| While it is widely-accepted that parasites are inherently harmful to hosts, we have not fully-characterized the factors modulating virulence and pathogenicity manifest in specific host-parasite systems. Further, general mechanisms underlying parasite-associated detriment to hosts have yet to be elucidated. Generalizations regarding these issues cannot be made without comprehensive assessment of existing empirical evidence. Using a novel meta-analytical approach, I evaluated potential determinants of parasite-associated mortality among hosts. Parasite effects were highly correlated with parasite transmission strategy, host taxonomy, and latitude. These patterns conform to ecological theory and the relationship between host mortality and latitude in particular may portend critical changes in host-parasite relationships due to global climate change. In a second meta-analysis, I tested the hypothesis that perturbations to host energy budgets drive parasite-associated consequences to host fitness by synthesizing studies of parasite-associated changes to host resting metabolic rate (RMR). Parasitism had a negligible overall effect on RMR, likely due to marked inconsistencies in the magnitude and directionality of effects across studies. In light of this, I recommend that a shift in research focus is necessary to properly assess energetic costs of parasitism and to determine the impacts of such costs on host fitness. |
