Ant-agonists: The Line Between Betrayal and Cooperation

Let’s play a fun little game! Imagine you and another person are suspected of committing a robbery together and the investigators are separately interrogating you. Both of you are stubborn and refusing to testify against the other, so the investigators devise a devious deal to entice you to rat on each other: if one of you testifies, the testifier goes free while the silent one goes to jail for 3 years. The catch is that if both of you testify, both will go to jail for 2 years, or if both of you stay silent, both will go to jail for 1 year. You are not allowed to discuss the dilemma with the other person, so you must figure out the best solution for you without knowing if the other will testify or stay silent. 

[1] An example payoff matrix representing the prisoner’s dilemma.

After pacing back and forth, you come to the conclusion that you would do best if you testify because you will always avoid the 3 years in jail … but then you realize your partner will also come to the same conclusion to testify … and then both of you would end up with 2 years … which would be worse than if you both stayed silent. So maybe you both should stay silent? Argh, what a dilemma. If only there was a secret way to know if you can trust your partner to stay silent.

Well, while you deliberate on your decision, it might bring you some comfort knowing ant queens face a similar problem. Maybe you can learn something from them. 

Founding a new colony is a very dangerous endeavor for ant queens, especially when done alone (haplometrosis). They are exposed to predation, starvation, competition, and other deadly challenges. However, co-founding a colony with another queen (pleometrosis) increases the chance of survival and enhances productivity. Unfortunately, co-founding comes at a risk too. Queens often end up fighting to the death, such that only the surviving queen will actually gain anything from the cooperation. Thus, queen ants face a dilemma when they found a new colony: should they co-found with another queen to increase their chances of survival but risk getting killed later on? 

[2] An example payoff matrix that represents the fitness points Queen A and Queen B will each gain depending on the strategy they each choose. If they both choose to co-found a colony and cooperate without conflict, they will receive moderate fitness points and benefit from the mutual cooperation (3). However, if one queen cooperates while the other chooses to go solo and fight, the cooperative queen faces a higher risk of death and thus receives fewer points (0), while the aggressive queen benefits more (4). If both queens go solo, they end up with the equal but less fitness points than if they had both cooperated (2), reflecting the challenges of founding a colony alone

While this might seem like a hopeless situation, just as yours is, queens have biological advantages that guide them towards safer decisions. First, queens may reap the same benefits with less risk if they co-found with a sister or a related queen, which is known as kin selection. This is advantageous because aggression is much less likely to happen between relatives. Second, some ant species have an evolutionary mechanism, called the green beard effect, that is like a secret message that only other ants with the same allele can recognize. The allele causes a perceptible trait such that the bearer of the trait can recognize it in others which will cause the bearer to behave differently with others – cooperate, avoid, or even kill – depending on if they have the same trait. Red fire ants, Solenopsis invicta, are a well-studied example of this phenomenon. One experiment showed that worker ants with the green-beard allele killed all queens that did not bear it. Interestingly, workers were able to distinguish between bearers and non-bearers based on an odor.

[3] A person with a green beard acting as a visual metaphor for distinct traits used to recognize allies in cooperative behavior. In the context of ant queens, recognition of other ant queens with the same genetic marker can significantly influence their chance of survival when founding a new colony.

Both kin selection and the green beard allow safe cooperation between individuals ranging from bacteria to ants to humans. Just as you are stuck deciding whether or not you should rat out your partner or stay silent, queen ants face a similar dilemma in choosing how to found their colony. Enter the green beard gene! This clever mechanism is truly an extraordinary evolutionary solution to the age-old question of who can I trust? In both cases, ants and humans, recognizing a reliable partner is the key to success. So while mathematicians and game theorists might urge you to betray your partner, biologists would probably suggest a solution for your future robberies: dye your beard green and pick a partner who has similar facial hair taste—because when it comes to cooperation, it’s all about knowing who’s got your back.


Further Reading: 
Aron, S., Deneubourg, JL. Colony co-founding in ants is an active process by queens. Sci Rep 10, 13539 (2020). https://doi.org/10.1038/s41598-020-70497-x 

Brams, Steven J. and Davis, Morton D.. "game theory". Encyclopedia Britannica, 24 Oct. 2024, https://www.britannica.com/science/game-theory. Accessed 6 December 2024. 

Keller, L., Ross, K. Selfish genes: a green beard in the red fire ant. Nature 394, 573–575 (1998). https://doi.org/10.1038/29064 

Ostwald, M.M., Guo, X., Wong, T. et al. Cooperation among unrelated ant queens provides persistent growth and survival benefits during colony ontogeny. Sci Rep 11, 8332 (2021). https://doi.org/10.1038/s41598-021-87797-5 

Media Credits: 
[1] Image by CMG Lee. https://commons.wikimedia.org/wiki/File:Prisoners_dilemma.svg 
[2] Image by author. 
[3] Public domain image. https://commons.wikimedia.org/wiki/File:BeardGreen.jpg