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90-496: The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals . Choanoflagellates are collared flagellates, having a funnel shaped collar of interconnected microvilli at the base of a flagellum . Choanoflagellates are capable of both asexual and sexual reproduction. They have a distinctive cell morphology characterized by an ovoid or spherical cell body 3–10  μm in diameter with

180-438: A holoparasite such as Cuscuta derives all of its nutrients from another plant. Parasitic plants make up about one per cent of angiosperms and are in almost every biome in the world. All these plants have modified roots, haustoria , which penetrate the host plants, connecting them to the conductive system—either the xylem , the phloem , or both. This provides them with the ability to extract water and nutrients from

270-511: A cause of gastroenteritis , is spread by the fecal–oral route from animals, or by eating insufficiently cooked poultry , or by contaminated water. Haemophilus influenzae , an agent of bacterial meningitis and respiratory tract infections such as influenza and bronchitis , is transmitted by droplet contact. Treponema pallidum , the cause of syphilis , is spread by sexual activity . Viruses are obligate intracellular parasites, characterised by extremely limited biological function, to

360-424: A characteristic arrangement, with nine fused pairs surrounding two central singlets. These arise from a basal body . In some flagellates, flagella direct food into a cytostome or mouth, where food is ingested . Flagella role in classifying eukaryotes . Among protoctists and microscopic animals , a flagellate is an organism with one or more flagella. Some cells in other animals may be flagellate, for instance

450-461: A choanoflagellate and three sponges confirm the placement of choanoflagellates as an outgroup to Metazoa (animals, also known as Animalia ) and negate the possibility that choanoflagellates evolved from metazoans (Lavrov, et al., 2005). Finally, a 2001 study of genes expressed in choanoflagellates has revealed that choanoflagellates synthesize homologues of metazoan cell signaling and adhesion genes. Genome sequencing shows that, among living organisms,

540-540: A combination of species traditionally attributed to the Codonosigidae and Salpingoecidae, while Clade 3 comprises species from the group taxonomically classified as Acanthoecidae. The mapping of character traits on to this phylogeny indicates that the last common ancestor of choanoflagellates was a marine organism with a differentiated life cycle with sedentary and motile stages. Choanoflagellates; The genome of Monosiga brevicollis , with 41.6 million base pairs,

630-526: A current that brings in food. In most such organisms, one or more flagella are located at or near the anterior of the cell (e.g., Euglena ). Often there is one directed forwards and one trailing behind. Many parasites that affect human health or economy are flagellates in at least one stage of life cycle, such as Naegleria , Trichomonas and Plasmodium . Flagellates are the major consumers of primary and secondary production in aquatic ecosystems - consuming bacteria and other protists. An overview of

720-527: A cylindrical or conical collar ( choanos in Greek). Movement of the flagellum draws water through the collar, and bacteria and detritus are captured by the microvilli and ingested. Water currents generated by the flagellum also push free-swimming cells along, as in animal sperm . In contrast, most other flagellates are pulled by their flagella. In addition to the single apical flagellum surrounded by actin-filled microvilli that characterizes choanoflagellates,

810-627: A faster rate than their hosts. Classic examples include interactions between vertebrate hosts and tapeworms , flukes , and those between the malaria-causing Plasmodium species, and fleas . Parasites reduce host fitness by general or specialised pathology , that ranges from parasitic castration to modification of host behaviour . Parasites increase their own fitness by exploiting hosts for resources necessary for their survival, in particular by feeding on them and by using intermediate (secondary) hosts to assist in their transmission from one definitive (primary) host to another. Although parasitism

900-595: A hormone or by diverting nutrients. For example, the trematode Zoogonus lasius , whose sporocysts lack mouths, castrates the intertidal marine snail Tritia obsoleta chemically, developing in its gonad and killing its reproductive cells. Directly transmitted parasites, not requiring a vector to reach their hosts, include such parasites of terrestrial vertebrates as lice and mites; marine parasites such as copepods and cyamid amphipods; monogeneans ; and many species of nematodes, fungi, protozoans, bacteria, and viruses. Whether endoparasites or ectoparasites, each has

990-522: A number of choanoflagellate relatives, such as members of Ichthyosporea or Mesomycetozoa , follow a parasitic or pathogenic lifestyle. The life histories of choanoflagellates are poorly understood. Many species are thought to be solitary; however, coloniality seems to have arisen independently several times within the group, and colonial species still retain a solitary stage. Over 125 extant species of choanoflagellates are known, distributed globally in marine , brackish and freshwater environments from

