Mutualistic Viruses and the Heteronomy of Life (original) (raw)
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Viruses in Host Evolution.edited
There is growing evidence that viruses have contributed to host evolution early in the evolution of life and throughout the subsequent evolution of biodiversity. It is important, from both a biological and medical perspective, that we grasp the essential principles involved. While virologists are familiar with the contribution of mutation to the evolutionary dynamics of the virus-host interaction, they may be less familiar with the role of partnerships and the principles and dynamics of symbiosis. We believe that an understanding of viral symbiosis complements the existing understanding of virology and offers the potential for novel virological research. This is of particular importance at a time when animal genomes, and the human genome in particular, have been found to contain large amounts of virus-derived DNA, formerly dismissed as junk but now increasingly recognized as contributing to host evolution, embryogenesis and physiology. In this paper we define the concept of viral symbiosis, clarifying the general principles involved before focusing on the particular example of the ERVWE1 locus in human evolution. From this we extrapolate the general principles to future biological and medical research.
Enemies with benefits: mutualistic interactions of viruses with lower eukaryotes
Archives of virology, 2018
Viruses represent some of the deadliest pathogens known to science. Recently they have been reported to have mutualistic interactions with their hosts, providing them direct or indirect benefits. The mutualism and symbiogenesis of such viruses with lower eukaryotic partners such as fungi, yeast, and insects have been reported but the full mechanism of interaction often remains an enigma. In many instances, these viral interactions provide resistance against several biotic and abiotic stresses, which could be the prime reason for the ecological success and positive selection of the hosts. These viruses modulate host metabolism and behavior, so both can obtain maximum benefits from the environment. They bring about micro- and macro-level changes in the hosts, benefiting their adaptation, reproduction, development, and survival. These virus-host interactions can be bilateral or tripartite with a variety of interacting partners. Exploration of these interactions can shed light on one of...
Studies in history and philosophy of biological and biomedical sciences, 2016
The view that life is composed of distinct entities with well-defined boundaries has been undermined in recent years by the realisation of the near omnipresence of symbiosis. What had seemed to be intrinsically stable entities have turned out to be systems stabilised only by the interactions between a complex set of underlying processes (Dupré, 2012). This has not only presented severe problems for our traditional understanding of biological individuality but has also led some to claim that we need to switch to a process ontology to be able adequately to understand biological systems. A large group of biological entities, however, has been excluded from these discussions, namely viruses. Viruses are usually portrayed as stable and distinct individuals that do not fit the more integrated and collaborative picture of nature implied by symbiosis. In this paper we will contest this view. We will first discuss recent findings in virology that show that viruses can be 'nice' and c...
Viruses and Evolution – Viruses First? A Personal Perspective
Frontiers in Microbiology, 2019
The discovery of exoplanets within putative habitable zones revolutionized astrobiology in recent years. It stimulated interest in the question about the origin of life and its evolution. Here, we discuss what the roles of viruses might have been at the beginning of life and during evolution. Viruses are the most abundant biological entities on Earth. They are present everywhere, in our surrounding, the oceans, the soil and in every living being. Retroviruses contributed to about half of our genomic sequences and to the evolution of the mammalian placenta. Contemporary viruses reflect evolution ranging from the RNA world to the DNA-protein world. How far back can we trace their contribution? Earliest replicating and evolving entities are the ribozymes or viroids fulfilling several criteria of life. RNA can perform many aspects of life and influences our gene expression until today. The simplest structures with non-protein-coding information may represent models of life built on structural, not genetic information. Viruses today are obligatory parasites depending on host cells. Examples of how an independent lifestyle might have been lost include mitochondria, chloroplasts, Rickettsia and others, which used to be autonomous bacteria and became intracellular parasites or endosymbionts, thereby losing most of their genes. Even in vitro the loss of genes can be recapitulated all the way from coding to non-coding RNA. Furthermore, the giant viruses may indicate that there is no sharp border between living and non-living entities but an evolutionary continuum. Here, it is discussed how viruses can lose and gain genes, and that they are essential drivers of evolution. This discussion may stimulate the thinking about viruses as early possible forms of life. Apart from our view "viruses first", there are others such as "proteins first" and "metabolism first."
Viruses, virophages, and their living nature
Acta Virologica, 2010
Over 100 years viruses have fascinated scientists around the world. Although biologists, chemists, physicians, veterinarians, and even physicists attempted to elucidate the nature of viruses, the question still remains "Are viruses alive?" Different theories have aimed at unifying our views of virology to provide an answer. However, the discovery of a mimivirus, its genome organization and replication cycle, in addition to the recently found virophage challenged the established frontier between viruses and parasitic cellular organisms. Consequently, the old controversy whether viruses are inert agents at the threshold of life or a different form of life was reignited. This review reopens the debate about the living nature of viruses from the classical concepts to the recent discoveries in order to rationally discuss our beliefs about the living or non-living character of viruses.
The Origin and Evolution of Viruses as Molecular Organisms
Nature Precedings, 2009
Viruses are the most abundant life forms and the repertoire of viral genes is greater than that of cellular genes. It is also evident that viruses have played a major role in driving cellular evolution, and yet, viruses are not part of mainstream biology, nor are they included in the Tree of Life. A reason for this major paradox in biology is the misleading dogma of viruses as viral particles and their enigmatic evolutionary origin. This article presents an alternative view about the nature of viruses based on their properties during the intracellular stage of their life cycle, when viruses express features comparable to those of many parasitic cellular species. Supporting this view about the nature of viruses is a novel hypothetical evolutionary model for their origin from parasitic cellular species that fused with their host cells. By losing their membrane and cellular structure within the host cell, these new types of parasitic species gained full access to precursors for the syn...
The Strange Lifestyle of Multipartite Viruses
PLOS Pathogens, 2016
Multipartite viruses have one of the most puzzling genetic organizations found in living organisms. These viruses have several genome segments, each containing only a part of the genetic information, and each individually encapsidated into a separate virus particle. While countless studies on molecular and cellular mechanisms of the infection cycle of multipartite viruses are available, just as for other virus types, very seldom is their lifestyle questioned at the viral system level. Moreover, the rare available "system" studies are purely theoretical, and their predictions on the putative benefit/cost balance of this peculiar genetic organization have not received experimental support. In light of ongoing progresses in general virology, we here challenge the current hypotheses explaining the evolutionary success of multipartite viruses and emphasize their shortcomings. We also discuss alternative ideas and research avenues to be explored in the future in order to solve the longstanding mystery of how viral systems composed of interdependent but physically separated information units can actually be functional.
Mutualism, parasitism and competition in the evolution of coviruses
Philosophical Transactions of the Royal Society B: Biological Sciences, 2000
Coviruses are viruses with the property that their genetic information is divided up among two or more different viral particles. I model the evolution of coviruses using information on both viral virulence and the interactions between viruses and molecules that parasitize them: satellite viruses, satellite RNAs and defective interfering viruses. The model ultimately, and inevitably contains within it single-species dynamics as well as mutualistic, parasitic, cooperative and competitive relationships. The model shows that coexistence between coviruses and the self-sufficient viruses that spawned them is unlikely, in the sense that the quantitative conditions for coexistence are not easy to satisfy I also describe an abrupt transition from mutualistic two-species to single-species dynamics, showing a new sense in which questions such as 'Is a lichen one species or two?' can be given a definite answer.