Effect of host-switching on the ecological and evolutionary patterns of parasites

Speciation via host-switching is a macroevolutionary process that emerges
from a microevolutionary dynamic where individual parasites switch hosts,
establish a new association, and reduce reproductive contact with the
original parasite lineage. Phylogenetic distance and geographic
distribution of the hosts have been shown to be determinants of the
capacity and opportunity of the parasite to change hosts. Although
speciation via host-switching has been reported in many host-parasite
systems, its dynamic on the individual, population and community levels is
poorly understood. Here we propose a theoretical model to simulate
parasite evolution considering host-switching events on the
microevolutionary scale, taking into account the macroevolutionary history
of the hosts, to evaluate how host-switching can affect ecological and
evolutionary patterns of parasites in empirical communities at regional
and local scales. In the model, parasite individuals can switch hosts
under variable intensity and have their evolution driven by mutation and
genetic drift. Mating is sexual and only individuals that are sufficiently
similar can produce offspring. We assumed that parasite evolution occurs
at the same evolutionary time scale as their hosts and that the intensity
of host-switching decreases as the host species differentiate. Ecological
and evolutionary patterns were characterised by the turnover of parasite
species among host species, and parasite evolutionary tree imbalance
respectively. We found a range of host-switching intensity that reproduces
ecological and evolutionary patterns observed in empirical communities.
Our results showed that turnover decreased as host-switching intensity
increased, with low variation among the model replications. On the other
hand, tree imbalance showed wide variation and non-monotonic tendency. We
concluded that tree imbalance was sensitive to stochastic events, whereas
turnover may be a good indicator of host-switching. We found that local
communities corresponded to higher host-switching intensity when compared
to regional communities, highlighting that spatial scale is a limitation
for host-switching.