Searching for evidence against the mutualistic nature of hereditary symbioses: a comment on Faeth.

Abstract: Associations between fungal endophytes and grasses have served as particularly useful systems for exploring the nature and significance of hereditary symbiosis. Here, we propose alternative explanations for recent work by Faeth, in which endophytes were proposed to function as reproductive parasites. Faeth argued that his data demonstrated a symbiosis-induced shift to earlier host reproduction that could generate parasitism through life-history trade-offs with growth/survival. We contend that identifying a symbiosis as mutualistic or parasitic requires studies that incorporate both correlations among demographic pathways and rates of symbiont transmission; such work can advance understanding of the ecology and evolution of symbiosis.