Relationship between Daphnia Activity and ecotoxicology
Published: 04-23-2021 In Case Studie
Daphnia, a valuable organism for quality ecotoxicological research
Daphnia in ecotoxicology research
Daphnia (also called “water flea”) is a very common organism in ecotoxicology research. In the wild, it lives in freshwater ecosystems such as lakes and ponds. It swims in a very particular manner, which is responsible for its common name: a regular beating with a set of antennae that leads to characteristic hops. Various factors such as light, temperature, presence of food, predators or presence of substances in water, including toxins and contaminators, may affect daphnia’s swimming activity. Due to its characteristics, daphnia can easily live in laboratory conditions, contributing to the suitability of this animal for laboratory research.
Basic toxicological research with daphnia is based only on the mortality of the individuals (to evaluate lethal concentration) or on the immobilization of the individuals (to evaluate effective concentration). However, there are more sensitive biomarkers available, such as swimming activity. Mobility in daphnia is affected by many substances, for which it is a very useful indicator of behavioral alteration caused by toxins.
What do we study?
Daphnia’s swimming behavior is very complex, which makes it a very sensitive biomarker of toxicity. Different parameters of the swimming activity can be studied. Each of them can reflect different alterations based on the compound examined. There is an extended body of scientific literature regarding the effects of particular substances on daphnia activity.
The most studied parameters of daphnia’s swimming activity are the following:
- Swimming time: time during which daphnia can move.
- Swimming speed: a measure of the speed of swimming; one of the most reliable and widely used parameters.
- Behavioral strength: the intensity displayed in behavior parameters of instantaneous movement.
- Hopping frequency: number of hops per minute.
- Horizontal distribution: number of daphnia per square centimeters or meters, or the percentage of time spent in a region of water; indicates collective response to different environmental factors.
- Vertical distribution and migration: assessment of the depth at which animals are aggregated.
- Time ratio of vertical to horizontal swimming: an index of which type of swimming dominates.
- Distance traveled: distance moved by daphnia during a certain time lapse (usually in millimeters); indicates locomotor activity.
- Swimming trajectory: pathway left by the movement of daphnia; characterized by length (usually in millimeters) and shape.
- Number of turnings/ turning angle: change in swimming direction.
- Resting time/ duration of quiescence: temporal immobilization followed by a return to normal swimming.
- Sinking rate: Short moments of sinking, which occur between hops.
- Gravitaxis: downward movement engaged in the presence of stressful factors.
- Swarming: collective behavioral response leading to vortex formation.
- Spinning: moving in small circles; characteristic in the presence of stressful factors.
From the list above, it can be seen that swimming behavior in daphnia is an incredibly rich parameter for the study of ecotoxicology. Different substances can affect many of the mentioned parameters in different ways.