Gravitaxis in the flagellate Euglena gracilis--results from NiZeMi, clinostat and sounding rocket flights

Many motile microorganisms including flagellates such as the green Euglena gracilis move up and down within the water column and use a number of external clues for their orientation, the most important of which may be light and gravity. The cells use positive phototaxis and negative gravitaxis to move closer to the surface of the water column which for energetic reasons is vital for their survival. However, most phytoplankton organisms cannot tolerate the bright irradiance of unfiltered solar radiation at the surface which also bleaches the photosynthetic pigments, disables the photosynthetic apparatus and impairs phototaxis, gravitaxis and motility in Euglena. Thus, it is not surprising that at higher irradiances negative phototaxis operates antagonistically to the responses described above to guide the cells into deeper water where they are protected from excessive radiation. Phototaxis and gravitaxis are not independent from one another: in a vertically positioned cuvette negative gravitaxis can be "titrated" by light impinging from above and is compensated at about 30 W m-2. While the photoreceptor for phototaxis has been identified in Euglena gracilis biochemically and spectroscopically, the gravireceptor is not yet known. Young cultures of Euglena gracilis show a positive gravitaxis, the ecological signficance of which is not yet understood while older cultures show negative gravitaxis. One hypothesis concerning the nature of graviperception is based on a passive physical process such as an asymmetric distribution of the mass within the cell. However, the observation that short term UV irradiation decreases the precision of negative gravitaxis rather indicates the involvement of an active physiological gravireceptor. Furthermore, some heavy metal ions have been found to change the direction of movement from positive to negative gravitaxis in young cells.     

Influence of the Gas-Water Interface on Transport of Microorganisms through Unsaturated Porous Media

In this article, a new mechanism influencing the transport of microorganisms through unsaturated porous media is examined, and a new method for directly visualizing bacterial behavior within a porous medium under controlled chemical and flow conditions is introduced. Resting cells of hydrophilic and relatively hydrophobic bacterial strains isolated from groundwater were used as model microorganisms. The degree of hydrophobicity was determined by contact-angle measurements. Glass micromodels allowed the direct observation of bacterial behavior on a pore scale, and three types of sand columns with different gas saturations provided quantitative measurements of the observed phenomena on a porous medium scale. The reproducibility of each break-through curve was established in three to five repeated experiments. The data collected from the column experiments can be explained by phenomena directly observed in the micromodel experiments. The retention rate of bacteria is proportional to the gas saturation in porous media because of the preferential sorption of bacteria onto the gas-water interface over the solid-water interface. The degree of sorption is controlled mainly by cell surface hydrophobicity under the simulated groundwater conditions because of hydrophobic forces between the organisms and the interfaces. The sorption onto the gas-water interface is essentially irreversible because of capillary forces. This preferential and irreversible sorption at the gas-water interface strongly influences the movement and spatial distribution of microorganisms.     

Effects of pressure on swimming behavior in planula larvae of the coral Porites astreoides (Cnidaria, Scleractinia)

Mechanisms governing the behavior of coral planulae are not well understood, particularly those manifesting themselves between the time when the larvae are released and when they settle. Larvae from the hermatypic coral Porites astreoides Lamarck were exposed to different levels of hydrostatic pressure—103.4, 206.9, 310.3, 413.8, and 517.1 kPa (including ambient pressure). Data were collected at stops of the above pressures for 15 min each, respectively. This was done in both an increasing sequence and a decreasing one. When exposed to increases in pressure from 103.4 kPa, larvae swam upward (negative barotaxis) in a spiraling motion. Upon exposure to decreasing pressure from 517.1 kPa, larvae moved downward (positive barotaxis), but the magnitude of the vertical movement was much less than in the case of increasing pressure. This suggests that these larvae are more sensitive to increased pressure than decreasing pressure. High variance was also observed in the responses of these larvae at both the intra- and inter-colony levels. Thus, this behavioral trait is variable within the population. The trait may be genetically based, and thus may be susceptible to alteration by natural selection, although this remains to be demonstrated. This study is the first to document these behavioral mechanisms in coral larvae.     

