Bacteria develop restraint for survival in a rock-paper-scissors community

Jun 20, 2011

It is a common perception that bigger, stronger, faster organisms have a distinct advantage for long-term survival when competing with other organisms in a given community.

But new research from the University of Washington shows that in some structured communities, increase their chances of survival if they evolve some level of restraint that allows competitors to survive as well, a sort of "survival of the weakest."

The phenomenon was observed in a community of three "nontransitive" competitors, meaning their relationship to each other is circular as in the children's game rock-paper-scissors in which scissors always defeats paper, paper always defeats rock and rock always defeats scissors.

In this case, the researchers created nontransitive communities of three strains of , one that produces two , one that is resistant to both antibiotics and one that is sensitive to both. The sensitive strain outgrows the resistant strain, which outgrows the producer, which kills the sensitive strain.

In communities in which the resistant strain curbed its pursuit of the producer, the resistant strain thrived. With no restraint, the resistant strain greatly reduced the population of the producer. But then the resistant strain was forced into greater competition with the strain sensitive to the antibiotics and the resistant strain's short-term gain meant its long-term demise.

"By becoming a better competitor in a well-mixed system, it could actually drive itself to ," said Joshua Nahum, a University of Washington graduate student in biology. "By growing faster, it actually can hurt its abundance."

Nahum is the lead author of a paper describing the work published online the week of June 22 in the . Co-authors are Brittany Harding, a UW biology undergraduate, and Benjamin Kerr, a UW associate professor of biology and the paper's corresponding author.

The researchers created 192 pools in which the bacteria could grow and interact. The bacteria could migrate among pools, and when migration occurred among neighboring pools the three strains formed multi-pool patches.

"The restrained patches, the ones that grew slower, seemed to last longer and the unrestrained patches, the ones that grew faster, burned themselves out faster," Nahum said.

To understand the process, imagine a community of three strains, Rock, Paper and Scissors, and then imagine the emergence of an unrestrained supercompetitor, Rock* (rock star), that is able to displace Scissors even faster than regular Rock can. But that also makes Rock* a better competitor against Rock, the researchers said. Eventually Rock* will be a victim of its own success, being preyed upon by Paper.

The irony, Kerr said, is that "by chasing your victim faster you actually help out the guy who's chasing you." Restraining exploitive behavior is beneficial to the patch in the long run, he said, and is a realistic embodiment of the proverb "The enemy of my enemy is my friend."

"In patches with faster growth, members of the unrestrained patch burn through their victims and then are left to face their victims' victims, their own enemies," he said.

The observed effect only applies to structured communities with limited migration, the researchers said. In an unstructured community with greater migration and mixing, a species that curbed its aggressiveness would not reduce its chances of being engulfed by its enemy.

The findings have potential implications for other ecological systems, including mating systems of certain lizards that could have analogs among some reptiles, fish, birds and insects.

Explore further: Survey of salmonella species in Staten Island Zoo's snakes

Related Stories

Rock-paper-scissors tournaments explain ecological diversity

Mar 14, 2011

According to classical ecology, when two species compete for the same resource, eventually the more successful species will win out while the other will go extinct. But that rule cannot explain systems such as the Amazon, ...

Resistant gut bacteria will not go away by themselves

Jun 19, 2007

E. coli bacteria that have developed resistance to antibiotics will probably still be around even if we stop using antibiotics, as these strains have the same good chance as other bacteria of continuing to colonise the gut, ...

Recommended for you

Compound from soil microbe inhibits biofilm formation

10 hours ago

Researchers have shown that a known antibiotic and antifungal compound produced by a soil microbe can inhibit another species of microbe from forming biofilms—microbial mats that frequently are medically harmful—without ...

Researcher among best in protein modeling contests

13 hours ago

A Purdue University researcher ranks among the best in the world in bioinformatics competitions to predict protein structure, docking and function, making him a triple threat in the world of protein modeling.

Survey of salmonella species in Staten Island Zoo's snakes

14 hours ago

For humans, Salmonella is always bad news. The bacterial pathogen causes paratyphoid fever, gastroenteritis and typhoid. But for snakes, the bacteria aren't always bad news. Certain species of Salmonella are a natural part ...

A long-standing mystery in membrane traffic solved

Mar 27, 2015

In 2013, James E. Rothman, Randy W. Schekman, and Thomas C. Südhof won the Nobel Prize in Physiology or Medicine for their discoveries of molecular machineries for vesicle trafficking, a major transport ...

User comments : 0

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.