, by periodically changing its own shape in a nonreciprocal way to overcome the scallop theorem originating from the time independence of the Stokes equation. Based on a liquid crystal elastomer (LCE) torus motor with zero-elastic-energy mode, this paper proposes a mechanism for light-powered self-sustained swimming of a torus at low Reynolds number. By adopting the well-established dynamic LCE model and viscous hydrodynamics for the motion of a thin torus in Stokes flow, the self-sustained swimming of the LCE torus under steady and homogeneous illumination is theoretically investigated. The light-driven moment propelling the self-sustained swimming is derived, and the translation velocity and rotation angular velocity of the LCE torus swimmer in Stokes fluid are analytically formulated by force balance and moment equilibrium. The results show that the translation velocity and rotation angular velocity of the self-sustained swimming only depend on several simple dimensionless parameters, including light intensity, penetration depth, elastic modulus, curvature and payload. Especially, there exists a critical payload for reverse swimming in the opposite direction. The results provide a theoretical basis for the LCE-based self-propelled motor with zero-elastic-energy mode, and the self-propulsion mechanism may also inspire the design of self-sustained swimmers based on other stimuli-responsive toruses.

Maneuvering Performance in the Colonial Siphonophore, Nanomia bijuga.

The colonial cnidarian, Nanomia bijuga, is highly proficient at moving in three-dimensional space through forward swimming, reverse swimming and turning. We used high speed videography, particle tracking, and particle image velocimetry (PIV) with frame rates up to 6400 s−1 to study the kinematics and fluid mechanics of N. bijuga during turning and reversing. N. bijuga achieved turns with high maneuverability (mean length–specific turning radius, R/L = 0.15 ± 0.10) and agility (mean angular velocity, ω = 104 ± 41 deg. s−1). The maximum angular velocity of N. bijuga, 215 deg. s−1, exceeded that of many vertebrates with more complex body forms and neurocircuitry. Through the combination of rapid nectophore contraction and velum modulation, N. bijuga generated high speed, narrow jets (maximum = 1063 ± 176 mm s−1; 295 nectophore lengths s−1) and thrust vectoring, which enabled high speed reverse swimming (maximum = 134 ± 28 mm s−1; 37 nectophore lengths s−1) that matched previously reported forward swimming speeds. A 1:1 ratio of forward to reverse swimming speed has not been recorded in other swimming organisms. Taken together, the colonial architecture, simple neurocircuitry, and tightly controlled pulsed jets by N. bijuga allow for a diverse repertoire of movements. Considering the further advantages of scalability and redundancy in colonies, N. bijuga is a model system for informing underwater propulsion and navigation of complex environments.

Dynamic Morphology and Swimming Properties of Rotating Miniature Swimmers With Soft Tails

Helical microswimmers are suitable for propelling at low Reynolds numbers. To date, artificial microswimmers with rigid helical tails have been significantly developed. However, swimmers made of soft materials, which are more adaptive in confined or complex environments, are still lack of adequate investigation. In our previous studies, we demonstrated that a magnetically actuated swimmer with a plate soft tail could form a helical structure in a rotating magnetic field to propel itself at low Reynolds numbers. In this paper, we report the different dynamic morphologies formed by the soft tail of the swimmers during a simple rotation. We prove that the pitch length of the formed helical structure dynamically decreases with the rotation frequency. The formed helical structure collapses down to a cylindricallike structure, when the pitch gap of the soft tail decreases to zero. The corresponding rotation frequency is defined as a morphological step-out frequency, which is different from the magnetic step-out frequency in previous works. At the morphological step-out frequency, the swimmers performs a pure rotation without a forward propulsion, which is defined as a “dynamic stop.” The pitch length and the morphological step-out frequency increase with the rigidity of the tail. More interestingly, we found that if the rotation frequency keeps increasing, the swimmer may achieve a reverse propulsion without changing any other input parameters. The dynamic stop and reverse swimming cannot be observed if the soft tails are too long. We expect that the dynamic swimming phenomena found in the swimmers with soft tails can be used for agile and delicate motion control of soft miniature swimmers, which will be the base of numerous biomedical applications.

Do traditional and reverse swimming training periodizations lead to similar aerobic performance improvements?

