Light-scattering studies of bull spermatozoa. II. Interaction and concentration effects.

The complete autocorrelation function of the intensity fluctuations of laser light scattered from motile bull spermatozoa is shown to depend upon several factors not previously considered. Samples of bull spermatozoa generally contain a substantial proportion of dead cells, which give rise to slowly decaying components of the autocorrelation function. Whereas previous work has concentrated on the form of the fast decaying autocorrelation component, we are concerned here with the relative amplitude and shape of the slow autocorrelation component and the general form of the composite function. In principle, the relative amplitudes of the fast and slow components of the autocorrelation function can be used as an assay of the proportion of swimming cells. We show that this amplitude ratio depends upon cell concentration, scattering cell geometry, and scattering angle. A simple model is developed to explain these results on the basis of the asymmetry of light scattered from these cells, motile/immotile cell interactions, wall-swimming effects, and geotactic reorientation of dead cells.     

Declination affects geomagnetic field-modulated geotaxis in fruit flies

Decades of research have established that the Earth’s magnetic field (geomagnetic field, GMF) is broadly used as a sensory cue for magnetic orientation in various animal taxa, including insects. In contrast to the investigation of the total intensity or inclination of the GMF, the effect of declination on horizontal magnetic movement has been explored in a few species, including flies, cockroaches, and dogs. However, the potential role of declination in the vertical movement in magnetosensitive organisms is yet to be reported. In this study, we provide the first evidence that declination within a natural range of change can affect static geotaxis in fruit flies, as assessed using the tube-positioning assay. In open-field measurements conducted at 22 domestic and foreign locations, the variation in declination was notably dependent upon the specific location, regardless of altitude, with similar variation in total intensity. Flies subjected to a geographic range of declination under the same total intensity and inclination exhibited remarkably different geotactic positioning scores, irrespective of GMF polarity. Notably, we observed a significant negative correlation between the geotactic score and the absolute value of declination, indicating that declination can induce negative geotaxis effects in flies. These results reveal that flies have evolved to incorporate a declination compass into their multimodal sensorimotor system and suggest that declination may be complementary to gravity in terms of environmental factor-driven negative geotaxis in flies.     

Effect of Viscosity on Formation and Sedimentation of Polytomella agilis Vertical Aggregates*

The response of vertical aggregates of Polytomella agilis to increased viscosity of the medium indicates that viscous resistance of the medium is a critical factor controlling the formation and sedimentation of protozoan aggregates. Aggregate formation time increased from 20 sec to 6.5 min as viscosity was increased 1.72 times. Sedimentation rate decreased about 140 μm/sec for each 10% increment in viscosity. Although there was a 60% decrease in speed of falling aggregates when relative viscosity was increased from 1.0 to 1.6, individually swimming P. agilis decreased less than 22% in speed even at a relative viscosity of 1.84 where aggregates did not form. Cells continued to accumulate near the surface by negative geotactic swimming after vertical aggregation ceased. Vertical aggregation is a cyclic process composed of 4 phases: a) accumulation-aggregation; b) aggregate sedimentation; c) ablation and dispersal; and d) negative geotaxis. Phase d is unique to motile microorganisms and only in such populations is vertical aggregation continuously selfperpetuating. Phases a-c occur with both motile and nonmotile bodies and are dependent upon viscous forces of the medium.     

Negative Geotactic Behavior of Paramecium Caudatum is Completely Described by the Mechanism of Buoyancy-Oriented Upward Swimming

This paper presents evidence that the negative geotactic behavior of Paramecium caudatum takes place by the mechanism of buoyancy-oriented upward swimming. Photographs of swimming pathways of the organisms were completely described by two dynamic equations for the translational motion of the center of gravity of the organism's body and for the rotational motion of the organism's body about its center of gravity, where the rotational torque is induced by a slight difference in position between the center of gravity and the center of buoyancy. It now seems unlikely that complicated mechanisms such as the statocyst mechanism and the gravity-propulsion mechanism, which have been proposed by many investigators, need be considered for other protozoa since preliminary observation and analysis of other ciliates such as Paramecium multimicronucleatum, Paramecium tetraurelia, and Tetrahymena pyriformis also strongly suggested that their negative geotaxis is due to buoyancy-oriented upward swimming.     