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1080-836: A parasite employs to identify and approach a potential host are known as "host cues". Such cues can include, for example, vibration, exhaled carbon dioxide , skin odours, visual and heat signatures, and moisture. Parasitic plants can use, for example, light, host physiochemistry, and volatiles to recognize potential hosts. There are six major parasitic strategies , namely parasitic castration ; directly transmitted parasitism; trophically -transmitted parasitism; vector -transmitted parasitism; parasitoidism ; and micropredation. These apply to parasites whose hosts are plants as well as animals. These strategies represent adaptive peaks ; intermediate strategies are possible, but organisms in many different groups have consistently converged on these six, which are evolutionarily stable. A perspective on

1170-618: A parasitic alien species. First used in English in 1539, the word parasite comes from the Medieval French parasite , from the Latinised form parasitus , from Ancient Greek παράσιτος (parasitos)  'one who eats at the table of another' in turn from παρά (para)  'beside, by' and σῖτος (sitos)  'wheat, food'. The related term parasitism appears in English from 1611. Parasitism

1260-456: A peculiar type of flagellate/ amoeboid organization, in which cells may present flagella and pseudopods , simultaneously or sequentially, while the helioflagellates (e.g., the cercozoan heliomonads/dimorphids , the stramenopile pedinellids and ciliophryids ) have a flagellate/ heliozoan organization. Parasitic This is an accepted version of this page Parasitism is a close relationship between species , where one organism,

1350-432: A phenomenon termed the biotrophy-necrotrophy switch . Pathogenic fungi are well-known causative agents of diseases on animals as well as humans. Fungal infections ( mycosis ) are estimated to kill 1.6 million people each year. One example of a potent fungal animal pathogen are Microsporidia - obligate intracellular parasitic fungi that largely affect insects, but may also affect vertebrates including humans, causing

1440-533: A predator, the European sparrowhawk , giving her time to lay her eggs in the host's nest unobserved. Host species often combat parasitic egg mimicry through egg polymorphism , having two or more egg phenotypes within a single population of a species. Multiple phenotypes in host eggs decrease the probability of a parasitic species accurately "matching" their eggs to host eggs. In kleptoparasitism (from Greek κλέπτης ( kleptēs ), "thief"), parasites steal food gathered by

1530-518: A second loricate species, Diaphanoeca grandis . Analysis of these genes found that the choanoflagellate silicon transporters show homology to the SIT-type silicon transporters of diatoms and have evolved through horizontal gene transfer . An additional 19 transcriptomes were published in 2018. A large number of gene families previously thought to be animal-only were found. Flagellate Flagella in eukaryotes are supported by microtubules in

1620-539: A single apical flagellum surrounded by a collar of 30–40 microvilli (see figure). Movement of the flagellum creates water currents that can propel free-swimming choanoflagellates through the water column and trap bacteria and detritus against the collar of microvilli, where these foodstuffs are engulfed. This feeding provides a critical link within the global carbon cycle , linking trophic levels . In addition to their critical ecological roles, choanoflagellates are of particular interest to evolutionary biologists studying

1710-573: A single host-species. Within that species, most individuals are free or almost free of parasites, while a minority carry a large number of parasites; this is known as an aggregated distribution . Trophically -transmitted parasites are transmitted by being eaten by a host. They include trematodes (all except schistosomes ), cestodes , acanthocephalans , pentastomids , many roundworms , and many protozoa such as Toxoplasma . They have complex life cycles involving hosts of two or more species. In their juvenile stages they infect and often encyst in

1800-430: A suitable fungus soon after germinating. Parasitic fungi derive some or all of their nutritional requirements from plants, other fungi, or animals. Plant pathogenic fungi are classified into three categories depending on their mode of nutrition: biotrophs, hemibiotrophs and necrotrophs. Biotrophic fungi derive nutrients from living plant cells, and during the course of infection they colonise their plant host in such

1890-1047: A variety of methods to infect animal hosts, including physical contact, the fecal–oral route , free-living infectious stages, and vectors, suiting their differing hosts, life cycles, and ecological contexts. Examples to illustrate some of the many possible combinations are given in the table. social behaviour (grooming) Among the many variations on parasitic strategies are hyperparasitism, social parasitism, brood parasitism, kleptoparasitism, sexual parasitism, and adelphoparasitism. Hyperparasites feed on another parasite, as exemplified by protozoa living in helminth parasites, or facultative or obligate parasitoids whose hosts are either conventional parasites or parasitoids. Levels of parasitism beyond secondary also occur, especially among facultative parasitoids. In oak gall systems, there can be up to five levels of parasitism. Hyperparasites can control their hosts' populations, and are used for this purpose in agriculture and to some extent in medicine . The controlling effects can be seen in

