Asymmetric competition between a hemiparasitic plant and a cyst nematode on a shared host plant

Abstract

Closely related parasites can compete for limited resources of a shared host. We extend prior work by examining the interactions of two parasites from different kingdoms. We conducted a greenhouse experiment to test for possible competition between a root hemiparasitic plant Rhinanthus serotinus (Schönh.) Oborny and a plant parasitic cyst nematode (Heterodera trifolii Goffart) which share a common host plant, the red clover (Trifolium pratense L.). Competition between these species was strongly asymmetric: the presence of nematodes reduced the biomass and flower production of the hemiparasitic plant by 74% and 81%, respectively. In fact, the performance of hemiparasites grown on nematode-infected hosts was about as poor as that of hemiparasites grown without a host plant. In contrast, the presence of the hemiparasitic plant did not affect the population size or number of cysts produced by the parasitic nematodes. These results demonstrate competition between an animal parasite and a plant parasite for a shared host resource.