Title: Endemicity and prevalence of multipartite viruses under heterogeneous between-host transmission,
Abstract: Multipartite viruses replicate through a puzzling evolutionary strategy.
Their genome is segmented into two or more parts, and encapsidated in separate
particles that appear to propagate independently. Completing the replication
cycle, however, requires the full genome, so that a persistent infection of a
host requires the concurrent presence of several particles. This represents an
apparent evolutionary drawback of multipartitism, while its advantages remain
unclear. A transition from monopartite to multipartite viral forms has been
described in vitro under conditions of high multiplicity of infection,
suggesting that cooperation between defective mutants is a plausible
evolutionary pathway towards multipartitism. However, it is unknown how the
putative advantages that multipartitism might enjoy affect its epidemiology, or
if an explicit advantage is needed to explain its ecological persistence. To
disentangle which mechanisms might contribute to the rise and fixation of
multipartitism, we here investigate the interaction between viral spreading
dynamics and host population structure. We set up a compartmental model of the
spread of a virus in its different forms and explore its epidemiology using
both analytical and numerical techniques. We uncover that the impact of host
contact structure on spreading dynamics entails a rich phenomenology of
ecological relationships that includes cooperation, competition, and
commensality. Furthermore, we find out that multipartitism might rise to
fixation even in the absence of explicit microscopic advantages. Multipartitism
allows the virus to colonize environments that could not be invaded by the
monopartite form, while homogeneous contacts between hosts facilitate its
spread. We conjecture that there might have been an increase in the diversity
and prevalence of multipartite viral forms concomitantly with the expansion of
agricultural practices.