The purpose of the present research was to analyze the modifications on aerobic swimming performance indicators after performing traditional and reverse training periodizations (TTP and RTP, respectively). Seventeen trained swimmers were divided into two groups: one group (N.=7) performed 10 weeks of TTP (based on high volumes and an increased intensity during the program) and the second one (N.=10) was involved in a similar period of RTP (based on low volumes and high intensity during the entire program). Velocity (v), heart rate (HR) and rate of perceived exertion (RPE) at the intensity of 4 mmol/L of blood lactate concentration, v, HR, RPE, stroke rate, stroke length and stroke index at the minimal intensity that elicits maximal oxygen uptake (vVO2max) and maximal oxygen uptake (VO2max) were analyzed pre- and post-training intervention. Stroke index significantly increased (2.9±0.3 vs. 3.1±0.2; P<0.05) and stroke rate and RPE at vVO2max significantly decreased after performing TTP. In the RTP group, VO2max significantly increased (50.9±6.6 vs. 54.1±4.7 mL/min/kg). In conclusion, RTP performed for 10 weeks was more effective than TTP to increase the VO2max in trained swimmers, but TTP yields a higher swimming efficiency, probably due to the higher volume of technical training performed during the training program.

Redox Sensing within the Genus Shewanella.

A novel bacterial behavior called congregation was recently described in Shewanella oneidensis MR-1 as the accumulation of cells around insoluble electron acceptors (IEA). It is the result of a series of “run-and-reversal” events enabled by modulation of swimming speed and direction. The model proposed that the swimming cells constantly sense their surroundings with specialized outer membrane cytochromes capable of extracellular electron transport (EET). Up to this point, neither the congregation nor attachment behavior have been studied in any other strains. In this study, the wild type of S. oneidensis MR-1 and several deletion mutants as well as eight other Shewanella strains (Shewanella putrefaciens CN32, S. sp. ANA-3, S. sp. W3-18-1, Shewanella amazonensis SB2B, Shewanella loihica PV-4, Shewanella denitrificans OS217, Shewanella baltica OS155, and Shewanella frigidimarina NCIMB400) were screened for the ability to congregate. To monitor congregation and attachment, specialized cell-tracking techniques, as well as a novel cell accumulation after photo-bleaching (CAAP) confocal microscopy technique were utilized in this study. We found a strong correlation between the ability of strain MR-1 to accumulate on mineral surface and the presence of key EET genes such as mtrBC/omcA (SO_1778, SO_1776, and SO_1779) and gene coding for methyl-accepting protein (MCPs) with Ca+ channel chemotaxis receptor (Cache) domain (SO_2240). These EET and taxis genes were previously identified as essential for characteristic run and reversal swimming around IEA surfaces. CN32, ANA-3, and PV-4 congregated around both Fe(OH)3 and MnO2. Two other Shewanella spp. showed preferences for one oxide over the other: preferences that correlated with the metal content of the environments from which the strains were isolated: e.g., W3-18-1, which was isolated from an iron-rich habitat congregated and attached preferentially to Fe(OH)3, while SB2B, which was isolated from a MnO2-rich environment, preferred MnO2.

Transformation of crustacean pathogenic bacterium Spiroplasma eriocheiris and expression of yellow fluorescent protein

Spiroplasma eriocheiris, the cause of crab trembling disease, is a wall-less bacterium, related to Mycoplasmas, measuring 2.0–10.0 μm long. It features a helical cell shape and a unique swimming mechanism that does not use flagella; instead, it moves by switching the cell helicity at a kink traveling from the front to the tail. S. eriocheiris seems to use a novel chemotactic system that is based on the frequency of reversal swimming behaviors rather than the conventional two-component system, which is generally essential for bacterial chemotaxis. To identify the genes involved in these novel mechanisms, we developed a transformation system by using oriC plasmid harboring the tetracycline resistant gene, tetM, which is under the control of a strong promoter for an abundant protein, elongation factor-Tu. The transformation efficiency achieved was 1.6 × 10−5 colony forming unit (CFU) for 1 μg DNA, enabling the expression of the enhanced yellow fluorescent protein (EYFP).

Autonomic adaptation after traditional and reverse swimming training periodizations.

The objective of the present study was to analyze the autonomic response of trained swimmers to traditional and reverse training periodization models. Seventeen swimmers were divided in two groups, performing a traditional periodization (TPG) or a reverse periodization (RPG) during a period of 10 weeks. Heart rate variability and 50 m swimming performance were analyzed before and after the training programs. After training, the TPG decreased the values of the high frequency band (HF), the number of differences between adjacent normal R-R intervals longer than 50 ms (NN50) and the percentage of differences between adjacent normal R-R intervals more than 50 ms (pNN50), and the RPG increased the values of HF and square root of the mean of the sum of the squared differences between adjacent normal R-R intervals (RMSSD). None of the groups improved significantly their performance in the 50-m test. The autonomic response of swimmers was different depending on the periodization performed, with the reverse periodization model leading to higher autonomic adaption. Complementary, the data suggests that autonomic adaptations were not critical for the 50-m swimming performance.

