These water fleas have a compound eye that responds to light stimulus, can perceive different color wavelengths, and can also track movements. They also use olfactory and chemical cues in order to help them locate and evaluate potential food sources, conspecifics, and potential predators.
Communication Channels: visual ; chemical
Perception Channels: visual ; tactile ; chemical
This species has not been evaluated by the International Union for Conservation of Nature and Natural Resources and is not considered endangered or threatened.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
The life cycle begins when a female produces a clutch of eggs (usually 6-10) that are released into her brood chamber, located under her carapace. Eggs hatch into juveniles within this brood chamber and are released when their mother molts, typically within 2-3 days. Juveniles, which already resemble adults, go through a series of molts and instars. Females are considered sexually mature after developing brood pouches, usually after 4-6 instars, usually 6-10 days. If conditions are not favorable, or if they have been produced sexually, eggs will be released into an ephippium, a hard, protective casing, where eggs enter diapause before hatching when conditions are more favorable.
Development - Life Cycle: diapause
There are no known adverse effects of this species on humans.
This species can provide cleaner water in ponds and lakes, by eating algae and other detritus that may build up in the water. It is also an indicator organism for water quality and is used in tests of water toxicity and detecting various pollutants. This species is easily cultivated, and is commonly fed to fish reared in aquaria.
Positive Impacts: pet trade ; research and education
These water fleas consume algae, bacteria and detritus in the water. They play a key part in aquatic food webs as prey to fishes and invertebrates.
This species is host to a number of bacteria (including one causing White Fat Cell Disease) and fungi, as well as some species of nematodes, amoebas and tapeworms.
Commensal/Parasitic Species:
These water fleas are filter feeders; filtration rates depend on temperature, body size, food density and quality, oxygen concentration, and water pH. These animals use leaf-like appendages called phylopods, located under their carapaces, to help produce a water current. Setae on their thoracic legs filter food particulates (generally smaller than 50 micrometers in diameter), which are then moved along a body groove to their mouths. Their primary diet consists of zooplankton and phytoplankton; they are also known to consume bacteria, detritus, and fungal spores.
Animal Foods: zooplankton
Plant Foods: algae; phytoplankton
Other Foods: fungus; detritus ; microbes
Foraging Behavior: filter-feeding
Primary Diet: herbivore (Algivore); planktivore ; mycophage ; detritivore
This species of water flea can be found in rocky pools along the Atlantic coastline of the northeastern United States. It is not considered to be widespread in this area, but is regularly found in certain pools in Maine. This species is also found in Western Europe, including England, Belgium, the Netherlands, Finland, areas of the Black Sea bordering Ukraine, and some Baltic Islands.
Biogeographic Regions: nearctic (Native ); palearctic (Native )
This species is found in freshwater and brackish (up to 8 ppt salinity) habitats including lakes, rivers, and temporary pools. Although they prefer temperatures between 18-22°C, they can tolerate a much broader range.
Habitat Regions: temperate ; freshwater
Aquatic Biomes: lakes and ponds; rivers and streams; temporary pools; brackish water
Lifespan of these water fleas depends heavily on environmental conditions such as oxygen levels, food availability, and temperature. In general, as temperature decreases, lifespan increases, with averages of 40 days at 25°C and 56 days at 20°C. Unstable environmental conditions tend to lead to shorter lifespans. While it has been suggested that males of this species have shorter lifespans than females, recent research shows evidence that this is likely not the case.
Range lifespan
Status: wild: 1 to 56 days.
Average lifespan
Status: captivity: 40-56 days.
These water fleas are very small, usually 2-5 mm long, with an overall shape similar to a kidney bean. The body is enclosed by a transparent shell-like structure, called a carapace, that is mostly made of chitin. Due to its transparent carapace, this species tends to be the color of what it is currently eating. The carapace extends into the head shields, an important diagnostic characteristic for this species. They have two sets of long, doubly branched antennae and six thoracic appendages that are held inside of the carapace and help to produce a current of water, carrying food and oxygen to their mouths and gills. They also have two large claws, used mainly for cleaning the carapace. They have one compound eye, which appears as an anterior dark spot, and one simple eye (ocellus). Males are smaller than females (typically only 2 mm long while females are 3-5 mm long) but have longer antennules and modified, hook-like first appendages used for clasping females during mating.
Range length: 2 to 5 mm.
Other Physical Features: ectothermic ; bilateral symmetry
Sexual Dimorphism: female larger; sexes shaped differently
Predators of this species include many species of fishes, insects and other invertebrates. They are larger than many other zooplankton species, which protects them from some invertebrate predators, and they migrate to upper water levels at night to avoid predators that feed during the day. Individuals can also alter their size and age at maturity, egg production levels, and perform swarming behavior and escape reactions to avoid predation.
Known Predators:
These water fleas reproduce both asexually and sexually and have a cyclic parthenogenetic life cycle, exhibiting heterogonic reproduction. In asexual reproduction, females produce diploid eggs that develop into exact clones; only females are produced during asexual reproduction cycles. However, during adverse conditions (low food availability, temperature extremes, high population density), this species amy reproduce sexually. During sexual reproduction, males grab onto females using their specialized second antennae. Females produce haploid eggs which are fertilized by males and encased in ephippia. These cases are carried on the female's back and fall off during her next molt. Eggs enter diapause and stay in ephippia until conditions are favorable. Sexual reproduction tends to take place in late fall months, with the ephippia-protected eggs providing a population burst when spring comes.
