Daphnia
Daphnia Temporal range:
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Daphnia pulex | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Branchiopoda |
Subclass: | Phyllopoda
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Superorder: | Diplostraca |
Order: | Anomopoda |
Family: | Daphniidae |
Genus: | Daphnia Müller, 1785 |
Subgenera | |
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Diversity | |
> 200 spp. | |
Synonyms [1] | |
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Daphnia is a genus of small
The two most commonly found species of Daphnia are D. pulex (small and most common) and D. magna (large). They are often associated with a related genus in the order Cladocera: Moina, which is in the Moinidae family instead of the Daphniidae, and is much smaller than D. pulex (roughly half the maximum length).
Appearance and characteristics
The body of a Daphnia species is usually 1–5 mm (0.039–0.197 in) long,[2] and is divided into segments, although this division is not visible.[3] The head is fused, and is generally bent down towards the body with a visible notch separating the two. In most species, the rest of the body is covered by a carapace, with a ventral gap in which the five or six pairs of legs lie.[3] The most prominent features are the compound eyes, the second antennae, and a pair of abdominal setae.[3] In many species, the carapace is translucent or nearly so, so they make excellent subjects for the microscope, as one can observe the beating heart.[3]
Even under relatively low-power
Due to its intermediate size, Daphnia spp. use both diffusion and circulatory methods, producing hemoglobin in low-oxygen environments.[4]
Systematics and evolution
Daphnia is a large genus – comprising over 200 species – belonging to the cladoceran family Daphniidae.[1] It is subdivided into several subgenera (Daphnia, Australodaphnia, Ctenodaphnia), but the division has been controversial and is still in development. Each subgenus has been further divided into a number of species complexes. The understanding of species boundaries has been hindered by phenotypic plasticity, hybridization, intercontinental introductions, and poor taxonomic descriptions.[5][6][7] Modern members of Daphnia belonging to the subgenera Daphnia and Ctenodaphnia are known since the Cretaceous, though the genus likely originated prior to the beginning of the Cretaceous.[8][9] There are numerous poorly studied and cryptic species among crustaceans of the genus Daphnia.[10]
Ecology and behaviour
Daphnia species are normally
Daphnia spp. are typically filter feeders, ingesting mainly unicellular algae and various sorts of organic detritus including protists and bacteria[2][12] Beating of the legs produces a constant current through the carapace, which brings such material into the digestive tract. The trapped food particles are formed into a food bolus which then moves down the digestive tract until voided through the anus located on the ventral surface of the terminal appendage.[12] The second and third pairs of legs are used in the organisms' filter-feeding, ensuring large, unabsorbable particles are kept out, while the other sets of legs create the stream of water rushing into the organism.[12]
Swimming is powered mainly by the second set of antennae, which are larger in size than the first set.[13] The action of this second set of antennae is responsible for the jumping motion.[13]
Daphnia spp. are known to show behavioral changes or modifications to their morphology in the presence of predator kairomones (chemical signals), including larger size at hatching, increased bulkiness, and the development of “neck-teeth". For example, juveniles of D. pulex have a larger size after hatching, along with developing neck-teeth at the back of the head, when in the presence of Chaoborus kairomones. These morphological defenses have shown to reduce mortality due to Chaoborus predation, which is a gape-limited predator. Chitin-related genes (deacetylases) are thought to play an important part in the expression/development of these morphological defenses in Daphnia. Chitin-modifying enzymes (chitin deacetylases) have been shown to catalyse the N-deacetylation of chitin to influence the protein-binding affinity of these chitin filaments.[14]
Life cycle
Most Daphnia species have a
Towards the end of the growing season, however, the mode of reproduction changes, and the females produce tough "resting eggs" or "winter eggs".[2] When environmental conditions deteriorate (e.g. crowding), some of the asexually produced offspring develop into males.[2] The females start producing haploid sexual eggs, which the males fertilise. In species without males, resting eggs are also produced asexually and are diploid. In either case, the resting eggs are protected by a hardened coat (consisting of two chitinous plates) called the ephippium, and are cast off at the female's next molt. The ephippia can withstand periods of extreme cold, drought, or poor food availability, and hatch – when conditions improve – into females (They are close to being classed as extremophiles) .[2]
Parasites
The diagram on the left shows the lifecycle of Pasteuria ramosa, a bacterial parasite of Daphnia. Susceptible hosts acquire the infection from spores in the sediment or in suspension. The parasite develops mainly in the host's body cavity and muscle tissue, increasing in density and eventually expanding to occupy the entire host. Typical effects on the host are sterility and gigantism. Spores are released mainly after the host dies and sinks to the substrate, and sometimes directly to the water via clumsy predation.
