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Cheating yeast help group

New results show that yeast populations grow better when a few individuals cheat the system

By | September 14, 2010

Yeast colonies with mooches, thieves and cheats actually grow faster and larger than colonies without these freeloading individuals, according to a study published 15th September in PLoS Biology, challenging the widely held belief that cheaters bring only bad news to cooperating populations.
Researchers found that when some yeast
cheat their neighbors out of glucose,
the entire population grows faster.

Image: Eric Miller, Max Planck
Institute of Evolutionary Biology
"This is a most surprising result," said linkurl:Laurence Hurst;http://www.bath.ac.uk/bio-sci/research/profiles/hurst-l.html of the University of Bath in the UK, who coauthored the study. "The theory of cooperation was one of the best worked theories in all of evolution. Everyone assumed that it had to be the case that the world is better off when everyone cooperates." The results may explain why yeast populations tolerate the presence of cheaters, added linkurl:Michael Travisano,;http://www.cbs.umn.edu/eeb/faculty/TravisanoMichael/ a biologist at the University of Minnesota, who was not involved in the research -- "because a mixed strategy is to everyone's benefit." Most yeast secrete invertase, which hydrolyzes sucrose into fructose and glucose, their preferred food. However, some yeast are known to cheat the system. Cheater yeast don't secrete invertase and therefore don't contribute to the glucose production, yet they still eat the glucose that is generated by the rest of the population. According to the theory of cooperation, which states that organisms are better off when everyone cooperates, yeast populations should be best off when all the yeast produce invertase. This would maximize the availability of glucose, which should enable more yeast growth. But when Hurst and his colleagues grew yeast populations with both producers and non-producers of invertase, this is not what they saw. Instead, the yeast grew the fastest and saw the highest population numbers when a proportion of the population was cheating. One reason populations with cheaters grew better has to do with the yeast's inability to efficiently use abundant resources, Hurst said. "If you can hop down to your local McDonald's for a Big Mac, and it's very easy and very cheap, then you don't mind if you eat half of it and throw the rest away," Hurst said. "If you were starving in Africa, you wouldn't even imagine doing that." With the cheater yeast using up some of the available glucose, the cooperators are able to use the remaining resources much more efficiently, he said, allowing the population to grow larger and more quickly. The team also modeled the experimental results in an effort to see whether their findings were specific to yeast growing on a petri dish, or whether they might apply to other organisms as well. The results showed that their experimental outcomes could be generalized -- cheats would benefit a population whenever certain criteria were met. These results imply that cooperation isn't always the most beneficial path for a population, Hurst said. Instead, the benefits of cooperation depend on the characteristics of the population itself. Under certain conditions, some amount of cheating is likely beneficial. But the story is not a simple one, said linkurl:Jeff Gore,;http://www.jgore.org/ a biophysicist at the Massachusetts Institute of Technology, who did not participate in the research. For example, "if the cheaters and cooperators are growing at different rates, the ratio of cooperators to cheaters won't be stable," Gore said. Thus, the population may be changing, and "you still have to ask what [it] is going to evolve to," and not just look at where it is now. R.C. MacLean, et al., "A mixture of "cheats" and "cooperators" can enable maximal group benefit," PLoS Biol, 8(9): e1000486, 2010.
**__Related stories:__***linkurl:Nice bacteria finish last;http://www.the-scientist.com/blog/display/57667/
[1st September 2010]*linkurl:The Cheating Amoeba;http://www.the-scientist.com/article/display/54804/
[July 2008]
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Comments

Avatar of: Roy Niles

Roy Niles

Posts: 32

September 15, 2010

How are they cheating if they are in the long run beneficial and presumably evolved to serve a beneficial purpose? Evolutionists should find a new term for innovative elements that are supported by a social group for its eventual benefit. Stop assuming these evolved strategies were to no purpose except to cheat. Group cultures can influence the genetic diversity of individual natures.
Avatar of: Ross Chandler

Ross Chandler

Posts: 2

September 15, 2010

It would be interesting to see the population dynamics over time. Their is an obvious ecological niche that is being supported. Are the so called cheaters through competition policy forcing the faster growth rates as a survival mechanism? What is the cell signalling language between the species, is it one of cooperation or attempted blocking? What is happening with the intracellular communication signals in each species and how are they reflected in gene expression?
Avatar of: anonymous poster

anonymous poster

Posts: 3

September 16, 2010

I keep re-reading the article and I can't figure out the dynamics by which the yeast that do not produce invertase manage to increase the population density. What are they doing that the invertase producing yeast are not doing? I am assuming that the larger population size is a function of the increased numbers of yeasts not producing invertase, but why are they proliferating more efficiently than the others, because they do not have to waste energy producing invertase? This explanation sounds plausible but it would be nice if the article actually specified what was going on.
Avatar of: Miguel Vicente

Miguel Vicente

Posts: 2

September 16, 2010

Mooches, thieves and cheats? The concepts work beautifully to construct a journalistic story, but should they be used to describe the genetics and physiology of yeast? Is it necessary to load what should otherwise be a scientific discussion with words having strong moral connotations?
Avatar of: Matthew Grossman

Matthew Grossman

Posts: 27

September 16, 2010

To me these results suggest that the hypothesis that the relationship between those yeast that don't produce invertase and those that do is one of cheating is wrong. This is actually quite interesting and further suggests the hypothesis that "The theory of cooperation was one of the best worked theories in all of evolution", as stated by coauthor of the study Hurst, is also wrong. Which begs the question, what is cooperation?
Avatar of: Steven Pace

Steven Pace

Posts: 22

September 16, 2010

If the reduced quanitities of available glucose really are the reason for the benefit to the colony? Of course, if you look at the colony as a single entity, it doesn't really matter which of the yeast cells produce the invertase, what matters is the total amount of invertase, and the resultant amount of glucose.\n
Avatar of: Steven Pace

Steven Pace

Posts: 22

September 16, 2010

My hypothesis:\nThe yeast are capable of producing more glucose than optimal for their growth. Why would this be useful? It allows them to produce the optimal amount of glucose in a larger variety of circumstances. When the yeast produce excess glucose, some of them can stop producing, and if this is regulated properly, it would mean optimal glucose levels in all but extreme circumstances.\nThe excess yeast prevent unfriendly organisms from stepping in and eating the glucose

September 17, 2010

Undoubtedly,the cheaters always take benefits from populations. Is Nature evolution mimicking cases in the society?
Avatar of: anonymous poster

anonymous poster

Posts: 2

September 17, 2010

If a colony is a clone of one progenitor cell, then this would seem to be not cheating but cooperation, similar to in multicellular organisms (cf. http://www.biomedcentral.com/abstractS/YDAY/1/OR012).
Avatar of: ROBERT DODGE

ROBERT DODGE

Posts: 29

September 17, 2010

I think the majority of respondents have it right. This is a presumably a colony of clones, so nobody "wins" by reproducing faster. If a subset of the colony grows faster by taking advantage of excess glucose, every individual "wins," and the colony is more fit than one does not exhibit this behavior. My muscle cells are not "cheating" my erythrocytes by taking their excess oxygen instead of getting their own.

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