Behavior of red king crab larvae: phototaxis, geotaxis and rheotaxis

Zoeae of Paralithodes camtschatica were positively phototactic to white light intensities above 1 x 10(13) q cm-2 s-1. Negative phototaxis occurred at low (1 x 10(12) q cm-2 s-1), but not high intensities (2.2 x 10(16) q cm-2 s-1). Phototactic response was directly related to light intensity. Zoeae also responded to red, green and blue light. Zoeae were negatively geotactic, but geotaxis was dominated by phototaxis. Horizontal swimming speed of stage 1 zoeae < 4 d old was 2.4 +/- 0.1 (SE) cm s-1 and decreased to 1.7 +/- 0.1 cm s-1 in older zoeae (P < 0.01). Horizontal swimming speed of stage 2 zoeae was not significantly different from > or = 4 d old stage 1 zoeae. Vertical swimming speed, 1.6 +/- 0.1 cm s-1, and sinking rate, 0.7 +/- 0.1 cm s-1, did not change with ontogeny. King crab zoeae were positively rheotactic and maintained position in horizontal currents less than 1.4 cm s-1. Starvation reduced swimming and sinking rates and phototactic response.     

Selective inhibition of flagellar activity in Chlamydomonas by nickel.

Flagellar activity in the biflagellate chlorophyte Chlamydomonas reinhardtii is selectively inhibited by Ni2+ or by treatment with Ca2+-chelating agents. Inhibitions of swimming speed, geotaxis, phototaxis, and pattern swimming result from qualitative and quantitative losses in the activity of individual flagella and in the coordination of activity between the 2 flagella of each cell. Addition of Ca2+ (a) prevents inhibition and (b) restores normal flagellar activity in inhibited cells. Mg2+ is partially effective in reversal of inhibition. Other ions do not cause similar inhibition or reversal of nickel inhibition. The characteristics of inhibition and reversal suggest that the primary target for nickel is a component of the flagellar apparatus, and that this component uses Ca2+ to perform its normal function in the regulation of flagellar activity. A 2nd target for nickel is a Ca-requiring process specific to phototaxis (and not involved in the photophobic response).     

Analysis of gamete and zygote motility in Allomyces

To study the mechanisms of chemotaxis in eukaryotes, the motility patterns of the gametes and zygotes and the chemotactic responses of the male gametes of the lower eukaryote Allomyces macrogynus were examined. Dark-field microscopy of the male gametes showed a smooth swimming pattern interrupted by very brief ‘jerks’ of the cell body that caused a change in swimming direction. Female gametes had a slower swimming velocity than the males and underwent more jerks or turns which accounted for their sluggish motility. The zygotes swam with the fastest velocity and were observed to have a helical swimming pattern involving a continuous turning of the cell body, a behavior absent from the gametes. Introduction of female gametes that produce the chemoattractant sirenin brought about an immediate change in the behavior of the male gametes. They moved in spirals (or helices) towards the source of the chemoattractant (the female gametes), undergoing only a few jerks to reorient the male cells. When very near the female cells, or in high concentrations of added sirenin, many very short motility tracks were observed that finally resulted in contact between the two gamete types. The results indicate that the poor swimming ability of the female gametes facilitates gamete contact, resulting in as many as 30–40 male gametes clustered on a single female cell. Further, male gamete orientation to the sirenin gradient is caused by the chemoattractant suppressing the jerk motion.     

Phototactic and geotactic responses inAllothrombium pulvinum larvae (Acari: Trombidiidae)

Phototactic and geotactic responses of larvae ofAllothrombium pulvinum Ewing were examined in the laboratory.Allothrombium pulvinum larvae showed positive phototaxis and negative geotaxis. Positive phototaxis and negative geotaxis in larvalA. pulvinum and other trombidioids are adaptive, because these mechanisms help mites that hatch in dark soil to find hosts on plants above ground in the light.     