Inactivation of Ca2+-induced ciliary reversal by high-salt extraction in the cilia of Paramecium

Intracellular Ca(2+) induces ciliary reversal and backward swimming in Paramecium. However, it is not known how the Ca(2+) signal controls the motor machinery to induce ciliary reversal. We found that demembranated cilia on the ciliated cortical sheets from Paramecium caudatum lost the ability to undergo ciliary reversal after brief extraction with a solution containing 0.5 M KCl. KNO(3), which is similar to KCl with respect to chaotropic effect; it had the same effect as that of KCl on ciliary response. Cyclic AMP antagonizes Ca(2+)-induced ciliary reversal. Limited trypsin digestion prevents endogenous A-kinase and cAMP-dependent phosphorylation of an outer arm dynein light chain and induces ciliary reversal. However, the trypsin digestion prior to the high-salt extraction did not affect the inhibition of Ca(2+)-induced ciliary reversal caused by the high-salt extraction. Furthermore, during the course of the high-salt extraction, some axonemal proteins were extracted from ciliary axonemes, suggesting that they may be responsible for Ca(2+)-induced ciliary reversal.

Alternate but Do Not Swim: A Test for Executive Motor Dysfunction in Parkinson Disease

The objective of this study is to learn if participants with Parkinson disease (PD), when compared to normal controls, are impaired in making simultaneous but independent right and left hand movements. Participants were tested with Luria's Alternating Hand Postures (AHP) test and modified AHP tests. Twelve PD participants without dementia and twelve matched controls were assessed for their ability to perform the parallel AHP test (both hands remaining in the same coronal plane) and with modifications of this test into swimming (alternative arm extension with finger extension and arm flexion with finger flexion) and reverse swimming (alternative arm extension-finger flexion and arm flexion-finger extension) movements. The participants with PD were significantly impaired when performing the parallel and the reverse swimming movements AHP tests, but not impaired on the swimming movements AHP test. Swimming movements may be phylogenetically and ontogenetically more primitive and not as heavily dependent on frontal-basal ganglia networks; thus performance of swimming movements during the parallel AHP test may decrease this test's sensitivity.

A comparison of the stress response and mortality of sea bream Pagrus major captured by hook and line and trammel net

Fisheries management policy to increase escapement of non-target species and sizes of fish from fishing gears is generally based on the assumption that injury and stress received during the capture-escape process do not result in a significant level of mortality after escape. However, there has been little research to validate this assumption. To investigate the stress response and mortality associated with capture-escape trauma, a series of comparative experiments were carried out using red sea bream Pagrus major captured by hook and line and trammel net. Cortisol levels in fish captured by hook and line were measured as an index of the stress associated with capture duration using commercially available plasma Cortisol RIA kits. Plasma cortisol levels of resting fish (12.21 ng ml −1, n = 12) were significantly lower than those for all fish captured. In hook and line caught fish, stress increased as capture duration was increased from 10 min to 3 h. Stress levels for capture periods of 6, 9, 12 and 18 h were lower than those for 1 and 3 h but above 10 min capture time and resting values. Fish behaviour during capture included initial flight response, successive struggles of decreasing magnitude, reverse swimming and finning to maintain position. Struggle activity reduced as time of capture increased. No mortalities occurred during capture or 38 days of post release monitoring. On the other hand, stress levels of fish after 10 min, 1.5, 3, 6, 9, 12 and 18 h captured by trammel net were significantly higher than resting fish and continued to rise with capture duration. Forty four percent of all fish captured by trammel net died, of which 28% occurred in the net in fish whose gill cover was held closed by the small mesh netting. Five percent of the fish died within 48 h post release and 11% were delayed mortalities between 8–18 days post release in fish with severe open wounds. No mortalities occurred between 19–38 days post release. We suggest that hook and line caught fish are able to exhibit an adaptive response to capture, in which a cessation of struggling resulted in the captured fish regaining their normal swimming position and allowed the fish to recover from struggling which reduces the probability of mortality. Adaptive behaviour was not possible in fish caught by trammel net in which the degree of entanglement remained constant or increased with capture duration. Ceasing or continuing to struggle did not reduce the degree of entanglement or reduce the constriction of netting around the fish body and gills. These results show that fish stress during capture may vary by gear type and that mortalities may be immediate or delayed after release from the fishing gear. Stress and injury incurred during encounter and subsequent escape may result in an unaccounted level of fishing mortality.

