Biology Reference
In-Depth Information
Epiphytes are usually defined as organisms that grow on plants, but do not derive
nutrients from their hosts (Linskens
1976
). However, one of the most extensively
studied relationships is the obligate partnership of the red alga
Vertebrata
(
Polysiphonia) lanosa,
which is a hemiparasite of the fucoid brown alga
Ascophyllum nodosum
(Taylor
1957
; Turner and Evans
1977
; Garbary et al.
1991
; Levin and Mathieson
1991
). Perhaps, hemiparasitism is an intermediate
step between simple epiphytism and parasitism. The rhizoids of
P. lanosa
penetrate
the host and obtain some nutrition from
A
.
nodosum
(Rawlence and Taylor
1972
;
Turner and Evans
1977
). However, the quantity of carbon obtained by
P. lanosa
is
minimal (Harlin and Craigie
1975
) and
P. lanosa
is pigmented and capable of
photosynthesis (Bidwell
1958
; Fralick and Mathieson
1975
). Field observations
suggest that the distribution and abundance of
V. lanosa
are highly dependent upon
the occurrence of injured host tissue and/or number of lateral shoots (Lobban and
Baxter
1983
; Burke
1986
; Pearson and Evans
1989
,
1990
; Longtin et al.
2009
).
Recent work by Longtin and Scrosati (
2009
)in
Ascophyllum nodosum
beds
has reinvestigated the various factors that affect the settlement of the red alga
V. lanosa
at the surface of
A. nodosum
including competitive interactions with
epiphytic filamentous brown algae (
Elachista fucicola
and
Pylaiella littoralis
)
(Longtin et al.
2009
)
11.2.2 Pigmented Endophytes
Numerous species of pigmented algal endophytes are associated with red, brown,
and green seaweeds (Goff
1982
; Correa
1996
; Bouarab et al.
2001a
; Bown et al.
2003
; Eggert et al.
2010
). They are generally small, filamentous algae that belong to
three main lineages of multicellular algae (Chlorophyta, Phaeophyceae, and
Rhodophyta) and inhabit mainly the intercellular spaces of their hosts. They appear
to be carbon independent of their hosts (Correa et al.
1988
; Correa
1990
; Eggert
et al.
2010
). Therefore, endophytism has arisen independently numerous times
throughout the diversification of the multicellular algal lineages and has likely
been constrained by selective pressure exerted on epiphytes by grazers (Peters
2003
; Amsler et al.
2009
; Aumack et al.
2011
) or by abiotic conditions and
environmental gradients leading to differential levels of desiccation in intertidal
seaweeds (Longtin et al.
2009
). During the last decade, additional information has
become available on the taxonomy, prevalence, and ecology of pigmented
endophytes in brown, red, and green algae and some culture and molecular studies
have revealed the occurrence of cryptic stages of the life cycles of some important
seaweeds such as kelps (Garbary et al.
1999a
,
b
; Hubbard et al.
2003
) or green algae
(Sussmann and DeWreede
2002
) growing endophytically in the tissues of various
algal hosts. Difficulties in isolating endophytes into pure culture and the lack of a
robust taxonomy constrain our ability to develop a full understanding of their
ecology and that of their hosts.
