Daphnia magna

Geographic Range

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 nearctic
  • native native
• palearctic palearctic
  • native native

Habitat

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 temperate
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• temporary pools
• brackish water brackish water

Physical Description

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.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes shaped differently

Development

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 diapause

Reproduction

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) 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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• parthenogenic parthenogenic
• sexual sexual
• asexual asexual
• fertilization fertilization
  • internal internal
• ovoviviparous ovoviviparous
• oviparous 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 female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • protecting
    • female
• pre-independence
  • provisioning
    • female

Lifespan/Longevity

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.

Behavior

This species lives in groups and is very abundant when present in a habitat. There is no social hierarchy, though there is competition for resources between individuals of this and other Daphnia species when present. They use their antennae to propel themselves with quick, upward, jumping-like movements in the water and exhibit diel vertical migration, moving to upper levels of water at night to feed and back down during the day to avoid predators. Their larger size excludes them from predation by species who feed on smaller g. Daphnia , but can cause problems when space and resources are limited. Even though these water fleas are one of the larger species in their genus, they can go extinct in habitats including Daphnia pulex and Daphnia longispina . This species goes through population density cycles, with numbers decreasing during cold or dry seasons.

• Key Behaviors
• natatorial natatorial
• nocturnal nocturnal
• motile motile
• social social

Home Range

Individuals of this species do not have distinct home ranges.

Communication and Perception

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 visual
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

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.

• Primary Diet
• herbivore herbivore
  • algivore
• planktivore planktivore
• mycophage mycophage
• detritivore detritivore

• Animal Foods
• zooplankton zooplankton

• Plant Foods
• algae
• phytoplankton phytoplankton

• Other Foods
• fungus
• detritus detritus
• microbes

• Foraging Behavior
• filter-feeding filter-feeding

Predation

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.

Ecosystem Roles

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.

Economic Importance for Humans: Positive

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 pet trade
• research and education

Economic Importance for Humans: Negative

There are no known adverse effects of this species on humans.

Conservation Status

This species has not been evaluated by the International Union for Conservation of Nature and Natural Resources and is not considered endangered or threatened.

Additional Links

Encyclopedia of Life

Contributors

Molly Elenbaas (author), University of Michigan-Ann Arbor, Alison Gould (editor), University of Michigan-Ann Arbor, Jeremy Wright (editor), University of Michigan-Ann Arbor.

References

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