Free-swimming Organisms Research Articles

X-Tracker: Automated Analysis of Xenopus Tadpole Visual Avoidance Behavior.

Xenopus laevis tadpoles exhibit an avoidance behavior when they encounter a moving visual stimulus. A visual avoidance event occurs when a moving object approaches the eye of a free-swimming animal at an approximately 90-degree angle and the animal turns in response to the encounter. Analysis of this behavior requires tracking both the free-swimming animal and the moving visual stimulus both prior to and after the encounter. Previous automated tracking software does not discriminate the moving animal from the moving stimulus, requiring time-consuming manual analysis. Here we present X-Tracker, an automated behavior tracking code that can detect and discriminate moving visual stimuli and free-swimming animals and score encounters and avoidance events. X-Tracker is as accurate as human analysis without the human time commitment. We also present software improvements to our previous visual stimulus presentation and image capture that optimize videos for automated analysis, and hardware improvements that increase the number of animal-stimulus encounters. X-Tracker is a high throughput, unbiased, and significant time-saving analysis system that will greatly facilitate visual avoidance behavior analysis of Xenopus laevis tadpoles, and potentially other free-swimming organisms. The tool is available at https://github.com/ClineLab/Tadpole-Behavior-Automation.

Physiological and Behavioral Characterization of Larval Olfaction in the Malaria Vector Mosquito Anopheles coluzzii.

When viewed from both academic and vector-control perspectives, the chemosensory biology of larval-stage anopheline mosquitoes is both enigmatic and paradoxical. As is true for all mosquito species, anopheline larvae are free-swimming organisms that use complex sensory processes to both locate nutrients and avoid predators. Because of their obligatory and therefore restrictive aquatic habitats, mosquito larvae are the most easily sampled and targeted mosquito life stage and as such they have been the focus of the majority of vector control strategies used to date. Although this might reasonably have resulted in the accumulation of a robust body of knowledge of the natural and molecular biology of larval-stage chemosensory processes, there is, instead, a paucity of such information relative to adults. Here, we describe two relatively simple laboratory-based bioassays that allow for the characterization of larval chemosensory-driven behaviors as well as an electrophysiological approach to examine the responses of larval peripheral neurons to volatile odorant stimuli. Taken together, these approaches provide a road map for the study of the chemosensory biology and chemical ecology during this important stage in the life cycle of anophelines that transmit malaria.

Efficacy of Surgical/Wound Washes against Bacteria: Effect of Different In Vitro Models

Topical antiseptics are often used to treat chronic wounds with biofilm infections and during salvage of biofilm contaminated implants, but their antibacterial efficacy is frequently only tested against non-aggregated planktonic or free-swimming organisms. This study evaluated the antibacterial and antibiofilm efficacy of four commercial surgical washes Bactisure, TorrenTX, minimally invasive lavage (MIS), and Betadine against six bacterial species: Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus pyogenes, Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli, which are commonly isolated from surgical site infections and chronic wound infections using different in vitro models. We determined minimum planktonic inhibitory and eradication concentration and minimum 1-day-old biofilm inhibition and eradication concentration of antiseptics in 96-well plates format with 24 h contact time. We also tested the efficacy of antiseptics at in-use concentration and contact time in the presence of biological soil against 3-day-old biofilm grown on coupons with shear in a bioreactor, such that the results are more applicable to the clinical biofilm situations. In the 96-well plate model, the minimum concentration required to inhibit or kill planktonic and biofilm bacteria was lower for Bactisure and TorrenTX than for MIS and Betadine. However, Betadine and Bactisure showed better antibiofilm efficacy than TorrenTX and MIS in the 3-day-old biofilm bioreactor model at in-use concentration. The minimal concentration of surgical washes required to inhibit or kill planktonic bacterial cells and biofilms varies, suggesting the need for the development and use of biofilm-based assays to assess antimicrobial therapies, such as topical antiseptics and their effective concentrations. The antibiofilm efficacy of surgical washes against different bacterial species also varies, highlighting the importance of testing against various bacterial species to achieve a thorough understanding of their efficacy.