Behavior of Biomphalaria glabrata, the intermediate host snail of Schistosoma mansoni, at different depths in water in laboratory conditions

Using three columns of different depths (1.10m, 8.40m and 10.40m), we investigated the possibility of Biomphalaria glabrata moving towards deep regions. In the 1.10m column, we noted that locomotion can occur in two manners: 1) when the foot is in contact with the substrate: a) sliding descent; b) sliding ascent; c) creeping descent; d) creeping ascent, 2) when the foot is not in contact with the substrate: a) sudden descent without emission of air bules; b) sudden descent with emission of air bules; c) sudden ascent. In the 8.40m column containing food on the bottom (experimental group), the snails remained longer at this depth when compared to those of the group which received no food (control). The sliding behavior was characteristic of locomotion occurring at 0 to 1m both in upward and downward directions. Creeping behavior was typical for the ascent of the snails that reached deeper levels. When the snails were creeping, the shell remained hanging as if it were heavier, a fact that may have been due to water entering the pulmonary chamber. In the 10.40m column, the snails slid downward to a depth of 4m or descended suddenly all the way to the bottom. Ascent occurred by creeping from the bottom to the surface. In the 8.40m and 10.40m columns, copulation, feeding and oviposition occurred at the deepest levels.     

Migration and trail affinity of snails, Littoraria scabra, on mangrove trees of Nananu-i-ra, Fiji Islands

The distribution of mobile species such as grazing snails may be influenced by migration patterns, which often are excluded from ecological studies. To highlight this point, the migration patterns of Littoraria scabra on mangrove trees were investigated during incoming and outgoing tides at Nanaru-i-ra, Fiji Islands. Marked snails were used to track the position of snails, relative to the ground, during advancing and receding tides. Snails were found to move quickly upward during incoming tides, potentially to avoid immersion. During the outgoing tide, snails migrated downward, but at a slower pace than upward movement, presumably as a consequence of active feeding on the newly replenished micro-organisms on the mangrove structures (i.e., stems and roots). Aggregation behavior during migration was also recorded by measuring the distance of marked snails to two nearest neighbors. Affinity to neighboring snails was found to be maintained throughout tidal cycles, although greater affinity was observed during incoming tides compared to outgoing tides. These migratory and aggregation behaviors may be a result of increased feeding and reproductive efficiency.     

Functional morphology of the pectoral fins in bamboo sharks, Chiloscyllium plagiosum: benthic vs. pelagic station-holding

Bamboo sharks (Chiloscyllium plagiosum) are primarily benthic and use their relatively flexible pectoral and pelvic fins to rest on and move about the substrate. We examined the morphology of the pectoral fins and investigated their locomotory function to determine if pectoral fin function during both benthic station-holding and pelagic swimming differs from fin function described previously in leopard sharks, Triakis semifasciata. We used three-dimensional kinematics and digital particle image velocimetry (DPIV) to quantify pectoral fin function in five white-spotted bamboo sharks, C. plagiosum, during four behaviors: holding station on the substrate, steady horizontal swimming, and rising and sinking during swimming. During benthic station-holding in current flow, bamboo sharks decrease body angle and adjust pectoral fin angle to shed a clockwise fluid vortex. This vortex generates negative lift more than eight times that produced during open water vertical maneuvering and also results in an upstream flow that pushes against the posterior surface of the pectoral fin to oppose drag. In contrast, there is no evidence of significant lift force in the wake of the pectoral fin during steady horizontal swimming. The pectoral fin is held concave downward and at a negative dihedral angle during steady horizontal swimming, promoting maneuverability rather than stability, although this negative dihedral angle is much less than that observed previously in sturgeon and leopard sharks. During sinking, the pectoral fins are held concave upward and shed a clockwise vortex with a negative lift force, while in rising the pectoral fin is held concave downward and sheds a counterclockwise vortex with a positive lift force. Bamboo sharks appear to sacrifice maneuverability for stability when locomoting in the water column and use their relatively flexible fins to generate strong negative lift forces when holding position on the substrate and to enhance stability when swimming in the water column.     

A simple animal can use a complex stimulus pattern to find a location: Nematode thermotaxis in soil

Newly hatched infective juveniles of the plant-parasitic nematode Meloidogyne incognita have recently been found to migrate in very shallow thermal gradients to a preferred temperature that is several °C above the temperature to which they were acclimated. Possible functions of this unusual behavior were explored by computer modeling of the movement of such nematodes in the dynamic thermal environment typical of soil. Reliable estimates were available for all the required parameters. The model predicts that, as the diurnal temperature fluctuations at the surface penetrate into the soil, a nematode located below the surface will move upward during part of the day and downward during the rest of the day. However, the distances moved upward and downward do not balance and there is a net change in depth over a period of days. The net change is upward or downward depending on the physiological parameters of the nematode and its depth. Using the best estimates available for the parameters, it is predicted that nematodes starting at any depth between 0 and 15 cm would move toward an intermediate depth of about 5 cm. It is hypothesized that, in the absence of chemical cues, this response leads the nematodes toward a level that is optimal for locating the roots of host plants. This suggests that simple organisms may make use of much more complex stimulus patterns than was previously realized.     

