Why daphnia is used for experiments

Assessing Toxic Risk. Invasion Ecology. Decay and Renewal. Watershed Dynamics. Lettuce Seed Bioassays Duckweed Bioassays. For example, the availability of genetic linkage maps and the transferability of crossing panels between laboratories can greatly advance the diagnosis of important ecological and environmental traits through quantitative trait locus QTL studies or the identification of heritable genotypes that affect gene expression using eQTL expression QTL approaches. These common natural stressors include environmental toxicants, bacterial infections, vertebrate and invertebrate predators and parasites, synthetic hormones, varying diets, UV radiation, hypoxia, acidity, salinity, and low ambient calcium levels Colbourne et al.

For example, members of Daphnia species complexes e. The multiple lineages independently colonized and adapted to these freshwater habitats and are characterized by various degrees of reproductive isolation and significant intraspecific among populations genetic subdivision Crease et al. Daphnia typically reproduces by cyclical parthenogenesis; this strategy entails both clonal reproduction during optimal environmental conditions and sexual reproduction otherwise. The sexual phase is often triggered by environmental stresses such as crowding, cooling, or change in photoperiod, as well as by predation but see Paland et al.

This unique reproductive system of Daphnia allows us to maintain both lines of genetically identical individuals in the laboratory, as well as lines of genetically variant clones; this allows us to understand if responses elicited from stressors do, or do not, have a genetic basis. Daphnia is an ideal system for studying multiple stressors because of its short generation time, well-studied ecology and evolutionary history, wide geographical distribution across many limnetic systems, high mutation and recombination rates, high sensitivity to changes in environmental conditions, unique cyclical parthenogenetic life history, and recent availability of many genomic tools.

It is now widely accepted that climatic change is impacting the structure, function, and biodiversity of freshwater ecosystems Sala et al. Indirect interactions producing complex outcomes in populations in freshwater communities have been noted with food quality and availability, toxic contaminants, and UV radiation. The effects may be also direct, i. Moreover, under climatic change, temperature fluctuations may exceed the thermal tolerance limits of keystone species, such as Daphnia , and lead to cascading effects up and down the trophic web, thereby impacting the functioning of the freshwater ecosystem Jeppesen et al.

Therefore, studying how climatic change independently and in concert with other stressors impacts the life history, ecology, physiology, and evolution of Daphnia should help us understand and predict major changes in freshwater ecosystems. Temperature has been shown to have great effects on the life history of Daphnia , inducing earlier emergence Carvalho and Kirika and shorter lifespan Bottrell In addition, as temperature increases, the filtering rate, metabolic rate, and demand for food also increase Burn Even an increase in temperature of as little as 1.

For example, for every rising degree of temperature, the predation on Daphnia galeata by the predatory cladoceran Leptodora kindtii and by planktivorous fish, started distinctly earlier in the season by Moreover, temperature changes can cause rapid microevolution of Daphnia populations and alter the community structure of freshwater habitats Van Doorslaer et al.

In a common garden experiment, Daphnia genetically adapted to increased temperature within one growing season Van Doorslaer et al. Clones of D. The clones showed evidence of micro-evolutionary adaptation to higher temperature by an increase in size at maturity Van Doorslaer et al.

Clearly, daphniids may adapt genetically to higher temperature quite rapidly. In addition, changes from more thermophobic to more thermophilic daphniid taxa are likely as the climate warms. For example, Lennon et al. These findings suggest that it is important to incorporate micro-evolutionary responses of keystone species and colonization of nonnative clones in models that aim to predict the effects of climatic change on populations, communities, and the dynamics of food webs Van Doorslaer et al.

Climatic change may directly affect water quality, by decreasing water availability, concentrating pollutants and contaminants, and increasing salinity Schindler The exposure and sensitivity of organisms to chemical toxins and heavy metals in water appear to be closely linked to ambient temperature and tend to be toxin-specific. Climatic change affects the rate of uptake and detoxification of toxins and the sensitivity of organisms through changes in rates of metabolism and feeding Cairns et al.

For example, in Daphnia , the rate of cadmium uptake, a major metal contaminant, significantly increases at higher temperatures, possibly because of elevated ventilation rates in response to increased metabolic rate and demand for oxygen Cairns et al.

These studies show that metals are more toxic at higher temperatures because of increased bioaccumulation. Nonmetallic toxins such as sodium dodecyl sulfate SDS also exhibit increased toxicity at high temperatures Folt et al. However, once food is taken into consideration, the interaction of temperature and toxins dramatically changes.

While higher food levels appear to protect Daphnia from the toxic effects of cadmium Heugens et al. Global warming has been also shown to affect the exposure of freshwater organisms to UV radiation Schindler et al. Elevated temperature in the environment leads to decreased influx of water to lakes from streams and ground-water tables.

In consequence, the supply of dissolved organic carbon from these terrestrial and wetland catchments decreases, and penetration of UV-B into lakes increases exponentially as dissolved organic carbon declines Schindler et al.

Furthermore, an increase in the ambient temperature induces changes at the molecular level that help Daphnia deal with damage from UV radiation. MacFadyen et al. The repair is less effective for UV-induced DNA damage at lower temperatures, owing to decreased efficiency of the enzyme.

