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104-554: Parasitism is a close relationship between species , where one organism, 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
208-434: 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
312-510: 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
416-657: A channel for contamination of the host species with bacteria , viruses and blood-borne parasites contained in the hematophagous organism. Thus, many animal and human infectious diseases are transmitted by hematophagous species, such as the bubonic plague , Chagas disease , dengue fever , eastern equine encephalitis , filariasis , leishmaniasis , Lyme disease , malaria , rabies , sleeping sickness , St. Louis encephalitis , tularemia , typhus , Rocky Mountain spotted fever , West Nile fever , Zika fever , and many others. Insects and arachnids of medical importance for being hematophagous, at least in some species, include
520-627: 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
624-432: A feeding practice, hematophagy has evolved independently in a number of arthropod, annelid , nematode and mammalian taxa. For example, Diptera (insects with two wings, such as flies ) have eleven families with hematophagous habits (more than half of the 19 hematophagous arthropod taxa). About 14,000 species of arthropods are hematophagous, even including some genera that were not previously thought to be, such as moths of
728-402: A few shark species when exposed to cleaner fish. In this experiment, cleaner wrasse (Labroides dimidiatus) and various shark species were placed in a tank together and observed. The different shark species exhibited different responses and behaviors around the wrasse. For example, Atlantic and Pacific lemon sharks consistently react to the wrasse fish in a fascinating way. During the interaction,
832-605: A food resource. Hematophagy Hematophagy (sometimes spelled haematophagy or hematophagia ) is the practice by certain animals of feeding on blood (from the Greek words αἷμα haima "blood" and φαγεῖν phagein "to eat"). Since blood is a fluid tissue rich in nutritious proteins and lipids that can be taken without great effort, hematophagy is a preferred form of feeding for many small animals, such as worms and arthropods . Some intestinal nematodes , such as Ancylostomatids , feed on blood extracted from
936-593: 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
1040-507: A mammal species hosts four species of nematode, two of trematodes, and two of cestodes. Humans have 342 species of helminth parasites, and 70 species of protozoan parasites. Some three-quarters of the links in food webs include a parasite, important in regulating host numbers. Perhaps 40 per cent of described species are parasitic. Symbiosis Symbiosis ( Ancient Greek συμβίωσις symbíōsis : living with, companionship < σύν sýn : together; and βίωσις bíōsis : living)
1144-507: A medieval Latin word meaning sharing food, formed from com- (with) and mensa (table). Commensal relationships may involve one organism using another for transportation ( phoresy ) or for housing ( inquilinism ), or it may also involve one organism using something another created, after its death ( metabiosis ). Examples of metabiosis are hermit crabs using gastropod shells to protect their bodies, and spiders building their webs on plants . Mutualism or interspecies reciprocal altruism
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#17327905749571248-830: 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
1352-630: 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
1456-430: 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
1560-536: 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
1664-571: 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
1768-491: A specific pollinator that is correspondingly adapted. The first flowering plants in the fossil record had relatively simple flowers. Adaptive speciation quickly gave rise to many diverse groups of plants, and, at the same time, corresponding speciation occurred in certain insect groups . Some groups of plants developed nectar and large sticky pollen, while insects evolved more specialized morphologies to access and collect these rich food sources. In some taxa of plants and insects,
1872-429: 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
1976-407: A supreme situation, the host species (fish or marine life) will display itself at a designated station deemed the "cleaning station". Cleaner fish play an essential role in the reduction of parasitism on marine animals. Some shark species participate in cleaning symbiosis, where cleaner fish remove ectoparasites from the body of the shark. A study by Raymond Keyes addresses the atypical behavior of
2080-1036: 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
2184-469: 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 ,
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#17327905749572288-472: 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,
2392-560: 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
2496-459: Is a long-term relationship between individuals of different species where both individuals benefit. Mutualistic relationships may be either obligate for both species, obligate for one but facultative for the other, or facultative for both. Many herbivores have mutualistic gut flora to help them digest plant matter, which is more difficult to digest than animal prey. This gut flora comprises cellulose-digesting protozoans or bacteria living in
2600-580: Is a mainstay food of the African Maasai . Many places around the world eat blood sausage . Some societies, such as the Moche , had ritual hematophagy, as well as the Scythians , a nomadic people of Eastern Europe , who drank the blood of the first enemy they killed in battle . Psychiatric cases of patients performing hematophagy also exist. Sucking or licking one's own blood from a wound to clean it
