Impact of epistasis and pleiotropy on evolutionary adaptation

TLDR

Evolutionary adaptation is often likened to climbing a hill, but in realistic fitness landscapes where mutations interact (epistasis) and affect multiple traits (pleiotropy), this process becomes more complex. The study investigates how epistasis and pleiotropy influence adaptive evolution in a model of asexual haploid populations with N loci each interacting with K others. They quantify the magnitude of epistatic interactions between substitutions and show it increases with the number of interacting loci K. The results show that at high mutation rates more epistatic substitution pairs arise, the highest fitness is achieved in landscapes with intermediate ruggedness balancing fitness potential and evolvability, and excessive ruggedness impedes adaptation, underscoring the importance of epistatic synergy for evolving high‑fitness genetic modules.

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.