Abstract
Cooperation, paying a cost to benefit others, is widespread. Cooperation can be promoted by pleiotropic 'win-win' mutations which directly benefit self (self-serving) and partner (partner-serving). Previously, we showed that partner-serving should be defined as increased benefit supply rate per intake benefit. Here, we report that win-win mutations can rapidly evolve even under conditions unfavorable for cooperation. Specifically, in a well-mixed environment we evolved engineered yeast cooperative communities where two strains exchanged costly metabolites, lysine and hypoxanthine. Among cells that consumed lysine and released hypoxanthine, ecm21 mutations repeatedly arose. ecm21 is self-serving, improving self's growth rate in limiting lysine. ecm21 is also partner-serving, increasing hypoxanthine release rate per lysine consumption and the steady state growth rate of partner and of community. ecm21 also arose in monocultures evolving in lysine-limited chemostats. Thus, even without any history of cooperation or pressure to maintain cooperation, pleiotropic win-win mutations may readily evolve to promote cooperation.
Highlights
Cooperation, paying a fitness cost to generate benefits available to others – is widespread and thought to drive major evolutionary transitions different cells must cooperate with each other and refrain from dividing in a cancerous fashion to
CoSMO models the metabolic cooperation between certain gut microbial species rhizobia 32, as well as other mutualisms metabolites are costly to produce exchanged metabolites are externally supplied have been found to operate in communities of un-engineered microbes
To define “direct” here, we adapt the framework from Chapter 10 of 41: A mutation in genotype A exerts a direct fitness effect on genotype B if the mutation can alter the growth rate of B even if the biomass of A is fixed 30
Summary
Cooperation, paying a fitness cost to generate benefits available to others – is widespread and thought to drive major evolutionary transitions different cells must cooperate with each other and refrain from dividing in a cancerous fashion to. Theoretical work suggests that cooperation can stabilize pleiotropy 27, and that pleiotropic linkage between self-serving and partner-serving traits is favored as cooperators evolve to resist cheater invasion 28. CoSMO models the metabolic cooperation between certain gut microbial species rhizobia 32, as well as other mutualisms metabolites are costly to produce exchanged metabolites are externally supplied have been found to operate in communities of un-engineered microbes. These include how fitness effects of interactions might affect spatial patterning and species composition in twospecies communities 39, as well as how cooperators might survive cheaters 14,21 (see Discussions in these articles). Our work suggests the possibility of pre-existing pleiotropy stabilizing nascent cooperation in natural communities
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