Examples of Symbiosis
Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. Those animals established a commensal relationship with humans in which the animals benefited but the humans received little benefit or harm. Symbiosis is a relationship between two or more organisms that live closely together. There are several types or classes of symbiosis: Commensalism: One organism benefits and the other is neither harmed nor helped. Microbes May Help Drive Evolution In some species, the bacteria cause sexual incompatibility. symbiosis, a close relationship between two species that benefits at least one of the one species benefits and the other species is neither helped nor harmed.
Examples of Symbiosis Examples of Symbiosis Symbiosis is a relationship between two or more organisms that live closely together. There are several types or classes of symbiosis: Commensalism One organism benefits and the other is neither harmed nor helped.
Mutualism Both organisms benefit. An obligate mutualist cannot survive without its partner; a facultative mutualist can survive on its own. Parasitism One organism the parasite benefits and the other the host is harmed. To be successful, a symbiotic relationship requires a great deal of balance. Even parasitism, where one partner is harmed, is balanced so that the host lives long enough to allow the parasite to spread and reproduce.
These delicate relationships are the product of long years of co-evolution. Bacteria were the first living things on the planet, and all of Earth's other creatures have been living and evolving with them for hundreds of millions of years. Today, microbes are essential for many organisms' basic functions, including nourishment, reproduction, and protection.
Microbes Can Alter Behavior Toxoplasma is a parasitic protist that can infect a range of animals, including mice, rats, and people. But to reproduce sexually, it must infect a cat. In an amazing and complex relationship, the parasite enters the brain of infected rodents, where it changes the host's behavior, making it more likely to be caught and eaten by a cat! Mice infected with toxoplasma lose their fear of cats. They are more active, and more likely to spend time exploring open spaces. Still, the overall damage to the cactus is small.
The white-winged dove left has a mutualistic relationship with the Saguaro Cactus. The cactus provides food for the bird in the form of a large fruit. The bird consumes the fruit, also ingesting the cactus' seeds. The bird then flies off, and later deposits the seeds in a new location with a nice dose of fertilizer to boot! In this way, the cactus gets its seeds transported away from the parent plant, allowing it to potentially colonize new places. This type of mutualism is known as a dispersive mutualism.
The Cattle Egret below left is often seen in the company of grazing animals. The grazers stir up insects, which the egret then eats. This is probably a loose sort of commensalism; there is no apparent benefit to the cattle. The commensalism is loose because the egrets will follow any cattle; in Florida, in fact, I have seen them following mowers. On the other hand, the oxpecker not pictured is a bird that rides around on the backs of cattle and other large animals such as rhinos.
The oxpecker feeds on ectoparasites of the cattle such as ticks and warns the animals of approaching predators; thus both organisms benefit in a loose mutualism. On the other hand, the oxpeckers also pick at scabs and wounds on the animals and may ingest bits of flesh and blood thus making them more like parasites. The natural world is complicated! Symbiosis in the seas: Some of the best examples of symbiosis are found in the oceans - not surprising since life has had longer to evolve and form close associations in the oceans.
Above, the corals are perhaps the best example of a mutualistic symbiosis. Tiny coral animals which individually resemble this freshwater hydra form huge colonies, with each hydroid encased in stone secreted by the animals.
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Collectively, these colonies can grow very large. Brain coral above right typically forms huge colonies; the dark "boulder" to the left of the picture immediately right is actually a colony of brain coral that may be thousands of years old the fish is 5 feet long.
Each hydroid in turn may harbor cells of photosynthetic algae usually dinoflagellates ; these algal endosymbionts are called zooxanthellae and give the coral its brown or green appearance. As mentioned above, the zooxanthellae "trade" sugars for nutrients; it's convenient that the wastes of the coral CO2, ammonia, etc.
Interestingly, both the corals and the zooxanthellae can survive without the other at least for a while ; under conditions of stress the corals are known to expel the endosymbionts in a phenomenon known as coral bleaching.
Under happier times, the corals direct their growth to maximize sun exposure for their algal guests; you can see this clearly in the photo of the Elkhorn Coral above.
This jellyfish spends its time upside down in the shallows of mangrove swamps exposing its algal endosymbionts to the sun. Two other mutualistic symbioses found on the coral reef are pictured to the right, although they are not as tight as the endosymbioses of coral and zooxanthellae. In the photo to the right, a barracuda takes an unusual heads-up posture. He has arrived at the large brain coral, which makes a conspicuous landmark seamark?
When the barracuda takes this pose, the Cleaning Fish know it is safe for them to approach - the 'cuda is looking for a cleaning, not a meal. The tiny fish will scour the skin, mouth and gills of the Barracuda, removing any ectoparasites they find and getting a good meal out of it. There was a line of about 6 barracuda waiting to get cleaned here; the others were behind me in the line.