Behavioral intermittence, Lévy patterns, and randomness in animal movement

The recent debate on both the existence and the cause of fractal (Lévy) patterns in animal movement resonates with much deeper and richer problems in movement ecology: (1) establishing mechanistic links between animal behavior and statistical patterns of movement, and (2) understanding what is the role of randomness (stochasticity) in animal motion. Here, the idea of behavioral intermittence is shown to be crucial to establish mechanistic connections between the behavior of organisms and the statistical properties they generate when moving. Attention is drawn to the fact that some random walk modeling procedures can impair the identification of intermittent biological mechanisms which could govern major statistical properties of movement. This fact, together with some misconceptions and prejudices regarding the role of randomness in animal motion may explain why stochastic processes have been disregarded as a potential source of adaptation in animal movement. In the near future, the advances in biotelemetry together with a more explicit consideration of behavioral intermittence, and the development of novel random walk approaches, could help us to set up the bases for a landscape-level behavioral ecology.     

Quantitative analysis of sperm plane circular movement in the blue mussels Mytilus edulis, M. trossulus and their hybrids

Fertilization success of free spawning organisms such as Mytilus species depends on gamete interactions. Therefore, gamete traits such as sperm movement are important for determining fertilization success in free spawning organisms. Since little is known about sperm movement pattern in Mytilus species, the purpose of this study was to investigate sperm movement pattern of blue mussel M. edulis, M. trossulus and their hybrids using computer-assisted sperm movement video analysis. Sperm of all genotypes were found to conduct circular movement in a two-dimensional plane. Furthermore, new sperm movement parameters, real time radius (R), angle change rate (θ) and the center of circular track (O(t)) were developed to verify and quantitatively describe the plane circular movement pattern using software (Image-J) that may be widely applied to sperm movement study in other organisms. Angle change rate was positively correlated to fertilization success. However, no correlation between fertilization and real time radius was detected. Although no interspecific differences were found in the radius, the F1 (first generation) hybrid sperm had a lower angle change rate than M. edulis and M. trossulus. Published studies have shown that sperm circular movement is more prevalent in aquatic broadcast spawning species than in species with mating behavior or internal fertilization. Therefore, a two-dimensional circular movement pattern in sperm may represent a trait that increases fertilization success for broadcast spawning species by either increasing gamete interaction rate at a small scale and/or avoiding swimming further away from the eggs before sperm detects the chemoattractant gradient.     

Temperature effects on bacterial movement.

Details are presented for the construction of a simple precision temperature-controlled chamber for investigating bacterial motile behavior. Independent of original incubation temperature, all species of motile bacteria observed showed a five- to sevenfold increase in average translational velocity (micrometers per second) as the environment temperature was incremented over the range from 10 to 50 degrees C. Temperature jumps downward produced transient tumbling or reciprocal behavior responses, depending on the mode of flagellar distribution, in all species examined. Upward temperature jumps induced accelerated velocities without tumbling or reversal. A partial capacity adaptation to temperature was noted, in that the greatest average translational velocity at any given observation temperature occurred when the organisms were grown at temperatures less than the optimum.     

Temperature effects on bacterial movement.

Details are presented for the construction of a simple precision temperature-controlled chamber for investigating bacterial motile behavior. Independent of original incubation temperature, all species of motile bacteria observed showed a five- to sevenfold increase in average translational velocity (micrometers per second) as the environment temperature was incremented over the range from 10 to 50 degrees C. Temperature jumps downward produced transient tumbling or reciprocal behavior responses, depending on the mode of flagellar distribution, in all species examined. Upward temperature jumps induced accelerated velocities without tumbling or reversal. A partial capacity adaptation to temperature was noted, in that the greatest average translational velocity at any given observation temperature occurred when the organisms were grown at temperatures less than the optimum.     

BEMOVI,software for extracting behavior and morphology from videos,illustrated with analyses of microbes

