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What Does Symbiosis Mean In Biology

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Commensalism: One Organism Benefits The Other Is Unharmed

What is Symbiosis?

Commensalistic relationships are those where one species receives all the benefit from its relationship with the other, but the other receives no benefit or harm. A good example of this type of relationship occurs between grazing cattle and cattle egrets. As the cattle graze in the grass, they stir up the insects living there, allowing the cattle egret a tasty meal. The cattle egrets get a meal, but the cattle receive nothing in return from the long-necked birds, nor are they harmed by the relationship.

Parasitism An Evolutionary Success Story

If one of the partners in the symbiosis discovers how to use the other effectively, it becomes a parasite. There is indeed a continuum between symbiosis and parasitism . The parasite exploits resources provided by another unrelated individual, the host, to the detriment of the latter. Parasitism is a long-lasting interaction with a host, unlike predation, where the interaction lasts only as long as the time of capture and digestion. However, from an evolutionary point of view, it can be said that predation is only an extreme form of parasitism. There are parasites that slowly kill their host. This is the case of plant parasitic fungi that complete their life cycle on dead tissues. When a cheetah grabs an antelope, there is an exchange of energy and only energy. In host parasite systems where the host survives , the duration of the interaction is quite different: the two organisms then live together, often one in the other, sometimes cell in cell or even genome within genome. The genetic information of each partner is expressed side by side and durably in a tiny portion of space .

Symbiosis: Definition Types And Examples

Content Curator| Updated On -Apr 5, 2022

Symbiosis is a developed interaction or close living relationship between organisms of different species that benefits one or both of the parties involved. Symbioses can be either obligate, in which the two species relationship is so dependent that neither can exist without the other or facultative in which the two species choose to form a symbiotic association and can survive on their own. Obligate symbioses are frequently long-lived, whereas facultative symbiosis are more recent behavioural adaptations given enough time, facultative symbiosis can evolve into obligate symbiosis.

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Symbiosis is a relationship between a single multicellular eukaryotic organism and one or more microorganisms, such as bacteria, viruses, eukaryotic microorganisms, or Archaea. The larger partner is commonly referred to as the host,’ while the smaller ones are referred to as symbionts.’ Whether the species benefit hurts or has no effect on one another, any association between two populations that live together is symbiotic.

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Various Types Of Symbiosis

Mutualism is a symbiosis between species in which both partners benefit. Mutualism is considered by some biologists to be the archetypal form of symbiosis. The examples of symbiosis that are discussed in the next section are all mutualisms.

Parasitism is another type of symbiotic association, in which one organism obtains nourishment from a host, usually without killing it. In most parasitisms, the parasite has a close and sometimes obligate relationship with the host. However, to be healthy, the host by no means needs the parasite, and in fact usually suffers a detriment from the symbiosis. Commensalism is a relationship in which one symbiont benefits from the interaction, while the host species is neither positively or negatively affected. For example, small epiphytic plants derive a substantial ecological benefit from living on larger plants, but the latter are not usually affected to a meaningful degree.

Examples Of Natural Symbioses

Symbiosis by Christian Klemkow

Most biologists, when confronted by the need to illustrate the concept of symbiotic mutualism, describe the case of lichens . Lichens are an obligate association between a fungus and an alga or blue-green bacterium . Lichen mutualisms are very distinctive, and they can be identified on the basis of the size, shape, color , and biochemistry of their biomass . Lichenologists have developed systematic and taxonomic treatments of lichens, even though these mutualisms are not true “organisms” in the conventionalmeaning of the word. The fungus benefits from the lichen mutualism through access to photosynthetic products of the alga or blue-green bacterium, while the phycobiont benefits from provision of a relatively moist habitat and enhanced access to inorganic nutrients .

Certain species of fungi also occur in intimate associations with the roots of vascular plants, in a mutualism referred to as mycorrhizae. The plant benefits from the mycorrhiza through increased access to inorganic nutrients, especially phosphate, while the fungus gains an advantage through access to nutritious exudates from the roots of the plant. This is a very widespread mutualismmost vascular plants have mycorrhizae.

