What is symbiosis?
Symbiosis refers to when two different species live together. It is usually said that both species must benefit for it to be called symbiosis, but this is not really true. When both species benefit from the partnership, the symbiosis is called ”mutualistic”. A common example is symbiosis between plants and insects. Insects visit flowers and fruit trees to feed on nectar. When they crawl into the flower, they also bring pollen that sticks to their bodies or legs. Then, as they fly to the next flower of the same species, they spread pollen and help flowers and fruit trees reproduce.
A hover fly with pollen grains stuck on its body - an example of symbiosis between insects and plants.
Photo: Andre-Karwath-CC-BY-SA
A bee with filled pollen baskets on its hind legs. The cooperation between pollinating insects and plants is called mutualistic, since both plant and insect benefit from the symbiosis.
Photo: Marc-Andrighetti-CC-BY-SA
Leafcutter ants cut pieces of leaves and carry to their nest...
...to feed the fungi that the ants are cultivating in the nest. By growing tje fungi, the ants also get food.
Photo: Christian-R.-Linder-CC-BY-SA
Tree roots with mycorrhiza - a symbiotic relationship between trees and fungi.
Photo: Wilhelm-Zimmerling-CC-BY-SA
Orchids are completely dependant on symbiosis with fungi to survive.
Photo: Jose-Manuel-Lopez-Pinto-CC-BY-SA
Us humans live in symbiosis with many of the bacteria found in and on our bodies. We have bacteria in our mouths and intestines that help break down nutrients such as proteins, fats and carbohydrates. In the nose and on the skin, they protect against dangerous microorganisms.
Fungi in many partnerships
Some ants and species of fungi live in symbiosis. The leafcutter ant collects leaves for its nest. The leaves become food for the fungus that lives in the nest. The leafcutter ants in turn feed on the fungus. Plants and fungi often live in symbiosis. The roots of the plant and the fungal filaments (mycelium) exchange water and nutrients with each other. This is called mycorrhiza. Some plants, such as orchids, depend entirely on mycorrhiza for survival.
The clownfish has a protective layer of mucus on its skin, which makes it immune to the anemone's venom. The anemone is a perfect protection for the clownfish, as predators prefer to stay away from its venomous tentacles. The clownfish keeps the anemone clean by eating its leftover food, parasites, and wave fresh water over the anemone's tentacles.
Photo: Alexander-Vasenin-CC-BY-SA
Most species of pistol shrimp live in symbiosis with fish in the goby family. Because the shrimp has such poor eyesight, the fish keeps watch, while the shrimp digs out the burrow with its practical claws. Both the fish and the shrimp benefit from the collaboration.
Photo: Steve-Childs-CC-BY
The hermit crab cooperates with small sea anemones. They protect the crab from predators, and at the same time they get a ride on the shell and get a better chance of catching food.
Photo: Nick-Hobgood-CC-BY-SA
The clownfish and the anemone, the pistol shrimp and the goby
The clownfish, which you may have seen in the film Finding Nemo, lives in symbiosis with sea anemones. It is immune to the anemone’s venom, and lives protected from predatory fish that cannot tolerate this venom. The clownfish also feeds on the leftovers of the anemone’s meals. The clownfish in turn protects the sea anemone from parasites, and predators that want to eat it.
The pistol shrimp and the goby also work closely together. The pistol shrimp shovels sand from the common burrow, using its large claws. Meanwhile, the goby keeps watch. An important symbiosis for the pistol shrimp, which has poor eyesight but is an excellent shoveler, and for the goby, which is a poor shoveler, but an excellent guard!
The head louse lives as a parasite on human scalp, where it draws blood from its host.
Photo: Gilles-San-Martin-CC-BY-SA
Tape worms are parasitic worms living in the intestines of humans and other vertebrates.
Photo: Diphyllobothrium_Ta-Ntalas-CC-BY-SA
A ladybug guarding a parasitoid wasp's egg cocoon.
Photo: Gilles-San-Martin-CC-BY-SA
The tongue-eating louse is a parasitic crustation that gets inside a fish through the fish's gills, and eats the fish's tongue. By replacing the tongue with itself, the fish can continue living while the parasite eats blood and mucus from the fish.
Photo: Marco-Vinci-CC-BY-SA
An ant that died of a parasitic fungi infection.
Photo: Bernard-DUPONT-CC-BY-SA
Zombie ants and intestinal worms
Another form of symbiosis is parasitism. In this case, only one species benefits from the symbiosis, and the other is disadvantaged by being harmed, having difficulty reproducing or even dying. Some parasites are found on the outside of the body, such as lice, ticks and fleas. Others are found inside the body, such as intestinal parasites and tapeworms.
There is a parasitic wasp that lays its eggs inside ladybirds. The larvae feed on the body of the ladybird without damaging internal organs. The larvae then spin a cocoon under the ladybird and have it guard the cocoon until the larvae hatch.
There are several species of sac fungi that parasitise insects and ants. The spores of the parasitic fungus enter the ant’s body and change the ant’s behaviour so that it climbs up a tall tree where it will firmly attach itself by biting into the tree. The ant then dies and the fungus forces its way out of the ant’s body to spread its spores to new ants. The higher up the fungus releases its spores, the easier it is to infect more ants.