Microbes are critical components of ecosystems and provide vital services (e.g., photosynthesis, decomposition, nutrient recycling). From the diverse roles microbes play in natural ecosystems, high levels of functional diversity result. Quantifying this diversity is challenging, because it is weakly associated with morphological differentiation. In addition, the small size of microbes hinders morphological and behavioral measurements at the individual level, as well as interactions between individuals. Advances in microbial community genetics and genomics, flow cytometry and digital analysis of still images are promising approaches. They miss out, however, on a very important aspect of populations and communities: the behavior of individuals. Video analysis complements these methods by providing in addition to abundance and trait measurements, detailed behavioral information, capturing dynamic processes such as movement, and hence has the potential to describe the interactions between individuals. We introduce BEMOVI, a package using the R and ImageJ software, to extract abundance, morphology, and movement data for tens to thousands of individuals in a video. Through a set of functions BEMOVI identifies individuals present in a video, reconstructs their movement trajectories through space and time, and merges this information into a single database. BEMOVI is a modular set of functions, which can be customized to allow for peculiarities of the videos to be analyzed, in terms of organisms features (e.g., morphology or movement) and how they can be distinguished from the background. We illustrate the validity and accuracy of the method with an example on experimental multispecies communities of aquatic protists. We show high correspondence between manual and automatic counts and illustrate how simultaneous time series of abundance, morphology, and behavior are obtained from BEMOVI. We further demonstrate how the trait data can be used with machine learning to automatically classify individuals into species and that information on movement behavior improves the predictive ability.     

The dynamic behavior of phycobilisome movement during light state transitions in cyanobacterium <Emphasis Type="Italic">Synechocystis</Emphasis> PCC6803

Light state transition is a physiological function of oxygenic organisms to balance the excitation of photosystem II (PSII) and photosystem I (PSI), hence a prerequisite of oxygen-evolving photosynthesis. For cyanobacteria, phycobilisome (PBS) movement during light state transition has long been expected, but never observed. Here the dynamic behavior of PBS movement during state transition in cyanobacterium Synechocystis PCC6803 is experimentally detected via time-dependent fluorescence fluctuation. Under continuous excitation of PBSs in the intact cells, time-dependent fluorescence fluctuations resemble “damped oscillation” mode, which indicates dynamic searching of a PBS in an “overcorrection” manner for the “balance” position where PSII and PSI are excited equally. Based on the parallel model, it is suggested that the “damped oscillation” fluorescence fluctuation is originated from a collective movement of all the PBSs to find the “balance” position. Based on the continuous fluorescence fluctuation during light state transition and also variety of solar spectra, it may be deduced that light state transition of oxygen-evolution organisms is a natural behavior that occurs daily rather than an artificial phenomenon at extreme light conditions in laboratory.     

Studies on the Characteristics of Normal and Alkali Soil Profiles from an Alkali Infested Area in Allahabad,India

The development of the profile is mainly the consequence of movement of water in the soil and we may distinguish the following three possibilities:

Firstly under humid condition there is an excess of rainfall over evaporation. Thus, there is a general tendency of downward movement of soil moisture and the soil is subjected to a leaching process, whereby the constituents are carried downwards and are either deposited in the lower horizons or completely removed in drainage water.

Secondly, under arid conditions with an excess of potential evaporation over rainfall, rain moistens the soil to a limited depth. After cessation of rain, the soil moisture rises again to the surface under the influence of evaporation with the result that translocation occurs in both directions, and in final stages of dessication, the deposition of salts from solution may occur throughout an appreciable depth of surface soil.

Thirdly, downward movement may be prevented by the presence of ground water, or the occurrence of impervious sub-soil layer. In such cases water movement can only occur laterally over the horizon of impedence. The impedence may not be complete, but intermediate stages can also be observed.

The development of alkali soil profile is governed either by the second or third or by the combination of both the processes mentioned above.

In India, saline soils, saline-alkali soils and alkali soils are commonly distributed. Leached soils are of very rare occurrence.     

Directional Locomotion of C. elegans in the Absence of External Stimuli

Many organisms respond to food deprivation by altering their pattern of movement, often in ways that appear to facilitate dispersal. While the behavior of the nematode C. elegans in the presence of attractants has been characterized, long-range movement in the absence of external stimuli has not been examined in this animal. Here we investigate the movement pattern of individual C. elegans over times of ∼1 hour after removal from food, using two custom imaging set-ups that allow us to track animals on large agar surfaces of 22 cm×22 cm. We find that a sizeable fraction of the observed trajectories display directed motion over tens of minutes. Remarkably, this directional persistence is achieved despite a local orientation memory that decays on the scale of about one minute. Furthermore, we find that such trajectories cannot be accounted for by simple random, isotropic models of animal locomotion. This directional behavior requires sensory neurons, but appears to be independent of known sensory signal-transduction pathways. Our results suggest that long-range directional behavior of C. elegans may not be driven by sensory cues.     

CnOtx, a member of the Otx gene family, has a role in cell movement in hydra.

