The directionality of asymmetric interactions between predators (definitive hosts) and prey (intermediate hosts) will impact trophic transmission in parasites. This study tests the prediction that trophically transmitted parasites are funneled towards asymmetric predator-prey interactions where intermediate hosts have few predators and definitive hosts have many prey (‘strong up-weak down’ asymmetry).  The distribution and position of trophically transmitted parasites was examined in four published food webs in relation to mismatch asymmetry of predator-prey interactions. 

Results/Conclusions

We found that trophically transmitted parasites exploit asymmetrically ‘strong up-weak down’ interactions in a nonrandom manner (compared to null models), and particular predator-prey pairs contain more trophically transmitted parasites than would be expected by random chance alone.  These findings suggest that food web topology has great bearing on the ecology of trophically transmitted parasites, and that consideration of parasite life cycles in the context of food web organization can provide insights into the forces affecting evolution of trophic transmission.