Symbiosis, mutualism and symbiogenesis

Abstract

Symbiosis is defined as two or more dissimilar entities living in or on one another in an intimate relationship. This definition encompasses both virus-virus and virus-host relationships. Symbiosis can be manifest as different lifestyles, from antagonistic (i.e., pathogenic) to mutualistic. Virus-virus and virus-host symbioses also manifest these different lifestyles, although the antagonistic lifestyles for virus-host relationships are the ones most studied, and hence most familiar. Studying viruses from the viewpoint of symbiosis emphasizes the relationships rather than the individuals in the partnerships. Symbiotic relationships can lead to the fusion of the entities, resulting in the formation of a new species, a process known as symbiogenesis. Plant viruses clearly have undergone repeated symbiogenesis in the evolution of the extant species, as evidenced by phylogenetic analyses, as well as a number of examples of viruses in the process of speciation. © 2008 Springer Berlin Heidelberg.