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Aphids and the bacterium Buchnera aphidicola

These small, sap-sucking insects are the bane of rose-growers everywhere. But despite the rest of the world’s general disdain for these critters, there is one species that truly couldn’t live without them.

The bacterium Buchnera aphidicola lives in specialised cells within the body of aphids. B. aphidicola allows the aphids to eat an extremely limited diet of sap – which lacks essential amino acids – by synthesising these vital amino acids themselves and gifting them to their six-legged hosts. Neither partner can reproduce successfully without the presence of the other, ensuring their relationship remains extremely exclusive.

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Acacia ants and the acacia plant

Two of nature’s most compatible roommates, the acacia ant (Pseudomyrmex sp.) and the acacia plant (Acacia drepanolobium), are so close they even share the same name.

The plant provides the ants with food and accommodation, and in return, the ants act as a security system, protecting the plant from potential predators.

Research suggests that the ants also pull their weight by helping to keep the tree disease-free. The ants are thought to play host to bacteria which prevent harmful pathogens from growing on the leaves of the acacia plant.

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Yucca moths and the yucca plant

Known commonly as the Spanish Dagger, the yucca plant’s (Yucca torreyi) fiery relationship with the yucca moth (Tegeticula yuccasella) depends on the moth pollinating the plant, while the plant provides the moth’s progeny with a food source.

But in this relationship of deadly passion, the yucca plant is able to kill the eggs of its pollinating partner if it senses the moth becoming too greedy.

In order to ensure that the moth doesn’t become a self-serving companion, the yucca plant can abort the development of its own flowers if they’re burdened by too many moth eggs.

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Zooxanthellae algae and hard, reef-building coral

The epitome of a supportive partner, the algae zooxanthellae is responsible for crafting the reef-building coral we know today and may hold the key to protecting it in the future. Hard corals provide the algae with a safe home to live in, while algae act as photosynthesising powerhouses, converting sunlight into energy and oxygen for the coral to use.

Research suggests that these algae could play a critical role in protecting coral reefs in the face of climate change. The different families of zooxanthellae living within the coral are thought to be able to shuffle themselves around in order to provide the coral with the algae best able to protect it from warming waters.

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Fig wasps and fig trees

Taking the meaning of “long-term relationship” to new heights, fig wasps (Pegoscapus sp.) and fig trees (Ficus costaricana) have been depending on each other for the last 65 million years. Female wasps lay their eggs in the flowers of fig trees before injecting the flower with special chemicals to transform it into a gall.

This gall acts to protect the young wasps inside. When the offspring eventually chew their way out, the female wasps can transfer pollen from one fig tree to another, facilitating the tree’s reproduction.

The relationship is so tight that it’s even thought to be ingrained in wasp’s DNA. Research suggests that fig wasps possess very few genes involved in detoxification, probably because the wasps are so well protected by the fig trees that they simply don’t need them.

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The tsetse fly and the bacterium Wigglesworthia glossinidia

A tiny villain, the tsetse fly (Glossina) is the sole vector responsible for transmitting a condition known as human African trypanosomiasis, or sleeping sickness, which affects tens of thousands of people each year. This vector-borne parasitic disease affects the central nervous system, which can prove fatal.

But this little fly has a weakness; it depends on a bacterium known as Wigglesworthia glossinidia to survive. Feeding solely on blood, the fly relies on the bacteria’s ability to synthesise vital vitamins it needs to survive. Researchers are attempting to target this bacterium in order to stop the flies from transmitting the deadly disease.

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Leafcutter ants and their fungus garden

While it might seem as though these ants are snip leaves to feed themselves, they are actually using them to feed another organism entirely. Leafcutter ants (Atta colombica) carry leaves to their colonies, where they are used as a food source for a fungus, which the ants then feed on.

In this way, the ants are able to transform an inedible food source into one they can eat, while the fungus gets its very own butler. The ants worship this fungus, keeping it safe from contaminants, removing weeds and even cleaning themselves before they touch it.