Fungal Endophytes: Out of Sight but Should Not Be out of Mind

Ecologists are becoming increasingly aware that a plant out in the field is not simply a plant but rather a merger of fungal cells with plant tissues; from endophytic fungi in the stems and leaves to mycorrhizal fungi in the roots (endophytic fungi are fungi which invade the stems and leaves of plants but cause no symptoms of disease). Moreover, ecologists know that these fungi can influence the outcome of plant-herbivore interactions. For instance, endophytic fungi in grasses have been shown to confer anti-herbivore and possibly anti-pathogen properties to their hosts (White and Cole 1985, Christensen and Latch 1991, Christensen et al. 1991, Clay 1991). Consequences of endophyte infection have been well studied only in certain grasses for which the antiherbivore properties have received particular attention. However, anti-herbivore effects of endophytes might be widespread among plants since endophytes have been discovered in almost all examined plants and are probably ubiquitous in the plant kingdom (Carroll 1986, Petrini 1986). In this paper, I shall discuss some hypotheses regarding the important role endophytes might play in plant-herbivore interactions. My main aim is to stimulate the testing of hypotheses about the ecological and evolutionary consequences of endophyte infection. First, I propose that certain plant defense traits are for protection against fungal endophytes and are an evolutionary consequence of endophyte infection. Second, I propose that leaf senescence, as well as nutrient reabsorption, are affected by endophytes. Finally, I wish to caution both plant and insect ecologists in the way they choose controls for experiments involving insect feeding, plant allelochemicals, and DNA gel electrophore-