Extensions to and Modulation of Defensive Mutualism in Grass Endophytes
The hypothesis that fungal endophytes (Ascomycota: Clavicipitaceae) are defensive mutualists with their grass hosts was rst formally proposed by Clay (1988) and Cheplick and Clay (1988). They postulated that the mutualism was based on the reciprocal exchange of resources and services between the symbionts . Grasses provide energy-carbohydrates from photosynthesis and mineral nutrients-and a stable place to live. In exchange, the fungi provide defense from herbivores and pathogens of the grasses. The mechanism of this defense is the production of toxic alkaloids like lolines, peramines, ergots, and lolitrems (Bush et al., 1997). In addition, other bene ts may be provided, like drought tolerance, but the primary bene t postulated to operate is herbivore defense.