Although, UV-induced DNA damage was observed to be higher at elevated temperatures, the efficiency of the repair mechanism also increased; thus, the net UV-induced DNA damage at lower temperature is still more serious compared to that occurring at higher temperatures MacFadyen et al. In contrast, Connelly et al. While many studies have reported the effects of UV radiation on Daphnia , very few studies focused on the interactive effects of UV and temperature on this important keystone species Rautio and Tartarotti Furthermore, Daphnia inhabits lakes with varying temperatures and UV exposures, ranging from clear-water, oligotrophic arctic lakes with high permeability of UV to canopy-covered eutrophic ponds Hessen This combination of a broad ecological setting provides the opportunity for investigating the interactive effects of UV and temperature.

Soft-water lakes on the Boreal Shield and other parts of North America and Northern Europe are currently experiencing a trend of rapid decline of calcium Keller et al. Calcium decline has likely emerged from a combination of at least three unrelated anthropogenic stressors: multiple cycles of forest re-growth after logging in the watershed, historical and ongoing deposition of acid Watmough ; Jeziorski et al.

Since crustaceans have high demands for calcium, they are expected to be most sensitive and to be the first impacted by this sharp decline in calcium levels Cairns and Yan Indeed, daphniids have a significantly higher demand for calcium, averaging 2. In laboratory experiments where animals are well-fed, calcium concentrations of 1. However, under natural conditions of ambient food, the animals do not survive at calcium concentrations below 1.

This likely explains the observation that the probability of observing daphniids significantly drops in lakes with calcium concentrations below 1. In the context of multiple stressors, several anthropogenic and natural stressors could have complex interactions with declining calcium levels. In addition, declining calcium levels may certainly interact synergistically with heavy metal contaminants in freshwater habitats.

Water hardness is well known to protect Daphnia and other animals from toxic effects of metal contaminants. For example, increased aqueous and body calcium in Daphnia directly decreases the efficiency of the uptake and assimilation efficiency of zinc and cadmium Tan and Wang Calcium acts as a competitive inhibitor of toxic metals by binding more efficiently to sites on the biotic ligand than do other metal cations Paquin et al.

Increasing calcium concentrations in the medium drastically diminish the toxic effects of cadmium Clifford and McGreer , zinc Clifford and McGreer , copper De Schamphelaere and Janssen , and nickel Kozlova et al. Consequently, calcium offers protection for Daphnia and other freshwater organisms from heavy metal contaminants Table 1.

The biota of soft-water lakes are already more susceptible to metal toxicity than are hard-water organisms, and with decreasing calcium levels, the exposure of animals to toxic levels of metal contaminants may well increase. In addition to these physical and chemical anthropogenic stressors, Daphnia may become more prone to biotic stressors with declining concentration of ambient calcium.

The animals could suffer greater susceptibility to invertebrate predators such as the phantom midge, Chaoborus. The midge is a gape-limited predator that targets Daphnia neonates because of the smaller size of this life-history stage Pastorok Daphnia have evolved ways that reduce predation by triggering phenotypically plastic changes in juveniles in response to kairomones released by the Chaoborus. These changes include formation of neck teeth Tollrian and an increased stability of the carapace Laforsch et al.

Since calcium forms a major part of the carapace Hessen and Rukke b , declining calcium levels could lead to reduced formation of neck teeth and to loss of rigidity of the carapace, making the animals more vulnerable to predation by Chaoborus. With the numerous experimental uses for water fleas, this model will have wide ranging implications across the research community.

Researchers can look forward to reading the further developments made and insights gained from using this model to study this important model organism. So not everything lurking in those floodwaters is to be feared — despite being one of the oldest model organisms in biological research, the humble water flea is still proving its use. View the latest posts on the On Biology homepage.

View the latest posts on the On Biology homepage Comments. About Latest Posts. To determine if sediment from parking lots contain compounds that are harmful for aquatic organisms.

As human population centers grow to cover more and more of the planet, watersheds are increasingly affected by the presence of buildings, roadways, and parking lots. A watershed is "the area of land that catches rain and snow and drains or seeps into a marsh, stream, river, lake or groundwater.

This project asks the question: "Can run-off from parking lots be toxic to organisms in nearby ponds and streams? As the name suggests, a bioassay uses living organisms as the "detector" for an experimental procedure. When doing environmental testing for toxins, the bioassay is typically a viability assay. You count how many organisms are present at the beginning of the experiment, expose the organisms to different concentrations of the suspsected toxin, and count the number of organisms that remain viable.

It is critically important to maintain a control population of the organisms, so that you don't mistake the naturally-occuring death rate of the organisms as the effect of toxins. The organism that you will use for testing water toxicity is Daphnia magna.

Daphnia magna common name "water fleas" are tiny freshwater crustaceans. They are filter feeders, and can survive in culture by eating algae, bacteria, or yeast. Figure 1. Photomicrograph of Daphnia , the common water flea. If you make a graph of the percentage of Daphnia that remain viable y-axis vs.

It is one useful measure for comparing the relative toxicities of compounds. To do this project, you should do research that enables you to understand the following terms and concepts:. Proceeds from the affiliate programs help support Science Buddies, a c 3 public charity, and keep our resources free for everyone.

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Earth and Environmental Science. Behavioral and Social Science. Using Daphnia to Monitor Water Toxicity.