Dispersal in small organisms: “varied, many, and often ingenious methods”

Turbulence and the diffusive layers around small organisms

The nematode Caenorhabditis elegans is an important model organism for biomedical research and genetic studies relevant to human biology and disease. Such studies are often based on high-resolution imaging of dynamic biological processes in the worm body tissues, requiring well-immobilized and physiologically active animals in order to avoid movement-related artifacts and to obtain meaningful biological information. However, existing immobilization methods employ the application of either anesthetics or servere physical constraints, by using glue or specific microfluidic on-chip mechanical structures, which in some cases may strongly affect physiological processes of the animals. Here, we immobilize C. elegans nematodes by taking advantage of a biocompatible and temperature-responsive hydrogel-microbead matrix. Our gel-based immobilization technique does not require a specific chip design and enables fast and reversible immobilization, thereby allowing successive imaging of the same single worm or of small worm populations at all development stages for several days. We successfully demonstrated the applicability of this method in challenging worm imaging contexts, in particular by applying it for high-resolution confocal imaging of the mitochondrial morphology in worm body wall muscle cells and for the long-term quantification of number and size of specific protein aggregates in different C. elegans neurodegenerative disease models. Our approach was also suitable for immobilizing other small organisms, such as the larvae of the fruit fly Drosophila melanogaster and the unicellular parasite Trypanosoma brucei. We anticipate that this versatile technique will significantly simplify biological assay-based longitudinal studies and long-term observation of small model organisms.

Animal microsurgery using microfluidics

Three processes associated with sex-meiosis, gametic union, and nuclear fusion-have a mechanical component, i.e., they require movements of supramolecular bodies. Times required for these processes are surprisingly high, probably because of the mechanical component, thus insuring that production of cells by sexual processes will require much longer than production of an equal number of cells by asexual processes. This is especially evident in direct comparisons of meiosis and mitosis. Meiosis requires much longer than two mitotic divisions. For unicellular organisms, and for small multicellular organisms in which the egg-to-egg time is very short, the additional time required by sexual processes at the cellular level lowers the feasibility of sex by slowing the reproduction rate. This is called the "cellular-mechanical" cost of sex. The cellular-mechanical cost of sex is at least twofold and will often exceed 10-fold by comparison with asexual reproduction in unicellular eucaryotes. The cellular mechanical cost of sex thus is a strong selective force acting against sex in unicellular and small organisms and, because it does not apply when the organism stops growing, tends to restrict sexuality to the end of the growth period.

All aquatic organisms rely on chemical stimuli at some point during their life cycles. These stimuli are typically associated with essential functions such as food‐, mate‐, or habitat‐finding, or predator avoidance. Historically, research on sensory ecology and behavior of aquatic organisms has been conducted using two‐channel choice flumes, which have many limitations when utilized on small organisms. Here, we describe functional features and results of pilot tests of an aquatic olfactometer, adapted from olfactometers used in studies on terrestrial arthropods, which eliminates these limitations. The initial implementation of this olfactometer is described. The structural integrity, hydrodynamics, and basic function of the olfactometer were tested and verified. The ability to clearly record the movements of a small organism within was also tested. Our experiments verify that the flow rate of water within the choice arena was accurate, water behaved as theorized in prior modeling, and chemical concentrations within each “zone” were distributed as expected based on computer simulations. We further show that video data could be obtained and analyzed using Ethovision XT to provide large amounts of raw data, including position, velocity, and acceleration, which can be used to investigate many potential questions associated with behavior. This olfactometer has the potential to become the new standard for research on chemotaxis and chemical ecology of small aquatic organisms.

Role of miRNAs in development and disease: Lessons learnt from small organisms

The ocean is regarded as a giant dumping area for many types of toxic chemicals and the ocean ecosystem is currently under enormous stress from a variety of pollution sources. There is an urgent need to monitor biological responses and quantitatively evaluate the change of environmental health. Microalgae are vitally important to the food web in the aquatic ecosystem and can be an important indicator to monitor water pollution due to their sensitivity to chemical changes in the environment. Zooplankton is an important trophic link between primary producers and predators in an aquatic system as they are widely distributed in water and mainly consume microalgae and are subsequently are fed by fish, shrimp, and crab. Algae and zooplankton can be used to assess bioaccumulation and biomagnification of the building-up process of a chemical in living organisms along the food chain. Aggregation-induced emission (AIE) is a photophysical phenomenon where light emission of a fluorogen is activated by aggregate formation to nanoparticles, which can be used as a sensing method in biological applications for toxic chemicals. This chapter updates the recent research advance on the use of AIE as a biosensor to quantitatively detect and evaluate bioaccumulation and biorelease of mercury in algae and zooplankton in an attempt to explain the mechanism and interactions between heavy metal ions and small organisms in the aquatic ecosystem.

