Abstract
Resistance (host capacity to reduce parasite burden) and tolerance (host
capacity to reduce impact on its health for a given parasite burden)
manifest two different lines of defence. Tolerance can be independent
from resistance, traded-off against it, or the two can be positively
correlated because of redundancy in underlying (immune) processes. We
here tested whether this coupling between tolerance and resistance could
differ upon infection with closely related parasite species. We tested
this in experimental infections with two parasite species of genus
Eimeria. We measured proxies for resistance (the (inverse of)
number of parasite transmission stages (oocysts) per gram of feces at
the day of maximal shedding) and tolerance (the slope of maximum
relative weight loss compared to day of infection on number of oocysts
per gram of feces at the day of maximal shedding for each host strain)
in four inbred mouse strains and four groups of F1 hybrids belonging to
two mouse subspecies, Mus musculus domesticus and
M. m. musculus. We found a negative correlation between
resistance and tolerance against E. falciformis, while the two
are uncoupled against E. ferrisi. We conclude that resistance and
tolerance against the first parasite species might be traded off, but
evolve more independently in different mouse genotypes against the
latter. We argue that evolution of the host immune defences can be
studied largely irrespective of parasite isolates if
resistance-tolerance coupling is absent or weak (E. ferrisi) but
host-parasite coevolution is more likely observable and best studied in
a system with negatively correlated tolerance and resistance
(E. falciformis).