The water flea Daphnia magna is a tiny freshwater crustacean found in Europe, Middle East, Central Asia and North America. This genus is reproduced by parthenogenesis under favorable environmental conditions but switches it to sexual reproduction in response to environmental stimuli, like shortened photoperiod, a  lack of food or increased population density. The planktonic crustacean Daphnia magna, also known as the waterflea, are a species of freshwater ecosystems, assisting in many ways. They are a principal grazer for algae, a primary forage for fish, as well as a sentine; of lentic inland waters. The genus Daphnia is a speciose with multiple lineages independently colonizing and adapting to diverse habitats. Ponds and lakes are the ones that primarily define these populations, since Daphnia is extremely sensitive to modern toxicants in their environment. At the same time, they are very adaptive to changes. What this genome does is exhibiting a range of context-dependent development of specialized phenotypes, like switching between clonal and sexual reproduction in response to the changes in their habitat. Additionally, they have a very short generation time, which in combination to their large brood sizes and ease of laboratory and field manipulation makes them perfect for testing chemical safety, for monitoring water quality, as well as a model for ecological and evolutionary research.

Nature’s Early-Warning System 

Daphnia is often used as a model organism to assess toxicity in pharmaceuticals, like antibiotics, anticancer drugs, antidepressants, ant-inflammatory drugs, beta-blockers, lipid-regulating agents and so many more. OECD’s daphnia toxicity tests based on immobilisations and lethality, are used in almost all toxicological studies. Daphnia’s “charisma” that makes them so helpful in research, is the same as the research. As scientists have found Daphnia proper for their projects, they have conducted thorough research in their biology. This extended research gives researchers the ability to distinguish the swimming behaviour and physiological endpoints. like swimming speed, distance travelled, hopping frequency, heart rate, ingestion rate, feeding rate, oxygen consumption, thoracic limb activity and so many more, data that they use to assess toxic effects.

Moreover, Daphnia magna has started quite recently being used for studying homology-directed repair (HDR). A practice extremely important to comprehend genome maintenance during parthenogenesis, effects of environmental toxicants on the genome, and improvement of HDR-mediated genome editing. Genomes are threatened by endogenously generated chemicals like reactive oxygen species and exogenous compounds, like mutagenic agents and radiation, which can lead to DNA double-strand breaks (DSBs). The sequenced genome of Daphnia reveals highly duplicated genes, resulting in tandem gene clusters. These tandem clusters may serve as a template for HDR-based repair to attenuate the effect of deleterious mutations during the parthenogenetic cycle, which suggests that Daphnia may have a unique HDR mechanism.

Furthermore, Daphnia magna has been proven helpful when it comes to heavy metal detection. Scientists have created a transgenic Daphnia that is extremely sensitive to heavy metals and responds to them, the moment they are exposed. 

Why Haven’t You Heard of Them? 

Even though Daphnia is one of the most commonly used model organisms to assess toxicity of an extremely wide range of pharmaceuticals, it is not well-known. There are a lot of different reasons for that. To begin with, this genus is commonly used in ecotoxicology and environmental monitoring, both not so well-known sectors like mainstream biomedical labs. These sectors are not very popular, as they don't follow human relevance, like mice do. Additionally, Daphnia’s genome has sequenced just in 2011 and CRISPR/transgenic work started the past few years. Moreover, it hasn't been part of any Nobel-winning discovery, like fruit flies, worms or zebrafish, meaning it is still catching up in terms of genetic branding. Lastly, Daphnia’s impact in research is indirect when it comes to humans, making it another contributor to why it is under-celebrated.

Tomorrow’s Role 

In conclusion, the water flea has a bright future ahead of it! It will be used as a biosensor that can report real-time water quality. Furthermore, it will be extremely helpful with climate change, as it sits at the base of freshwater food webs helping scientists understand how warming, droughts, microplastics and chemical mixtures affect the various ecosystems. In addition, a lot of platforms have started using Daphnia to analyze how stress and pollutants affect our lifespan, helping us understand how the environment can impact the pace of our aging.