2704-667: 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,
2808-416: Is an exploitative three-party interaction where one species, the mimic, has evolved to mimic another, the model, to deceive a third, the dupe. In terms of signalling theory , the mimic and model have evolved to send a signal; the dupe has evolved to receive it from the model. This is to the advantage of the mimic but to the detriment of both the model, whose protective signals are effectively weakened, and of
2912-527: Is any symbiotic relationship in which one symbiont lives within the tissues of the other, either within the cells or extracellularly. Examples include diverse microbiomes : rhizobia , nitrogen-fixing bacteria that live in root nodules on legume roots; actinomycetes , nitrogen-fixing bacteria such as Frankia , which live in alder root nodules; single-celled algae inside reef-building corals ; and bacterial endosymbionts that provide essential nutrients to about 10%–15% of insects. In endosymbiosis,
3016-429: Is any symbiotic relationship in which the symbiont lives on the body surface of the host , including the inner surface of the digestive tract or the ducts of exocrine glands . Examples of this include ectoparasites such as lice ; commensal ectosymbionts such as the barnacles , which attach themselves to the jaw of baleen whales ; and mutualist ectosymbionts such as cleaner fish . Contrastingly, endosymbiosis
3120-544: Is any type of a close and long-term biological interaction , between two organisms of different species . The two organisms, termed symbionts , can be either in a mutualistic , a commensalistic , or a parasitic relationship. In 1879, Heinrich Anton de Bary defined symbiosis as "the living together of unlike organisms". The term is sometimes more exclusively used in a restricted, mutualistic sense, where both symbionts contribute to each other's subsistence. Symbiosis can be obligatory , which means that one, or both of
3224-442: 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
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3328-431: Is damaged or killed by another through a chemical secretion. An example of competition is a sapling growing under the shadow of a mature tree. The mature tree can rob the sapling of necessary sunlight and, if the mature tree is very large, it can take up rainwater and deplete soil nutrients. Throughout the process, the mature tree is unaffected by the sapling. Indeed, if the sapling dies, the mature tree gains nutrients from
3432-461: Is evidence that RNA from host species may also be taken up and have regulatory consequences in blood feeding insects. A study on the yellow fever mosquito Aedes aegypti has shown that human blood microRNA has-miR-21 are taken up during blood feeding and transported into the fat body tissues. Once in the fat body they target and regulate mosquito genes such as vitellogenin , which is a yolk protein used for egg production. The phlebotomic action opens
3536-639: 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 ,
3640-410: Is known as co-development. In cases of co-development the symbionts send signals to their host which determine developmental processes. Co-development is commonly seen in both arthropods and vertebrates. One hypothesis for the origin of the nucleus in eukaryotes (plants, animals, fungi, and protists ) is that it developed from a symbiogenesis between bacteria and archaea. It is hypothesized that
3744-585: 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
3848-419: 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
3952-590: Is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their propagules, including both abiotic vectors such as the wind and living ( biotic ) vectors like birds. In order to attract animals, these plants evolved a set of morphological characters such as fruit colour, mass, and persistence correlated to particular seed dispersal agents. For example, plants may evolve conspicuous fruit colours to attract avian frugivores, and birds may learn to associate such colours with
4056-572: Is the relationship between the siboglinid tube worms and symbiotic bacteria that live at hydrothermal vents and cold seeps . The worm has no digestive tract and is wholly reliant on its internal symbionts for nutrition. The bacteria oxidize either hydrogen sulfide or methane, which the host supplies to them. These worms were discovered in the late 1980s at the hydrothermal vents near the Galapagos Islands and have since been found at deep-sea hydrothermal vents and cold seeps in all of
4160-468: 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
4264-422: The globe by combat , but by networking ." About 80% of vascular plants worldwide form symbiotic relationships with fungi, in particular in arbuscular mycorrhizas . Flowering plants and the animals that pollinate them have co-evolved. Many plants that are pollinated by insects (in entomophily ), bats , or birds (in ornithophily ) have highly specialized flowers modified to promote pollination by
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4368-420: The sandfly , blackfly , tsetse fly , bedbug , assassin bug , mosquito , tick , louse , mite , midge , and flea . Hematophagous organisms have been used by physicians for beneficial purposes ( hirudotherapy ). Some doctors now use leeches to prevent the clotting of blood on some wounds following surgery or trauma. The anticoagulants in the laboratory-raised leeches' saliva keeps fresh blood flowing to
4472-503: 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
