Impact of Epistasis and Pleiotropy on Evolutionary Adaptation

TL;DR

This study explores how epistasis and pleiotropy influence evolutionary adaptation, revealing that moderate landscape ruggedness optimizes fitness gains and that interactions between loci are vital for developing high-fitness genetic modules.

Contribution

It introduces a quantitative measure of epistatic interactions and demonstrates their increasing role with more loci interactions, highlighting optimal ruggedness for adaptation.

Findings

Higher K increases epistatic interactions.

High mutation rates lead to more epistatic pairs on the line of descent.

Optimal fitness occurs at intermediate landscape ruggedness.

Abstract

Evolutionary adaptation is often likened to climbing a hill or peak. While this process is simple for fitness landscapes where mutations are independent, the interaction between mutations (epistasis) as well as mutations at loci that affect more than one trait (pleiotropy) are crucial in complex and realistic fitness landscapes. We investigate the impact of epistasis and pleiotropy on adaptive evolution by studying the evolution of a population of asexual haploid organisms (haplotypes) in a model of N interacting loci, where each locus interacts with K other loci. We use a quantitative measure of the magnitude of epistatic interactions between substitutions, and find that it is an increasing function of K. When haplotypes adapt at high mutation rates, more epistatic pairs of substitutions are observed on the line of descent than expected. The highest fitness is attained in landscapes with an intermediate amount of ruggedness that balance the higher fitness potential of interacting genes with their concomitant decreased evolvability. Our findings imply that the synergism between loci that interact epistatically is crucial for evolving genetic modules with high fitness, while too much ruggedness stalls the adaptive process.