Individual-based modeling of shelled pteropods

Shelled pteropods are cosmopolitan, free-swimming organisms of biogeochemical and commercial importance. They are widely used as sentinel species for the overall response of marine ecosystems to environmental stressors associated with climate change and changes in ocean chemistry. However, currently we are unable to project the effects of climate change on shelled pteropods at the population level, due to the missing spatio-temporal characterization of the response of pteropods to environmental stressors, and the limited information on the pteropod life history and life-cycle. In this study, we implement a shelled pteropod Individual-Based Model (IBM), i.e. we simulate a pteropod population as a set of discrete individuals over several generations, life-stages (eggs, larvae, juveniles and adults) and as a function of temperature, food availability, and aragonite saturation state. The model is able to provide an abundance signal that is consistent with the abundance signal measured in the temperate region. In addition, the modeled life-stage progression matches the reported size spectrum across the year, with two major spawning periods in spring and fall, and maturation in March and September. Furthermore, our IBM correctly predicts the abundance maxima of younger, smaller and potentially more susceptible life-stages in spring and winter. Thus, our model provides a tool for advancing our understanding of the response of pteropod populations to future environmental changes.

Zooplankton composition and abundance from Nideban Reservoir, Udgir Dist. Latur

Zooplanktons are the microscope free swimming organisms of aquatic system. There are represented by a wide array of taxonomic groups of which the members belonging to protozoa, Rotifera, Cladocera and Copepoda are most common and often dominate the entire communities. They have many remarkable features which hamper their predation by higher organisms. The members of Zooplankton community are important for their role in trophic dynamics, energy transfer in the aquatic ecosystem. They provide food for fishes in the water bodies and play a major role in the fish production. The zooplankton community was studied by monthly samples taken from Oct. 2018 to Feb. 2019. The reservoir water is used for agriculture and fishery activities.

Refining the interpretation of oxygen isotope variability in free-swimming organisms

Serially sampled oxygen isotope ratios (δ18O) from fossil and modern cephalopods may provide new insight into the behavior and longevity of individuals. Interpretation of these data is generally more difficult than similar data from bivalves or brachiopods because the measured δ18O from shell combines both seasonal change and depth change over the life of an individual. In this paper, a simple null model is presented combining the three fundamental controls on a measured δ18O profile in a free-swimming organism: swimming behavior, seasonal water column change, and time averaging in sampling. Model results indicate that seasonal variability in δ18O in a free-swimming organism can be interpreted in locations with strong seasonality through most of the swimming range but is complicated by swimming velocity and is sometimes best expressed by changes in δ18O variance rather than simple sinusoidal patterns. In other locations with a stable thermocline or seasonal ranges in only a small portion of the water column, no variability caused by seasonality would be expected. Furthermore, large ranges of δ18O (~ 4‰) are possible within and between individuals in settings with persistent thermoclines like the tropics, depending on the swimming depth limits and behavior of individuals. These results suggest that future interpretation of serially sampled δ18O should consider seasonal water column variation from either modern or modeling sources in addition to comparison to co-occurring benthic and planktonic organisms. Additionally, this modeling casts doubt on the promise of isotope sclerochronology alone as a growth chronometer in ammonites and other free-swimming fossil organisms and highlights the need for other methods of quantitatively determining age.

Directional Hydrodynamic Sensing by Free-Swimming Organisms.

Many aquatic organisms detect the presence of moving objects in their environment, such as predators, by sensing the hydrodynamic disturbances the movements produce. The resultant water flow is readily detectable by stationary organisms, but free-swimming organisms are carried with the surrounding water and may not detect the bulk surrounding flow, which limits the available information about the source. We have developed a theory that clarifies what information is contained in disturbances generated by an attacking predator that is available to a free-swimming organism and might be extracted from local flow deformations alone. The theory shows that, depending on how well the deformations can be measured in space and time, an organism can reduce the range of possible locations, speeds, sizes, and arrival times of the predator. We apply the theory to planktonic copepods that have mechanosensory hairs along a pair of antennules. The study reveals the presence of "blind spots," potential ambiguities in resolving from which of two sides a predator attacks, and whether it generates a bow wave or suction. Our findings lead to specific testable hypotheses concerning optimal escape strategies, which are helpful for interpreting the behavior of evasive prey and designing free-swimming robots with sensory capabilities.

