Daphnia , small planktonic crustacean genus, 0.2-5 millimeter in length (0.01-0.20 inches). Daphnia is a member of the Cladocera order, and is one of several small water crustaceans commonly called water fleas because their wicky swimming style (Wiktionary) resembles a flea movement. Daphnia lives in a variety of aquatic environments ranging from acid swamps to lakes and freshwater pools.
The two most widely available species of Daphnia are D.a, pulex (small and most common) and D.a, magna (large). They are often associated with related genes in the Cladocera order: Moina , which are in the Moinidae family, not Daphniidae and much less than D. pulex (approx. ). Daphnia eggs are usually sealed in ephippia (thick shells, consisting of two chitinous plates, which wrap and protect winter eggs from cladocrystals).
Video Daphnia
Appearance and characteristics
The body Daphnia is typically a length of 1-5 millimeters (0.04-0.20 inches), and is divided into several segments, although this division is not visible. The head is united, and generally bends toward the body with a position visible separating the two. In most species, other body parts are covered by carapace, with ventral cleft in which five or six pairs of legs are exposed. The most prominent features are compound eyes, second antenna, and a pair of abdominal setae. In many species, the carapace is translucent or nearly finished and as a result they make an excellent subject for the microscope as can be observed in a heart beat.
Even under a relatively low power microscope, the eating mechanism can be observed, with immature young moves in the parent pouch; In addition, eyes that are moved by ciliary muscles can be seen, as well as blood cells that are pumped around the circulatory system by a simple heart. The heart is at the top of the back, just behind the head, and the average heart rate is about 180 bpm under normal conditions. Daphnia, like many other animals, is susceptible to alcohol poisoning, and makes an excellent subject for studying the effects of depressants on the nervous system because of the translucent exoskeleton and the seemingly changing heart rate. They are tolerant to being observed living under cover and appear uninjured when returning to open water. This experiment can also be done using caffeine, nicotine or adrenaline, each producing an increased heart rate.
Because of its medium size, Daphnia uses diffusion and circulation methods, producing hemoglobin in low-oxygen environments.
Maps Daphnia
Systematics and evolution
Daphnia is a large genus - made up of over 200 species - belongs to the Cladoceran family of Daphniidae. It is divided into several subgenera ( Daphnia , Australodaphnia , Ctenodaphnia ), but the division is still controversial and still under development. Each subgenus has been subdivided into a number of species complexes. Understanding of species boundaries has been hindered by phenotypic plasticity, hybridization, intercontinental introductions and poor taxonomic descriptions.
Ecology and behavior
Daphnia species are usually r -picked, meaning they invest in early reproduction and have a short lifespan. Duration of a person Daphnia depends on factors such as temperature and predator abundance, but can be 13-14 months in some cold, oligotrophic fish-free lakes. Under typical conditions, however, the life cycle is much shorter, usually not exceeding 5-6 months.
Daphnia is typically a filter feeder, swallowing mainly unicellular algae and various types of organic detritus including protists and bacteria. The beating of the feet produces a constant stream through the carapace that carries the material to the gastrointestinal tract. The trapped food particles are formed into bolus food that then travels down the gastrointestinal tract to urine through the anus located on the ventral surface of the terminal complement. The second and third legs are used in the screening of the organism, ensuring that large, unabsorbed particles are kept out, while the other set of feet creates a flow of water flowing into the organism.
Swimming is mainly powered by a second antenna antenna, which is bigger than the first set. The action of this second antenna is responsible for jumping.
Life cycle
Most Daphnia species have a life cycle based on "cyclical parthenogenesis", alternating between parthenogenetic (asexual) reproduction and sexual reproduction. For most of the growth season, females reproduce asexually. They produce diploid parent eggs every time they moult; This parent can contain at least 1-2 eggs in smaller species, such as D. cucullata , but can be over 100 larger species, such as D.Ã , Magna . Under typical conditions, these eggs hatch after a day, and remain in the parent bag for about three days (at 20 ° C). They are then released into the water, and pass through 4-6 instars further for 5-10 days (longer under adverse conditions) before reaching the age at which they can reproduce. Children who are produced asexually are usually female.
Toward the end of the growing season, however, the reproductive mode changes, and females produce a strong "egg break" or "winter eggs". As environmental conditions deteriorate (eg crowding), some offspring produced asexually develop into males. Females begin to produce haploid sexual eggs, which are fertilized males. In species without stud, rest eggs are also produced asexually and diploid. In both cases, resting eggs are protected by a hardened layer called ephippium , and disposed of in the next female magazine. Ephippia can withstand extreme cold periods, drought or lack of food availability, and hatch - when conditions improve - become females (They are almost classified as extremophiles).
Preservation
Some species of Daphnia are considered threatened. The following are listed as susceptible to the IUCN: Daphnia nivalis , Daphnia coronata , Daphnia occidentalis , and Daphnia jollyi . Some species are halophiles, and can be found in hypersaline lake environments, for example the Makgadikgadi Pan.
Usage
Daphnia spp. is a popular living food in the maintenance of tropical fish and the sea. They are often fed for tadpoles or small species of amphibians such as African dwarf frog ( Hymenochirus boettgeri ).
Daphnia can be used in certain environments to test the toxic effects on the ecosystem, which makes it an indicator genus, especially useful because of its short-term and reproductive ability. Because they are almost transparent, their internal organs are easily studied in live specimens (eg to study the effect of temperature on the heart rate of these ectothermic organisms). Daphnia is also commonly used for experiments to test aspects of climate change, such as ultraviolet radiation (UVR) that seriously damages zooplankton species (eg reducing feeding activity).
Because of their thin membranes, which allow the drugs to be absorbed, they are used to monitor the effects of certain drugs, such as adrenaline or capsaicin, on the heart.
Invasive Species
Some daphnia species or daphnia-like water bugs have developed permanent and temporary defenses against fish that eat them like thorns and long hooks on the body that also cause them to become entangled in fishing lines and water clouds with their high numbers. Species like Bythotrephes longimanus AKA "spiny water bug" and formerly known as Bythotrephes cederstroemi (native to Northern Europe and Asia), Cercopagis pengoi AKA "fishhook waterflea "(native to the brackish periphery of the Black Sea and Caspian Sea) and Daphnia lumholtzi (native to east Africa, the Asian sub-continent of India and eastern Australia) possess these and great characteristics. care must be taken to prevent them from spreading further in the waters of North America.
Some native species of North American daphnia can develop sharp spikes at the ends of the body and helmet-like structures in the head when they detect predators, but these are entirely temporary for the daphnia species and they do not completely overwhelm or break the original predators. from eating it. While daphnia is an important base of the food chain in freshwater lakes (and vernal pools), they become a nuisance when they are not eaten by native macroscopic predators and there are some concerns that endless native water fleas and ticks and the ends of daphnia up-compete with which is invasive. (This may not be the case, however, and the new colonist is largely likely to be a distorted and clogging disorder.)
See also
- List Daphnia species
- Moina, sometimes referred to as Daphnia
- Rotifer
- Zooplankton
- Crustacean
References
External links
- Data related to Daphnia on Wikispecies
- Daphnia Genomic Consortium
- Daphnia Pictures and Information at MBL Aquaculture
- Daphnia : An Aquarist's Guide
- Waterflea.org: Community resources for kladoceran biology
- Daphnia spp: taxonomy, facts, life cycle, references in GeoChemBio
Source of the article : Wikipedia
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