Impacts of selective predation on infection prevalence and host susceptibility

Predation can alter diverse ecological processes, including host–parasite
interactions. Selective predation, whereby predators preferentially feed
on certain prey types, can affect prey density and selective pressures.
Studies on selective predation in infected populations have primarily
focused on predators preferentially feeding on infected prey. However,
there is substantial evidence that some predators preferentially consume
uninfected individuals. Such different strategies of prey selectivity
likely modulate host–parasite interactions, changing the fitness payoffs
both for hosts and their parasites. Here we investigated the effects of
different types of selective predation on infection dynamics and host
evolution. We used a host–parasite system in the laboratory (Daphnia
dentifera infected with the horizontally transmitted fungus, Metschnikowia
bicuspidata) to artificially manipulate selective predation by removing
infected, uninfected, or randomly selected prey over approximately 8–9
overlapping generations. We collected weekly data on population
demographics and host infection and measured susceptibility from a subset
of the remaining hosts in each population at the end of the experiment.
After 6 weeks of selective predation pressure, we found no differences in
host abundance or infection prevalence across predation treatments.
Counterintuitively, populations with selective predation on infected
individuals had a higher abundance of infected individuals than
populations where either uninfected or randomly selected individuals were
removed. Additionally, populations with selective predation for uninfected
individuals had a higher proportion of individuals infected after a
standardized exposure to the parasite than individuals from the two other
predation treatments. These results suggest that selective predation can
alter the abundance of infected hosts and host evolution.