Diet mixing in a parasitic plant: A choice or a constraint?

Background/Question/Methods It is common for herbivores to mix diets, either to obtain a superior mix of nutrients, or to avoid consuming too much of any one toxin.  Like herbivores, parasitic plants can be specialists or generalists.  We observed that the parasitic plant Cuscuta indecora often adopts a mixed diet in the field.  Although we commonly observe Cuscuta parasitizing multiple hosts simultaneously, it is not clear if this broad diet is adaptive or represents a constraint limiting selection of preferred hosts.  We determined 1) if diet mixing was adaptive or “making the best of a bad situation," 2) the optimum ratio of hosts, and 3) if Cuscuta changes its foraging preferences to maintain the optimum ratio of hosts.  To do this, we examined the effects of a mixed diet on the parasitic plant Cuscuta indecora in the field and in the laboratory.  We assessed preference (number of coils and flowers) using Manly’s index and performance by measuring Cuscuta biomass.  

Results/Conclusions Our results indicated that Cuscuta does not perform best on a mixture of host plants.  Rather, diet mixing probably indicates that plants are “making the best of a bad situation” by attacking sub-optimum hosts when they cannot locate the best host.