ARS | Publication request: Asexual Endophytes and Associated Alkaloids Alter Arthropod Community Structure and Increase Herbivore Abundances on a Native Grass

Submitted to: Ecology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 6, 2009
Publication Date: December 1, 2009
Repository URL: http://jani@lifesci.ucsb.edu
Citation: Jani, A.J., Faeth, S.H., Gardner, D.R. 2009. Asexual Endophytes and Associated Alkaloids Alter Arthropod Community Structure and Increase Herbivore Abundances on a Native Grass. Ecology Letters (2009) 12:1-12; (www.blackwellpublishing.com) DOI: 10.1111/j.1461-0248.2009.01401.x

Interpretive Summary: Endophytic fungi, or endophytes, are minute microbial organisms that exist in a symbiotic relationship with their host plant. They may produce toxic secondary compounds which are believed to protect the plants against herbivory. In many agronomic grasses endophytes increase vigor of the plant, decrease insect herbivory and may alter local insect populations. However, little is known about native grasses and the effects of endophytes and their secondary compounds with surrounding ecological community. In this study, a native grass of the southwestern US, known as sleepy grass (Achnatherum robustum), was investigated to see how the endophytes and the associated alkaloids influence the insect communities on the grass. In contrast to what has been previously found in agronomic grasses we found that the enodphytic alkaloids in this native grass were correlated with increased numbers and types of insects associated with the plant. Unlike what has been found in agronomic grass systems the alkaloids in this native grass may have a negative effect on the natural enemies of the insects and not on the insects themselves.

Technical Abstract: Dispite their minute biomass, microbial symbionts of plants potentially alter herbivory, diversity and community structure. Infection of grasses by asexual endophytic fungi often decreases herbivore loads and alters arthropod diverisy. However, most studies to date have involved agronomic grasses and often consider only infection status (infected vs. uninfected), without explicity measuring endophyte-produced alkaloids, which vary among endophyte isolates and may impact consumers. We combined field experiments and population surveys to investigate how endophyte infection and associated alkaloids influence abundances, species richness, evenness and guild structure of arthropod communities on a native grass, Achnatherum robustum (sleepygrass). Surprisingly, we found that endophyte-produced alkaloids were associated with increased herbivore abundances and species richness. Our results suggest that, unlike what has been found in agronomic grass systems, high alkaloid levels in native grasses may not protect host grasses from arthropod herbivores, and may instead more negatively affect natural enemies of herbivores.