Defensive Mutualism and Grass Endophytes: Still Valid after All These Years?

Dan Janzen (Janzen, 1985) suggested that all mutualisms could be classi ed into four basic functional groups: seed dispersal, pollination, resource harvest (including food processing), and protection. In 1988 I published the paper “Fungal endophytes of grasses: A defensive mutualism between plants and fungi” (Ecology 69: 10-16). The primary hypothesis was that many grass-endophyte associations represent a defensive mutualism where endophytes produce physiologically active alkaloid compounds that help to protect their host plants against herbivory. I was honored to learn that this is the most highly cited paper ever written on endophytes (as of February 2008). An analysis using Web of Science (search using defens* mutual*) suggested that there were a few publications using the phrase “defensive mutualism” before 1988 but none of this work was cited. After 1988 there was a rapid increase in citations and new publications referring to “defensive mutualism” (see Figure 2.1).