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Parasitoidism: A Symbiotic Relationship Where The Host Dies

Science fiction is replete with examples of parasitoidism, but so is everyday life. In this type of symbiotic relationship, the host usually dies. Many science fiction movies feature this type of relationship between humans and aliens, like in the “Alien” movie series. In parasitoidism, the host serves as a home for the larvae of the parasite. As the larvae mature, they escape the body of the host, killing it in the process. In nature, braconid wasps lay their eggs atop the body of a tomato hornworm, and as the wasp larvae grow, they feed off the body of the hornworm, killing it during metamorphosis.

Symbiosis: The Art Of Living Together

Symbiosis is a term describing any relationship or interaction between two dissimilar organisms. The specific kind of symbiosis depends on whether either or both organisms benefit from the relationship.


Planet Earth is inhabited by millions of speciesâat least! Because different species often inhabit the same spaces and shareâor compete forâthe same resources, they interact in a variety of ways, known collectively as symbiosis. There are five main symbiotic relationships: mutualism, commensalism, predation, parasitism, and competition.

To explore these relationships, letâs consider a natural ecosystem such as the ocean. Oceanic environments are known for their species diversity. Imagine you are on a diving expedition to explore the worlds beneath the waves. If we were in the warm waters of the Pacific or Indian Oceans, weâd likely spot an excellent example of mutualism: the relationship between clownfish and sea anemones. In a mutualistic relationship, both species benefit. Sea anemones live attached to the surface of coral reefs. They trap their prey with stinging cells called nematocysts, which are located on their tentacles. Nematocysts release toxins when a small animal contacts an anemoneâs tentacle. This paralyzes the stung animal, allowing the anemone to easily bring the animal into its mouth for ingestion.

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Phoresy Relationships: Transport Hosts And Food Sources

A phoresy symbiotic relationship occurs when one organism lives on or near the body of another, but not as a parasite, and performs a beneficial service to the host and itself. A species of marine life, the remora fish, attach themselves to the bodies of whales, manta rays, sharks and turtles via sucking discs atop their heads. The remora, also called shark suckers, don’t harm the host nor take anything from it other than eating the parasitic sea creatures that infest it. Remora fish also use the disc to hitchhike a ride from the host. Oxpecker birds are common sites atop the backs of rhinoceros where they eat the parasites and ticks living there. They also fly in the air and scream when danger nears, providing a warning for the rhinoceros or zebra host.

B Classification Based On Impact On Symbiotic Partners

Types of Symbiosis (Mutualism, Commensalism, Parasitism)

Table 1 shows several types of symbioses based on the impact on the symbiotic partners.

Effect on Species A

From the table, we can derive five main categories of symbiotic relationships among organisms. They are:

  • . Neutralism is a lack of benefit or detriment experienced by either members of the pair of interacting organisms.
  • . Commensalism occurs when one member of the association benefits while the other is not affected. Type 0,+ includes phoresis, which is the transport of one species by another.
  • . Mutualism occurs when the symbiotic association is advantageous to both members of the pair.
  • . Parasitism is a situation in which the association is disadvantageous or destructive to one of the organisms and beneficial to the other.
  • . Amensalism is found when the association is disadvantageous to one member while the other is not affected.

There is one other theoretical category of biological interactions, but, if occurring, it would be rare and short-lived:

  • . Synnecrosis occurs when an interaction is detrimental to both species.

It is important to note that these interactions are not always static. In many cases, two species will interact differently under different conditions. This is particularly true in, but not limited to, cases where species have multiple, drastically different life stages.

