Cooperation

Cooperation is EVERYWHERE (see below for cooperation between aphids and ants). Scientists think cooperation occurs for two different reasons: (1) Reciprocity: I give you something you need, and you give me something I need (i.e. aphids need protection from predators, ants need carbon-rich honeydew). (2) Kin selection: we’re closely related, so I’ll help you out even though it might hurt me (i.e. ant colonies are dubbed “the super organism” by E.O. Wilson because an ant colony functions as a cooperative unit).

Wenying Shou at the Fred Hutchison Cancer Research center is also interested in cooperation– cooperative systems are difficult to study, so Shou created her own using yeast cells. Unlike some cooperative systems, Shou’s system is obligatory– meaning, the cells have to cooperate or they will die. In her system, each cell (pictured above) is unable to generate a compound necessary for its survival (let’s call these compounds yellow and red) while each cell also over-produces the compound that its neighbor cell needs– in other words, the yellow cell over-produces yellow but cannot produce red. These cells cannot survive alone, they must be close enough to each other to exchange these essential nutrients.

In order to cooperate, each cell pays a cost- it takes energy to over-produce the compound that the other cell requires. This is analogous to each citizen’s “obligatory” participation in the government– we pay taxes, and (ideally) enjoy the common resources these taxes provide (i.e. parks, schools, police).

Not everyone wants to cooperate, however. When a cell, or person, continues to take the common resource but stops contributing to the system (halts excess compound production or evades taxes) we call them “cheaters”. And cooperation begets cheaters. That’s why we’ve developed the IRS, an entire division of the government that stops cheaters via “policing”. Now Shou’s lab asks– what “policing” methods do cells use to combat cheating?

Cancer cells are ultimate cheaters. Imagine the lung cells in your body as cooperators– working together to deliver oxygen to your body. Cancerous cells (cells that have a mutation causing continued, uncontrollable replication) arise in our body every day but our body has “policing” mechanisms to destroy these mutant cells. By studying cooperation and cheaters, we can learn more about how our body polices cheater cells and why these policing strategies sometimes fail.

Shou WY, Ram S, Villar JMG (2007): Synthetic cooperation in engineered yeast populations. PNAS 104: 1877-1882.