4576-407: The tentacles of Ritteri sea anemones . The territorial fish protects the anemone from anemone-eating fish, and in turn, the anemone stinging tentacles protect the clownfish from its predators . A special mucus on the clownfish protects it from the stinging tentacles. A further example is the goby , a fish which sometimes lives together with a shrimp . The shrimp digs and cleans up a burrow in
4680-511: 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
4784-440: The 21st century, the latter has become the definition widely accepted by biologists. In 1949, Edward Haskell proposed an integrative approach with a classification of "co-actions", later adopted by biologists as "interactions". Relationships can be obligate, meaning that one or both of the symbionts entirely depend on each other for survival. For example, in lichens , which consist of fungal and photosynthetic symbionts,
4888-458: 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
4992-709: 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
5096-432: The average mammal species is host to 4 nematodes, 2 cestodes, and 2 trematodes. Mimicry is a form of symbiosis in which a species adopts distinct characteristics of another species to alter its relationship dynamic with the species being mimicked, to its own advantage. Among the many types of mimicry are Batesian and Müllerian, the first involving one-sided exploitation, the second providing mutual benefit. Batesian mimicry
5200-585: The capillaries of the gut, and about 75 percent of all species of leeches (e.g., Hirudo medicinalis ) are hematophagous. The spider Evarcha culicivora feeds indirectly on vertebrate blood by specializing on blood-filled female mosquitoes as their preferred prey. Some fish , such as lampreys and candirus ; mammals , especially vampire bats ; and birds, including the vampire finch , Hood mockingbird , Tristan thrush , and oxpeckers , also practise hematophagy. Hematophagous animals have mouth parts and chemical agents for penetrating vascular structures in
5304-411: The competition can also be for other resources. Amensalism is a non-symbiotic, asymmetric interaction where one species is harmed or killed by the other, and one is unaffected by the other. There are two types of amensalism, competition and antagonism (or antibiosis). Competition is where a larger or stronger organism deprives a smaller or weaker one of a resource. Antagonism occurs when one organism
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#17327905749575408-467: The decaying sapling. An example of antagonism is Juglans nigra (black walnut), secreting juglone , a substance which destroys many herbaceous plants within its root zone. The term amensalism is often used to describe strongly asymmetrical competitive interactions, such as between the Spanish ibex and weevils of the genus Timarcha which feed upon the same type of shrub. Whilst the presence of
5512-860: 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
5616-621: The dupe, which is deprived of an edible prey. For example, a wasp is a strongly-defended model, which signals with its conspicuous black and yellow coloration that it is an unprofitable prey to predators such as birds which hunt by sight; many hoverflies are Batesian mimics of wasps, and any bird that avoids these hoverflies is a dupe. In contrast, Müllerian mimicry is mutually beneficial as all participants are both models and mimics. For example, different species of bumblebee mimic each other, with similar warning coloration in combinations of black, white, red, and yellow, and all of them benefit from
5720-848: The endosymbiont adapts to the host's lifestyle, the endosymbiont changes dramatically. There is a drastic reduction in its genome size, as many genes are lost during the process of metabolism , and DNA repair and recombination, while important genes participating in the DNA-to-RNA transcription , protein translation and DNA/RNA replication are retained. The decrease in genome size is due to loss of protein coding genes and not due to lessening of inter-genic regions or open reading frame (ORF) size. Species that are naturally evolving and contain reduced sizes of genes can be accounted for an increased number of noticeable differences between them, thereby leading to changes in their evolutionary rates. When endosymbiotic bacteria related with insects are passed on to
5824-406: 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 ,
5928-490: 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
6032-557: The fact that mitochondria and chloroplasts divide independently of the cell, and that these organelles have their own genome. The biologist Lynn Margulis , famous for her work on endosymbiosis , contended that symbiosis is a major driving force behind evolution . She considered Darwin 's notion of evolution, driven by competition, to be incomplete and claimed that evolution is strongly based on co-operation , interaction , and mutual dependence among organisms. According to Margulis and her son Dorion Sagan , " Life did not take over
6136-440: 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
6240-415: The fungal partners cannot live on their own. The algal or cyanobacterial symbionts in lichens, such as Trentepohlia , can generally live independently, and their part of the relationship is therefore described as facultative (optional), or non-obligate. When one of the participants in a symbiotic relationship is capable of photosynthesis, as with lichens, it is called photosymbiosis. Ectosymbiosis
6344-474: The generation of phenotypic diversity and complex phenotypes able to colonise new environments. Evolution originated from changes in development where variations within species are selected for or against because of the symbionts involved. The hologenome theory relates to the holobiont and symbionts genome together as a whole. Microbes live everywhere in and on every multicellular organism. Many organisms rely on their symbionts in order to develop properly, this
