Shape Of Flagellum Research Articles

The history of short-tailed whip scorpions: changes in body size and flagellum shape in Schizomida

Representatives of Schizomida, known as short-tailed whip scorpions, are an understudied group within Megoperculata. They are found subterraneanly in tropical and sub-tropical regions. They lack eyes, have superior mobility, and possess a flagellum which is relevant to their mating, but in general little is known about their general biology. Fossil representatives of Schizomida from a variety of time periods are available for study. Using 23 fossil specimens (14 of which are described here for the first time) and 86 extant individuals from the literature, changes in both body size and flagella shape in Schizomida were compared over time. Measurements of prosoma length and leg length were used as a proxy for body size, and a comparative size analysis was carried out. Individuals from the Cretaceous period were found to be significantly smaller than extant individuals, contrary to our expectations. For flagellum shape, images were used to create reconstructions, which were then analysed using an elliptic Fourier analysis followed by a principal component analysis. The morphological diversity of the male flagellum shape was found to have decreased between the Cretaceous and modern fauna. We discuss potential explanations for our findings, although a greater understanding of the general biology of Schizomida is required to properly interpret our results.

Patterns in schizomid flagellum shape from elliptical Fourier analysis

The arachnid order Schizomida is a relatively understudied group of soil-dwelling predators found on all continents except Antarctica. While efforts to understand their biology are growing, there is still much to know about them. A curious aspect of their morphology is the male flagellum, a sexually dimorphic, tail-like structure which differs in shape across the order and functions in their courtship rituals. The flagellar shape is important for taxonomic classification, yet few efforts have been made to examine shape diversity across the group. Using elliptical Fourier analysis, a type of geometric morphometrics based on shape outline, we quantified shape differences across a combined nearly 550 outlines in the dorsal and lateral views, categorizing them based on genus, family, biogeographic realm, and habitat, with special emphasis on Caribbean and Cuban fauna. We tested for allometric relationships, differences in disparity based on locations and sizes in morphospace among these categories, and for clusters of shapes in morphospace. We found multiple differences in all categories despite apparent overlaps in morphospace, evolutionary allometry, and evidence for discrete clusters in some flagellum shapes. This study can serve as a foundation for further study on the evolution, diversification, and taxonomic utility of the male flagellum.

Penetration mechanics of a beetle intromittent organ with bending stiffness gradient and a soft tip.

Hyper-elongated structures and their penetration are widespread among insects, for example, intromittent organs, ovipositors, and piercing-sucking mouthparts. The penetration of thin structures with high aspect ratio without buckling and rupturing is mechanically very challenging. However, this problem is economically solved in nature, and the solutions might be helpful for, for example, in the development of harmless catheters. We focus on the penetration process of a hyper-elongated structure of a cassidine beetle intromittent organ, termed a flagellum. We applied a three-point bending test for the flagellum to measure its bending stiffness along the entire flagellum. We demonstrated the bending stiffness gradient, in which the basal half is relatively stiff and the apical half is softer, whose good performance during copulation had been previously numerically demonstrated. The stiffness gradient is the result of the flagellum shape, which is cylindrical and tapered toward the tip. Moreover, the curved tip comprises a harder outer curve and a softer inner curve. Considering the findings of preceding studies, the flagellum works in the following way: (i) the bending stiffness gradient supports the flagellum, easily fitting to a shape of a highly coiled spermathecal duct, (ii) the stiffness property of the very tip may make the tip tougher, and (iii) the curled tip and homogeneously cylindrical shape of the organ help the very tip to fit the shape of the spermathecal duct of the female. Our study shows that the apparently simple flagellum penetration is achieved with numerous elaborate mechanical adaptations.

Nonlinear amplitude dynamics in flagellar beating.

The physical basis of flagellar and ciliary beating is a major problem in biology which is still far from completely understood. The fundamental cytoskeleton structure of cilia and flagella is the axoneme, a cylindrical array of microtubule doublets connected by passive cross-linkers and dynein motor proteins. The complex interplay of these elements leads to the generation of self-organized bending waves. Although many mathematical models have been proposed to understand this process, few attempts have been made to assess the role of dyneins on the nonlinear nature of the axoneme. Here, we investigate the nonlinear dynamics of flagella by considering an axonemal sliding control mechanism for dynein activity. This approach unveils the nonlinear selection of the oscillation amplitudes, which are typically either missed or prescribed in mathematical models. The explicit set of nonlinear equations are derived and solved numerically. Our analysis reveals the spatio-temporal dynamics of dynein populations and flagellum shape for different regimes of motor activity, medium viscosity and flagellum elasticity. Unstable modes saturate via the coupling of dynein kinetics and flagellum shape without the need of invoking a nonlinear axonemal response. Hence, our work reveals a novel mechanism for the saturation of unstable modes in axonemal beating.