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Competition: Where One Or Both Inhibit The Population Of The Other

Competition between species occurs when both entities vie for the same resources in the ecosystem. This type of symbiotic relationship works in reverse one or both organisms suffer because of the existence of each other. Invasive species upset the delicate balance in ecological communities when they procure the resources meant for the native organisms. Yellow starthistle, for example, a native species of Europe, more than likely hitched a ride to the U.S., where it invades ecological communities and pushes out natural grasses. Because starthistle is a rapid-growing plant, it roots suck up all the water and nutrients, stealing these resources from the natural grasses, which often wither and die. Even organisms of the same family can experience competition, like when the green anole lizard, a native of many Southern states, has to compete with the brown anole lizard for food sources and habitat, originally introduced to the region from Cuba.

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  • Margulis, L., and D. Sagan. 1986. Microcosmos: Four Billion Years of Evolution from Our Microbial Ancestors. New York: Summit Books.
  • Nair, S. 2005. Bacterial associations: Antagonism to symbiosis. In . Goa, India: National Institute of Oceanography, pp. 115-124.
  • O’Hara, A., and F. Shanahan. 2006. The gut flora as a forgotten organ. EMBO Rep 7: 688-93. PMID 16819463.
  • Sapp, J. 1994. Evolution by Association. Oxford University Press.

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Symbiosis And Animal Parasitism

Scientists estimate that up to 50% of all animal species are parasitic symbionts. Some phyla such as the Platyhelminthes, Nematoda, and Arthropoda contain large a number of parasitic species. Hosts and parasites have coevolved together and under natural conditions many have become mutually tolerant. Host organisms can live independently, but, in most cases, the parasite’s association with its host is obligatory. Animal parasites affect the health of humans and domesticated animals throughout the world. In most warm climates parasitic infections from flukes, nematodes, and arthropods greatly diminish the quality of life for people.

Helminths are widely distributed parasites of vertebrates. Infections caused by helminths such as schistosoma, hookworms, and filarial nematodes are a major cause of sickness of humans inhabiting the tropics. Helminths have complex lifecycles. They live for a long period within host animals, and they often possess a remarkable ability to evade the host’s defense mechanisms. The prevalence of helminthic infections in some areas is high however, only a few hosts develop disease. Helminths do not multiply in humans, and therefore the severity of the disease depends on the extent of the original infection. However, some helminthes may accumulate after repeated infection of a host.

Protocooperation Symbiosis: Not Obligatory But Beneficial To Both

Copy of Symbiotic by Sophia Harris

The clown fish and the anemone represent protocooperation symbiosis, a relationship that benefits both, but unlike the termite’s and its symbionts, both can survive independently of the other. The fish has a home within the fat, wavy arms of the anemone that protects the fish from predators the fish also protects the anemone from its predators and sometimes even brings it food.

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Sea Anemones And Jellyfish

The sea anemoneAnthopleura xanthogrammica, contains two types of symbiotic algae: zoochlorellae and zooxanthellae. The relative proportion of each algal symbiont in the animal depends on the water temperature. The anemones position themselves in ways to increase the exposure of their symbionts to light.

Cassiopea xamachana is a jellyfish that has been used to study how an invertebrate selects its algal symbionts. The lifecycle of Cassiopea includes a sexual medusoid stage, which contains algae that does not swim freely, but rather lies upside down in shallow waters, a behavioral adaptation that allows the algae in its tentacles to receive maximum daylight for photo-synthesis, and gives the animal its common name, the upside-down jellyfish.

Examples Of Symbiotic Parasites:

  • Symbiosis of fleas on dogs: this is an easily observed example and one which seriously annoys both pets and their owners. Fleas use the dog as a place to live and reproduce, as well as feeding on their blood. Dogs do not benefit in any way, but can develop diseases spread by the fleas.
  • Symbiosis of cuckoos and other birds: the cuckoo is a a bird which is a parasite as it abuses the nests of other bird species. When they arrive at a nest containing eggs, they displace them and then put in their own before leaving. When the original nesting bird returns, they rear the eggs without realizing they have been duped.

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Type : Partners Live As One Organism

nitrogenMonotropa unifloraflowering plantDardanus pedunculatusHermit crabanemones

This kind of symbiosis is called endosymbiosis. Examples are:

Almost for certain, this happened to form the eukaryotecell. That’s the type of cell all animals and plants are made of. The organelles inside the cell, such as mitochondria and chloroplasts, contain some DNA. This DNA is the remnant of a once separate bacterium. The theory is that the eukaryote cell evolved by the fusion of several bacteria or archaea organisms.

