DAPHNIA, a genus of small planktonic crustaceans , are 0.2–5
millimetres (0.01–0.20 in) in length.
Daphnia are members of the
Cladocera , and are one of the several small aquatic crustaceans
commonly called water fleas because their saltatory (Wiktionary)
swimming style resembles the movements of fleas .
Daphnia live in
various aquatic environments ranging from acidic swamps to freshwater
lakes, ponds, streams and rivers.
The two most readily available 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
Daphniidae and is much smaller than D.
pulex (approximately half the maximum length).
Daphnia eggs for sale
are generally enclosed in ephippia (a thick shell, consisting of two
chitinous plates, that encloses and protects the winter eggs of a
* 1 Appearance and characteristics
* 2 Systematics and evolution
* 3 Ecology and behaviour
* 4 Life cycle
* 5 Conservation
* 6 Uses
* 7 Invasive species
* 8 See also
* 9 References
* 10 External links
APPEARANCE AND CHARACTERISTICS
Play media The beating heart of
Daphnia under the microscope
The body of
Daphnia is usually 1–5 millimetres (0.04–0.20 in)
long, and is divided into segments , although this division is not
visible. 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. The most prominent features
are the compound eyes , the second antennae , and a pair of abdominal
setae . In many species, the carapace is translucent or nearly so and
as a result they make excellent subjects for the microscope as one can
observe the beating heart.
Even under relatively low-power microscopy , the feeding mechanism
can be observed, with immature young moving in the brood pouch;
moreover, the eye being moved by the ciliary muscles can be seen, as
well as blood cells being pumped around the circulatory system by the
simple heart. The heart is at the top of the back, just behind the
head, and the average heart rate is approximately 180 bpm under normal
conditions. Daphnia, like many animals, are prone to alcohol
intoxication, and make excellent subjects for studying the effects of
the depressant on the nervous system due to the translucent
exoskeleton and the visibly altered heart rate . They are tolerant of
being observed live under a cover slip and appear to suffer no harm
when returned to open water. This experiment can also be performed
using caffeine , nicotine or adrenaline , each producing an increase
in the heart rate.
SYSTEMATICS AND EVOLUTION
List of Daphnia species
Daphnia is a large genus – comprising over 200 species –
belonging to the cladoceran family
Daphniidae . 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.
ECOLOGY AND BEHAVIOUR
Daphnia Overview The five trunk limbs, used in
Daphnia species are normally r-selected , meaning that they invest in
early reproduction and so have short lifespans. An individual Daphnia
life-span depends on factors such as temperature and the abundance of
predators , but can be 13–14 months in some cold, oligotrophic
fish-free lakes. In typical conditions, however, the life cycle is
much shorter, not usually exceeding 5–6 months.
Daphnia are typically filter feeders , ingesting mainly unicellular
algae and various sorts of organic detritus including protists and
bacteria 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. The second and third pair
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.
Swimming is powered mainly by the second set of antennae, which are
larger in size than the first set. The action of this second set of
antennae is responsible for the jumping motion.
Resting egg pouch (ephippium) and the juvenile daphnid that just
has hatched from it
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 a brood of diploid eggs
every time they moult ; these broods can contain as few as 1–2 eggs
in smaller species, such as D. cucullata , but can be over 100 in
larger species, such as D. magna . Under typical conditions, these
eggs hatch after a day, and remain in the female's brood pouch for
around three days (at 20 °C). They are then released into the water,
and pass through a further 4–6 instars over 5–10 days (longer in
poor conditions) before reaching an age where they are able to
reproduce. The asexually produced offspring are typically female.
Towards the end of the growing season, however, the mode of
reproduction changes, and the females produce tough "resting eggs" or
"winter eggs". When environmental condition deteriorate (e.g.
crowding), some of the asexually produced offspring develop into
males. 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 called the ephippium, and are cast
off at the female's next moult. The ephippia can withstand periods of
extreme cold, drought or lack of food availability, and hatch – when
conditions improve – into females (They are close to being classed
as extremophiles) .
Daphnia species are considered threatened . The following are
listed as vulnerable by IUCN :
Daphnia nivalis ,
Daphnia coronata ,
Daphnia occidentalis , and
Daphnia jollyi . Some species are
halophiles , and can be found in hypersaline lake environments, an
example of which is the
Makgadikgadi Pan .
Daphnia spp. are a popular live food in tropical and marine fish
keeping . They are often fed to tadpoles or small species of
amphibians such as the
African dwarf frog
African dwarf frog (Hymenochirus boettgeri).
Daphnia may be used in certain environments to test the effects of
toxins on an ecosystem , which makes them an indicator genus ,
particularly useful because of its short lifespan and reproductive
capabilities. Because they are nearly transparent, their internal
organs are easy to study in live specimens (e.g. to study the effect
of temperature on the heart rate of these ectothermic organisms).
