In the Red Sea, a tiny fish has been cornered by a group of hunters working as a team. One of them chased it into a coral crevice, while the others circled around to block off any exists. With no escape, the predators – a group of yellow saddle goatfish – close in on their prey.
The goatfish are one of the few examples of fish that hunt in groups, and their strategy has just been described by Carine Strubin, Marc Steinegger and Redouan Bshary from the University of Neuchatel. Bshary has spent over a decade in the Red Sea, studying the local fish. “I spent a long time working on cleaner wrasses,” he says. “During that time, one happens to see a lot of things.”
The planet’s land plants are engaged in an ancient alliance with the so-called “AM fungi” that grow into their roots. One plant might be colonised by many fungi, and a single fungus could connect up to many plants. The fungi harvest nutrients like phosphorus and nitrogen from the soil and channel them to their hosts. In return, the plants provide the fungi with the sugars and carbohydrates they need to grow.
This symbiotic partnership covers the planet in green. It’s common to 80 percent of land plants, and is credited with driving the evolution of this group some 470 million years ago. Now, Toby Kiers from Vrije University in Amsterdam has found that plants and fungi have maintained their grand alliance by setting up a strong market economy.
Most life on this planet goes about their business as single cells. Only rarely do these singletons unite in cooperative societies, creating bigger and more complex living things, from trees to humans. This transition from single-celled to ‘multicellular’ life is one of the most important transitions in the evolution of life on Earth and it has happened many times over.
There are two main routes to a multicellular life. Single cells can merge together, and some modern species recap how this might have happened. Individual slime moulds join to form mobile slugs, while myxobacteria can merge into predatory swarms. Alternatively, cells can multiply but remain attached, staying united in their division. The choanoflagellates, possibly the closest living relatives of animals, can do this, creating simple colonies from single cells.
So we have a reasonable, if basic, understanding of how multicellular creatures first evolved. But we’re still largely in the dark about why. What benefit did cells gain from sticking together, rather than swimming solo? John Koschwanez from Harvard University thinks he has one answer: by sticking together, clumps of cells became better at foraging for nutrients. The multicellular life was a well-fed one.
The cleaner fish Laborides dimidiatus is cross between a janitor and a medic. It runs special “cleaning stations”, which other fish and ocean animals visit for a regular scrub. The cleaners remove parasites from their clients, even swimming into the open jaws of predators like moray eels and groupers. They’re like living toothbrushes and scrubs. And they work hard – every day, a single cleaner inspects over two thousand clients, and some clients visit the stations more than a hundred times a day.
The cleaners, and their relationships with their clients, make a classic case study for biologists studying the evolution of cooperation. The tiny fish clearly get benefits in the form of a meal, and they enjoy a sort of diplomatic immunity from otherwise hungry hunters. On the face of it, the clients also benefit by getting scrubbed of harmful parasites. Now, Peter Waldie from the University of Queensland has shown how important this hygiene is.
What happens when you dump 8,000 fire ants into a tray of water? Nathan Mlot from the Georgia Institute of Technology wanted to find out. Mlot scooped the ants into a beaker, swirled it around to roll them into a ball, and decanted them into a half-filled tray.
Over the next three minutes, the ball of ants slowly widened and flattened into a living, waterproof raft. By trapping air bubbles trapped among their interlocking bodies, the ants boosted their natural ability to repel water and kept themselves afloat. Humans build rafts by lashing together planks of wood or reeds; the fire ants do so by holding onto each other.
The experiment might seem odd, but it mirrors conditions that the fire ant (Solenopsis invicta) regularly has to cope with in its natural environment. The ant hails from the Brazilian rainforest floodplains of Argentina, where rising water regularly submerges their nests. They respond by weaving their own bodies into rafts. The ants also come together to construct bridges, ladders and walls, but the rafts are the longest-lasting of these living structures. In this form, they can float and sail for months.
In 1888, a biologist called Henry Orr was collecting spotted salamander eggs from a small, swampy pool when he noticed that some of them were green. He wrote, “The internal membrane of each egg was coloured a uniform light green by the presence in the membrane of a large number of minute globular green Algae.” Orr decided that the eggs “present a remarkable case of symbiosis.” The salamanders and the algae co-existed in a mutually beneficial relationship.
Orr was right that the two species have formed a partnership, but he was wrong in one crucial regard. He thought that the algae (Oophila amblystomatis) simply hung around next to the salamander embryos in the same egg. They don’t. More than 120 years later, Ryan Kerney from Dalhousie University has found that the algae actually invade the cells of the growing embryo, becoming part of its body.
With algae inside them, the salamanders become solar-powered animals, capable of directly harnessing the energy of the sun in the style of plants.
Meerkats already look like a textbook case of a cooperative social animal. They live in groups of up to 50 individuals. All of them help to dig and guard the community’s burrows. They babysit, feed and teach the colony’s pups, regardless of whose offspring they are. The society already seems like the model of altruism, but there is a way of making meerkats even more cooperative – injecting them with a hormone called oxytocin.
Two party leaders have to cooperate in a coalition government, despite their political differences. A referee and a linesman have to make a decision that could spell success or failure in an international sporting tournament. Two heads have to direct the same groovy body towards saving the galaxy. From politics to sport to interstellar hitchhiking, there are many situations that require two people to work together.
Now, Bahador Bahrami from the Interacting Minds Project has found evidence that two proverbial heads can indeed be better than one… but only under certain circumstances. Through a simple experiment where volunteers cooperated to find a hidden image in a screen, Bahrami found that pairs trump individuals if they freely discuss their disagreements, not just about what they saw but how confident they were in their decision.