Nekton and Macro-Crustacean Habitat Use of Mississippi Micro-Tidal Salt Marsh Landscapes

Salt marshes have long been recognized as productive habitats that form an important trophic link between the aquatic and terrestrial biomes through the dynamic intertidal zone. This project focused on the distribution of nekton (free-swimming organisms) and common macro-crustaceans within the intertidal to assess the breadth of habitat use by these assemblages based on geo-spatial and hydrological variables. Sampling was conducted on the flooded marsh intertidal in August and September 2011 at three sites in the micro-tidal Grand Bay National Estuarine Research Reserve, MS, using bottomless lift nets and pit traps in a landscape design. The sampled assemblage data were compared with concurrent site hydrological analyses in order to determine how distribution on the salt marsh intertidal may be influenced by defined inundation components (e.g., inundation time and frequency of inundation) and by the distance to the nearest water source. A total of 3238 organisms were collected comprising 12 fish and 13 macro-crustacean species. A two-way nested analysis of similarities (ANOSIM) indicated that the density of the assemblage varied by site (p = 0.1 %) and across the salt marsh intertidal (marsh level (MLV); p = 1.4 %). Overall, assemblages were found to be strongly influenced by the inundation characteristics along the marsh elevation gradient as well as by the unique micro-topography of each site.

Immunolocalization of anti-hsf1 to the acetabular glands of infectious schistosomes suggests a non-transcriptional function for this transcriptional activator.

Schistosomiasis is a chronically debilitating disease caused by parasitic worms of the genus Schistosoma, and it is a global problem affecting over 240 million people. Little is known about the regulatory proteins and mechanisms that control schistosome host invasion, gene expression, and development. Schistosome larvae, cercariae, are transiently free-swimming organisms and infectious to man. Cercariae penetrate human host skin directly using proteases that degrade skin connective tissue. These proteases are secreted from anucleate acetabular glands that contain many proteins, including heat shock proteins. Heat shock transcription factors are strongly conserved activators that play crucial roles in the maintenance of cell homeostasis by transcriptionally regulating heat shock protein expression. In this study, we clone and characterize the schistosome Heat shock factor 1 gene (SmHSF1). We verify its ability to activate transcription using a modified yeast one-hybrid system, and we show that it can bind to the heat shock binding element (HSE) consensus DNA sequence. Our quantitative RT-PCR analysis shows that SmHSF1 is expressed throughout several life-cycle stages from sporocyst to adult worm. Interestingly, using immunohistochemistry, a polyclonal antibody raised against an Hsf1-peptide demonstrates a novel localization for this conserved, stress-modulating activator. Our analysis suggests that schistosome Heat shock factor 1 may be localized to the acetabular glands of infective cercariae.

Nutrient salvaging and metabolism by the intracellular pathogen Legionella pneumophila

The Gram-negative bacterium Legionella pneumophila is ubiquitous in freshwater environments as a free-swimming organism, resident of biofilms, or parasite of protozoa. If the bacterium is aerosolized and inhaled by a susceptible human host, it can infect alveolar macrophages and cause a severe pneumonia known as Legionnaires' disease. A sophisticated cell differentiation program equips L. pneumophila to persist in both extracellular and intracellular niches. During its life cycle, L. pneumophila alternates between at least two distinct forms: a transmissive form equipped to infect host cells and evade lysosomal degradation, and a replicative form that multiplies within a phagosomal compartment that it has retooled to its advantage. The efficient changeover between transmissive and replicative states is fundamental to L. pneumophila's fitness as an intracellular pathogen. The transmission and replication programs of L. pneumophila are governed by a number of metabolic cues that signal whether conditions are favorable for replication or instead trigger escape from a spent host. Several lines of experimental evidence gathered over the past decade establish strong links between metabolism, cellular differentiation, and virulence of L. pneumophila. Herein, we focus on current knowledge of the metabolic components employed by intracellular L. pneumophila for cell differentiation, nutrient salvaging and utilization of host factors. Specifically, we highlight the metabolic cues that are coupled to bacterial differentiation, nutrient acquisition systems, and the strategies utilized by L. pneumophila to exploit host metabolites for intracellular replication.