Defensive Symbiosis: A Mutualistic Relationship

Symbiosis: Mutualism, Commensalism, and Parasitism | The Biology Central | Ecology

The relationship between ants and aphids, for example is a mutualistic one defined as defensive symbiosis. The ant acts like shepherds over the aphids. Aphids provide honeydew for the ants, and the ants herd the aphids into their shelter at night for protection against predators, escorting them back outside in the morning. Some ant species are even known to take aphid eggs into the nest’s storage chambers during the cold winter months. Often called ant cattle, sometimes ants remove the wings from aphids to keep them from flying away. The ants may also release chemicals that cause the aphids to become more docile.

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Symbiotic Relationships Keep A Delicate Balance

The importance of symbiotic relationships to all living organisms on the Earth cannot be understated. All across the globe, in every ecological community in the world, from those viewable with the naked eye to those only seen under the lens of the microscope, symbiotic relationships remain crucial to maintaining balance in nature’s multiple processes.

Symbiotic relationships cross taxonomies and species and involve most all living creatures on the planet in some way or another. Symbiotic relationship help to provide people with food, populate the planet with trees and plants, and keep animal and plant populations in balance. Symbiotic relationships can help individual species to evolve or change and even thrive. Without symbiotic relationships, there would not be any coral reefs, trees might not proliferate as far and wide as they do, aided by the birds and insects that transport seeds afar, and even human beings might not have survived long enough to evolve into Homo sapiens Earth’s modern humans.

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Chemosynthesis: Tubeworms In Hydrothermal Vent Ecosystems

The mid ocean ridge system slices through the Pacific, Atlantic, Indian, and Southern Oceans and is home to most of the hydrothermal vent sites that have been studied. Miles down, these strange ecosystems have been known only since the 1970s.

Near ridge systems, cold, dense water on the ocean floor percolates into the earth’s crust and is heated by magma just below the surface, making it less dense and more buoyant. Now as hot as 400°C , the water surges up through the sea floor into the deep ocean, where the surrounding water is nearly freezing. Minerals dissolved in the plume precipitate to form chimneys called black smokers, which discharge thick clouds of suspended minerals into the water. A thriving community of animals surrounds the vent while it is active destined to cool eventually, the vent and its living community will die. It behooves vent animals to produce young which disperse regularly across the ocean floor, where some will chance upon other vent ecosystems during their ephemeral existence.

Hydrothermal vent ecosystems are models of very old and sheltered environments that may have been the least perturbed places on earth during mass extinctions. Asteroid impact, surface volcanism, and other causes of mass extinctions may have left the vent biota alone. In these migrating hotspots on the ocean floor, we may have the ancestors of some of the earliest life forms.

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Where To Learn More

“Biology 160, Animal Behavior: Symbiosis and Social Parasitism.” Department of Biology, University of California at Riverside . <> .

Knutson, Roger M. Furtive Fauna: A Field Guide to the Creatures Who Live on You.New York: Penguin Books, 1992.

Lanner, Ronald M. Made for Each Other: A Symbiosis of Birds and Pines.New York: Oxford University Press, 1996.

Lembke, Janet. Despicable Species: On Cowbirds, Kudzu, Hornworms, and Other Scourges.New York: Lyons Press, 1999.

Margulis, Lynn. Symbiotic Planet: A New Look at Evolu tion. New York: Basic Books, 1998.

Mutualism and Commensalism. Neartica: The Natural World of North America . <> .

“Parasites and Parasitism.” University of Wales, Aberystwyth . <> .

Sapp, Jan. Evolution by Association: A History of Symbiosis. New York: Oxford University Press, 1994.

Symbiosis and Commensalism. The Sea Slug Forum . <> .

Trager, William. Living Together: The Biology of Animal Parasitism. New York: Plenum Press, 1986.

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