Meeting Description: Viruses parasitize every organism on Earth: other viruses, bacteria, archaea, unicellular eukaryotes to large multicellular plants and animals. In many cases, viruses peacefully coexist with their hosts but in most cases, especially after spilling-over from reservoirs to novel hosts, they induce diseases that affect host’s fitness. Hence, viruses are essential agents in populations and ecosystems’ dynamics. Viruses are not only pathogens, but in some well described cases, they contributed to evolutionary innovations in their hosts. Researchers from different disciplines tend to study viruses at specific levels of biological organization, but the ultimate host of any virus is an individual cell. It is inside the cell wherein the virus expresses its genes, kidnaps the cellular machinery to produce its own proteins and uses these proteins to interact with a number of host cell factors in order to ensure reproduction and spread to neighboring cells, from there to colonize tissues and organs, then be transmitted to other susceptible hosts, to spread in the host populations and, ultimately, to reach diverse ecosystems.
At each level (cellular, organismal, population, and ecosystems), different selective pressures operate on viruses. For example, whereas at the cellular and within-organism levels replicate fast may provide advantages, at the population level such strategy may not be optimal, as it jeopardizes transmission between hosts. The recent advent of microfluidic techniques coupled with high-throughput next-generation sequencing (NGS) allow characterizing single-cell infection dynamics, both in terms of virus replication and of host responses; making possible for the first time to get a precise picture of the evolutionary dynamics of virus spreading among cells within tissues and organs. For the first, time, we may be able of weighting the contribution of mutation/recombination, drift and selection in shaping viral populations at this very fundamental level. NGS is also allowing to characterize the dynamics of viral populations at the entire individual host level. Likewise, as we have seen in recent responses to Ebola, Chikungunya and Zika epidemics, NGS has permitted to precisely trace chains of transmission, thus disentangling the roles of different evolutionary forces at the host-population level. Finally, NGS now allows exploring the virome of entire ecosystems, to hunt for viruses in their reservoirs and to understand which factors may perturb virus’ stability.
Despite all these advances, we still miss a complete theory linking all these levels and that allows to predict the behavior of viral populations at higher levels by understanding basic dynamics at the lower levels and back. Tackling this problem is what we are aiming with this Working Group (WG). The WG will be attended by experimental molecular virologists and viral ecologists and epidemiologists that will share recent experimental advances and findings with theoreticians, trying to come out with basic principles that can pave down the way to a predicting multi-level theory of virus diversity and evolution.