Résumé
Parasite strategies of host exploitation may be affected by host defence
strategies and multiple infections. In particular, within-host competition
between multiple parasite strains has been shown to select for higher
virulence. However, little is known on how multiple infections could
affect the coevolution between host recovery and parasite virulence. Here,
we extend a coevolutionary model introduced by van Baalen (1998) to
account for superinfection. When the susceptibility to superinfection is
low, we recover van Baalen's results and show that there are two
potential evolutionary endpoints: one with avirulent parasites and poorly
defended hosts, and another one with high virulence and high recovery.
However, when the susceptibility to superinfection is above a threshold,
the only possible evolutionary outcome is one with high virulence and high
investment into defence. We also show that within-host competition may
select for lower host recovery, as a consequence of selection for more
virulent strains. We discuss how different parasite and host strategies
(superinfection facilitation, competitive exclusion) as well as
demographic and environmental parameters, such as host fecundity or
various costs of defence, may affect the interplay between multiple
infections and host-parasite coevolution. Our model shows the interplay
between coevolutionary dynamics and multiple infections may be affected by
crucial mechanistic or ecological details.