What a symbiotic relationship is

A relationship of mutual benefit or dependence; a close and often long-term interaction between two or more different biological species. The word symbiosis (from Ancient Greek ) was first used in 1877 to describe the mutualistic relationship in lichens. In 1879, the German mycologist Heinrich Anton de Bary defined it as “the living together of unlike organisms.

The definition of symbiosis is controversial among scientists.

Some believe symbiosis should only refer to persistent mutualisms, while others believe it should apply to any types of persistent biological interactions. Sometimes a symbiotic relationship benefits both species, sometimes one species benefits at the other’s expense, and in other cases neither species benefits.

Ecologists use a different term for each type of symbiotic relationship:

Mutualism -- both species benefit
Commensalism -- one species benefits, the other is unaffected
Parasitism -- one species benefits, the other is harmed
Competition -- neither species benefits
Neutralism -- both species are unaffected

Nature’s best examples of symbiosis

Resources or services that may be scarce for one organism may be cheap and easy for another to provide.

Biologist Cameron Currie from the University of Wisconsin in Madison, USA, cites bacteria cosily dwelling inside humans as a classic example.

“Our own bodies have hundreds or even thousands of species of symbiotic microbes inside them - we couldn’t survive without their beneficial effects,” he said.

Here are a few examples of symbiotic relationships between different species.

Sea anemones and hermit crabs

Sea anemones (Calliactus spp) hitchhike on the back of hermit crabs, scoring a ride across the seabed and extending their tentacles to eat the crab’s leftovers. Crabs actively recruit these passengers.

After poking an anemone with its pincers - causing it to release its grip from its current home - the crab holds it in place so the anemone can reattach to the crab’s own shell. In return, the anemones fend off hungry octopuses and other predators using their barbed tentacles. The crabs return the favour by driving away creatures that eat anemones, such as starfish and fireworms.

Goby fish and snapping shrimp

Danger! That’s what the frantically flapping tail of a goby fish says to the near-blind snapping shrimp (Alfeus spp). In a crafty collaboration, snapping shrimps construct and maintain burrows in the seabed, while the fish stands guard. During construction, shrimps leave the burrow to deposit excavated sand.

Throughout this hazardous venture, shrimps maintain constant contact with their gobies using their antennae. In some cases, gobies even hover above their shrimp, allowing it to take its load further from the burrow’s entrance. Sighting potential threats, the fish waggles its tail against the shrimps’ antennae or into the burrow entrance, warning the shrimp of the danger.

In return, the fish can call the burrow home, sleeping in it with the shrimp at night and using it as a convenient bolthole in the face of peril.

African oxpeckers and zebras

African oxpeckers (Buphagus africanus and Buphagus erythrorhynchus) feed on the backs of zebra, elephants, hippopotamuses and other large African animals. Once thought to be friendly tick-eating helpers, they’re actually vampire birds, sucking blood out of open tick-wounds. This shows how the line between symbiotic assistant and parasite can be blurred. Oxpeckers do eat ticks as well, and some animals may be happy to sacrifice a bit of blood for this service.

Oxpeckers may also be tolerated because they produce a hissing scream when startled - like a personal danger alarm.

Facts and pix: Internet.