In this study we analyse how the optimization of equilibrium properties is affected when a quasispecies evolves in an environment perturbed through frequent bottleneck events (Aguirre, et al. 2008). By means of a simple model we demonstrate that high neutrality may be detrimental when the population has to overcome repeated reductions in the population size, and

that the property to be optimized in this situation is the time required to regenerate the quasispecies, i.e. its adaptability. In the scenario described, neutrality and adaptability cannot be simultaneously optimized. When fitness is equated with long-term survivability, high neutrality is the appropriate strategy in constant environments, while populations evolving in fluctuating environments are fitter when their neutrality is low, such that they

can respond Erismodegib chemical structure faster MK-8669 cost to perturbations. Our results might be relevant to better comprehend how a minoritary virus could displace the circulating quasispecies, a fact observed in natural infections and essential in viral evolution (de la Torre and Holland, 1990; Aguirre and Manrubia, 2007). Aguirre, J., Manrubia, S. C., and Lázaro, E. (2008). A trade-off between neutrality and adaptability limits the optimization of viral quasispecies (preprint). Aguirre, J. and Manrubia, S. C. (2007). Out-of-equilibrium competitive dynamics of quasispecies. Europhys. Lett. 77:38001. Eigen, M. (1971). Selforganization of matter and the evolution of biological macromolecules. Naturwissenschaften 58:465–523. de la Torre, J. C. and Holland, J. J. (1990). RNA virus

quasispecies populations can suppress vastly superior mutant progeny. J. Virol. 64: 6278–6281. E-mail: aguirreaj@inta.​es Molecular Evolution in the Primitive Earth: Nonlinear Analysis of Archaea tRNAs Compared to Computer-Generated Random Sequences G. Bianciardi1, L. Borruso2 1Dipartimento second di Patologia Umana e Oncologia, Università di Siena, Via delle Scotte 6, 53100 Siena, Italia/ Centro Studi di Esobiologia, Milano, Italy; 2Dipartimento di Scienze e Tecnologie Alimentari Microbiologiche (DISTAM), Università degli Studi di Milano, Italia Nothing is known about the way(s) from which life born, and plausibile pathways of prebiotic evolution remain obscure, however, in that context, RNA may be considered the most oldest known informational genetic polymer (Howland, 200). Billions years ago, according to the exon theory of genes (Di Giulio, 1998), small RNAs translated into peptides of 15–20 aminoacids: minigenes of pre-tRNAs codifying RNA hairpin structures. The dimerization of two equal RNA hairpin structures may have lead to the formation of the cruciform structure of the tRNA molecule: tRNAs may reflect the primordial genes of that era. Nucleotide sequence data of tRNAs in archaea were obtained from the GeneBank library*.