Evolutionary Dynamics of Giant Viruses and their Virophages

TL;DR

This paper uses mathematical models to explore how virophages influence the evolution and extinction risk of giant viruses, revealing complex dynamics and potential evolutionary shifts caused by virophage interactions.

Contribution

It introduces a mathematical framework to analyze the evolutionary dynamics between giant viruses and virophages, highlighting their impact on virus evolution and extinction risk.

Findings

Virophages tend to evolve to inhibit giant viruses more strongly.

Presence of virophages can lead to the extinction of virophage populations.

Virophages can cause giant viruses to evolve towards weaker reproductive traits.

Abstract

Giant viruses contain large genomes, encode many proteins atypical for viruses, replicate in large viral factories, and tend to infect protists. The giant virus replication factories can in turn be infected by so called virophages, which are smaller viruses that negatively impact giant virus replication. An example are Mimiviruses that infect the protist Acanthamoeba and that are themselves infected by the virophage Sputnik. This paper examines the evolutionary dynamics of this system, using mathematical models. While the models suggest that the virophage population will evolve to increasing degrees of giant virus inhibition, it further suggests that this renders the virophage population prone to extinction due to dynamic instabilities over wide parameter ranges. Implications and conditions required to avoid extinction are discussed. Another interesting result is that virophage presence can fundamentally alter the evolutionary course of the giant virus. While the giant virus is predicted to evolve towards increasing its basic reproductive ratio in the absence of the virophage, the opposite is true its presence. Therefore, virophages can not only benefit the host population directly by inhibiting the giant viruses, but also indirectly by causing giant viruses to evolve towards weaker phenotypes. Experimental tests for this model are suggested.