Because of their thin membrane, which allows drugs to be absorbed,
they are used to monitor affects of certain drugs, such as adrenaline
or capsaicin, on the heart.
Fishhook waterflea (above) and
Bythotrephes longimanus (spiny
water flea) (below)
Some species of daphnia or water fleas that resemble daphnia have
developed permanent, non-temporary 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
Bythotrephes longimanus AKA "spiny water
flea" and formerly known as Bythotrephes cederstroemi (native to
Northern Europe and Asia),
Cercopagis pengoi AKA "fishhook waterflea"
(native in the brackish fringes of the Black Sea and the Caspian Sea)
Daphnia lumholtzi (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 the body and helmet-like structures on the head
when they detect predators, but this is overall temporary for such
daphnia species and they do not completely overwhelm or discourage
native predators from eating them. While daphnia 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 there is some concern that the original spineless and
hookless water fleas and daphnia end up out-competed by the invasive
ones. (This may not be the case, however, and the new invaders may
mostly be a tangling and clogging nuisance.)
* Crustaceans portal
List of Daphnia species
Moina , which are sometimes referred to as Daphnia
* ^ A B A. Kotov; L. Forró; N. M. Korovchinsky; A. Petrusek (March
2, 2012). "Crustacea-
Cladocera checkList" (PDF ). World checklist of
Cladocera species. Belgian
Biodiversity Platform. Retrieved
October 29, 2012.
* ^ N.N.Smirnov (2014). The physiology of the Cladocera. Amsterdam:
* ^ A B C D E F G Dieter Ebert (2005). "Introduction to Daphnia
biology". Ecology, Epidemiology, and Evolution of Parasitism in
Daphnia. Bethesda, MD: National Center for Biotechnology Information.
ISBN 978-1-932811-06-3 .
* ^ A B C D E F "Daphnia". Oneida Lake Education Initiative. Stony
Brook University . Retrieved October 9, 2013.
* ^ A B "Investigating factors affecting the heart rate of
Nuffield Foundation . January 25, 2012. Retrieved October 9,
* ^ Niles Lehman; Michael E. Pfrender; Phillip A. Morin; Teresa J.
Crease; Michael Lynch (1995). "A hierarchical molecular phylogeny
within the genus Daphnia".
Molecular Phylogenetics and Evolution . 4
(4): 395–407. PMID 8747296 . doi :10.1006/mpev.1995.1037 .
* ^ Derek J. Taylor; Paul D. N. Hebert; John K. Colbourne (1996).
"Phylogenetics and evolution of the
Daphnia longispina group
(Crustacea) based on 12S rDNA sequence and allozyme variation" (PDF ).
Molecular Phylogenetics and Evolution . 5 (3): 495–510. PMID 8744763
. doi :10.1006/mpev.1996.0045 .
* ^ Sarah J. Adamowicz; Paul D. N. Hebert; María Christina
Marinone (2004). "Species diversity and endemism in the
Argentina: a genetic investigation". Zoological Journal of the Linnean
Society . 140 (2): 171–205. doi :10.1111/j.1096-3642.2003.00089.x .
* ^ A B Barbara Pietrzak; Anna Bednarska; Magdalena Markowska;
Maciej Rojek; Ewa Szymanska; Miroslaw Slusarczyk (2013). "Behavioural
and physiological mechanisms behind extreme longevity in Daphnia".
Hydrobiologia . 715 (1): 125–134. doi :10.1007/s10750-012-1420-6 .
* ^ A B C Z. Maciej Gliwicz (2008). "Zooplankton". In Patrick
O'Sullivan; C. S. Reynolds. The Lakes Handbook: Limnology and Limnetic
John Wiley & Sons
John Wiley & Sons . pp. 461–516. ISBN 978-0-470-99926-4 .
* ^ A B Stanley L. Dodson; Carla E. Cáceres; D. Christopher Rogers
Cladocera and other Branchiopoda". In James H. Thorp; Alan P.
Covich. Ecology and Classification of North American Freshwater
Invertebrates (3rd ed.).
Academic Press . pp. 773–828. ISBN
* ^ C. Michael Hogan (2008). "Makgadikgadi". The Megalithic Portal.
* ^ "The amazing
Daphnia water flea". AquaDaily. February 16, 2009.
Retrieved February 18, 2009.
* ^ USGS Nonindigenous Aquatic Species: Bythotrephes longimanus
* ^ Central Michigan University:
Zooplankton of the Great Lakes:
* ^ Washington Department of Fish
* Wd : Q269354
* ADW : Daphnia
BugGuide : 352881
* EoL : 41238
* GBIF : 2234785
* ITIS : 83873
* NCBI : 6668
* WoRMS : 148370