Geotaxis in protozoa I. A propulsion-gravity model for Tetrahymena (Ciliata)

A propulsion-based model for negative geotaxis of ciliated protozoa is presented which views geotaxic reorientation as the unbalancing of gyrational torque by a sedimentation torque. The balanced gyrational torque results from the location of the propulsive center of effort forward of the body center of mass. When gravity is ignored, the propulsive forces generating the gyrational moments may be confined to an envelope surrounding the cell. The effect of gravity is to induce sedimentation of the body-plus-envelope system. Viscous resistance to this sedimentation at the envelope “surface” is transmitted to the beating cilia whose net constant energy output must now deal with a new source of dissipation (not “present” when gravity was ignored) which is maximal in the downswing portion of the gyration cycle. In such a manner sedimentation resistance acts as a counter torque to the downswing gyrational moment of force and an enhancing torque to the upswing moment thereby generating a net upward reorientation of the gyrational axis. Upon addition of the translational component of propulsion, the negative geotaxis behavior pattern is completed. The forward location of the center of effort which provides the basic validity indicator for the model is verified by observations from the ciliate Tetrahymena.     

Geotaxis in the springtail Folsomia candida

Laboratory assays demonstrated the presence of a small positive geotaxis response to a 15° incline by Folsomia candida Willem (Collembola: Isotomidae). Negative phototaxis played an additive role to positive geotaxis when the experimental apparatus were exposed to light. The geotactic response was negatively affected by cold acclimation and decreasing surrounding temperature, but unaffected by food deprivation. The reduced mobility of springtails at low temperature did not seem to play a role in the corresponding decreased geotaxis. The low level of geotaxis and its further decrease with exposure to low temperature support an earlier suggestion that F. candida do not respond to cooling temperatures of fall by relocation to warmer deeper soil layers, but remain in the upper soil layers and increase their cold tolerance to continue foraging in the food‐rich upper soil layers.     

Ontogenetic shift in geotaxis for walleye pollock,Theragra chalcogramma free embryos and larvae: potential role in controlling vertical distribution

Synopsis The behavioral capability of walleye pollock,Theragra chalcogramma free embryos and larvae to control vertical distribution was assessed by examining buoyancy during resting and swimming orientation and activity as they developed in complete darkness from hatching to first feeding readiness (1 to 7 d post hatching at 6° C). Free embryos exhibited positive geotaxis 1 d post hatching, actively swimming through a density gradient to remain in the lower water column. Activity increased with free embryo development and by 7 d post hatching, feeding-ready larvae reversed their vertical orientation, now exhibiting negative geotaxis as they migrated to the upper water column. The results indicate that even at the earliest developmental stages, walleye pollock possess the capability to control vertical distribution. Laboratory results are compared with patterns of vertical distribution observed in the sea.     

Zur definition von pro- und Metageotaxis bei Insekten

The word progeotaxis is used in two different ways: it means, that either the geotactic turning tendency is a function of the slope or that a geomenotactic angle of orientation is dependent on the slope. Metageotaxis means, that either the geotactic turning tendency or the geomenotactic angle of orientation is independent of the slope. It is shown: if menotaxis is controlled according to the bicomponent modulation, a menotactic orientation angle should always be independent of the slope. Therefore it would be possible, that an animal with “progeotactic” turning tendency shows a “metageotactic” menotactic orientation angle and controls this orientation angle according to the bicomponent modulation. The honey bee seems to be such an animal. InTenebrio molitor receptors on the antennae and in the pro-mesothoracic joint only affect the sign of the geotactic turning tendency but not its amount. This seems to be a small indication of the control of menotaxis in this animal according to the compensation theory. Inlocusts geotactic turning tendency is at a higher slope indepent of and at a lower slope dependent on the slope. The arguments indicate, that one should no longer use the terms progeotaxis and metageotaxis or at least give a more precise definition of them.     

Selective Inhibition of Flagellar Activity in Chlamydomonas by Nickel

Flagellar activity in the biflagellate chlorophyte Chlamydomonas reinhardtii is selectively inhibited by Ni²⁺ or by treatment with Ca²⁺-chelating agents. Inhibitions of swimming speed, geotaxis, phototaxis, and pattern swimming result from qualitative and quantitative losses in the activity of individual flagella and in the coordination of activity beween the 2 flagella of each cell. Addition of Ca²⁺ (a) prevents inhibition and (b) restores normal flagellar activity in inhibited cells. Mg²⁺ is partially effective in reversal of inhibition. Other ions do not cause similar inhibition or reversal of nickel inhibition. The characteristics of inhibition and reversal suggest that the prmary target for nickel is a component of the flagellar apparatus, and that this component uses Ca²⁺ to perform its normal function in the regulation of flagellar activity. A 2nd target for nickel is a Carequiring process specific to phototaxis (and not involved in the photophobic response).     