Stomach contents of 941 juvenile and adult haddock collected at monthly intervals at the Highlands Ground off Cape Cod, Massachusetts, from February 1958 to January 1959 were analyzed. Approximately equal numbers of both sexes were represented. Weight of stomach contents from individual fish ranged from 0 to 48.2 grams; average weight was 2.2 grams. There were no indications of important differences between males and females in species of animals preyed upon or quantities of food ingested. Mean stomach content weight increased as haddock size increased from 25 to 70 centimeters in length, but specimens longer than 70 centimeters contained unexpectedly small quantities of food. There was a marked seasonal variation in the quantity of food in the stomachs. A low feeding rate prevailed during late summer, fall, winter, and early spring, followed by heavy feeding in June. Water temperature appeared to be relatively unimportant in affecting the feeding rate. A wide variety of small benthic organisms were represented in the diet. The more important species are listed. The principal food groups, in order of decreasing importance were: Crustacea, Annelida, Pisces, Echinodermata, and Mollusca. Some differences in diet were associated with haddock size. Small organisms (amphipods, cumaceans, brittlestars) were more common in small haddock. Relatively large foods (decapod crustaceans, fish) were prevalent in large haddock only. Distinct seasonal changes in diet composition were detected. Crustacea and Pisces varied substantially and quite sharply, as opposed to Echinodermata which exhibited smaller, more gradual changes. The proportion of Annelida in the diet was quite uniform throughout the year.

Small aquatic organisms harbour deep phylogeographic patterns and highly structured populations even at local scales. These patterns indicate restricted gene flow, despite these organisms' high dispersal abilities, and have been explained by a combination of (1) strong founder effects due to rapidly growing populations and very large population sizes, and (2) the development of diapausing egg banks and local adaptation, resulting in low effective gene flow, what is known as the Monopolization hypothesis. In this study, we build up on our understanding of the mitochondrial phylogeography of the halophilic rotifer Brachionus plicatilis in the Iberian Peninsula by both increasing the number of sampled ponds in areas where secondary contact is likely and doubling sample sizes. We analyzed partial mitochondrial sequences of 252 individuals. We found two deep mitochondrial DNA lineages differing in both their genetic diversity and the complexity of their phylogeographic structure. Our analyses suggest that several events of secondary contact between clades occurred after their expansion from glacial refugia. We found a pattern of isolation-by-distance, which we interpret as being the result of historical colonization events. We propose the existence of at least one glacial refugium in the SE of the Iberian Peninsula. Our findings challenge predictions of the Monopolization hypothesis, since coexistence (i.e., secondary contact) of divergent lineages in some ponds in the Iberian Peninsula is common. Our results indicate that phylogeographic structures in small organisms can be very complex and that gene flow between diverse lineages after population establishment can indeed occur.

Linking allometric macrobenthic processes to hypoxia using the Peters mass balance model

Sinking or floating is the natural state of planktonic organisms and particles in the ocean. Simulating these conditions is critical when making measurements, such as respirometry, because they allow the natural exchange of substrates and products between sinking particles and water flowing around them and prevent organisms that are accustomed to motion from changing their metabolism. We developed a rotating incubator, the RotoBOD (named after its capability to rotate and determine biological oxygen demand, BOD), that uniquely enables automated oxygen measurements in small volumes while keeping the samples in their natural state of suspension. This allows highly sensitive rate measurements of oxygen utilization and subsequent characterization of single particles or small planktonic organisms, such as copepods, jellyfish, or protists. As this approach is nondestructive, it can be combined with several further measurements during and after the incubation, such as stable isotope additions and molecular analyses. This makes the instrument useful for ecologists, biogeochemists, and potentially other user groups such as aquaculture facilities. Here, we present the technical background of our newly developed apparatus and provide examples of how it can be utilized to determine oxygen production and consumption in small organisms and particles.

