Balance of nature: viruses are a vital component (Introduction)

by David Turell , Friday, July 19, 2019, 15:47 (1736 days ago) @ David Turell

A new article expands on the point:

https://biodesign.asu.edu/news/plant-viruses-may-be-reshaping-our-world-0

"Recent advances in the field of virology, however, suggest that viruses play a more significant and complex role than previously appreciated, and may be essential to the functioning of diverse ecosystems. (my bold)

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"Recent studies in the field of virology have shown that viruses are sometimes beneficial to the organisms they infect.

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"Vectors play an outsized role in the world of plant viruses. Unlike animal viruses, plant viruses are not usually transmitted through direct contact between infected and uninfected individuals. Instead, plant viruses disseminate through vectors, (especially insects) as well as through pollen and seeds.

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"Many kinds of vectors can transmit plant viruses, including arachnids, fungi, nematodes, and some protists, though more than 70 percent of known plant viruses are transmitted by insects, most from the biological order Hemiptera, which includes cicadas, aphids, planthoppers, leafhoppers and shield bugs.

"Insects of this kind can make use of mouthparts constructed for piercing and extracting sap or plant cell material. Insect transmission of plant viruses can occur through excretion of virus particles in saliva following feeding on an infected plant. Alternately, the plant virus can become permanently incorporated into the insect’s salivary glands, allowing the vector to transmit the virus to new plants throughout the insect’s lifetime.

"Intriguingly, a number of insect-transmitted plant viruses may have evolved mechanisms to influence vector behavior, making infected plants more attractive to sap-feeding insects or ensuring that infected plants produce chemicals that promote insect behaviors that help facilitate transmission.

"In addition to their complex and varied chains of infection, some plant viruses have another unique property. Such viruses transmit their genomes in multiple packets, each containing only part of the virus’ complete genetic code, encapsulated in a separate virus particle. This peculiar strategy, which requires the co-transmission of several viral particles to a new host in order to ensure the integrity of the viral genome, is a feature believed to be unique to plant viruses. The nature and evolution of these so-called multipartite viruses remains a biological puzzle.

"Plant viruses display considerable ingenuity in their strategies, which are highly dependent on their given environment. Some are generalists, invading multiple species, while other viruses are specialists that favour a narrow range of plant hosts. This selectivity may develop with time, through a process known as adaptive radiation. This typically occurs when a virus faces a heterogeneous habitat and becomes adaptively specialized to exploit particular ecological resources while becoming maladapted to exploit others. Such specialization acts to limit competition between different viral lineages or species. Alternatively, generalist viruses infect multiple plant hosts but must compete for these resources with other viruses. This situation tends to result in a viral population of low diversity dominated by the most acutely adapted viral genotypes.

"While researchers agree that viruses lack a single common ancestor, a detailed picture of how (and when) they emerged in the web of life remains deeply contested. Three common hypotheses compete for dominance as an explanatory framework, though they are not mutually exclusive. Perhaps viruses evolved from free-living cells, as the devolution or regressive hypothesis states. They could also have originated from RNA and DNA molecules that somehow escaped from living cells. Alternatively, viruses may have once existed as self-replicating entities that evolved alongside cells, eventually losing their independent status.

"Ongoing metaviromic research of viral diversity is helping to uncover foundational relationships among viruses and pinpoint common origins among many plant, fungal and arthropod viruses. Of particular concern for the future are the ways in which human-caused disruptions to ecosystems across the planet, which are occurring at rates unprecedented in earth’s history, are reforming virus, vector and host relationships."

Comment: Once again the workings of vital ecosystems are enmeshed in newly discovered ways with viruses playing a large role. The last paragraph above notes the dangers in damaging those systems.