Description[ edit ] Daphnia magna is a typical water flea of the genus Daphnia. The intestine is hook-shaped and possesses two digestive cecae. The head is equipped with two antennae and a large compound eye.
The upper photo shows a dry pool in July The lower photo shows a close-up of the sediment surface in the pool. The dry sediment has more It has been proposed that in water bodies without predation, the composition of Daphnia species is influenced by size-dependent competition, with larger species out-competing smaller species.
There is, however, some debate about the efficiency of size-dependent processes in the absence of predation. A pH between 6. Behavioral Ecology The English name for Daphnia, waterflea, originates from the jumping-like behavior they exhibit while swimming.
This behavior stems from the beating of the large antennae, which they use to direct themselves through the water.
The rapid downbeat produces a quick upward movement, whereas the relatively high density of the animals creates a sinking. Motionless Daphnia sink rapidly to the ground.
A second well-known behavior of Daphnia is diel vertical migrationin which they migrate toward upper levels of the water body during nighttime and then back downward during the early morning and daytime. This behavior probably developed as a predator avoidance strategy. During daylight, the Daphnia hide from fish that hunt visually by moving to darker depths, whereas during nighttime, they take advantage of the richer food planktonic algae in the well-illuminated upper water levels.
Inverse diel vertical migration has been described as a strategy to escape other predators that migrate themselves. Part of the behavioral repertoire of Daphnia that is key to diel vertical migration is phototaxis. Phototactic-positive genotypes spend much time in the upper water level, whereas phototactic-negative genotypes spend most of their time close to the bottom sediments.
Phototactic behavior is also influenced by the presence of fish. If Daphnia sense that fish are present in the water, they behave more phototactically negative than they would otherwise. Daphnia are also known to migrate toward or away from the banks of ponds or lakes.
Again, the most likely explanation for this behavior is predator avoidance. Certain species of Daphnia, e.
Furthermore, they may browse over the surface substrates to pick up small particles. This behavior is more apparent when food is limited and seems to enrich the diet. The stirring movement of the Daphnia brings small particles into suspension, which are then ingested by filter feeding.
Evolutionary Genetics Following the pioneering work of P. Hebert, the population genetics of Daphnia have been intensively studied around the world. It also helped explain phylogenetic relationships among species later refined with DNA data.
Because of their clonal reproduction, Daphnia present a superb tool for quantitative genetic studies, which can enhance our understanding of their evolutionary ecology. Within- and between-clone comparisons can demonstrate genetic variation for various traits within and between populations, thus helping to reconstruct the evolutionary history of a population.
For nearly every trait that has been investigated, genetic variation has been reported. Examples include age and size at maturity, size at birth, aging, reaction norms for life history traits, vertical migrationphototactic behavior, fish escape behavior, production of defense spines and helmets, resistance against parasitesimmune response, competitive ability, Malthusian growth rate, carrying capacity under stable conditions, and many more.
Furthermore, complex matrices of genetic covariances among traits have shown that, in a first approximation, most traits share some covariance with other traits, indicating that an evolutionary change of many traits is constrained by the evolution of other traits.
For those Daphnia species that have been karyologically investigated, between 20 and 24 chromosomes have been counted 2N Zaffagnini With the announcement that the genome sequence of D. With Daphnia, one of the first organisms with a well-known ecology will be sequenced, which is a milestone in the field of ecological genetics.Clones of D.
magna vary strongly in their phototactic behavior. Phototactic-positive genotypes spend much time in the upper water level, whereas phototactic-negative genotypes spend most of their time close to the bottom sediments. Phototactic behavior is also influenced by the presence of fish.
Daphnia magna is a typical water flea of the genus Daphnia. The females reach up to 5 mm in size, the males about 2 mm, and are thus among the largest species in the genus.
The body is protected by a translucent carapace, made of chitin, a transparent polysaccharide. Daphnia magna is a small planktonic crustacean (adult length –5 mm) that belongs to the subclass grupobittia.com inhabits a variety of freshwater environments and is broadly distributed throughout the northern hemisphere, and in South Africa..
The species has been subject of biological research since the 18th century. It is widely used in . THE PHOTOTACTIC BEHAVIOR OF DAPHNIA MAGNA AS AN INDICATOR OF PREDATOR AVOIDANCE Abstract Daphnias Magna have different species, they are planktonic that belong to phyllopoda.
The present paper had the purpose to study the phototactic behavior of Daphina Magna or water flea (hereby, the two terms are used interchangeably). The analysis of phototactic behavior in D. magna was found to be useful for the rapid detection of relatively low concentrations of a range of toxic compounds.
The results obtained showed that with the analysis of phototactic behavior, it was possible to detect the presence of all the 11 toxic compounds over short exposure time periods (between and 48 h). May 15, · Phototactic behavior in Daphnia magna Straus as an indicator of toxicants in the aquatic environment.
Saf. 67, Michels E., De Meester L. (). The influence of food quality on the phototactic behavior of Daphnia magna Straus. Hydrobiologia , Michels E., Semsari S., Bin C., De Meester L. ().