Comprehensive multiphase (CMP) NMR, first described in 2012, combines all of the hardware components necessary to analyze all phases (solid, gel, and solution) in samples in their natural state. In combination with spectral editing experiments, it can fully differentiate phases and study the transfer of chemical species across and between phases, providing unprecedented molecular-level information in unaltered natural systems. However, many natural samples, such as swollen soils, plants, and small organisms, contain water, salts, and ionic compounds, making them electrically lossy and susceptible to RF heating, especially when using high-strength RF fields required to select the solid domains. While dedicated reduced-heating probes have been developed for solid-state NMR, to date, all CMP-NMR probes have been based on solenoid designs, which can lead to problematic sample heating. Here, a new prototype CMP probe was developed, incorporating a loop gap resonator (LGR) for decoupling. Temperature increases are monitored in salt solutions analogous to those in small aquatic organisms and then tested in vivo on Hyalella azteca (freshwater shrimp). In the standard CMP probe (solenoid), 80% of organisms died within 4 h under high-power decoupling, while in the LGR design, all organisms survived the entire test period of 12 h. The LGR design reduced heating by a factor of ∼3, which allowed 100 kHz decoupling to be applied to salty samples with generally ≤10 °C sample heating. In addition to expanding the potential for in vivo research, the ability to apply uncompromised high-power decoupling could be beneficial for multiphase samples containing true crystalline solids that require the strongest possible decoupling fields for optimal detection.

WHILE engaged in investigations (carried out with the aid of a Government grant) on the oyster beds in the River Blackwater, a jelly-fish (about 8 cms. in diameter) kept as a pet was given large numbers of oyster larvae to see what it would do with them. From the fate of the oyster larvae it was at once seen that the adult jelly-fish, Aurelia aurita, feeds definitely and—normally—automatically on smaller plankton organisms in a manner resembling that in which bivalves, some worms, and other animals feed on plankton. On adding the oyster larvae to the jar in which the jelly-fish was living, it was observed that the larvae were quickly formed up on the ex-umbrella surface of the jelly-fish in lines embedded in mucus and were also swept on to and retained in quantity on the oral arms. This immediately raised suspicion, and the jelly-fish was thereupon fed at intervals and carefully observed.1 It was found that small plankton organisms of about the size of oyster larvae were collected from the ex-umbrella surface of the jelly-fish and carried, mainly by ciliary action, towards the rim of the umbrella. The rhythmic waves of contraction of the bell or umbrella assist in carrying the strings of collected plankton-food to the edge of the umbrella, whence they are transferred—by a process not yet fully worked out—either to the oral arms or to the under surface of the rim of the umbrella. At the rim of the umbrella in this jelly-fish there is narrow curtain fringe cut normally into 8 segments so that one portion of the fringe lies between two of the marginal sense-organs (tentaculocysts). The fringe therefore resembles that often seen at the rim of a parasol except that it consists normally of 8 segments. The tentacles arise from the edge of the umbrella at the base of and outside this fringe.

Interest is one of the important factors in science education. The purpose of this study was to investigate factors affecting the follow-up interest of elementary school students on topics of 'Small Organisms' World'. The follow-up interests of the students on the topic were grouped into three categories; the developed-expanded-deepened (EDD), the simply expanded and maintained (SEM), and the stoped or decreased (SD) types. Each types had specific distinguishing features. Through the examination of students' responses and the in-depth interviews, the factors affecting on the follow-up interests of the students were analyzed. The factors were classified into two types of the external factor and the internal one. While the external factors were mainly related to the instructional materials used in science class and teaching methods, the internal factors were related to the desire for knowing, prior knowledge, students' experience and attitude toward the topics of science. In relation to the types of the follow-up interests, these factors were affected by different causes. The EDD type was most affected by internal factors, such as desire for knowing and prior knowledge. The SEM type was shown to be most affected by external factors, such as instructional materials. The SD type was mainly influenced by external factors, such as teaching methods. From the analysis of internal factors, it was revealed that the attitude and the prior knowledge about the topic are related with the follow-up interests. There was a positive relationship between the levels of science attitude and science knowledge. The students who had EDD type had a higher level of attitude and knowledge. However, there were some students who had higher level of scientific knowledge with SD type. The results of in-depth interviews showed that they were influenced by negative perceptions about science and stress on their grades. In conclusion, each follow-up interest type were caused by the external factors contained in the processes of the science class and the internal ones associated with the individual features and were influenced by the science class. So, the teacher should help the students be able to have the EDD type of follow-up interest which is persisted even after the completion of the science curriculum. For this, when the teachers design science curriculum and plan lesson, they should consider both internal and external factors significantly influencing the students' follow-up interests.

9 - Microfluidic devices for immobilization and micromanipulation of single cells and small organisms