PS 44-97 - The role of diet mixing generalist holoparasite, Cuscuta gronovii

Background/Question/Methods

Studies on diet mixing (feeding on more than one host species) have broadly explored generalist herbivores and have documented improved performance for a range of animals from insects to mammals; however, examination of the benefits of diet mixing for parasitic plants has been much more limited. In this study, we examined whether a generalist holoparasite, Cuscuta gronovii, benefits when using a mixed diet versus using a single host species. In three replicate experiments, we created all six possible pairing for three species of plants, one from each of three families (Asteraceae, Fabaceae, and Lamiaceae). Each plant species was paired with itself and with each of the other two species; in so doing, three single-species pairs and three mixed-species pairs were created. In so structuring the experiment, a nested ANOVA was used in each experiment, with diet treatment acting as a fixed effect, plant pair being nested within diet treatment, and block treated as a random effect. In a fourth experiment, we asked a similar question, but used three species all from the Asteraceae family.

Results/Conclusions

Diet treatment had a significant effect in three of the four experiments. While three mixed-species pairs had higher performance measurements compared to the three single species pairs in those three experiments, the patterns did not fully support a benefit of diet mixing in all situations. In contrast, plant pair and the species associated with those pairs always explained the majority of variation in plant parasite performance. Our findings suggest that some plant hosts act as low-quality hosts, while others act has high-quality hosts; C. gronovii performance was only enhanced by diet mixing in situations where C. gronovii performance was examined from the perspective of a low-quality host in the presence of a high-quality host. In other words, C. gronovii established and produce more seeds on a low-quality host because it was able to colonize that low-quality host from the nearby high-quality host. Our study suggests that the benefit of diet mixing seen for herbivores cannot be generalized to include parasitic plants.