Thigmomorphogenesis: Field and laboratory studies of Abies fraseri in response to wind or mechanical perturbation

Field- and greenhouse-grown Abies fraseri (Pursh) Poir. (Fraser fir) were analyzed for wind- or mechanically-induced flexure changes. These changes included inhibition of stem and needle elongation, reinforcement of branch bases around the stem, and increased radial growth in the direction of the mechanical perturbation (MP). Mature trees exposed to high wind conditions were severely flag-formed. These modified tree crowns had a lower drag than crowns of non-flag formed trees in wind-tunnel tests. In both field-grown and greenhouse-grown A. fraseri , MP induced a decrease in flexibility and increased elasticity of the stems. The increased radial growth of the stems overrode the increase in elasticity, resulting in the overall decrease in flexibility. The increase in radial growth caused by wind or mechanical flexure was due to greater cell divisions of the vascular cambium, resulting in increased numbers of tracheids. The decrease in stem elongation in these trees was due, at least in part, to a decrease in tracheid length. The potential biological and mechanical significance of these induced growth changes in trees are addressed. The data support the thigmomorphogenetic theory, which states that plants respond to wind and other mechanical perturbations in a way that is favorable to the plant for continued survival in windy environments.     

In situ measurements of hydrodynamic forces imposed on Chondrus crispus Stackhouse

Among the hydrodynamic forces experienced by intertidal organisms, drag and the impingement force are thought to have the greatest effect on macroalgae. These forces are modified by biotic factors such as algal morphology, reconfiguration, and the presence of a canopy. However, much of what is known about the hydrodynamics of macroalgae has been garnered from low-velocity laboratory flume studies. Few field studies have measured drag and none have directly measured the effects of the canopy on force. To examine in situ hydrodynamic forces imposed on the turf forming macroalga Chondrus crispus, compact digital force sensors were developed that measure and record the 3-dimensional force imposed on a macroalga without disturbing the surrounding canopy. Sensors were positioned within natural Chondrus beds and the effects of the canopy, algal morphology, and sea state on in situ hydrodynamic force were examined. Additionally, the predictions of a new model for drag on flexible macroalgae were tested by simultaneously measuring force and water velocity. Digital force recordings indicated that Chondrus only experience drag; lift and impingement force were negligible in all combinations of factors. Canopies significantly reduced drag by 15-65%. Morphology and size also influenced drag, such that lower forces were imposed on small planar algae than large arborescent individuals. Further, planar algae experienced low drag in all combinations of sea and canopy state, indicating that these individuals may not be as susceptible to wave disturbance as arborescent individuals. Overall, these data indicate that the ability for Chondrus to grow large, arborescent individuals is dependent on the drag reducing properties of the canopy, while more hydrodynamically harsh habitats may be accessible to planar morphologies. Additionally, these data suggest that drag models for canopy forming macroalgae must incorporate the effects of the canopy to predict drag accurately in situ.     

Energy cost and efficiency of sculling a Venetian gondola

Oxygen uptake was measured on four male subjects during sculling gondolas at constant speeds from approximately 1 to approximately 3 m.s-1. The number of scullers on board in the different trials was one, two or four. Tractional water resistance (drag, D, N) was also measured in the same range of speeds. Energy cost of locomotion per unit of distance (C, J.m-1), as calculated from the ratio of O2 uptake above resting to, increased with v according to a power function (C = 155.2.v1.67; r = 0.88). Also D could be described as a power function of the speed: D = 12.3.v2.21; r = 0.94). The overall efficiency of motion, as obtained from the ratio of D to C, increased with speed from 9.2% at 1.41 m.s-1 to 14.5% at 3.08 m.s-1. It is concluded that, in spite of this relatively low efficiency of motion, the gondola is a very economic means. Indeed, at low speeds (approximately 1 m.s-1), the absolute amount of energy for propelling a gondola is the same as that for waking on the level at the same speed for a subject of 70 kg body mass.     

Effects of coating roughness and biofouling on ship resistance and powering

Abstract

Predictions of full-scale ship resistance and powering are made for antifouling coating systems with a range of roughness and fouling conditions. The estimates are based on results from laboratory-scale drag measurements and boundary layer similarity law analysis. In the present work, predictions are made for a mid-sized naval surface combatant at cruising speed and near maximum speed. The results indicate that slime films can lead to significant increases in resistance and powering, and heavy calcareous fouling results in powering penalties up to 86% at cruising speed. The present estimates show good agreement with results from full-scale ship power trials.     