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#17327905749576448-556: The genus Calyptra . Hematophagy in insects, including mosquitoes, is thought to have arisen from phytophagous or entomophagous origins. Several complementary biological adaptations for locating the hosts (usually in the dark, as most hematophagous species are nocturnal and silent to avoid detection) have also evolved, such as special physical or chemical detectors for sweat components , CO 2 , heat, light, movement, etc. In addition to these biological adaptations that have evolved to help blood-feeding arthropods locate hosts, there
6552-419: The herbivores' intestines. Coral reefs result from mutualism between coral organisms and various algae living inside them. Most land plants and land ecosystems rely on mutualism between the plants, which fix carbon from the air, and mycorrhyzal fungi, which help in extracting water and minerals from the ground. An example of mutualism is the relationship between the ocellaris clownfish that dwell among
6656-424: 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
6760-427: The host cell lacks some of the nutrients which the endosymbiont provides. As a result, the host favors endosymbiont's growth processes within itself by producing some specialized cells. These cells affect the genetic composition of the host in order to regulate the increasing population of the endosymbionts and ensure that these genetic changes are passed onto the offspring via vertical transmission ( heredity ). As
6864-439: 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
6968-420: 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
7072-452: 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
7176-651: 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
7280-424: 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
7384-475: 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
7488-423: 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
7592-472: 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
7696-467: 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
7800-439: 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
7904-577: 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
8008-533: 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
8112-436: The mouth to examine the gills, specifically the buccopharyngeal area, which typically holds the most parasites. When the shark begins to close its mouth, the wrasse finishes its examination and goes elsewhere. Male bull sharks exhibit slightly different behavior at cleaning stations: as the shark swims into a colony of wrasse fish, it drastically slows its speed to allow the cleaners to do their job. After approximately one minute,
8216-403: 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
8320-463: The non-essential genes of the intracellular bacteria. This can be due to lack of selection mechanisms prevailing in the relatively "rich" host environment. Competition can be defined as an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource (such as food , water , and territory ) used by both usually facilitates this type of interaction, although
8424-508: The offspring strictly via vertical genetic transmission, intracellular bacteria go across many hurdles during the process, resulting in the decrease in effective population sizes, as compared to the free-living bacteria. The incapability of the endosymbiotic bacteria to reinstate their wild type phenotype via a recombination process is called Muller's ratchet phenomenon. Muller's ratchet phenomenon, together with less effective population sizes, leads to an accretion of deleterious mutations in
8528-417: 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
8632-532: 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,
8736-410: The relationship has become dependent, where the plant species can only be pollinated by one species of insect. The acacia ant ( Pseudomyrmex ferruginea ) is an obligate plant ant that protects at least five species of "Acacia" ( Vachellia ) from preying insects and from other plants competing for sunlight, and the tree provides nourishment and shelter for the ant and its larvae. Seed dispersal
8840-599: The relationship. Cleaning symbiosis is an association between individuals of two species, where one (the cleaner) removes and eats parasites and other materials from the surface of the other (the client). It is putatively mutually beneficial, but biologists have long debated whether it is mutual selfishness, or simply exploitative. Cleaning symbiosis is well known among marine fish, where some small species of cleaner fish – notably wrasses , but also species in other genera – are specialized to feed almost exclusively by cleaning larger fish and other marine animals. In
8944-456: The saliva of several hematophagous species, such as leeches ( hirudin ). Hematophagy is classified as either obligatory or facultative . Obligatory hematophagous animals cannot survive on any other food. Examples include Rhodnius prolixus , a South American assassin bug , and Cimex lectularius , the human bed bug. Facultative hematophages, meanwhile, acquire at least some portion of their nutrition from non-blood sources in at least one of
9048-439: The sand in which both the shrimp and the goby fish live. The shrimp is almost blind, leaving it vulnerable to predators when outside its burrow. In case of danger, the goby touches the shrimp with its tail to warn it, and both quickly retreat into the burrow. Different species of gobies ( Elacatinus spp. ) also clean up ectoparasites in other fish, possibly another kind of mutualism. A spectacular example of obligate mutualism
