Hemiparasites can transmit indirect effects from their host plants to herbivores

Abstract

Parasitic plants can serve as critical intermediaries between their hosts and other organisms; however these relationships are not well understood. To investigate the relative importance of plant traits in such interactions, we studied the role of the root hemiparasite, Castilleja levisecta (Orobanchaceae), as a mediator of interactions between the host plants it parasitizes and the lepidopteran herbivore Euphydryas editha (Nymphalidae), whose caterpillars feed on Castilleja and sequester iridoid glycosides from it. We tested whether the hemiparasite's size, leaf N concentration, and iridoid glycoside concentrations were influenced by the identity of its host plant, and then whether these traits influenced outcomes for the herbivore. We found that the hemiparasite's size and leaf N depended on the host it parasitized, and these traits in turn affected outcomes for E. editha. Specifically, Euphydryas editha survival increased with hemiparasite size and caterpillar mass increased with leaf N; caterpillars with greater mass were more likely to survive during diapause. We also found preliminary evidence that host identity influenced iridoid glycoside sequestration by the herbivore. Mean iridoid glycoside concentrations in caterpillars ranged from 1-12% depending on the host being parasitized by Castilleja. This study demonstrates that root parasitism can result in strong indirect effects on higher trophic levels, influencing organisms' survival, growth, and chemical interactions.

Preference, performance, and chemical defense in an endangered butterfly using novel and ancestral host plants

“…In previous work we found that greenhouse-grown C. levisecta produced largely aucubin, and E. editha larvae that ate it contained both aucubin and catalpol 52 ; this contrasts with our findings here. These differences in plant chemistry are likely because plants in the previous study were grown in the greenhouse, whereas plants used in the present study were field collected.…”

“…Iridoid glycoside uptake. In general, overall IG concentrations in larvae were similar to those in previous studies of related taxa at similar ontogenetic stages 41,51,52 . Concentrations were highest when larvae ate Plantago or C. hispida leaves and lower if they ate C. hispida bracts or either tissue type of C. levisecta.…”

Root hemiparasitic plants are associated with more even communities across North America

“…The potential impacts of hemiparasites on communities aligns with a growing body of literature demonstrating that organisms with a parasitic lifestyle act as facilitators to alter patterns of co‐occurrence and trophic complexity (Hatcher et al, 2012 ). For example, because many parasites can serve as both predators and prey, they play an outsized role in food webs relative to their biomass (Haan et al, 2018 ; Lafferty et al, 2006 ). Parasites can also influence the outcome of trophic interactions at a community scale (Hudson et al, 2006 ).…”

A parasite indirectly affects nutrient distribution by common mycorrhizal networks between host and neighboring plants

“…In ecological communities, species are linked to each other in networks of direct and indirect interactions (Hartley et al 2015, Haan et al 2018. As a consequence, changes in the presence of some species may have cascading effects at other trophic levels that can indirectly affect ecological processes.…”