Differential roles of OxyR-controlled antioxidant enzymes alkyl hydroperoxide reductase (AhpCF) and catalase (KatB) in the protection ofPseudomonas aeruginosaagainst hydrogen peroxide in biofilm vs. planktonic culture

The role of the Pseudomonas aeruginosa OxyR-controlled antioxidants alkyl hydroperoxide reductase CF (AhpCF) and catalase B (KatB) was evaluated in biofilm vs. planktonic culture upon exposure to hydrogen peroxide. AhpCF was found to be critical for survival of biofilm bacteria while KatB was more important for survival of planktonic free-swimming organisms.

Minimum size limit for useful locomotion by free-swimming microbes.

Formulas are derived for the effect of size on a free-swimming microbe's ability to follow chemical, light, or temperature stimuli or to disperse in random directions. The four main assumptions are as follows: (i) the organisms can be modeled as spheres, (ii) the power available to the organism for swimming is proportional to its volume, (iii) the noise in measuring a signal limits determination of the direction of a stimulus, and (iv) the time available to determine stimulus direction or to swim a straight path is limited by rotational diffusion caused by Brownian motion. In all cases, it is found that there is a sharp size limit below which locomotion has no apparent benefit. This size limit is estimated to most probably be about 0.6 micron diameter and is relatively insensitive to assumed values of the other parameters. A review of existing descriptions of free-floating bacteria reveals that the smallest of 97 motile genera has a mean length of 0.8 micron, whereas 18 of 94 nonmotile genera are smaller. Similar calculations have led to the conclusion that a minimum size also exists for use of pheromones in mate location, although this size limit is about three orders of magnitude larger. In both cases, the application of well-established physical laws and biological generalities has demonstrated that a common feature of animal behavior is of no use to small free-swimming organisms.

Scanning currents in Stokes flow and the efficient feeding of small organisms

The feeding behaviour of many small, free-swimming organisms involves the creation of a scanning current by the coordinated movement of a group of appendages. In this paper, we study the generation of scanning currents in Stokes flow in a number of simple models, utilizing the movement of Stokeslets, spheres, or stalks to set up an average scanning drift in a suitable far-field formulation. Various mechanisms may then be classified by the rate of decay at infinity of the mean scanning current. In addition, optimal scanning can be investigated by minimizing the mean power-required to create a current of prescribed amplitude. The simple mechanisms for scanning described here provide a framework within which the appendage movements of small aquatic organisms can be analysed and the relative merits of scanning and swimming strategies can be investigated.

POTENTIAL DAMAGE OF OIL WASTES IN COASTAL ESTUARY SEDIMENTS1

ABSTRACT Bayou Casotte, Mississippi, an estuarine waterway near the eastern end of Mississippi Sound, has been altered to accommodate an extensive industrial complex including a large oil refinery. Several small oil spill accidents recently occurred in the bayou; the most serious, on June 13, 1981, involved 600 barrels of asphaltic crude. The ecological effects of continued exposure to low level oily wastes were estimated by examining pollution levels in sediments both in 10-foot cores and surface samples. Petroleum hydrocarbons (PHC) and other hydrocarbons occur at levels as high as 12,300 micrograms per gram (µg/g or ppm to total hydrocarbons, dry weight) in surficial sediments and 1,000 µg/g at 120 centimeter sediment depths. Dredging operations have removed most polluted sediments very near the refinery site in the bayou, but dispersal of petroleum wastes has caused PHCs to be dominant pollutants in other regions where no dredging has occurred and where care is required if any dredging is permitted. Toxicological examination of sheepshead minnows, mysid shrimp and amphipods reveals significant mortalities to mysids from bioassay exposures to surficial sediments. Settling rate determinations, leach-ability, community structure vulnerability, and sediment disturbance probability are factors assimilated into an “environmental stress index” that indicates this to be a potentially harmful site to bottom feeders and, if sediments are disturbed, to free swimming organisms in sensitive life stages.

