Evolutionary game theory: molecules as players
The application of game theory in understanding people and animal behavior is a very common study; however, its application to cellular and subcellular levels of life rather than multicellular organisms is a less common study, but just as important to investigate. This article focuses on the subcellular level considering genes, viruses, and molecules as the players, where their genetics and environment determine their different traits and in turn, strategies. The goal of the review is to successfully show that game theory can be applied to analyze scenarios and interactions at the molecular level.
Strategies are classified into four different types of social behavior based on its effects on the direct fitness of its players: selfishness, mutual benefit, altruism, and spite. Direct fitness, in this case, is defined to be the fitness component that is gained by the player through the impact of the strategy on its ability to reproduce, as reproduction is the main goal for simple cell organisms. Therefore, the direct fitness of the players also represents their individual payoffs of this analysis. It is also important to note that molecules with different strategies reproduce to a different extent, resulting in having a different payoff, and one and the same molecule can be involved in different games while exhibiting different social behavior depending on the partner of the interaction.
The following payoff matrix shows a simple two player game analysis is shown between alleles in diploid genomes involving population genetics:
| S | D | |
| S | wSS | 2wSD(1-k) |
| D | 2wSDk | wDD |
where D refers to an allele undergoing meiotic drive while S refers to a susceptible allele. k is the probability that the driving allele D is transferred from a heterozygous parent to the offspring instead of the susceptible allele S. wSD, wDD and wSS are the relative fitness’s of the different genotypes over an entire life cycle. However, for a gene to “drive,” there must be a probability higher than a fair 50%.
When k = 1, meiotic drive is at its maximal where driving allele D is transmitted to the gametes of the heterozygote. For k = ½, both have the same chance of 50% to be transmitted, so no meiotic drive occurs. Furthermore, for ½ < k < 1, meiotic drive exists in varying degrees. Interesting enough, depending on the order of the payoffs, four different situations that we are familiar with from class material may arise: 1) Prisoners Dilemma where the driving allele can invade and reach fixation, 2) A snowdrift game where the allele can invade but not reach fixation, 3) A harmony game where the allele can neither invade nor reach fixation, 4) a coordination game where the allele cannot invade but can reach fixation in the gametes.
Though there always are many more mechanisms at play when analyzing these scenarios, it is still possible to get an understanding of the behavior of these organisms through breaking them down to more simpler interactions, and connecting the pieces afterward.
Bohl, Katrin & Hummert, Sabine & Werner, Sarah & Basanta, David & Deutsch, Andreas & Schuster, Stefan & Theißen, Günter & Schroeter, Anja. (2014). Evolutionary game theory: Molecules as players. Mol. BioSyst.. 10. 10.1039/C3MB70601J.