256 A. Elizabeth Arnold
and 15.2; Figure 15.1). Endophytes are known
from mosses and other non-vascular plants, ferns
and their allies, conifers, and angiosperms (Stone
et al.2000), and have been recovered in ecosys-
tems ranging from hot deserts (Suryanarayanan
et al.2005, Hoffman and Arnold 2008) to tundra
(Fisheret al.1995, Higginset al.2007), man-
groves (Kumaresan and Suryanarayanan 2002,
Gilbertet al.2002a), and temperate croplands
(Arnold and Lewis 2005).
Mostendophyteresearchhasfocusedonasingle
family (Clavicipitaceae), some of whose members
occur within above-ground tissues of some tem-
perate grasses (Saikkonenet al.1998, Clay and
Schardl 2002). These vertically transmitted, sys-
temic endophytes infect at least 300 species of
grasses, and are recognized for their ability to pro-
duce secondary compounds, includin galkaloids,
which benefit hosts by deterrin gor sickenin gher-
bivores (e.g., Clayet al.1985, Siegelet al.1990,
Wilkinsonet al.2000, but see Faeth and Sullivan
2003). In contrast, fungal endophytes of tropi-
cal trees are transmitted primarily by contagious
spread (horizontal transmission), rather than by
maternal inheritance (Arnold and Herre 2003,
Arnoldet al.2003, Herreet al.2005b). These
endophytes accumulate after leaf flush, growing
intercellularly and subsistin gon carbon in the
apoplast (see Clay 2001). Tropical endophytes
are highly localized within leaves, with individual
infections typically occupyin gonly ca. 2 mm^2 in
area (Lodgeet al. 1996).
In tropical forests, foliar endophytes reproduce
byhyphalfragmentationand/orbytheproduction
of sexual or asexual spores on dead or senescent
tissue (see Herreet al.2005b). Spores and hyphal
fragments may be released passively, or are lib-
erated by physical disturbance from wind, rain,
or tree- or branch-fall events. Insect herbivores
also may transmit fungal propagules (see below).
Many fungi, including the endophyte-rich genus
Phyllosticta, produce slimy spores that rely at least
in part on rain for dispersal (Kirket al.2001).
Althoughheavywindandrainareespeciallyeffec-
tive in movin gspores, even li ght precipitation
can disperse conidia ofColletotrichum, a common
genus of pathogenic and endophytic fungi (Guyot
et al.2005). Similarly, light wind and the currents
produced by diurnal cycles of heatin gand cool-
ing are significant for dispersal of dry propagules,