Quantifying the associations between fungal endophytes and biocontrol-induced herbivory of invasive purple loosestrife (Lythrum salicaria L.)

Abstract

Fungal endophytes are one of several groups of heterotrophic organisms that associate with living plants. The net effects of these groups of organisms on each other and ultimately on their host plants depend in part on how they facilitate or antagonize one another. In this study we quantified the associations between endophyte communities and herbivory induced by a biological control in the invasive Lythrum salicaria at various spatial scales using a culture-based approach. We found positive associations between herbivory damage and endophyte isolation frequency and richness at the site level and weak, positive associations at the leaf level. Herbivory damage was more strongly influenced by processes at the site level than were endophyte isolation frequency and community structure, which were influenced by processes at the plant and leaf levels. Furthermore, endophytic taxa found in low herbivory sites were nested subsets of those taxa found at high herbivory sites. Our findings suggest that endophyte communities of L. salicaria are associated with, and potentially facilitated by, biocontrol-induced herbivory. Quantifying the associations between heterotrophic groups ultimately may lead to a clearer understanding of their complex interactions with plants.

• community assembly
• host-microbe interactions
• microbial symbiont
• nestedness
• spatial structure

Acknowledgments

We thank G. May for providing laboratory resources, as well as M. Howard and P. Lenz for their assistance in the field and laboratory. We thank G. May and D. Tilman for thoughtful feedback on the manuscript, as well as the executive editor L. Taylor and two anonymous reviewers for their comments. Financial support provided by the NSF-IGERT Introduced Species and Genotypes program ( DGE-0653827) to A.S.D and G.L.Q, the NSF Graduate Research Fellowship program ( NSF 00039202) and the University of Minnesota Bell Museum Dayton Award to A.S.D and the University of Minnesota Life Sciences Summer Undergraduate Research Program to J.I.S.