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Dynamical coexistence of molecules

This article discusses the difficult transitions and unique characteristics of major evolutionary transformations in organisms, with a focus on the origin of higher levels of evolution. It explores concepts such as replication, heredity, variation, and complexity increase, as well as the role of replicators and parasites in molecular evolution. The stochastic corrector model and the dynamics of compartmentation are also examined, along with the evolution of replicases and the challenges associated with trade-offs in replicase efficiency. Overall, this research sheds light on the coexistence of molecules in evolutionary processes.

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Dynamical coexistence of molecules

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  1. Dynamical coexistence of molecules Eörs Szathmáry Collegium Budapest (Institute for Advanced Study)

  2. The major transitions (1995) * * * * * These transitions are regarded to be ‘difficult’

  3. Difficulty of a transition • Selection limited (special environment) • Pre-emption: first comer  selective overkill • Variation-limited: improbable series of rare variations (genetic code, eukaryotic nucleocytoplasm, etc.)

  4. Difficult transitions are ‘unique’ • Operational definition: all organisms sharing the trait go back to a common ancestor after the transition • These unique transitions are usually irreversible (no cell without a genetic code, no bacterium derived from a eukaryote can be found today)

  5. A common theme: origin of higher levels of evolution • multiplication • heredity • variation hereditary traits affecting survival and/or reproduction

  6. Increase in complexity • Duplication and divergence • ‘symbiosis’ • epigenesis

  7. Egalitarian and fraternal major transitions (Queller, 1997)

  8. The formose ‘reaction’: non-informational replication formaldehyde autocatalysis glycolaldehyde Butlerow, 1861

  9. Von Kiedrowski’s replicator

  10. Classification of replicators Limited (# of individuals) >,  (# of types) Umlimited (# of individuals) << (# of types)

  11. Eigen’s paradox (1971) • Early replication must have been error-prone • Error threshold sets the limit of maximal genome size to <100 nucleotides • Not enough for several genes • Unlinked genes will compete • Genome collapses • Resolution???

  12. Molecular hypercycle (Eigen, 1971) autocatalysis heterocatalytic aid

  13. Parasites in the hypercycle (Maynard Smith, 1979) short circuit parasite

  14. Population structure is necessary! • Good-bye to the well-stirred flow reactor • Adhesion to surface or compartmentation • Hypercycles (with more than 4 members) spiral on the surface and resist parasites, BUT • Are not resistant to short-circuits • Collapse if the adhesive surface is patchy • Only compartmentation saves them

  15. The stochastic corrector model for compartmentation Szathmáry, E. & Demeter L. (1987) Group selection of early replicators and the origin of life. J. theor Biol.128, 463-486. Grey, D., Hutson, V. & Szathmáry, E. (1995) A re-examination of the stochastic corrector model. Proc. R. Soc. Lond. B 262, 29-35.

  16. The stochastic corrector model (1986, ’87, ’95, 2002) metabolic gene replicase membrane

  17. Dynamics of the SC model • Independently reassorting genes • Selection for optimal gene composition between compartments • Competition among genes within the same compartment • Stochasticity in replication and fission generates variation on which natural selection acts • A stationary compartment population emerges

  18. Group selection of early replicators • Many more compartments than templates within any compartment • No migration (fusion) between compartments • Each compartment has only one parent • Group selection is very efficient • Selection for replication synchrony

  19. Bubbles and permeability We do not know where lipids able to form membranes had come from!!!

  20. A ‘metabolic’ system on the surface (2000)

  21. A cellular automaton simulation • Reaction: template replication • Diffusion (Toffoli-Margolus algorithm) • Metabolic neighbourhood respected Metabolic Replication Grey sites: neighbourhood Black: empty site X: potential mothers

  22. Parasite on metabolism • Parasites do not kill the system • Can be selected for to perform useful function

  23. Nature420, 360-363 (2002).

  24. Maximum as a function of molecule length • Target and replicase efficiency • Copying fidelity • Trade-off among all three traits: worst case

  25. Evolution of replicases on the rocks • All functions coevolve and improve despite the tradeoffs • Increased diffusion destroys the system • Reciprocal altruism on the rocks

  26. ‘Stationary’ population efficient replicases parasites

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