Daphnia – the perfect model organism to study implications of environmental pollution

Main area:Aquatic biology
Target group:Biology, Biochemistry
Educational level:Bachelor, Masters
Project description:

Daphnia species are important components in the pelagic food web of lakes since they feed heavily on phytoplankton and bacteria in the water column. On the other hand, Daphnia are themselves food for fish fry and invertebrates and because of this dual role as important consumers on primary producers and prey for higher tropic levels they are considered as key-organism in the pelagic food web. The food consumed by a daphnia is mainly used for growth and reproduction while a small part is respired. In optimal conditions, i.e. plenty of food and optimal physical/chemical conditions, the respired part will be low, but if the animal is exposed to stress, the respiration is increased causing a loss of energy. This in turn will affect other processes such as the uptake of food and the production of offspring, which lowers the survival chances of the population. Such situations also occur when Daphnia ingest naturally occurring cyanobacteria containing toxic peptides, which have been shown to disrupt the gut epithelium causing accumulation of toxins in the animal’s blood. Or when Daphnia are exposed to pesticides which are designed to either stimulate or inhibit nervous impulses in agricultural pests (mainly insects), but which may end up in the aquatic environment and there interact with non-target organisms. Many Daphnia species are easy to keep in laboratory cultures and because of their ability to perform parthenogenetic reproduction it is possible to have establish unique clonal populations – ideal for running eco-toxicological test. Furthermore, Daphnia tolerates handling quite well and are almost transparent which makes it possible to observe activities of organs and other structures inside live Daphnia. The overall scientific question that could be asked is: to what extend do a specific compound, being natural or artificial, affect the survival and well-being of a multicellular and fairly advanced organism like Daphnia and which implications could this have for the food web structure and processes? A variety of experimental setups s can be perform. Some ideas are listed below:

1. Cellular and physiological damages to internal organs like the heart, gut and gills of live Daphnia when exposed to water-soluble pollutants such as pesticides, hormones and chemicals.

2. Destruction of the development of eggs and embryos (either inside live Daphnia or extracted and cultures in an artificial substrate) when exposed to the same pollutants as above

3. Physiological (e.g. feeding) and behavioral (e.g. swimming) changes when exposed to dissolved natural compounds (e.g. algae exudates or humic substances) or chemical pollutants (e.g. pesticides)

4. The impact of “good” and “bad” food particles on growth rate and reproduction success

5. Bioaccumulation of dissolved natural or chemical toxins in Daphnia and the transfer to higher trophic levels

The detection methods will depend on the specific purpose and could include image and video documentation, microscopy, and visual observations. As part of the project you´ll learn how to establish and grow your own cultures of Daphnia and the microalgae they will feed on.

Methods used:Growing cultures, does-response experiments, blood sampling, gut content analyses, behavior, microscopy, etc.
Keywords:Daphnia, Toxic compounds, Ecotoxicology, Foodweb
Supervisor(s):  Kirsten S. Christoffersen