# The rugged adaptive landscape of an emerging plant RNA virus

## TL;DR

This study explores how an RNA virus adapts to a new plant host, revealing a complex evolutionary landscape with multiple fitness peaks and limited pathways.

## Contribution

The paper reconstructs the fitness landscape of Tobacco etch potyvirus adapting to Arabidopsis thaliana, showing a rugged and holey structure with epistatic interactions.

## Key findings

- The fitness landscape of the virus shows multiple peaks and holes, indicating a rugged structure.
- Epistatic effects between mutations are prevalent, especially reciprocal sign epistasis.
- The final viral genotype is stuck in a suboptimal fitness peak, not the global maximum.

## Abstract

RNA viruses are the main source of emerging infectious diseases owed to the evolutionary potential bestowed by their fast replication, large population sizes and high mutation and recombination rates. However, an equally important parameter, which is usually neglected, is the topography of the fitness landscape, that is, how many fitness maxima exist and how well connected they are, which determines the number of accessible evolutionary pathways. To address this question, we have reconstructed the fitness landscape describing the adaptation of Tobacco etch potyvirus to its new host, Arabidopsis thaliana. Fitness was measured for most of the genotypes in the landscape, showing the existence of peaks and holes. We found prevailing epistatic effects between mutations, with cases of reciprocal sign epistasis being common at latter stages. Therefore, results suggest that the landscape was rugged and holey, with several local fitness peaks and a very limited number of potential neutral paths. The viral genotype fixed at the end of the evolutionary process was not on the global fitness optima but stuck into a suboptimal peak.