9152-497: The sexually mature forms. Examples of this include many mosquito species, such as Aedes aegypti , whose both males and females feed on pollen and fruit juice for survival, but the females require a blood meal to produce their eggs. Fly species such as Leptoconops torrens can also be facultative hematophages. In anautogenous species, the female can survive without blood but must consume blood in order to produce eggs (obligatory hematophages are by definition also anautogenous). As
9256-409: The shark remains passive and the wrasse swims to it. It begins to scan the shark's body, sometimes stopping to inspect specific areas. Commonly, the wrasse would inspect the gills, labial regions, and skin. When the wrasse makes its way to the mouth of the shark, the shark often ceases breathing for up to two and a half minutes so that the fish is able to scan the mouth. Then, the fish passes further into
9360-497: The shark returns to normal swimming speed. Symbiosis is increasingly recognized as an important selective force behind evolution; many species have a long history of interdependent co-evolution . Although symbiosis was once discounted as an anecdotal evolutionary phenomenon, evidence is now overwhelming that obligate or facultative associations among microorganisms and between microorganisms and multicellular hosts had crucial consequences in many landmark events in evolution and in
9464-411: The site of an injury, actually preventing infection and increasing chances of full recovery. In a recent study a genetically engineered drug called desmoteplase based on the saliva of Desmodus rotundus (a vampire bat) was shown to improve recovery in stroke patients. Many human societies also drink blood or use it to manufacture foodstuffs and delicacies. Cow blood mixed with milk , for example,
9568-488: The skin of hosts , mostly of mammals, birds, and fish. This type of feeding is known as phlebotomy (from the Greek words, phleps "vein" and tomos "cutting"). Once phlebotomy is performed (in most insects by a specialized fine hollow "needle", the proboscis , which perforates skin and capillaries ; in bats by sharp incisor teeth that act as a razor to cut the skin), blood is acquired either by sucking action directly from
9672-447: The symbionts depend on each other for survival, or facultative (optional), when they can also subsist independently. Symbiosis is also classified by physical attachment. Symbionts forming a single body live in conjunctive symbiosis, while all other arrangements are called disjunctive symbiosis. When one organism lives on the surface of another, such as head lice on humans, it is called ectosymbiosis ; when one partner lives inside
9776-451: The symbiosis originated when ancient archaea, similar to modern methanogenic archaea, invaded and lived within bacteria similar to modern myxobacteria, eventually forming the early nucleus. This theory is analogous to the accepted theory for the origin of eukaryotic mitochondria and chloroplasts, which are thought to have developed from a similar endosymbiotic relationship between proto-eukaryotes and aerobic bacteria. Evidence for this includes
9880-466: 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
9984-773: The tissues of another, such as Symbiodinium within coral , it is termed endosymbiosis . The definition of symbiosis was a matter of debate for 130 years. In 1877, Albert Bernhard Frank used the term symbiosis to describe the mutualistic relationship in lichens . In 1878, the German mycologist Heinrich Anton de Bary defined it as "the living together of unlike organisms". The definition has varied among scientists, with some advocating that it should only refer to persistent mutualisms , while others thought it should apply to all persistent biological interactions (in other words, to mutualism, commensalism , and parasitism , but excluding brief interactions such as predation ). In
10088-403: 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
10192-502: 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,
10296-479: The veins or capillaries, from a pool of escaped blood, or by lapping (again, in bats). To overcome natural hemostasis (blood coagulation), vasoconstriction , inflammation, and pain sensation in the host, hematophagous animals have evolved chemical solutions, in their saliva for instance, that they pre-inject—and anesthesia and capillary dilation have evolved in some hematophagous species. Scientists have developed anticoagulant medicines from studying substances in
10400-588: 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
10504-474: The weevil has almost no influence on food availability, the presence of ibex has an enormous detrimental effect on weevil numbers, as they consume significant quantities of plant matter and incidentally ingest the weevils upon it. Commensalism describes a relationship between two living organisms where one benefits and the other is not significantly harmed or helped. It is derived from the English word commensal , used of human social interaction . It derives from
10608-470: 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
10712-433: The world's oceans. Mutualism improves both organism's competitive ability and will outcompete organisms of the same species that lack the symbiont. A facultative symbiosis is seen in encrusting bryozoans and hermit crabs . The bryozoan colony ( Acanthodesia commensale ) develops a cirumrotatory growth and offers the crab ( Pseudopagurus granulimanus ) a helicospiral-tubular extension of its living chamber that initially
10816-440: Was situated within a gastropod shell. In a parasitic relationship, the parasite benefits while the host is harmed. Parasitism takes many forms, from endoparasites that live within the host's body to ectoparasites and parasitic castrators that live on its surface and micropredators like mosquitoes that visit intermittently. Parasitism is an extremely successful mode of life; about 40% of all animal species are parasites, and
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