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1980-469: A variety of routes. To give a few examples, Bacillus anthracis , the cause of anthrax , is spread by contact with infected domestic animals ; its spores , which can survive for years outside the body, can enter a host through an abrasion or may be inhaled. Borrelia , the cause of Lyme disease and relapsing fever , is transmitted by vectors, ticks of the genus Ixodes , from the diseases' reservoirs in animals such as deer . Campylobacter jejuni ,

2070-474: A way as to keep it alive for a maximally long time. One well-known example of a biotrophic pathogen is Ustilago maydis , causative agent of the corn smut disease. Necrotrophic pathogens on the other hand, kill host cells and feed saprophytically , an example being the root-colonising honey fungi in the genus Armillaria . Hemibiotrophic pathogens begin their colonising their hosts as biotrophs, and subsequently killing off host cells and feeding as necrotrophs,

2160-429: Is 55 megabases in size. Homologs of cell adhesion, neuropeptide and glycosphingolipid metabolism genes are present in the genome. S. rosetta has a sexual life cycle and transitions between haploid and diploid stages . In response to nutrient limitation, haploid cultures of S. rosetta become diploid. This ploidy shift coincides with mating during which small, flagellated cells fuse with larger flagellated cells. There

2250-563: Is a kind of symbiosis , a close and persistent long-term biological interaction between a parasite and its host. Unlike saprotrophs , parasites feed on living hosts, though some parasitic fungi, for instance, may continue to feed on hosts they have killed. Unlike commensalism and mutualism , the parasitic relationship harms the host, either feeding on it or, as in the case of intestinal parasites, consuming some of its food. Because parasites interact with other species, they can readily act as vectors of pathogens, causing disease . Predation

2340-675: Is aggregated. Coinfection by multiple parasites is common. Autoinfection , where (by exception) the whole of the parasite's life cycle takes place in a single primary host, can sometimes occur in helminths such as Strongyloides stercoralis . Vector-transmitted parasites rely on a third party, an intermediate host, where the parasite does not reproduce sexually, to carry them from one definitive host to another. These parasites are microorganisms, namely protozoa , bacteria , or viruses , often intracellular pathogens (disease-causers). Their vectors are mostly hematophagic arthropods such as fleas, lice, ticks, and mosquitoes. For example,

2430-516: Is also evidence of historical mating and recombination in S. rosetta . S. rosetta is induced to undergo sexual reproduction by the marine bacterium Vibrio fischeri . A single V. fischeri protein, EroS fully recapitulates the aphrodisiac-like activity of live V. fisheri . The single-cell amplified genomes of four uncultured marine choanoflagellates, tentatively called UC1–UC4, were sequenced in 2019. The genomes of UC1 and UC4 are relatively complete. An EST dataset from Monosiga ovata

2520-443: Is by definition not a symbiosis, as the interaction is brief, but the entomologist E. O. Wilson has characterised parasites as "predators that eat prey in units of less than one". Within that scope are many possible strategies. Taxonomists classify parasites in a variety of overlapping schemes, based on their interactions with their hosts and on their life cycles , which can be complex. An obligate parasite depends completely on

2610-461: Is difficult to constrain, but was probably in the late Precambrian, > 600  million years ago . External relationships of Choanoflagellatea. Cristidiscoidea Fungi Ichthyosporea Corallochytrea Filasterea Animalia (Metazoa) Choanoflagellatea The choanoflagellates were included in Chrysophyceae until Hibberd, 1975. Recent molecular phylogenetic reconstruction of

2700-554: Is formed within the choanoflagellate cell and is then secreted to the cell surface. In nudiform choanoflagellates, lorica assembly takes place using a number of tentacles once sufficient costal strips have been produced to comprise a full lorica. In tectiform choanoflagellates, costal strips are accumulated in a set arrangement below the collar. During cell division, the new cell takes these costal strips as part of cytokinesis and assembles its own lorica using only these previously produced strips. Choanoflagellate biosilicification requires

2790-645: Is found in the ant Tetramorium inquilinum , an obligate parasite which lives exclusively on the backs of other Tetramorium ants. A mechanism for the evolution of social parasitism was first proposed by Carlo Emery in 1909. Now known as " Emery's rule ", it states that social parasites tend to be closely related to their hosts, often being in the same genus. Intraspecific social parasitism occurs in parasitic nursing, where some individual young take milk from unrelated females. In wedge-capped capuchins , higher ranking females sometimes take milk from low ranking females without any reciprocation. In brood parasitism ,

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2880-585: Is often unambiguous, it is part of a spectrum of interactions between species , grading via parasitoidism into predation, through evolution into mutualism , and in some fungi, shading into being saprophytic . Human knowledge of parasites such as roundworms and tapeworms dates back to ancient Egypt , Greece , and Rome . In early modern times, Antonie van Leeuwenhoek observed Giardia lamblia with his microscope in 1681, while Francesco Redi described internal and external parasites including sheep liver fluke and ticks . Modern parasitology developed in

