Evolutionary accessibility of modular fitness landscapes

Abstract

A fitness landscape is a mapping from the space of genetic sequences, which is modeled here as a binary hypercube of dimension $L$, to the real numbers. We consider random models of fitness landscapes, where fitness values are assigned according to some probabilistic rule, and study the statistical properties of pathways to the global fitness maximum along which fitness increases monotonically. Such paths are important for evolution because they are the only ones that are accessible to an adapting population when mutations occur at a low rate. The focus of this work is on the block model introduced by A.S. Perelson and C.A. Macken [Proc. Natl. Acad. Sci. USA 92:9657 (1995)] where the genome is decomposed into disjoint sets of loci (`modules') that contribute independently to fitness, and fitness values within blocks are assigned at random. We show that the number of accessible paths can be written as a product of the path numbers within the blocks, which provides a detailed analytic description of the path statistics. The block model can be viewed as a special case of Kauffman's NK-model, and we compare the analytic results to simulations of the NK-model with different genetic architectures. We find that the mean number of accessible paths in the different versions of the model are quite similar, but the distribution of the path number is qualitatively different in the block model due to its multiplicative structure. A similar statement applies to the number of local fitness maxima in the NK-models, which has been studied extensively in previous works. The overall evolutionary accessibility of the landscape, as quantified by the probability to find at least one accessible path to the global maximum, is dramatically lowered by the modular structure.

26 pages, 12 figures; final version with some typos corrected

References in corpus (9)

• Quantitative analyses of empirical fitness landscapes
• Evolutionary accessibility of mutational pathways
• The pace of evolution across fitness valleys
• Exact Results for Amplitude Spectra of Fitness Landscapes
• Adaptive walks and extreme value theory
• The number of accessible paths in the hypercube
• Evolutionary accessibility in tunably rugged fitness landscapes
• Accessibility percolation on n-trees
• Increasing paths in regular trees

Cited by in corpus (11)

• Adaptation in tunably rugged fitness landscapes: The Rough Mount Fuji Model
• Universality classes of interaction structures for NK fitness landscapes
• Analysis of adaptive walks on NK fitness landscapes with different interaction schemes
• Multidimensional epistasis and the transitory advantage of sex
• Accessibility percolation in random fitness landscapes
• From Adaptive Dynamics to Adaptive Walks
• Geometry of fitness landscapes: Peaks, shapes and universal positive epistasis
• Accessibility Percolation on Cartesian Power Graphs
• Distribution of the number of fitness maxima in Fisher's Geometric Model
• Evolutionary accessibility of random and structured fitness landscapes
• Predictability of the imitative learning trajectories