Hydrodynamic effects in fast AFM single-molecule force measurements

Atomic force microscopy (AFM) allows the critical forces that unfold single proteins and rupture individual receptor–ligand bonds to be measured. To derive the shape of the energy landscape, the dynamic strength of the system is probed at different force loading rates. This is usually achieved by varying the pulling speed between a few nm/s and a few m/s, although for a more complete investigation of the kinetic properties higher speeds are desirable. Above 10 m/s, the hydrodynamic drag force acting on the AFM cantilever reaches the same order of magnitude as the molecular forces. This has limited the maximum pulling speed in AFM single-molecule force spectroscopy experiments. Here, we present an approach for considering these hydrodynamic effects, thereby allowing a correct evaluation of AFM force measurements recorded over an extended range of pulling speeds (and thus loading rates). To support and illustrate our theoretical considerations, we experimentally evaluated the mechanical unfolding of a multi-domain protein recorded at 30 m/s pulling speed.Abbrevations AFM atomic force micrcoscopy - pN piconewton - BR bacteriorhodopsin - DFS dynamic force spectroscopy - Ig27 immunoglobulin 27 - If27-8 immunoglobulin 27 octameric construct - BFP biomembrane force probe     

Ocean waves, nearshore ecology, and natural selection

Although they are subjected to one of the most stressful physical environments on earth, wave-swept rocky shores support a highly diverse community of plants and animals. The surprising presence of such diversity amidst severe environmental adversity provides a unique opportunity for exploration of the role of extreme water flows in community ecology and natural selection. Methods are described by which the maximal water velocity and acceleration can be predicted for a site on the shore, and from these values maximal hydrodynamic forces are calculated. These forces can limit the range and foraging activity of some species, and can determine the rate of disturbance in others, but in general, wave-swept organisms have surprisingly high factors of safety. This apparent over-design can help to explain the diversity of forms present on wave-swept shores, and provides examples of how mechanics can limit the ability of natural selection to guide specialization. Although flow itself may commonly be prohibited from selecting for optima in morphology, it nonetheless continues to play a potentially important role in evolution by providing a mechanism for breaking or dislodging individuals that have been selected by other means.     

Influence of surface penetration on measured fluid force on a hand model

The purpose of this study was to quantify the effect of wave drag due to surface penetration on drag and lift forces (C_d and C_l) acting on a hand model. The values of C_d and C_l had been acquired to gain the hydrodynamic characteristics of the swimmer's hand and predict force on the swimmer's hand. These values have also been used to benchmark computational fluid dynamics analysis. Because the previous studies used a hand/forearm model which penetrated the water's surface, the values of C_d and C_l include the effect of the surface wave on the model. Wave formation causes pressure differences between the frontal and rear sides of a surface-penetrating model as a result of depressions and elevations in the water's surface. This may be considered as wave drag due to surface penetration. Fluid forces due to wave drag on the forearm should not be included in the measured C_d and C_l of a swimmer's hand that does not sweep near the water's surface. Two hand/forearm models are compared, one with the hand rigidly connected to the forearm. The other model was constructed to isolate the fluid forces acting on the hand from the influence of wave drag on the forearm. The measurements showed that the effect of wave drag on the hand model caused large increases in the values of C_d, up to 46–98% with lesser increases in C_l of 2–12% depending on the hand orientation. The present study provides an improved method to determine the values of C_d and C_l that eliminates the effect of wave drag on a hand/forearm model by isolating the measurement of fluid forces on the forearm of the hand/forearm model in order to separately acquire the forces on the hand.     

Male secondary sexual traits are hydrodynamic devices for enhancing swimming performance in a monogamous filefish Paramonacanthus japonicus

The Japanese filefish Paramonacanthus japonicus has extreme sexual dimorphism in its overall shape, even though its mating system is monogamy with biparental care. This sexual dimorphism is mainly due to the development of secondary sexual traits in males. Males become more slender in body with elevated soft dorsal and anal fins as they mature. We examined the function of such male secondary sexual traits by field research and fluid-dynamic analysis. Underwater observations showed that movement rate and steady swimming speed of males were higher than those of females. Male and female P. japonicus showed similar feeding habits and egg-tending behavior, although males attacked potential egg predators more frequently. A wind-tunnel experiment using the air bearing and spring system showed that the drag coefficient of males was significantly lower than that of females, indicating a lower male hydrodynamic drag performance. Also, male elevated soft dorsal and anal fins are considered to give rise to higher thrust performance in monacanthids. Thus, these results suggest that male secondary sexual traits are hydrodynamic devices for enhancing swimming performance that seem to be actually functional under natural conditions. We discuss the evolution of such conspicuous male sexual traits in P. japonicus. Electronic Publication     