Mating System: polygynandrous (promiscuous)
Peak egg production is during spring months (April and May), but eggs can be produced during summer and fall as well. During spring months, a female can produce eggs every four days; eggs/juveniles remain in brood pouches for 2-3 days. Number of eggs produced at one time can be anywhere from 1-100, with an average of 6-10 eggs per brood. A female can reproduce up to 25 times throughout her lifetime, although the average is only 6 times.
Breeding interval: Females produce eggs as often as every four days during their breeding season.
Breeding season: These water fleas reproduce most frequently during April and May, though they are known to reproduce during summer and fall as well.
Range number of offspring: 1 to 100.
Average number of offspring: 8.
Range gestation period: 1 to 4 days.
Average gestation period: 3 days.
Average time to independence: 3 days.
Range age at sexual or reproductive maturity (female): 6 to 10 days.
Range age at sexual or reproductive maturity (male): 6 to 10 days.
Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); parthenogenic ; sexual ; asexual ; fertilization (Internal ); ovoviviparous ; oviparous
Females keep their eggs and recently hatched young in their brood chambers for several days, providing nutrients during development. Once juveniles are released there is no additional parental care.
Parental Investment: female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Protecting: Female); pre-independence (Provisioning: Female)
Daphnia magna is a small planktonic crustacean (adult length 1.5–5.0 mm) that belongs to the subclass Phyllopoda.
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, thus they are among the largest species in the genus.[2] The body is protected by a translucent carapace made of chitin, a transparent polysaccharide.[3] It has a ventral opening and five pairs of thoracic limbs, used to help the filtering process.[4] Spike rows run along the back of the carapace. The intestine is hook-shaped and has two digestive ceca. The head has two antennae and a large compound eye.[5][6]
Adult females can be distinguished from those of otherwise similar species such as D. pulex by the absence of a comb on the abdominal claw and the presence of two distinct combs on the abdomen. The males are smaller than the females and have larger first antennas, a diagnostic feature that distinguishes them from small females.
Daphnia magna is a key species in many lentic habitats. It can be found in lakes and shallow ponds rich in organic matter sediment.[6] Numerous natural predators are known and can lead to plastic phenotypic responses. In the presence of kairomones, Daphnia spp. develop conspicuous protective structures as an elongated spine and a large body size.[7] In response to temperature differences, D. magna has shown both phenotypic plasticity and the ability to genetically evolve to deal with the heat stress of warmer, urban pond waters. Populations of Daphnia have also developed increased resistance to local pesticides.[8] Another factor that affects both phenotypic and behavioural plasticity of D. magna is the salinity of its surroundings.[9]
Daphnia magna is an important primary consumer and prey of many planktivorous fishes.[10] Other invertebrate predators are the larvae of the phantom midge Chaoborus and hemipterans (Notonecta) and Triops. The large size of the adults protects them from predation from some planktivorous invertebrates.
Daphnia magna is widespread in the Northern Hemisphere and in particular in the holarctic.[2] It can be found in fresh and brackish water bodies of different sizes, from lakes to ponds and ephemeral rock pools near the sea. D. magna tolerates higher levels of salinity (up to one-fifth the salinity of sea water) than most other species of the genus.[3]
Daphnia magna is mainly found in the pelagic zone of water bodies, as it feeds primarily on suspended particles in the water column (mainly algae, but also bacteria and detritus). Nevertheless, compared to other species of Daphnia, it is more often found in association with the substrate where it is able to exploit benthic food sources as periphyton[11] and sediment.[4]
The results of genetic research confirm the deep split between Eastern and Western mitochondrial haplotype super-clades of D. magna. A narrow contact zone has been found between these two super-clades in the eastern part of Western Siberia, with proven co-occurrence in a single lake in the Novosibirsk region. However, at present there is no evidence suggesting that the two mitochondrial super-clades represent cryptic species. Rather, they may be explained by secondary contact after expansion from different refugia. Interestingly, Central Siberia has previously been found to be an important contact zone also in other cladoceran species, and may thus be a crucial area for understanding the Eurasian phylogeography of freshwater invertebrates.[12]
The main feeding strategy of D. magna is the filtering of suspended particles.[4] A specialized filtering apparatus, formed by the thoracic appendices, generates a water current within the thoracic opening of the carapace, which permits the collection and the ingestion of unicellular algae, bacteria, and detritus. D. magna can also feed on periphyton[11] and detritus,[4] an ability that can offer a competitive advantage to this species over strictly pelagic filter feeders in some environments where suspended food sources might be temporally limited.
As most of the other species of the genus Daphnia, D. magna reproduces by cyclical parthenogenesis. This form of reproduction is characterised by the alternating production of asexual offspring (clonal reproduction) and at certain time sexual reproduction through haploid eggs that need to be fertilised.