Experimental study on the effect of a surrounding fluid on bovine sperm motility in three dimensions

We constructed an experimental system that can observe bovine sperm motility in three dimensions, simultaneously from the vertical and horizontal directions. The comparison of the experiments conducted using cover glass and square tubing indicates that the effect of the cover glass on the sperm motility is not negligible. Based on this result, we investigated a three-dimensional trajectory of a motile sperm in the square tubing by simultaneously observing through two high-speed cameras. In addition, we investigated the effect of different viscosities of the surrounding fluid on the sperm motility. The experimental results indicate that the increasing viscosity causes a decline in the sperm motility. Furthermore, we focus on the width of the sperm head and the flagellar shape. At low viscosity, the time variation of the head widths is relevant with the two directions and varies periodically. In contrast, at high viscosity, an almost constant value is maintained and periodical time variations are not observed for both directions. Moreover, a difference in the viscosity is observed for the tortuosity of the flagellum shape. These results suggest that the three-dimensional flagellar structure of the bovine sperm is a helix whose cross-sectional shape is an ellipse with quite a large aspect ratio. Further, the results state whether the rotation or nonrotation of the sperm is dependent on the balance between the viscous resistance acting on the sperm and the torque due to the flagellar shape. The experimental results obtained will be useful in clarifying the mechanics of sperm motility under their actual environmental conditions at high viscosity.

Bacterial rheotaxis

The motility of organisms is often directed in response to environmental stimuli. Rheotaxis is the directed movement resulting from fluid velocity gradients, long studied in fish, aquatic invertebrates, and spermatozoa. Using carefully controlled microfluidic flows, we show that rheotaxis also occurs in bacteria. Excellent quantitative agreement between experiments with Bacillus subtilis and a mathematical model reveals that bacterial rheotaxis is a purely physical phenomenon, in contrast to fish rheotaxis but in the same way as sperm rheotaxis. This previously unrecognized bacterial taxis results from a subtle interplay between velocity gradients and the helical shape of flagella, which together generate a torque that alters a bacterium's swimming direction. Because this torque is independent of the presence of a nearby surface, bacterial rheotaxis is not limited to the immediate neighborhood of liquid–solid interfaces, but also takes place in the bulk fluid. We predict that rheotaxis occurs in a wide range of bacterial habitats, from the natural environment to the human body, and can interfere with chemotaxis, suggesting that the fitness benefit conferred by bacterial motility may be sharply reduced in some hydrodynamic conditions.

In vitro effects of Bisphenol A on sperm motility characteristics in Perca fluviatilis L. (Percidae; Teleostei)

Summary In the present study, the effects of Bisphenol A (BPA) on sperm motility and velocity were investigated in perch (Perca fluviatilis L.). Sperm of five mature males was separately collected in a syringe. The sperm samples were diluted in an immobilizing solution containing 180 mm NaCl, 2.7 mm KCl, 1.4 mm CaCl2, 2.4 mm NaHCO3, pH 8.0 (340 mOsmol kg−1) at ratio 1 : 50 (sperm : IS). The sperm motility was triggered in an activation solution composed of 50 mm NaCl, 20 mm Tris, pH 8.5 containing different concentrations of BPA (2, 1.5, 1.25, 1.0, 0.5, 0.25, 0.125 and 0.0 mm) at ratio 1 : 50 (sperm : AS). At 15 s post-activation, sperm motility and velocity decreased significantly in activation medium containing 1.5 and 1 mm BPA, respectively. The motility of sperm was totally inhibited in 2 mm of BPA. Sperm motility duration decreased with increasing BPA concentrations. In the control, 25.3% of spermatozoa were still motile at 90 s post-activation, while only 1.3% was in 0.12 mm. However, sperm velocity was higher in activation medium containing 0.12 mm BPA at 15 s post-activation. There was no significant difference between the control and DMSO test group, the latter being used for dissolving BPA. The results of this study indicate that BPA decreases both motility and velocity of exposed sperm, in vitro. BPA may damage the flagella as ‘C’ shape of flagella was observed, once motility period of sperm cells are finished.

Description of hake (Merlucius merlucius) spermatozoa: flagellar wave characteristics and motility parameters in various situations