2970-419: Is seen in some species of anglerfish , such as Ceratias holboelli , where the males are reduced to tiny sexual parasites , wholly dependent on females of their own species for survival, permanently attached below the female's body, and unable to fend for themselves. The female nourishes the male and protects him from predators, while the male gives nothing back except the sperm that the female needs to produce

3060-409: Is similar in size to filamentous fungi and other free-living unicellular eukaryotes, but far smaller than that of typical animals. In 2010, a phylogenomic study revealed that several algal genes are present in the genome of Monosiga brevicollis . This could be due to the fact that, in early evolutionary history, choanoflagellates consumed algae as food through phagocytosis . Carr et al. (2010) screened

3150-402: Is surrounded by a distinguishing extracellular matrix or periplast . These cell coverings vary greatly in structure and composition and are used by taxonomists for classification purposes. Many choanoflagellates build complex basket-shaped "houses", called lorica , from several silica strips cemented together. The functional significance of the periplast is unknown, but in sessile organisms, it

3240-469: Is then carried to a nest, sometimes alongside other prey if it is not large enough to support a parasitoid throughout its development. An egg is laid on top of the prey and the nest is then sealed. The parasitoid develops rapidly through its larval and pupal stages, feeding on the provisions left for it. Koinobiont parasitoids, which include flies as well as wasps, lay their eggs inside young hosts, usually larvae. These are allowed to go on growing, so

3330-475: Is thought to aid attachment to the substrate. In planktonic organisms, there is speculation that the periplast increases drag, thereby counteracting the force generated by the flagellum and increasing feeding efficiency. Choanoflagellates are either free-swimming in the water column or sessile , adhering to the substrate directly or through either the periplast or a thin pedicel. Although choanoflagellates are thought to be strictly free-living and heterotrophic ,

3420-406: The M. brevicollis genome for known eukaryotic meiosis genes. Of 19 known eukaryotic meiotic genes tested (including 8 that function in no other process than meiosis), 18 were identified in M. brevicollis . The presence of meiotic genes, including meiosis specific genes, indicates that meiosis, and by implication, sex is present within the choanoflagellates. The genome of Salpingoeca rosetta

3510-505: The snubnosed eel is probably a facultative endoparasite (i.e., it is semiparasitic) that opportunistically burrows into and eats sick and dying fish. Plant-eating insects such as scale insects , aphids , and caterpillars closely resemble ectoparasites, attacking much larger plants; they serve as vectors of bacteria, fungi and viruses which cause plant diseases . As female scale insects cannot move, they are obligate parasites, permanently attached to their hosts. The sensory inputs that

3600-423: The spermatozoa of most animal phyla. Flowering plants do not produce flagellate cells, but ferns , mosses , green algae , and some gymnosperms and closely related plants do so. Likewise, most fungi do not produce cells with flagellae, but the primitive fungal chytrids do. Many protists take the form of single-celled flagellates. Flagella are generally used for propulsion . They may also be used to create

3690-504: The 19th century. In human culture, parasitism has negative connotations. These were exploited to satirical effect in Jonathan Swift 's 1733 poem "On Poetry: A Rhapsody", comparing poets to hyperparasitical "vermin". In fiction, Bram Stoker 's 1897 Gothic horror novel Dracula and its many later adaptations featured a blood-drinking parasite. Ridley Scott 's 1979 film Alien was one of many works of science fiction to feature

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3780-539: The Acanthoecidae, has been supported as a monophyletic group. This clade possess a synapomorphy of the cells being found within a basket-like lorica, providing the alternative name of "Loricate Choanoflagellates". The Acanthoecid lorica is composed of a series of siliceous costal strips arranged into a species-specific lorica pattern." The choanoflagellate tree based on molecular phylogenetics divides into three well supported clades . Clade 1 and Clade 2 each consist of

3870-711: The Arctic to the tropics, occupying both pelagic and benthic zones. Although most sampling of choanoflagellates has occurred between 0 and 25 m (0 and 82 ft), they have been recovered from as deep as 300 m (980 ft) in open water and 100 m (330 ft) under Antarctic ice sheets. Many species are hypothesized to be cosmopolitan on a global scale [e.g., Diaphanoeca grandis has been reported from North America , Europe and Australia (OBIS)], while other species are reported to have restricted regional distributions. Co-distributed choanoflagellate species can occupy quite different microenvironments, but in general,