AN EXPERIMENTAL OIL SPILL: THE DISTRIBUTION OF AROMATIC HYDROCARBONS IN THE WATER, SEDIMENT, AND ANIMAL TISSUES WITHIN A SHRIMP POND

ABSTRACT A common practice in the mariculture of shrimp on the Texas coast is the application of fuel oil on the surface of the pond. This thin oil layer serves to eliminate large aquatic insects which are predators of the small juvenile shrimp. Ordinarily, a common diesel fuel is used and it is removed from the pond after one day's treatment. In this experimental spill study, a high aromatic (38%) #2 fuel oil was utilized in higher quantity than normal and the residue was not removed. Mortalities of juvenile shrimp (Penaeus setiferus) and other invertebrates associated with the pond were recorded over a period of 96 hours following the oil treatment. A peak in the level of mortality occurred 48 hours after the spill, coinciding with the peak in the concentration of naphthalenes (naphthalene, methylnaphthalenes in the tissues of caged and free swimming organisms occurred at the point (48 hours) at which the concentration of these compounds was maximal in the water column. The concentration of naphthalenes in the sediment reached a peak approximately 12 days after the maximum peak in the tissues and water. While the pond water and sediments studied contained measureable levels of naphthalenes, the shrimp and clams (Rangia cuneata) were shown to release a major portion of accumulated naphthalenes by day 96. Oysters and sediment measured at this same time interval showed levels between 3 and 6 parts per million (ppm) total naphthalenes. Shrimp, clams, and oysters taken to the laboratory 38 days after the spill released naphthalenes to background or near background levels. The data compiled in this study were compared to the findings of various field and laboratory investigations.

The relations between membrane potential and parameters of ciliary beat in free-swimming Paramecium caudatum.

ABSTRACT A method of analysing the parameters of ciliary beat as a function of membrane potential in free-swimming organisms is presented. The method obviates artefacts which may be produced on impaling small organisms with micro-electrodes. Changes in the membrane potential of Paramecium caudatum produce two effects : an increase in frequency of beat of up to (23 ± 3) % mV−1 at 25 °C for both depolarizations and hyperpolarizations which falls to zero within a few minutes, and a change in the direction of ciliary beat of (9 ± 1) degree mV-1 for depolarizations only, which in a spiralling organism do not accommodate to the field. The orientation of P. caudatum towards the cathode in an electric field is due principally to changes in the angle of ciliary beat on the cathodal side of the organism ; changes in frequency seem to be relatively unimportant. Axial spinning during normal locomotion in P. caudatum is satisfactorily accounted for by transverse components of ciliary thrust. The oblique orientation of P. caudatum near boundaries is caused by an asymmetry (geometrical or electrical or both) over the surface of the organism. Comparison with observations on extracted organisms indicates that a change in the direction of beat of 9° is associated with an increase in calcium concentration at the ciliary apparatus of about 25 %.

Geotaxis in motile micro-organisms.

ABSTRACT It is suggested that the principal cause of geotaxis in many motile micro-organisms is a gravity-induced hydrodynamic torque, the size of which depends upon the shape of the organism. The nature of the torque has been investigated using small scale models. An expression for the distribution of organisms in long, vertical columns has been derived. The distribution of Paramecium in long, vertical columns has been determined, and it has been shown that the strength of the hydrodynamic interaction is sufficient to account for the negative geotaxis usually exhibited by this organism. The induction of positive geotaxis in certain circumstances has been considered. The survival value of negative geotaxis for free-swimming organisms in search of food may explain the characteristic shape of many protozoa.

Summer Foods of Lesser Scaup in Subarctic Taiga

Reports on the food of 25 adult and 38 juvenile Aythya affinis, collected in June-Sept 1967 along the Yellowknife Highway north of Great Slave Lake. The vegetation, physiography and ponds of the area, the collecting and statistical methods are briefly described. Approx 99% of the scaup diet was animal material; juveniles in mid-summer fed on freeswimming organisms such as Chaoborinae (phantom midges) and Conchostraca (clam shrimps); in late summer they, as did adults in June, fed on bottom organisms such as amphipods, odonates and corixids. Seeds, copepods and cladocerans were seldom or never eaten.

