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Ecology, 88(3), 2007, pp. 541–549
Ó 2007 by the Ecological Society of America

DIVERSITY AND HOST RANGE OF FOLIAR FUNGAL ENDOPHYTES:
ARE TROPICAL LEAVES BIODIVERSITY HOTSPOTS?
A. ELIZABETH ARNOLD1

AND

F. LUTZONI

Department of Biology, Duke University, Durham, North Carolina 27708 USA

Key words: Ascomycota; Barro Colorado Island; diversity; endophytic fungi; host affinity; ITSrDNA;latitudinal gradient; richness; symbiosis; tropical forests.

INTRODUCTION
Comprising interactions that range from mutualism to
antagonism, fungal symbioses with plants are key
determinants of biomass, nutrient cycling, and ecosystem productivity in terrestrial habitats from the poles to
the equator (e.g., Clay and Holah 1999, Hawksworth
2001, Gilbert 2002). Most plant-associated fungicatalogued to date have been recognized because of the
fruitbodies they produce in association with their hosts
(e.g., plant pathogens, mycorrhizal fungi). Yet plants in
all major lineages, including liverworts, mosses, seedfree vascular plants, conifers, and angiosperms, also
form cryptic symbioses with fungi that penetrate and
persist within healthy aboveground tissues such as
leaves. Foliarfungal endophytes (i.e., endophylls or
mycophyllas) are a fundamental but frequently overlooked aspect of plant biology: all plant species surveyed
thus far harbor one or more endophytic symbionts in
their photosynthetic tissues (Stone et al. 2000).
The presence of obligately heterotrophic endophytes
within photosynthetic tissues of plants raises the
Manuscript received 20 September 2005;revised 24 April
2006; accepted 2 May 2006. Corresponding Editor: G. S.
Gilbert. For reprints of this Special Feature, see footnote 1, p.
539.
1
Present address: Division of Plant Pathology and
Microbiology, Department of Plant Sciences, University of
Arizona, Tucson, Arizona 85721 USA.
E-mail: arnold@ag.arizona.edu

question of the ecological importance of these cryptic
symbionts.Studies of the systemic, maternally inherited
endophytes (Clavicipitaceae, Ascomycota) associated
with over 300 species of grasses indicate that an array
of plant phenotypic traits—including drought tolerance,
leaf chemistry, tolerance of heavy metals in soils, and
propensity for vegetative reproduction—are directly
attributable to the presence of endophytes (Clay and
Schardl 2002). However,this model system of endophyte biology, arguably the most familiar to ecologists,
represents a special case. The photosynthetic tissues of
the vast majority of terrestrial plants are colonized by
endophytes that accumulate by contagious spread (i.e.,
horizontal transmission). These endophytes undergo
spatially limited or localized growth within particular
tissues, accumulate as tissues age, andcomprise a
tremendous richness of species spanning at least four
phyla of Fungi (see Frohlich and Hyde 1999, Arnold et
¨
al. 2003, 2007; A. E. Arnold, J. Miadlikowska, K. L.
Higgins, S. D. Sarvate, P. S. Gugger, A. Way, V. Hofstetter, F. Kauff, and F. Lutzoni, unpublished manuscript).
Horizontally transmitted endophytes are frequently
thought to have little to no direct effect on theplants
they inhabit. However, several recent studies show that
plants can respond to endophyte infection in ecologically meaningful ways. Redman et al. (2002) demonstrated that endophytes enhance thermotolerance and
salinity tolerance of temperate plants, augmenting their
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SPECIAL FEATURE

Abstract. Fungal endophytes are found in asymptomatic photosynthetic tissues of all
major lineages ofland plants. The ubiquity of these cryptic symbionts is clear, but the scale of
their diversity, host range, and geographic distributions are unknown. To explore the putative
hyperdiversity of tropical leaf endophytes, we compared endophyte communities along a
broad latitudinal gradient from the Canadian arctic to the lowland tropical forest of central
Panama. Here, we use molecular...