Abstract
The fitness landscape metaphor has been central in our way of thinking about adaptation. In this scenario, adaptive walks are idealized dynamics that mimic the uphill movement of an evolving population towards a fitness peak of the landscape. Recent works in experimental evolution have demonstrated that the constraints imposed by epistasis are responsible for reducing the number of accessible mutational pathways towards fitness peaks. Here, we exhaustively analyse the statistical properties of adaptive walks for two empirical fitness landscapes and theoretical NK landscapes. Some general conclusions can be drawn from our simulation study. Regardless of the dynamics, we observe that the shortest paths are more regularly used. Although the accessibility of a given fitness peak is reasonably correlated to the number of monotonic pathways towards it, the two quantities are not exactly proportional. A negative correlation between predictability and mean path divergence is established, and so the decrease of the number of effective mutational pathways ensures the convergence of the attraction basin of fitness peaks. On the other hand, other features are not conserved among fitness landscapes, such as the relationship between accessibility and predictability.
Highlights
IntroductionAdaptive processes may be studied with the aid of fitness landscapes
In evolutionary biology, adaptive processes may be studied with the aid of fitness landscapes
The concept of the fitness landscape is central in evolutionary biology, and recent efforts have been concentrated on surveying how the topography of fitness landscapes steers evolution [16,17]
Summary
Adaptive processes may be studied with the aid of fitness landscapes This concept establishes a relation between the genotype of an individual and its reproductive success such that higher fitness represents best-suited specimens [1,2]. In this context, natural evolution is depicted by an uphill movement in the genotype 2 configuration space of an evolving population [3]. Natural evolution is depicted by an uphill movement in the genotype 2 configuration space of an evolving population [3] This hill-climbing metaphor for adaptive evolution has inspired a huge body of theoretical works, including proposals of fitness landscape models [4,5,6]. In a seminal work, where a genetic reconstruction of the protein β-lactamase was accomplished, Weinreich demonstrated that the number of accessible paths towards fitter genotypes is remarkably smaller than the ensemble of possible trajectories owing to epistasis [10,11], and so evolution seems to be much more predictable and reproducible than previously expected [12]
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