3960-532: The SiT gene family evolved via a lateral gene transfer event between Acanthoecids and Stramenopiles. This is a remarkable case of horizontal gene transfer between two distantly related eukaryotic groups, and has provided clues to the biochemistry and silicon-protein interactions of the unique SiT gene family. Félix Dujardin , a French biologist interested in protozoan evolution, recorded the morphological similarities of choanoflagellates and sponge choanocytes and proposed

4050-458: The agents of ringworm ; and plants such as mistletoe , dodder , and the broomrapes . There are six major parasitic strategies of exploitation of animal hosts, namely parasitic castration , directly transmitted parasitism (by contact), trophically-transmitted parasitism (by being eaten), vector-transmitted parasitism, parasitoidism , and micropredation. One major axis of classification concerns invasiveness: an endoparasite lives inside

4140-696: The air or soil given off by host shoots or roots , respectively. About 4,500 species of parasitic plant in approximately 20 families of flowering plants are known. Species within the Orobanchaceae (broomrapes) are among the most economically destructive of all plants. Species of Striga (witchweeds) are estimated to cost billions of dollars a year in crop yield loss, infesting over 50 million hectares of cultivated land within Sub-Saharan Africa alone. Striga infects both grasses and grains, including corn , rice , and sorghum , which are among

4230-407: The choanoflagellate species Salpingoeca rosetta . Evidence has also been reported for the presence of conserved meiotic genes in the choanoflagellates Monosiga brevicollis and Monosiga ovata . The Acanthoecid choanoflagellates produce an extracellular basket structure known as a lorica. The lorica is composed of individual costal strips, made of a silica-protein biocomposite. Each costal strip

4320-525: The choanoflagellates are most closely related to animals. Because choanoflagellates and metazoans are closely related, comparisons between the two groups promise to provide insights into the biology of their last common ancestor and the earliest events in metazoan evolution. The choanocytes (also known as "collared cells") of sponges (considered among the most basal metazoa) have the same basic structure as choanoflagellates. Collared cells are found in other animal groups, such as ribbon worms , suggesting this

4410-470: The combined data set ( concatenated ) along with sequences from other closely related species ( animals and fungi ) demonstrate that choanoflagellates are strongly supported as monophyletic and confirm their position as the closest known unicellular living relative of animals. Previously, Choanoflagellida was divided into these three families based on the composition and structure of their periplast: Codonosigidae, Salpingoecidae and Acanthoecidae. Members of

4500-472: The concentration of silicic acid within the cell. This is carried out by silicon transporter (SiT) proteins. Analysis of choanoflagellate SiTs shows that they are similar to the SiT-type silicon transporters of diatoms and other silica-forming stramenopiles . The SiT gene family shows little or no homology to any other genes, even to genes in non-siliceous choanoflagellates or stramenopiles. This suggests that

4590-864: The deer tick Ixodes scapularis acts as a vector for diseases including Lyme disease , babesiosis , and anaplasmosis . Protozoan endoparasites, such as the malarial parasites in the genus Plasmodium and sleeping-sickness parasites in the genus Trypanosoma , have infective stages in the host's blood which are transported to new hosts by biting insects. Parasitoids are insects which sooner or later kill their hosts, placing their relationship close to predation. Most parasitoids are parasitoid wasps or other hymenopterans ; others include dipterans such as phorid flies . They can be divided into two groups, idiobionts and koinobionts, differing in their treatment of their hosts. Idiobiont parasitoids sting their often-large prey on capture, either killing them outright or paralysing them immediately. The immobilised prey

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4680-461: The divergence of the crown group choanoflagellates (craspedids) at 786.62 million years. Choanoflagellate is a hybrid word from Greek χοάνη khoánē meaning " funnel " (due to the shape of the collar) and the Latin word flagellum (whence English flagellum ). Each choanoflagellate has a single flagellum , surrounded by a ring of actin -filled protrusions called microvilli , forming

4770-409: The energy that would have gone into reproduction into host and parasite growth, sometimes causing gigantism in the host. The host's other systems remain intact, allowing it to survive and to sustain the parasite. Parasitic crustaceans such as those in the specialised barnacle genus Sacculina specifically cause damage to the gonads of their many species of host crabs . In the case of Sacculina ,

4860-491: The evolutionary options can be gained by considering four key questions: the effect on the fitness of a parasite's hosts; the number of hosts they have per life stage; whether the host is prevented from reproducing; and whether the effect depends on intensity (number of parasites per host). From this analysis, the major evolutionary strategies of parasitism emerge, alongside predation. Parasitic castrators partly or completely destroy their host's ability to reproduce, diverting