The responses of Philophthalmus gralli and P. megalurus miracidia to light, gravity and magnetic fields

Miracida of an eyefluke of birds, Philophthalmus gralli, which are positively geotactic, exhibited a positive north-seeking magnetotaxis when subjected to magnetic field strengths from 3 × 10^?4 to 2 × 10^?2 T. A closely-related species, P. megalurus, which is positively geotactic only in complete darkness, exhibited no magnetotaxis under similar conditions. A positive phototactic response overrode the north-seeking magnetotaxis when P. gralli miracidia were subjected to both stimuli in a competing system. No detector mechanisms for magnetic fields are known in miracidia of digenetic trematodes. The order of responsiveness for P. gralli miracidia then is: geotaxis > phototaxis > magnetotaxis.     

Kinematic Comparison of Forward and Backward Swimming and Maneuvering in a Self-Propelled Sub-Carangiform Robotic Fish

We make a thorough kinematic comparison of forward and backward swimming and maneuvering on a self-propelled robot platform that uses sub-carangifbrm swimming as the primary propulsor. An improved Central Pattern Generator （CPG） model allowing free adjustment of phase relationship and directional bias is employed to achieve flexible swimming and smooth transition. Considering the characteristics of forward swimming in carangiform fish and backward swimming in anguilliform fish, various backward swimming patterns for the sub-carangiform robotic fish are suitably created by reversing the direction of propagating propulsive waves. Through a combined use of the CPG control and closed-loop swimming direction control strategy, flexible and precise turning maneuvers in both forward and backward swimming are implemented and compared. By contrast with forward swimming, backward swimming requires a higher frequency or an increased lateral displacement to reach the same relative swimming speed. Noticeably, the phase difference shows a greater impact on forward swimming than on backward swimming. Our observations also indicate that the robotic fish achieves a larger turning rate in forward maneuvering than in backward maneuvering, yet these two maneuvers display comparable turning precision.     

Rhizobium meliloti swims by unidirectional, intermittent rotation of right-handed flagellar helices.

The 5 to 10 peritrichously inserted complex flagella of Rhizobium meliloti MVII-1 were found to form right-handed flagellar bundles. Bacteria swam at speeds up to 60 microns/s, their random three-dimensional walk consisting of straight runs and quick directional changes (turns) without the vigorous angular motion (tumbling) seen in swimming Escherichia coli cells. Observations of R. meliloti cells tethered by a single flagellar filament revealed that flagellar rotation was exclusively clockwise, interrupted by very brief stops (shorter than 0.1 s), typically every 1 to 2 s. Swimming bacteria responded to chemotactic stimuli by extending their runs, and tethered bacteria responded by prolonged intervals of clockwise rotation. Moreover, the motility tracks of a generally nonchemotactic ("smooth") mutant consisted of long runs without sharp turns, and tethered mutant cells showed continuous clockwise rotation without detectable stops. These observations suggested that the runs of swimming cells correspond to clockwise flagellar rotation, and the turns correspond to the brief rotation stops. We propose that single rotating flagella (depending on their insertion point on the rod-shaped bacterial surface) can reorient a swimming cell whenever the majority of flagellar motors stop.     

Differences in ATP Generation Via Glycolysis and Oxidative Phosphorylation and Relationships with Sperm Motility in Mouse Species