Influence of hydrodynamic forces on population structure of Pinna nobilis L., 1758 (Mollusca: Bivalvia): The critical combination of drag force, water depth, shell size and orientation

The effects of hydrodynamics on size, shape and distribution of benthic organisms are still not completely understood. Benthic organisms that inhabit wave-swept environments usually have small sizes and ethological adaptations to reduce drag and increase resistance force. Water speeds produced by waves in intertidal habitats can be more than 10 times higher than those in subtidal environments. However, comparatively small water speeds can produce high drag forces (F_d) on large subtidal organisms.Pinna nobilis is a subtidal epibenthic large bivalve-mollusc endemic to the Mediterranean Sea, a common inhabitant of Posidonia oceanica meadows. It lives partially buried in the seabed and shows a characteristic population structure. Small individuals are usually located at shallow sites whereas large individuals are only observed in deeper levels or sheltered locations. Also, some populations show a common orientation of the shell. These features are widespread throughout the Mediterranean, but their causes are unknown.The present work is a study on the relationship between population structure of P. nobilis and the habitat hydrodynamics. The main factor considered was Drag force due to the water flow produced by waves. Drag forces (F_d) supported by two populations located at different depths in the same P. oceanica meadow were estimated according to both the size and orientation of shells. Also, F_d acting on the individuals during the greatest storm recorded in the zone in the previous 9 years, were calculated. Drag coefficients (C_d), necessaries to estimate F_d, were estimated in the towing tank of the “Ecuela Técnica Superior de Ingenieros Navales (ETSIN)” of the Polytechnic University of Madrid.The results show significant differences in F_d acting in both populations. Despite the important increment of water speed with wave shoaling, individuals of the shallow population (SP), located at 6 m depth, withstand less F_d than those of the deep population (DP), at 13 m depth. The main reasons of this F_d reduction in SP are both the small size of the individuals and their common orientation, having the dorso-ventral side of the shell towards the main water flow. This fact, together with previous data showing higher mortality, less density of individuals, and less maximum asymptotic length, evidence that selective pressures regulate these population parameters, producing a trade-off between hydrodynamics, shell size and orientation, for each shore type and water depth.Combining the data of F_d supported by each population for different wave types, approximate values of the optimal mean F_d and the maximum dislodgement force withstood by P. nobilis were estimated (< 9 Newton (N) and ≈ 45 N respectively).     

Biomechanical factors contributing to self-organization in seagrass landscapes

Field observations have revealed that when water flow is consistently from one direction, seagrass shoots align in rows perpendicular to the primary axis of flow direction. In this study, live Zostera marina shoots were arranged either randomly or in rows perpendicular to the flow direction and tested in a seawater flume under unidirectional flow and waves to determine if shoot arrangement: a) influenced flow-induced force on individual shoots, b) differentially altered water flow through the canopy, and c) influenced light interception by the canopy. In addition, blade breaking strength was compared with flow-induced force to determine if changes in shoot arrangement might reduce the potential for damage to shoots.

Under unidirectional flow, both current velocity in the canopy and force on shoots were significantly decreased when shoots were arranged in rows as compared to randomly. However, force on shoots was nearly constant with downstream distance, arising from the trade-off of shoot bending and in-canopy flow reduction. The coefficient of drag was higher for randomly-arranged shoots at low velocities (< 30 cm s^− 1) but converged rapidly among the two shoot arrangements at higher velocities. Shoots arranged in rows tended to intercept slightly more light than those arranged randomly. Effects of shoot arrangement under waves were less clear, potentially because we did not achieve the proper plant size–row spacing ratio. At this point, we may only suggest that water motion, as opposed to light capture, is the dominant physical mechanism responsible for these shoot arrangements. Following a computation of the Environmental Stress Factor, we concluded that even photosynthetically active blades may be damaged or broken under frequently encountered storm conditions, irrespective of shoot arrangement.

We hypothesize that when flow is generally from one direction, seagrass bed patterns over multiple scales of consideration may arise as a cumulative effect of individual shoot self-organization driven by reduced force and drag on the shoots and somewhat improved light capture.