4950-601: The factors that influence the distribution and dispersion of choanoflagellates remain to be elucidated. A number of species , such as those in the genus Proterospongia , form simple colonies , planktonic clumps that resemble a miniature cluster of grapes in which each cell in the colony is flagellated or clusters of cells on a single stalk. In October 2019, scientists found a new band behaviour of choanoflagellates: they apparently can coordinate to respond to light. The choanoflagellates feed on bacteria and link otherwise inaccessible forms of carbon to organisms higher in

5040-444: The family Cuculidae , over 40% of cuckoo species are obligate brood parasites, while others are either facultative brood parasites or provide parental care. The eggs of some brood parasites mimic those of their hosts, while some cowbird eggs have tough shells, making them hard for the hosts to kill by piercing, both mechanisms implying selection by the hosts against parasitic eggs. The adult female European cuckoo further mimics

5130-542: The family Codonosigidae appear to lack a periplast when examined by light microscopy, but may have a fine outer coat visible only by electron microscopy . The family Salpingoecidae consists of species whose cells are encased in a firm theca that is visible by both light and electron microscopy. The theca is a secreted covering predominately composed of cellulose or other polysaccharides . These divisions are now known to be paraphyletic , with convergent evolution of these forms widespread. The third family of choanoflagellates,

5220-599: The group Sarcomastigophora . The autotrophic flagellates were grouped similarly to the botanical schemes used for the corresponding algae groups. The colourless flagellates were customarily grouped in three groups, highly artificial: Presently, these groups are known to be highly polyphyletic . In modern classifications of the protists, the principal flagellated taxa are placed in the following eukaryote groups, which include also non-flagellated forms (where "A", "F", "P" and "S" stands for autotrophic, free-living heterotrophic, parasitic and symbiotic, respectively): Although

5310-424: The host and parasitoid develop together for an extended period, ending when the parasitoids emerge as adults, leaving the prey dead, eaten from inside. Some koinobionts regulate their host's development, for example preventing it from pupating or making it moult whenever the parasitoid is ready to moult. They may do this by producing hormones that mimic the host's moulting hormones ( ecdysteroids ), or by regulating

5400-442: The host to complete its life cycle, while a facultative parasite does not. Parasite life cycles involving only one host are called "direct"; those with a definitive host (where the parasite reproduces sexually) and at least one intermediate host are called "indirect". An endoparasite lives inside the host's body; an ectoparasite lives outside, on the host's surface. Mesoparasites—like some copepods , for example—enter an opening in

5490-422: The host's body and remain partly embedded there. Some parasites can be generalists, feeding on a wide range of hosts, but many parasites, and the majority of protozoans and helminths that parasitise animals, are specialists and extremely host-specific. An early basic, functional division of parasites distinguished microparasites and macroparasites. These each had a mathematical model assigned in order to analyse

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5580-453: The host's body; an ectoparasite lives outside, on the host's surface. Like predation, parasitism is a type of consumer–resource interaction , but unlike predators , parasites, with the exception of parasitoids, are much smaller than their hosts, do not kill them, and often live in or on their hosts for an extended period. Parasites of animals are highly specialised , each parasite species living on one given animal species, and reproduce at

5670-656: The host's endocrine system. A micropredator attacks more than one host, reducing each host's fitness by at least a small amount, and is only in contact with any one host intermittently. This behavior makes micropredators suitable as vectors, as they can pass smaller parasites from one host to another. Most micropredators are hematophagic , feeding on blood. They include annelids such as leeches , crustaceans such as branchiurans and gnathiid isopods, various dipterans such as mosquitoes and tsetse flies , other arthropods such as fleas and ticks, vertebrates such as lampreys , and mammals such as vampire bats . Parasites use

5760-425: The host. A parasitic plant is classified depending on where it latches onto the host, either the stem or the root, and the amount of nutrients it requires. Since holoparasites have no chlorophyll and therefore cannot make food for themselves by photosynthesis , they are always obligate parasites, deriving all their food from their hosts. Some parasitic plants can locate their host plants by detecting chemicals in

5850-477: The host. The parasitism is often on close relatives, whether within the same species or between species in the same genus or family. For instance, the many lineages of cuckoo bees lay their eggs in the nest cells of other bees in the same family. Kleptoparasitism is uncommon generally but conspicuous in birds; some such as skuas are specialised in pirating food from other seabirds, relentlessly chasing them down until they disgorge their catch. A unique approach

5940-423: The hosts suffer increased parental investment and energy expenditure to feed parasitic young, which are commonly larger than host young. The growth rate of host nestlings is slowed, reducing the host's fitness. Brood parasites include birds in different families such as cowbirds , whydahs , cuckoos , and black-headed ducks . These do not build nests of their own, but leave their eggs in nests of other species . In