Conservation
Several Daphnia species are considered
Uses
Daphnia spp. are a popular live food in tropical and marine
Daphnia spp. are used in scientific studies as a
Because of their thin membranes, which allow 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 species have developed permanent defenses against fish eating them, such as spines and long hooks on the body, which also cause them to become entangled on fishing lines and cloud water with their high numbers. Species such as Daphnia lumholtzi[18][19][20][21] (native to east Africa, the Asian subcontinent of India, and east Australia) have these characteristics and great care should be taken to prevent them from spreading further in North American waters.
Some species of Daphnia native to North America can develop sharp spines at the end of their bodies and helmet-like structures on their heads when they detect predators,[22][23] but this is overall temporary for such species and they do not completely overwhelm or discourage native predators from eating them. While Daphnia spp. are an important base of the food chain in freshwater lakes (and vernal pools), they become a nuisance when they are unable to be eaten by native macroscopic predators, and some concern exists that the original spineless and hookless water fleas and spp. end up outcompeted by the invasive ones. (This may not be the case, however, and the new invaders may mostly be a tangling and clogging nuisance.)
In the water bodies of the world, at least 15 species of Daphnia and hybrids are non-native species, many of which pose a great threat to aquatic ecosystems.[24]
See also
References
- ^ a b A. Kotov; L. Forró; N. M. Korovchinsky; A. Petrusek (March 2, 2012). "Crustacea-Cladocera checkList" (PDF). World checklist of freshwater Cladocera species. Belgian Biodiversity Platform. Retrieved October 29, 2012.
- ^ ISBN 978-1-932811-06-3.
- ^ a b c d e f "Daphnia". Oneida Lake Education Initiative. Stony Brook University. Retrieved October 9, 2013.
- S2CID 219208202. Retrieved 2018-04-11.
- PMID 8747296.
- PMID 8744763. Archived from the original(PDF) on 2007-04-18.
- .
- PMID 21595889.
- .
- ^
Chin, Tiffany; Cristescu, Melania (2021). "Speciation in Daphnia". INVITED REVIEWS AND SYNTHESES. S2CID 225026378. This review cites this research. Kotov, Alexey A.; Garibian, Petr G.; Bekker, Eugeniya I.; Taylor, Derek J.; Karabanov, Dmitry P. (2020-06-17). "A new species group from the Daphnia curvirostris species complex (Cladocera: Anomopoda) from the eastern Palaearctic: taxonomy, phylogeny and phylogeography".ISSN 0024-4082.
- ^ .
- ^ ISBN 978-0-470-99926-4.
- ^ ISBN 978-0-08-088981-8.
- S2CID 36557263.
- ^ C. Michael Hogan (2008). "Makgadikgadi". The Megalithic Portal.
- S2CID 205115549.
- PMID 28379975.
- ^ USGS: Nonindigenous Aquatic Species: Daphnia lumholtzi
- ^ Center for Freshwater Biology - University of New Hampshire: Daphnia lumholtzi
- ^ ISSG: Global Invasive Species Database: Daphnia lumholtzi (crustacean) Archived 2016-03-04 at the Wayback Machine
- ^ James A. Stoeckel, Illinois Natural History Survey: Daphnia lumholtzi: The Next Great Lakes Exotic? Archived 2016-12-20 at the Wayback Machine
- ^ Elizabeth A. Colburn (2004), Vernal Pools: Natural History and Conservation, page 118 of paperback second edition from 2008
- ^ Patrick Lavens and Patrick Sorgeloos, Manual on the Production and Use of Live Food for Aquaculture: Daphnia and Moina
- ISSN 2073-4441.
External links
- Data related to Daphnia at Wikispecies
- Daphnia Genomics Consortium
- Daphnia: An Aquarist's Guide
- Waterflea.org: a Community resource for cladoceran biology
- Daphnia spp.: taxonomy, facts, life cycle, references at GeoChemBio Archived 2021-04-10 at the Wayback Machine