Mouse sperm produce enough ATP to sustain motility by anaerobic glycolysis and respiration. However, previous studies indicated that an active glycolytic pathway is required to achieve normal sperm function and identified glycolysis as the main source of ATP to fuel the motility of mouse sperm. All the available evidence has been gathered from the studies performed using the laboratory mouse. However, comparative studies of closely related mouse species have revealed a wide range of variation in sperm motility and ATP production and that the laboratory mouse has comparatively low values in these traits. In this study, we compared the relative reliance on the usage of glycolysis or oxidative phosphorylation as ATP sources for sperm motility between mouse species that exhibit significantly different sperm performance parameters. We found that the sperm of species with higher oxygen consumption/lactate excretion rate ratios were able to produce higher amounts of ATP, achieving higher swimming velocities. Additionally, we show that the species with higher respiration/glycolysis ratios have a higher degree of dependence upon active oxidative phosphorylation. Moreover, we characterize for the first time two mouse species in which sperm depend on functional oxidative phosphorylation to achieve normal performance. Finally, we discuss that sexual selection could promote adaptations in sperm energetic metabolism tending to increase the usage of a more efficient pathway for the generation of ATP (and faster sperm).     

Mutations that impair swarming motility in Serratia marcescens 274 include but are not limited to those affecting chemotaxis or flagellar function.

Serratia marcescens exists in two cell forms and displays two kinds of motility depending on the type of growth surface encountered (L. Alberti and R. M. Harshey, J. Bacteriol. 172:4322-4328, 1990). In liquid medium, the bacteria are short rods with few flagella and show classical swimming behavior. Upon growth on a solid surface (0.7 to 0.85% agar), they differentiate into elongated, multinucleate, copiously flagellated forms that swarm over the agar surface. The flagella of swimmer and swarmer cells are composed of the same flagellin protein. We show in this study that disruption of hag, the gene encoding flagellin, abolishes both swimming and swarming motility. We have used transposon mini-Mu lac kan to isolate mutants of S. marcescens defective in both kinds of motility. Of the 155 mutants obtained, all Fla- mutants (lacking flagella) and Mot- mutants (paralyzed flagella) were defective for both swimming and swarming, as expected. All Che- mutants (chemotaxis defective) were also defective for swarming, suggesting that an intact chemotaxis system is essential for swarming. About one-third of the mutants were specifically affected only in swarming. Of this class, a large majority showed active "swarming motility" when viewed through the microscope (analogous to the active "swimming motility" of Che- mutants) but failed to show significant movement away from the site of initial inoculation on a macroscopic scale. These results suggest that bacteria swarming on a solid surface require many genes in addition to those required for chemotaxis and flagellar function, which extend the swarming movement outward. We also show in this study that nonflagellate S. marcescens is capable of spreading rapidly on low-agar media.     

Aerobic and anaerobic swimming speeds of spermatozoa investigated by twin beam laser velocimetry.

The motility of bovine and ovine spermatozoa has been studied under aerobic and anaerobic conditions, using a dual beam laser velocimeter. Cells swimming under aerobic conditions were found to be characterized by a translational swimming speed and a rotation rate that were approximately double those of cells swimming in an anaerobic environment. Both types of spermatozoa have been found to exhibit a sudden coordinated transition between fast and slow swimming states when the available oxygen is exhausted. This transition from aerobic to anaerobic swimming states has also been shown to be reversible. Studies of the duration of aerobic motility using the same apparatus have shown that the cells have a constant motile efficiency over the temperature range 32 degrees-42 degrees C.     

Two alternating motor programs drive navigation in Drosophila larva

When placed on a temperature gradient, a Drosophila larva navigates away from excessive cold or heat by regulating the size, frequency, and direction of reorientation maneuvers between successive periods of forward movement. Forward movement is driven by peristalsis waves that travel from tail to head. During each reorientation maneuver, the larva pauses and sweeps its head from side to side until it picks a new direction for forward movement. Here, we characterized the motor programs that underlie the initiation, execution, and completion of reorientation maneuvers by measuring body segment dynamics of freely moving larvae with fluorescent muscle fibers as they were exposed to temporal changes in temperature. We find that reorientation maneuvers are characterized by highly stereotyped spatiotemporal patterns of segment dynamics. Reorientation maneuvers are initiated with head sweeping movement driven by asymmetric contraction of a portion of anterior body segments. The larva attains a new direction for forward movement after head sweeping movement by using peristalsis waves that gradually push posterior body segments out of alignment with the tail (i.e., the previous direction of forward movement) into alignment with the head. Thus, reorientation maneuvers during thermotaxis are carried out by two alternating motor programs: (1) peristalsis for driving forward movement and (2) asymmetric contraction of anterior body segments for driving head sweeping movement.