The evolution of cooperation and diversity in public good producing organisms

• Main Author: Lee, William
• Other Authors: Jansen, Vincent
• Published: Royal Holloway, University of London 2013
• Subjects: 577; siderophores : pseudogamy : diversity : evolution : chromodynamics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589617

In a population of altruists, all individuals thrive. But altruists are exploited by cheating individuals which do not perform altruistic acts but still benefit from those. In these conditions cooperation cannot easily evolve. This issue is resolved by kin recognition: altruists recognise each other through the use of a conspicuous tag. These altruists do well until cheaters acquire the signalling tag and disrupt the cooperation. But altruists using a different tag can then invade the population, followed by new cheaters. This mechanism can lead to a diversity of tags coexisting in the population. However it has not yet been applied in realistic biological systems. In this thesis, I formulated mathematical and simulation models to investigate the effect of diversity on the evolutionary dynamics in systems where different altruists compete with cheaters. In particular, I focused on organisms producing public goods, i.e. goods that can profit to the whole population. I considered two biological systems models: gynodioecious populations of plants, where hermaphrodites produce pollen that can be used by female-only individuals, and bacteria producing an iron-chelating molecule, called siderophore, that can be exploited by both producers and non-producers. I found that diversity in gynodioecious plants is dependent on population structure. In particular, I found that the maximal level of diversity occurs when the population structure does not favour altruists or cheaters. Next, I found a number of important results in siderophore-producing bacteria. By considering a detailed ecological model, I derived Hamilton's rule in a metapopulation and found that the level of cooperation in a population depends on the length of interaction between strains. Finally, I discovered a novel evolutionary mechanism generating and maintaining diversity and showed that it results from non-equilibrium mechanisms. These findings explain why cheaters appear readily in experiments but are rare in natural populations. My results demonstrate the importance of integrating ecological details in order to understand the mechanisms leading to cooperation and diversity, and will provide a basis and framework for future studies on the emergence and maintenance of diversity.