Life History of Proterometra dickermani Anderson, 1962

The azygiid trematode, Proterometra dickermani Anderson, 1962, is shown to complete its life cycle in a single host species, the snail Goniobasis livescens (Menke). No vertebrate hosts have been found in nature, and experiments have produced infections in sunfish (Lepomis gibbosus L. and L. macrochirus Rafinesque) and bass [Micropterus salmoides (Lackp~de)] on rare occasions only. Cercariae reach full maturity within the germinal sac in the snail host. Embryonated eggs are deposited and miracidia hatch in the germinal sacs. Some of the miracidia develop into primary germinal sacs without leaving the individual host; others escape and enter other snails. It is probable that an occasional cercaria leaves the snail and is ingested by a fish. Two complete cycles occur during a year, with hatching of miracidia in early spring and late summer. The extreme progenesis in this cycle indicates a primitive position of the genus Proterometra Horsfall, 1933. Five valid species have been ascribed to the genus Proterometra Horsfall, 1933, of the trematode family Azygiidae Odhner, 1911. The life cycles of four of these have been described: P. macrostoma (Faust, 1918) Horsfall, 1933 by Horsfall (1933, 1934) and by Dickerman (1934, 1945); P. catenaria Smith, 1934 by Smith (1934); P. hodgesiana Smith, 1932 by Smith (1936); and P. sagittaria Dickerman, 1946 by Dickerman (1946). The cycles of these species are similar. The adults usually inhabit the pharynx or esophagus of fishes of the family Centrarchidae. Eggs pass from the host in feces. Hussey (1945) observed hatching of miracidia of P. macrostoma after considerable manipulation of the material. No other instances of free miracidia have been reported, and it has been assumed that hatching normally occurs after ingestion of the eggs by the snail. The snail hosts are of the family Pleuroceridae; species of Goniobasis Lea are involved in each of the cycles, and Pleurocera acuta Rafinesque has been reported as an additional intermediate host for P. macrostoma and P. sagittaria. The germinal sac stages-variously described as sporocysts and rediaeoccur in the vicinity of the rectum. The exact location has been stated to be the coelom (Dickerman, 1945), liver and (Horsfall, 1933), or mantle (Smith, 1934). The cercariae which develop in the second or possibly a third generation of germinal sacs are of the Mirabilis group of furcocystocercous cercariae. When they emerge from the snail host, the distome is enclosed within a cavity in the tail. As free-swimming organisms the cercariae appear attractive to fish which avidly ingest them. In the fish the body leaves the tail and assumes the position of an adult in the pharynx, esophagus, or stomach. The cercariae of all four species are more mature than is usual in larval trematodes. EXPERIMENTS AND OBSERVATIONS Anderson (1962) reported the introduction of P. dickermani cercariae taken from infections of the snail, Goniobasis livescens (Menke), into sunfish (Lepomis gibbosus L. and L. macrochirus Rafinesque) with recovery of five specimens after numerous attempts. During addiReceived for publication 23 November 1962. * This investigation was supported by research grant E 3654 from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Public Health Service. t Contribution from the Department of Biology, New Mexico State University and the Biological Station of The University of Michigan.

Life History and Ecological Notes on the Tubenose, Aulorhynchus flavidus, a Hemibranch Fish of Western North America

The tubenose, or tube-snout, Aulorhynchus flavidus Gill, attains a length of at least 165 mm, but the mean standard length of adults examined was 142.9 mm. The range of the tubenose is Sitka, Alaska, to Punta Banda, Baja California, and diving observations reveal them to be present through the year in southern California. The fish have been observed and collected in rocky crevices, kelp beds, eel grass, and over sand bottom. They are found from the surface to 100 feet. They feed on small, free-swimming organisms. The major spawning area studied is considered for a possible correlation of the peculiar conditions there with spawning habits. The tubenose mainly establishes its nest on and attaches its eggs to the giant kelp, Macrocystis pyrifera. The nests are closely guarded by males who actively drive off intruders. The nest building habit and territorial behavior is reminiscent of that of the sticklebacks, and the morphological evidence of the close relationships between the two groups is in part confirmed. Egg masses have been observed from depths of 17 to 120 ft, but most commonly 35 to 58 ft. The presence of eggs and young fish during the entire year suggests that spawning is not seasonal. It is probable that the tubenose serves as an important link in the food chain of some California game fishes.