The objective of this study was to complement published hake (Merlucius merlucius) sperm motility characteristics by obtention of data more specifically dependent on flagella: beat frequency, flagellar wave amplitude, wave length, number of waves along the length of the flagellum and curvature of the wave. The changes of these parameters are described in relation to the time period elapsed since activation are described using high resolution video images of flagella while quantifying the progression during the swimming period from the activity initiation to full cessation of movement several minutes later. The main characteristic of the swimming period of hake spermatozoa shows a progressive decrease of forward displacement resulting from a cumulative decrease of several activity descriptors: the beat frequency, the percentage of motile cells, the wave amplitude, the number of flagellar waves and the linearity and shape of flagella. All these parameters decrease within 7–8 min after activation in a converging fashion, which leads to full immotility. Measurements of motility parameters at different temperatures also bring additional information about energetic needs for motility of hake sperm. The wave shape of the flagella showed that: (i) the contact of flagella with sea water, not only triggers immediately its motility, but also provokes rapidly local osmotic damages such as blebs which partly impair the correct wave propagation from head vicinity to flagellar tip; (ii) fully developed waves become more and more restricted to the proximal flagellum while the tip becomes devoid of any wave; (iii) the wave amplitude decreases as a function of time during the motility period. The combination of these factors contributes to motility limitations (<100 s) during which the spermatozoa are efficiently able to reach the egg for fertilization. Temperature effects (5–32°C) on these performance characteristics were also studied; this allows to conclude that the amount of energy needed to sustain motility becomes rapidly limiting. A quantitative evaluation of all these sperm motility features leads to a better definition of the conditions for controlled propagation of this species. The motility parameters are also useful as quantitative descriptors of sperm swimming ability in situations such as: (i) varying salinity (osmolality) of the medium (swimming solution) and (ii) activating motility in seminal fluid at various dilution ratios in sea water. All together, our results lead to a better understanding of hake sperm biological features, including its sperm flagella behaviour.

The optimal elastic flagellum

Motile eukaryotic cells propel themselves in viscous fluids by passing waves of bending deformation down their flagella. An infinitely long flagellum achieves a hydrodynamically optimal low-Reynolds number locomotion when the angle between its local tangent and the swimming direction remains constant along its length. Optimal flagella therefore adopt the shape of a helix in three dimensions (smooth) and that of a sawtooth in two dimensions (nonsmooth). Physically, biological organisms (or engineered microswimmers) must expend internal energy in order to produce the waves of deformation responsible for the motion. Here we propose a physically motivated derivation of the optimal flagellum shape. We determine analytically and numerically the shape of the flagellar wave which leads to the fastest swimming for a given appropriately defined energetic expenditure. Our novel approach is to define an energy which includes not only the work against the surrounding fluid, but also (1) the energy stored elastically in the bending of the flagellum, (2) the energy stored elastically in the internal sliding of the polymeric filaments which are responsible for the generation of the bending waves (microtubules), and (3) the viscous dissipation due to the presence of an internal fluid. This approach regularizes the optimal sawtooth shape for two-dimensional deformation at the expense of a small loss in hydrodynamic efficiency. The optimal waveforms of finite-size flagella are shown to depend on a competition between rotational motions and bending costs, and we observe a surprising bias toward half-integer wave numbers. Their final hydrodynamic efficiencies are above 6%, significantly larger than those of swimming cells, therefore indicating available room for further biological tuning.

Optimum Flagellum Shape of a Micromachine Imitating a Microorganism.

The purpose of the present study is to develop micromachines imitating flagellated micro-organisms. The speed of advance, the radius of trajectory and the power consumption of a micromachine are computed by using the boundary element method to optimize seven parameters that express the shape of an actual microorganism and six parameters that stand for the flagellum shape of a micromachine. The optimum cross-sectional shape of the flagellum is an ellipse which is somewhat inclined with respect to the principal normal line of the flagellum spiral. The optimum thickness distribution of the flagellum is such that the position of maximum thickness is very close to the head of the machine. The optimization leads to the reduction of power consumption by 22 percent compared with the power consumed by the actual microorganism.

A Redescription of “Trithyreus sawadai” (Uropygi: Schizomidae) from the Bonin Islands

A description of a meagerly known whip-scorpion species, “Trithyreus sawadai KISHIDA, 1930”, which is now regarded as a species of the genus Schizomus, is given for the first time. In spite of insufficient original treatment which was presented only by figures, the specific name has still validity in the Zoological Nomenclature. Originally this animal was found from “the Bonin Islands”, but this time it was exclusively discovered from Chichi-jima Island in the same Islands. It may be allied to “Trithyreus” luzonicus HANSEN known from Luzon in the Philippines, but can be distinguished by the shape of flagellum of both sexes from all the other “Trithyreus” hitherto known.

The effect of formaldehyde on the shape of bacterial flagella.

SUMMARY: Addition of formalin (40% formaldehyde) to a concentration of 5–10% (v/v) to a bacterial culture before flagellar staining may change the shape of the flagella as seen in the stained preparation. With many bacteria, if not a majority, the formalin has no effect on the flagellar shape. The coiled, the straight, the small-amplitude and the typical undulant flagellar shapes evidently are mainly due to formalin fixation. The effect of formalin on flagellar shape may have taxonomic significance and should be recorded. Formalin fixation is advantageous in flagellar staining in that it kills the bacteria and makes for nicer preparations, especially when the bacteria are capsulated.