6030-472: The intermediate host. When the intermediate-host animal is eaten by a predator, the definitive host, the parasite survives the digestion process and matures into an adult; some live as intestinal parasites . Many trophically transmitted parasites modify the behaviour of their intermediate hosts, increasing their chances of being eaten by a predator. As with directly transmitted parasites, the distribution of trophically transmitted parasites among host individuals

6120-420: The internal organization of organelles in the cytoplasm is constant. A flagellar basal body sits at the base of the apical flagellum, and a second, non-flagellar basal body rests at a right angle to the flagellar base. The nucleus occupies an apical-to-central position in the cell, and food vacuoles are positioned in the basal region of the cytoplasm. Additionally, the cell body of many choanoflagellates

6210-407: The internal relationships of choanoflagellates allows the polarization of character evolution within the clade. Large fragments of the nuclear SSU and LSU ribosomal RNA , alpha tubulin , and heat-shock protein 90 coding genes were used to resolve the internal relationships and character polarity within choanoflagellates. Each of the four genes showed similar results independently and analysis of

6300-471: The intestinal infection microsporidiosis . Protozoa such as Plasmodium , Trypanosoma , and Entamoeba are endoparasitic. They cause serious diseases in vertebrates including humans—in these examples, malaria, sleeping sickness, and amoebic dysentery —and have complex life cycles. Many bacteria are parasitic, though they are more generally thought of as pathogens causing disease. Parasitic bacteria are extremely diverse, and infect their hosts by

6390-441: The large blue butterfly, Phengaris arion , its larvae employing ant mimicry to parasitise certain ants, Bombus bohemicus , a bumblebee which invades the hives of other bees and takes over reproduction while their young are raised by host workers, and Melipona scutellaris , a eusocial bee whose virgin queens escape killer workers and invade another colony without a queen. An extreme example of interspecific social parasitism

6480-567: The largest group is the parasitoid wasps in the Hymenoptera. The phyla and classes with the largest numbers of parasitic species are listed in the table. Numbers are conservative minimum estimates. The columns for Endo- and Ecto-parasitism refer to the definitive host, as documented in the Vertebrate and Invertebrate columns. A hemiparasite or partial parasite such as mistletoe derives some of its nutrients from another living plant, whereas

6570-537: The marine worm Bonellia viridis has a similar reproductive strategy, although the larvae are planktonic. Examples of the major variant strategies are illustrated. Parasitism has an extremely wide taxonomic range, including animals, plants, fungi, protozoans, bacteria, and viruses. Parasitism is widespread in the animal kingdom, and has evolved independently from free-living forms hundreds of times. Many types of helminth including flukes and cestodes have complete life cycles involving two or more hosts. By far

6660-407: The next generation. Adelphoparasitism, (from Greek ἀδελφός ( adelphós ), brother ), also known as sibling-parasitism, occurs where the host species is closely related to the parasite, often in the same family or genus. In the citrus blackfly parasitoid, Encarsia perplexa , unmated females may lay haploid eggs in the fully developed larvae of their own species, producing male offspring, while

6750-523: The occurrence of flagellated cells in eukaryote groups, as specialized cells of multicellular organisms or as life cycle stages, is given below (see also the article flagellum ): In older classifications, flagellated protozoa were grouped in Flagellata (= Mastigophora ), sometimes divided into Phytoflagellata (= Phytomastigina, mostly autotrophic) and Zooflagellata (= Zoomastigina, heterotrophic). They were sometimes grouped with Sarcodina (ameboids) in

6840-462: The origins of multicellularity in animals. As the closest living relatives of animals, choanoflagellates serve as a useful model for reconstructions of the last unicellular ancestor of animals. According to a 2021 study, crown group craspedids (and perhaps crown group choanoflagellates if Acanthoecida arose within Craspedida) appeared 422.78 million years ago, Although a previous study from 2017 recovered

6930-479: The parasite, lives on or inside another organism, the host , causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson characterised parasites as "predators that eat prey in units of less than one". Parasites include single-celled protozoans such as the agents of malaria , sleeping sickness , and amoebic dysentery ; animals such as hookworms , lice , mosquitoes , and vampire bats ; fungi such as honey fungus and

7020-417: The point where, while they are evidently able to infect all other organisms from bacteria and archaea to animals, plants and fungi, it is unclear whether they can themselves be described as living. They can be either RNA or DNA viruses consisting of a single or double strand of genetic material ( RNA or DNA , respectively), covered in a protein coat and sometimes a lipid envelope. They thus lack all