Why do electric fishes swim backwards? An hypothesis based on gymnotiform foraging behavior interpreted through sensory constraints

Fishes producing high-frequency wavelike electrical discharges maintain a relatively rigid body axis and swim forwards and backwards with equal ease. Using stop-action videotape filming we have observed the gymnotiform Apteronotus albifrons feeding on zooplankton and oligochaete annelids. Here it is reported that reverse swimming is characteristic of two foraging behaviors: searching for prey and assessing it. In assessing a potential prey item, fish typically scan it from tail to head by swimming backwards, then ingest it after a short forward lunge. A scan in the opposite direction-from head to tail by forward swimming-would have the prey located near the tail and out of position for the final lunge. Food choice experiments indicate that these electrosensing fish feed equally well, and take larger rather than smaller zooplankton, under light and dark conditions. Furthermore, electric fish take normal (light) colored and darkened prey (Daphnia) in a 50: 50 ratio under both dark and light conditions. These results are consistent with the interpretation that electrosensory cues are being used to detect zooplankton and other prey. Together, our observations support Lissmann's (1958, 1974) and Lissmann & Machin's (1958) assertion that backwards swimming is a component of a locomotory pattern guided by the constraints produced by an active electrical sense.

The role of the notochard in forward and reverse swimming and burrowing in the amphioxus Branchiostoma lanceolatum

Analyses of high speed cinefilm have shown that amphioxus swims either forward or backward with undulatory movement generated at the leading end, the wave of displacement passing along the body with increasing amplitude. The leading end, whether this is “head” or tail, is evidently more rigid than the trailing end, flexibility at each end changing with reversal in direction of swimming. It is suggested that control of the amplitude of the waves of displacement in different regions of the body in swimming is a function of the notochord, contraction of the muscular notochordal plates increasing its stiffness. Connections between the central nervous system and the notochordal plates via the notochordal pits are already known to exist.As exposure to light invariably induces swimming in dark–adapted animals, it seems probable that the eyes function in initiating movement. The rate of increase in number and size of the eye cups during larval and adult growth and their pattern of distribution in the nerve cord are given. In the adult the eye cups occur predominantly in the anterior and posterior regions of the body. This may be of significance in providing the stimulus for changes in flexibility of these regions in swimming.High speed cinefilm has also shown that amphioxus can burrow “head” or tail‐first and move through sand in a forward or a reverse direction. It is suggested that rapid reversal of direction is of greater importance in movement through sand than in swimming.

Analysis of locomotion in a siphonophore colony

The siphonophoreNanomia caraswims forwards and backwards by means of its nectophores. Reverse swimming is a through-conducted response in which the circular muscle in each nectophore contracts and radial fibres (‘fibres of Claus’) in the velum simultaneously shorten, deflecting the water jet emitted through the velar opening forwards. Forward-swimming contractions may be synchronized initially in all nectophores or may be asynchronous, but in both cases colonial control is involved. The fibres of Claus do not contract in forward swimming. Synchronized forward swimming ('F') is through-conducted from the siphosome at a velocity estimated at 75 to 150 cm/s. It may also be evoked by stimulation of posterior (older) nectophores. Stimulation of anterior (younger) nectophores or of the float elicits only reverse swimming (‘R’). Stimulation of nectophores in a 'transitional’ zone may evoke eitherForRcomplete in all nectophores, but never responses intermediate between the two. Evidence is given that nectophores undergo sensory transformation during life, initially serving for the evocation only ofR, later only forF. The basis of this transformation is not understood. No comparable change in motor capacity occurs. Use of excess Mg2+in various concentrations shows that striated muscle action is suppressed more readily than that of unstriated muscle and that both are suppressed more readily than is transmission of excitation between nectophores and stem. Surgical operations on whole specimens and on detached nectophores show that there is a single conduction route for theFresponse, histologically identified as an exumbrellar nerve tract. Transection of this tract obliteratesFconduction without affecting theRresponse. It is shown that transmission of the latter must occur in the entire exumbrellar ectoderm of the nectophore or in special conducting elements (undetected) associated with it. Neither mesogloeal nor endodermal conduction appear to be involved in locomotory responses. The existence of two separate conduction systems in the stem, connected with those demonstrated in the nectophores, is inferred.Nanomiaresponds to sudden illumination of the siphosome byFbehaviour. Nectophores and float, however, are not photosensitive. Autotomy of nectophores is a highly organized process, involving compensatory stem adjustments. The locomotory behaviour of siphonophores and chondrophores is reviewed and new information is provided for several species. Co-ordination of activities is widespread. The locomotory behaviour ofNanomiais typical of the long-stemmed Physonectae.