Symbiosis: Some organisms just have to be together
Mutualism is the type of relationship that most people associate with symbiosis, with the most famous example being bees and flowers. Flowering plants, collectively known as angiosperms, are reliant on animals for pollination. Many angiosperms rely on bees, so they have evolved with attractive colors of smells to entice bees to them.
Flowers produce nectar, a sugary substance that bees feed on. While feeding, they inadvertently pick up pollen. Once they have had their fill from this plant, they move onto another to get more nectar, transferring the pollen from plant to plant in the process. Hopefully, this pollen will fertilize a plant of the same species, leading to the production of seeds. This is the perfect example of mutualism. Neither organism can live without the other.
Ants also provide examples of mutualism. While researching rhinos in Africa, I was shown a species of Acacia tree, commonly called the whistling thorn. It whistles because it has enlarged, hollow pods all over its branches that the wind blows through. While I was flicking the branches, simulating an herbivore such as a giraffe feeding, an army of ants stormed out of the pods ready to attack. In this example, the ants benefit by having a safe home, and the tree benefits from the protection that the ants provide.
Farmer ants have a remarkable symbiotic relationship with aphids. Aphids are tiny green insects, more commonly known as greenflies. Aphids produce a sweet, sugary substance from their anus that farmer ants feed on. Since the aphids produce this essential substance that the ants consume, the ants try and keep the aphids alive. Farmer ants protect aphids from predators and even keep their eggs warm in nests during winter. The aphids have an army of bodyguards; the ants have an endless supply of food.
Many large herbivores - such as rhinos, buffalos, and antelope - have a symbiotic relationship with birds, collectively known as ox-peckers. These ox-peckers perch on the backs of the animals while feeding off ticks and other parasitic creatures. The birds benefit from an easy meal, whereas the herbivores benefit from pest removal. An additional benefit is being alerted to predators. If a tiger was stalking a buffalo, the birds are more likely to see it first and will flee and squawk. This alerts the buffalo to an unseen danger, giving it early warning and allowing it to escape.
Some symbiotic relationships benefit only one party, which is called commensalism. The best example of this is the clown fish. As any young person knows from the animated movie, Nemo, that they live within the stinging tentacles of anemones. They have a layer of mucus covering their skin that makes them immune to the stinging cells of the anemone, allowing clown fish to live in a place that predators dare not venture. Although anemones do not benefit from this relationship, they aren't harmed by it. Meanwhile, the clown fish benefits enormously.
Another example is a tiny crustacean called a copepod that lives on the eyes of Greenland sharks. This tiny animal has two hooks that it attaches to the cornea of a shark's eyes. It moves around feeding on the surface of the eye, which can cause blindness. However, since Greenland sharks live in deep waters under the ice in darkness, they do not need use of their eyesight. The shark isn't really affected, but the copepod can't live without the shark.
There are many examples of the parasitic type of symbiosis. From fleas on dogs, to ringworm in cattle, to elephants stripping Acacia bark, parasitism is rife in the natural world.
A superb example, as we are nearing Christmas, is mistletoe. Mistletoe is a parasitic plant that lives on trees. It attaches itself to tree branches, where it "taps" into the plants vascular tissue; the cellular tubes that transport sugar and water around the plant. It then proceeds to extract water and nutrients from the plant. It doesn't need roots of its own because it steals from the host tree, which eventually leads to the tree's death.
All parasites need hosts, and hosts suffer as a result. In Africa, ticks were a common problem for me, personally. They fed on my blood, which could have given me serious diseases. All ticks are parasites. The list or parasitic blood-feeders also includes mosquitoes, leeches and vampire bats. The hosts suffer in this relationship and may even die as a result.
There are even genetic parasites. Viruses are parasites that use cells as hosts. They alter RNA in order to reproduce. Viruses can cause serious diseases in humans and other organisms. They cannot exist without hosts to exploit.
Symbiosis is everywhere
If you are reading this article with your pet dog or cat, you are enjoying a mutually symbiotic relationship right now. Pets survive because people feed them, while humans benefit from their companionship. If you have flowers in your garden that you are watering daily, while enjoying their smell and beauty, it is a symbiotic relationship. Right at this very moment, all over and in your body, bacteria are feeding on your dead skin cells and helping you digest your food. This is a type of symbiosis that you don't even notice, but you would not be alive to read this article without it.
David Canavan has an MSc in Behavioral Ecology and teaches science, math and ICT at Garden International School. David is fascinated by science and loves animals, especially the dangerous kind; the more dangerous the better. You may contact David at email@example.com .
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Last modified: October 19, 2007