Finally, everyone who has seen "Finding Nemo" knows about the association between Clownfish and Anemones. By working its way carefully into the anemone, the clownfish gradually accustoms the anemone to the chemical makeup of the fish's skin; this gradual acclimatization prevents the anemone from stinging the clownfish while fish with a different "taste" will be stung and eaten. The fish gets a safe house and some tidbits; the anemone gets cleaned and has the clownfish working as lures to bring in potential prey, or chasing away fish that would harm the anemone.
Some scientists do not see any benefit for the anemone and classify this as a commensalism.
- Examples of Symbiosis
The Sea Lamprey, above left, is a sort of temporary parasite. It latches onto a fish and uses the teeth to hold on and rasp away the skin, leaving an open wound for the lamprey to feed on. It drops off, usually without killing the "host". Sea Lampreys are not specific on any species of fish; they will latch onto any living thing and try to feed. The wasp above has stung and paralyzed a spider. It will take the spider to a nest and lay an egg on it.
The larvae will consume the still-living spider; often from the inside. This is usually considered to be a parasitoid relationship. Two more mutualistic relationships from the Costa Rican forests. These algae help to camouflage the sloth against the lichen-covered tree note the brown fur of the baby, not yet covered with algae.
There is even a moth that lives only in the sloth's fur and consumes the algae; this is a commensal relationship between the moth and the sloth. Below, a mutualistic relationship.
The Acacia Tree is partially protected by large thorns, but it gets extra protection from Acacia Ants. The plant does 3 things to lure in the ants. First, the large thorns are hollow and provide a place for the ants to live. Second, the plants have swollen glands, nectaries, which produce a sugary solution the ants drink. The nectaries are obvious in the photo below. In return for the room and board the ants chase off herbivores, kill and eat herbivorous insects, and destroy and plants that try to compete with the acacia.
The horsehair worm starts life as an egg laid in a puddle.
The puddle dries out and a grasshopper or similar insect comes along and eats the egg, which promptly hatches and burrows through the gut of the insect into its body cavity or hemolymph. Here, surrounded by the nutritious blood of the insect it grows until it reaches adulthood. At that point it starts producing chemicals which take over the brain of the insect and cause the insect to seek out water, which it jumps into.
The worm then exits the hopper and lives in the puddle, mating and laying more eggs. The grasshopper, if it doesn't drown, may survive the ordeal. Below, a social parasite. This cricket lives in an ant nest. It disguises itself with a chemical signature that fools the ants into thinking it is just another ant.
It is free to roam the nest and it even gets the ants to feed it. The Brown-Headed Cowbirds above are nest parasites. They originally followed the bison on the Great Plains, feeding on insects kicked up by the large herds.
Since the bison themselves migrated, following the melting snows and eating the fresh spring grass, the cowbirds had to move as well. This presented a problem, as it's hard to incubate eggs on the move. Lay the eggs in other birds' nests, and trick the other birds into raising your young. The cowbirds hatch out first, push the other eggs out of the nest, and the nest-builders often much smaller than the rapidly growing cowbird end up feeding it instead of their own young.
Even though the other birds may pattern their eggs the cowbirds are up to the challenge. Cowbirds hesitate entering forests, but roads, farms, powerlines and other human intrusions give them a pathway deep into the woods where they are free to parasitize the nests of birds which until the arrival of humans didn't have to worry about the cowbirds.
Some of these bird species are on the verge of extinction as a result. Bromeliads left, above left avoid the hassle of crating a trunk to lift their leaves above the forest floor and closer to the sun. They simply grow on the branches of trees. Since the bromeliads don't take any nutrients from the trees this is usually classified as a commensalism, but if there are a lot of bromeliads left the tree will need to add extra wood to support the weight a bromeliad can trap up to 10 gallons 80 pounds of water in its leaves.
So, if there are a lot of bromeliads the relationship overall turns into a negative for the tree. The bromeliads also host a number of organisms in the water they trap; the wastes from the animals living there undoubtedly fertilizes the bromeliad in a mutualistic relationship. The tree at lower left is absolutely covered with epiphytes. Leeches below left are usually thought of as ectoparasites although some are predators.
They attach to a vertebrate host and take a blood meal before dropping off. Most aren't adapted to a single vertebrate host, but they are highly adapted to sucking blood; their saliva includes anesthetics to help keep the host from noticing the bite, as well as anticoagulants to keep the blood flowing.
Below is a larval mussel freshwater clam. If there is any case of "good" parasitism, this may be it. The little mussels go into the mouth and pass over the gills.
Here, they clamp down by closing the shell and digging in with the little teeth pictured at the edge of the shell.