The asexual eggs (up to few dozens per clutch) are diploid and usually develop into females, or in response to adverse environmental stimuli, into males.
Asexual eggs hatch in the female brood pouch 1 day after being laid and are released after 3 days. Juveniles go through four to about six moults before becoming mature over a period of 5–10 days. An adult female produces one clutch with up to 100 eggs every 3–4 days until her death. It can live over 3 months in the laboratory at 20 °C.[13]
In response to unfavourable environmental conditions (which could lead to the freezing or the drying up of the pond), the same female can produce haploid resting eggs (usually two at a time), which when fertilised by males, are wrapped within a protective shell called an ephippium. These resting eggs enter a phase of diapause and are able to resist long periods of adverse environmental conditions over a long period of time. Hatching is triggered in response to specific stimuli such as increasing photoperiod and temperatures. The hatchlings from resting eggs develop exclusively into females.
Some clones of D. magna that do not produce males reproduce by automictic parthenogenesis, in which two haploid cells produced by meiosis fuse to produce a female zygote without fertilisation. This tends to make the resulting daughters homozygous, which may be deleterious.[14]
The name "water fleas" might come from the typical swimming behavior of Daphnia species which is reminiscent of a series of jumps. The movement of the big second antennae generates an upward movement of the whole animal followed by its sinking (hop and sink). Although less common than for other lake dwelling species, vertical and horizontal migration patterns of this species have been observed.[15]
Diel vertical migration (DVM)[15] consists in the daily movement of animals from the upper water layers, where they spend the night, to the deep and dark layers, where they spend the day. This behavior reduces exposure of diurnal visual predators (such as many fish) by finding refuge in the dark near the bottom and then feeding undisturbed during the night in the food-rich upper water layers.[3] The basis of this behaviour is phototactic behavior (movements of entire organisms to, or away from, a light source). In D. magna phototactic behavior has an innate component (genetic) and an inducible component (for example in the presence of fish kairomones).[7]
In Diel horizontal migration, D. magna finds refuge within submerged plant-beds near the shore during daytime and migrates to open waters during the night. Cases of reversed migration patterns are documented when the risk of visual predation during the day is higher at the bottom or in the littoral zones (for example in the presence of fish that hunt within submerged plant‑beds).[4][16]
Daphnia magna, as the smaller D. pulex, is able to switch to a feeding behavior, termed browsing behavior, when suspended food is scarce. This feeding strategy consists in the stirring up of sediment particles from the bottom with the use of the second antennae and by the subsequent filtration of the suspended particles.[4][16]
Daphnia magna has become a model system to study the evolution and ecology of host-parasite interaction.[3] Animals collected from natural habitats are frequently infected.[17] Many parasites that infect D. magna have been identified and studied (Table 1), D. magna shows parasite-induced behavioural characteristics that can differ among genotypes.[18]
Daphnia magna can be looked at as a complex ecosystem, colonized by a community of commensal, symbiotic and pathogenic microorganisms[19][20] called microbiota. The close proximity of the microbiota to its host allows for a tight interaction, capable of influencing development,[21] disease resistance[22][23] and nutrition.[24] The absence of microbiota in D. magna has been shown to cause a slower growth, a decrease in fecundity and a higher mortality compared to D. magna with microbiota.[25] The gut microbiota changes upon death and its complexity is reduced and stabilized in case of starvation.[26]
Daphnia magna presents numerous advantages when used as experimental organism. Its transparency allows for the observations of its inner anatomical structures at the microscope, while its reproduction through cyclical parthenogenesis allows to generate clones (asexual reproduction) or to perform crossing between strains (sexual reproduction). In the research field, D. magna is considered easy to keep in the laboratory. Some of its advantages for experiments are a fast generation time, limited storage usage, easy and cheap feeding and simple maintenance.
Daphnia magna is used in different field of research, such as ecotoxicology, population genetics, the evolution of sex, phenotypic plasticity, ecophysiology (including global change biology) and host-parasite interactions.[27]
Historically, D. magna allowed researchers to test some interesting theories and conduct pioneering studies:
Other recent experiments used the resting eggs of Daphnia present in a pond sediment to reconstruct the evolutionary history of that population in relation to one of its parasites (P. ramosa),[30] an example of resurrection biology.
In ecotoxicology D. magna is specified to be used in the OECD Guidelines for the Testing of Chemicals, Tests No. 202 "Daphnia sp., Acute Immobilisation Test",[31] and Test No. 211 "Daphnia magna Reproduction Test".[32] Test No. 202 is a 48-hour acute toxicity study, where young Daphnia are exposed to varying concentrations of the substance under test and the EC50 determined. Other Daphnia species than D. magna may occasionally be used, but labs mostly use D. magna as standard. Test No. 211 is a 21-day chronic toxicity test, at the end of which, the total number of living offspring produced per parent animal alive at the end of the test is assessed, to determine the lowest observed effect concentration of the test substance.
This article incorporates text from this source, which is available under the CC BY 4.0 license. Daphnia magna is a small planktonic crustacean (adult length 1.5–5.0 mm) that belongs to the subclass Phyllopoda.