Otx genes have been identified in a variety of organisms and are commonly associated with the patterning of anterior structures. In some vertebrates, Otx genes are also expressed in the prechordal mesoderm, where they may have a role in cell movement. Here we report the characterization of CnOtx, an Otx gene in hydra, thereby providing evidence that Otx genes appeared early in metazoan evolution. CnOtx is expressed at high levels in developing buds and aggregates, where it appears to have a role in the cell movements that are involved in the formation of new axes. Further, the gene is expressed at a low level throughout the body column of hydra. This latter pattern may reflect a role for CnOtx in specifying tissue as competent to be anterior, although the gene does not have a direct role in the formation of the head.     

Effects of UV-B on motility and photobehavior in the green flagellate,Euglena gracilis

UV-B inhibits the motility of the green flagellate, Euglena gracilis, at fluences rates higher than those expected to occur in the natural sunlight even when the stratospheric ozone layer is partially reduced by manmade pollutants. The phototactic orientation of the cells, however, is drastically impaired by only slightly enhanced levels of UV-B irradiation. Since only negative phototaxis (movement away from a strong light source) is impaired while positive phototaxis (movement toward a weak light source) is not, the delicate balance by which the organisms adjust their position in their habitat is disturbed. Under these conditions the cells are unable to retreat from hazardous levels of radiation and are eventually killed not by the UV-B irradiation but by photobleaching of their photosynthetic pigments in the strong daylight at the surface.     

Intraspecific,size-dependent variation in the movement behaviour of a brackish-water isopod: a resource-free laboratory experiment

Intraspecific variability represents an important, yet inadequately investigated factor affecting the movement behaviour and ecology of mobile organisms. Here, the influence of sex, seasonality and body size on the movement behaviour of the brackish isopod Lekanesphaera hookeri were examined under resource-free laboratory conditions. The mean step length, total path length and average speed were determined twice during the year for adult and juvenile isopods encompassing a 10-fold range in body length. The scale-independent fractal dimension D was used to quantify the tortuosity of the movement paths. No relationships were observed between sex or season and all the movement metrics. In contrast, isopods' body size scaled negatively with the fractal dimension D of movement paths with a breakpoint at 2.6 mm, roughly corresponding to the size of morphometric maturation. No other relationships were observed between the body length of isopods and mean step length, total path length and average speed. The results indicate a sex- and season-independent ontogenetic shift in movement behaviour in L. hookeri. This suggests that in sphaeromatid isopods post-embryonic development determines not only continuous variations in size and proportions, but also a discontinuous change in the movement strategy adopted to interact with the surrounding space. Overall, these findings underscore the need to account explicitly for such changes in models predicting the spatial distribution of organisms characterised by wide intra-population size variation.     

Orientation of the photosynthetic flagellate,Peridinium gatunense,in hypergravity

The photosynthetic freshwater flagellate,Peridinium gatunense, uses both positive phototaxis and negative gravitaxis to move upwards in the water column. At higher fluence rates approaching those at the surface of their habitat, the cells tend to become unoriented and thus stop their upward movement. Orientation and motility ofPeridinium gatunense has been studied in the slow rotating centrifuge microscope (NIZEMI), which allows observation of swimming behavior during centrifugation acceleration between 1g and 5g. The movement vectors were analyzed by real time image analysis capable of tracking many cells simultaneously. At 1g the orientation was not very precise, but the degree of orientation increased significantly at higher acceleration forces up to about 3g. Most cells were capable of swimming even against an acceleration vector of 3.8g; at higher acceleration forces the cells were not able to cope with the centrifugal force. The linear velocity of cells swimming against 1g was about 20% lower than that of cells moving in other directions. The velocity decreased even more in cells swimming against higher acceleration forces.     

Effects of SmartWater,a fluorescent mark,on the dispersal,behavior, and biocontrol efficacy of Phytoseiulus persimilis

New marking methods for studying small biocontrol agents (especially predatory mites) are needed because many current techniques are expensive, ineffective or not applicable to small organisms. The objective of this study was to determine whether SmartWater, a liquid and permanent fluorescent dye, can be used to mark Phytoseiulus persimilis for experimentation without any deleterious effects on its dispersal, behavior, reproduction, and biocontrol efficacy. Our results show that there were no significant differences in movement, inter-plant dispersal, feeding behavior, survivability, and reproduction between marked P. persimilis and control individuals sprayed with water. We also found that the SmartWater mark lasted for the duration of the mites’ life, indicating strong durability over time. Marking efficacy may be reduced, due to a trade-off between batch marking efficacy and the possibility of drowning study organisms. However, we feel future research could improve liquid marking techniques that would reduce this risk. Overall, this study concludes that SmartWater could be a useful marking tool for predatory mites in both laboratory and field studies.