Fitness Landscapes Arising from the Sequence-Structure Maps of Biopolymers
Peter F. Stadler
Fitness landscapes are an important concept in molecular evolution
since evolutionary adaptation as well as in vitro selection of
biomolecules can be viewed as a hill-climbing-like process. Global
features of landscapes can be described by statistical measures such
as correlation functions or the fraction of neutral (equally fit)
neighbors. Simple spin-glass-like landscape models borrowed from
statistical physics lend themselves to detailed mathematical analysis
but lack several basic features of natural landscapes.
Biologically relevant landscape models are based on the assumption
that genotypes give rise to phenotypes that are evaluated by their
environment and hence determine the genotype's fitness. In the case of
in vitro evolution of biopolymers the phenotypes are the three
dimensional shapes of the molecules. A large degree of neutrality,
giving rise to neutral networks and shape space covering, is a generic
feature of RNA and polypeptide sequence-structure maps. These
properties are inherited by the fitness landscapes independent of the
details of the structure-to-fitness evaluation.
Neutrality qualitatively changes the dynamics of evolution. While
rugged landscapes without neutral neighbors lead to localized
populations, trapping in local optima, and the existence of a critical
replication rate beyond which sequence information is lost, we find
diffusion in sequence space and ever-lasting innovation of novel
mutants on landscapes arising from RNA or protein folding.
Fitness Landscapes - Molecular Evolution -
RNA Secondary Structures - Biopolymer Folding -
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