7110-535: The population movements of the host–parasite groupings. The microorganisms and viruses that can reproduce and complete their life cycle within the host are known as microparasites. Macroparasites are the multicellular organisms that reproduce and complete their life cycle outside of the host or on the host's body. Much of the thinking on types of parasitism has focused on terrestrial animal parasites of animals, such as helminths. Those in other environments and with other hosts often have analogous strategies. For example,

7200-432: The possibility of a close relationship as early as 1841. Over the past decade, this hypothesized relationship between choanoflagellates and animals has been upheld by independent analyses of multiple unlinked genetic sequences: 18S rDNA, nuclear protein-coding genes, and mitochondrial genomes (Steenkamp, et al., 2006; Burger, et al., 2003; Wainright, et al., 1993). Importantly, comparisons of mitochondrial genome sequences from

7290-614: The presence of certain bacteria, trigger the swarming and subsequent sexual reproduction of choanoflagellates. The ploidy level is unknown; however, the discovery of both retrotransposons and key genes involved in meiosis previously suggested that they used sexual reproduction as part of their life cycle. Some choanoflagellates can undergo encystment, which involves the retraction of the flagellum and collar and encasement in an electron dense fibrillar wall. On transfer to fresh media, excystment occurs; though it remains to be directly observed. Evidence for sexual reproduction has been reported in

7380-475: The taxonomic group Flagellata was abandoned, the term "flagellate" is still used as the description of a level of organization and also as an ecological functional group . Another term used is "monadoid", from monad . as in Monas , and Cryptomonas and in the groups as listed above. The amoeboflagellates (e.g., the rhizarian genus Cercomonas , some amoebozoan Archamoebae , some excavate Heterolobosea ) have

7470-466: The testes of over two-thirds of their crab hosts degenerate sufficiently for these male crabs to develop female secondary sex characteristics such as broader abdomens, smaller claws and egg-grasping appendages. Various species of helminth castrate their hosts (such as insects and snails). This may happen directly, whether mechanically by feeding on their gonads, or by secreting a chemical that destroys reproductive cells; or indirectly, whether by secreting

7560-476: The trophic chain. Even today, they are important in the carbon cycle and microbial food web . There is some evidence that choanoflagellates feast on viruses as well. Choanoflagellates grow vegetatively, with multiple species undergoing longitudinal fission; however, the reproductive life cycle of choanoflagellates remains to be elucidated. A paper released in August 2017 showed that environmental changes, including

7650-403: The tropics, however effectively cheat by taking carbon from a fungus rather than exchanging it for minerals. They have much reduced roots, as they do not need to absorb water from the soil; their stems are slender with few vascular bundles , and their leaves are reduced to small scales, as they do not photosynthesize. Their seeds are small and numerous, so they appear to rely on being infected by

7740-506: The usual machinery of the cell such as enzymes , relying entirely on the host cell's ability to replicate DNA and synthesise proteins. Most viruses are bacteriophages , infecting bacteria. Parasitism is a major aspect of evolutionary ecology; for example, almost all free-living animals are host to at least one species of parasite. Vertebrates, the best-studied group, are hosts to between 75,000 and 300,000 species of helminths and an uncounted number of parasitic microorganisms. On average,

7830-585: The way that the CHV1 virus helps to control the damage that chestnut blight , Cryphonectria parasitica , does to American chestnut trees, and in the way that bacteriophages can limit bacterial infections. It is likely, though little researched, that most pathogenic microparasites have hyperparasites which may prove widely useful in both agriculture and medicine. Social parasites take advantage of interspecific interactions between members of eusocial animals such as ants , termites , and bumblebees . Examples include

7920-471: The world's most important food crops. Orobanche also threatens a wide range of other important crops, including peas , chickpeas , tomatoes , carrots , and varieties of cabbage . Yield loss from Orobanche can be total; despite extensive research, no method of control has been entirely successful. Many plants and fungi exchange carbon and nutrients in mutualistic mycorrhizal relationships. Some 400 species of myco-heterotrophic plants, mostly in

8010-547: Was published in 2006. The major finding of this transcriptome was the choanoflagellate Hoglet domain and shed light on the role of domain shuffling in the evolution of the Hedgehog signaling pathway . M. ovata has at least four eukaryotic meiotic genes. The transcriptome of Stephanoeca diplocostata was published in 2013. This first transcriptome of a loricate choanoflagellate led to the discovery of choanoflagellate silicon transporters. Subsequently, similar genes were identified in

8100-406: Was the morphology of their last common ancestor. The last common ancestor of animals and choanoflagellates was unicellular, perhaps forming simple colonies; in contrast, the last common ancestor of all eumetazoan animals was a multicellular organism, with differentiated tissues, a definite "body plan", and embryonic development (including gastrulation). The timing of the splitting of these lineages

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