Host genotype determines the future infection success of a virulent parasite

Background/Question/Methods

It is well-documented that hosts vary in their ability to acquire and transmit parasites.  While the quantity of infectious particles produced by a host is known to vary with host species, genotype and condition, less is known about how hosts can affect the quality of the parasites they release.  We studied the effects of host genotype on parasite quality using the aquatic microcrustacean, Daphnia dentifera, and its fungal parasite, Metschnikowia bicuspidata.  In a series of laboratory experiments, we raised Metschnikowia in varying conditions; 1) multiple parasite isolates each grown in different host genotypes 2) multiple parasite isolates each grown in the same host genotype and 3) one parasite isolate grown in multiple host genotypes.  After growing Metschnikowia in these conditions for one generation, we tested parasite infectivity.

Results/Conclusions

We found that host genotype affected per-spore infectivity.  When parasite isolates were grown in different host genotypes, there was variation in parasite infectivity.  However, when these same parasite isolates were raised in a common host for just one generation, there was no detectable difference in infectivity among isolates.  Additionally, we successfully induced variation in infectivity in one parasite isolate by growing it in multiple host genotypes.  This study demonstrates that host genotype can influence infectivity of spores generated during an infection, altering the outcome of infection for the next host.  This suggests that parasite variation observed in nature may be partially caused by phenotypic differences induced by hosts.  Thus, host variation can have a greater effect on parasite dynamics than previously recognized.