Microbes are savvy when contributing to the common good

May 9, 2018 by Bex Caygill, University College London
Slime moulds exist as single-celled organisms but come together cooperatively to form a fruiting body. Credit: Usman Bashir

Microbes vary their contribution to a community to maximise the return on their investment according to a new study led by UCL and the University of Bath.

Scientists made the discovery while investigating one of the fundamental questions in biology – why individuals have evolved to cooperate rather than simply exploiting the contributions of their rivals.

The study, published in PNAS, found that when are in groups mostly made up of their relatives, they contribute heavily to , which benefits the . In contrast, when they are in a group outnumbered by unrelated individuals, they exploit the contributions of the others.

Author Professor Chris Thompson, (UCL Centre for Life's Origin and Evolution and UCL Division of Biosciences), explained: "This research throws new light on the evolution and maintenance of cooperation. Cooperation is fundamental to the success of most organisms on the planet, from microbes to humans. However, understanding why cheaters do not invade and collapse cooperative systems still remains a puzzle."

The team studied the social amoeba Dictyostelium discoideum or slime mould. Slime moulds live in the soil as single-celled organisms, but come together to form a slug-like creature when they run out of food.

The newly formed slug will eventually form a fruiting composed of a stem and spores. This process requires cooperation between the individual amoebae to form a successful fruiting body.

The scientists investigated what factors caused the individual amoebae to "choose" whether to sacrifice themselves to form the stem of the fruiting body for the collective good, or to exploit the contribution of others and form spores that would go on to reproduce.

Traditionally biologists trying to solve this puzzle labelled individuals as either co-operators or cheaters. However, this study shows that even simple microbes follow the economic principles of collective investment, varying their contribution depending on how much stake they have in the success of the fruiting body.

"Many attempts to solve this problem rely on the assumption that individuals can either 'cheat' or 'cooperate'. In these cases, cheating would usually the best strategy and thus cooperation collapses, an idea demonstrated by games such as the Prisoner's Dilemma," explained Professor Thompson.

"Our studies demonstrate a solution to the problem, because an even better strategy is to cheat if you can get away with it and cause little damage to group success. However, if group success would be compromised, individuals should change their strategy and cooperate, which helps stabilise cooperation. The fact that we observe this behaviour in a simple microbe is truly remarkable."

Author Professor Jason Wolf (Milner Centre for Evolution at the University of Bath), explained: "Our research shows that even the simplest microbe can act like a savvy investor. Rather than being labelled as either cheaters or co-operators, each individual can potentially benefit from varying their level of investment into cooperation depending on the investments of others.

"If one person has an 80 per cent share of a company and another has a 20 per cent share, it makes economic sense for the person with 80 per cent to invest more than the other person because they have more at stake if the project fails.

"In a similar way, microbes with one genotype invest more resources in making the stalk if most of the others in the group share the same genes. If they don't invest, they have more to lose because their stake is larger. Microbes of a minority genotype have less to lose if the fruiting body fails so go for maximum return by forming spores."

The researchers found that an equal mixture of two phenotypes led to neither group investing sufficiently, creating a fruiting body that collapsed under its own weight.

Explore further: Why slimy cheats don't win

More information: Strategic investment explains patterns of cooperation and cheating in a microbe. PNAS May 7, 2018. doi.org/10.1073/pnas.1716087115

Related Stories

Why slimy cheats don't win

March 31, 2015

Darwin's evolutionary theory predicts survival of the fittest. So why do different survival tactics co-exist, if evolution should always favour the winning strategy?

Study to find out why you're a slime ball

June 28, 2005

A University of Manchester scientist has been awarded £150,000 to study slime! But this is no ordinary slime, says biologist Chris Thompson, who believes it could unravel mysteries of evolution that even Darwin couldn't ...

Dawkins' fabled cooperative gene discovered in microbes

March 9, 2017

Geneticists from the Universities of Manchester and Bath are celebrating the discovery of the elusive 'greenbeard gene' that helps explain why organisms are more likely to cooperate with some individuals than others

Some cheaters can keep it in their genes

March 13, 2008

A new study examining social behaviour suggests certain individuals are genetically programmed to cheat and often will do... providing they can get away with it.

Arms races and cooperation among amoebae in the wild

March 5, 2018

Microbes are fast becoming the darlings of the social behavior set because their interactions can be understood right down to their genes. They do interesting things, too: Bacteria steal iron from each other, kill each other ...

Recommended for you

After a reset, Сuriosity is operating normally

February 23, 2019

NASA's Curiosity rover is busy making new discoveries on Mars. The rover has been climbing Mount Sharp since 2014 and recently reached a clay region that may offer new clues about the ancient Martian environment's potential ...

Study: With Twitter, race of the messenger matters

February 23, 2019

When NFL player Colin Kaepernick took a knee during the national anthem to protest police brutality and racial injustice, the ensuing debate took traditional and social media by storm. University of Kansas researchers have ...

Solving the jet/cocoon riddle of a gravitational wave event

February 22, 2019

An international research team including astronomers from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has combined radio telescopes from five continents to prove the existence of a narrow stream of material, ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.