Biology Reference
In-Depth Information
D. pulchra
, a variety of bacteria and eukaryotes have been shown to produce cyclic
dipeptides that can act as AHL mimics and affect QS-regulated behavior in other
bacteria (Dobretsov et al.
2009
; Dickschat
2010
). Recently, Kanagasabhapathy
et al. (
2009
) suggested that certain epibiotic bacteria from the brown macroalga
Colpomenia sinuosa
may play a role in defense mechanisms and suppress the
settlement of other competitive bacteria by producing quorum sensing inhibitors
(QSI) or QSI-like compounds.
11.3.3 Allelopathic Interactions and Induced Defenses
Allelopathy was initially defined when a plant secretes toxic biochemicals, such as
phytotoxic root exudates (Bais et al.
2003
) into its environment. These toxic
compounds, called allelochemicals, can have adverse effects on the growth of
other plants that come in contact with them. Allelopathy provides a strong advan-
tage in the competition for space by interfering with settlement and/or expansive
growth of competitors. According to Gross (
2003
), in aquatic environments, alle-
lopathy could be extended to include negative influences between photosynthetic
organisms and other organisms as well as antifouling strategies (see also Chap.
9
by
Amsler).
One of the most dramatic and recent examples of allelopathy between
macroalgae in temperate systems is seen in the introduced Japanese alga
Bonnemaisonia hamifera,
which has become one of the most common red algae
in Sweden during the last decades (Svensson et al.
2009
). Its life history involves an
alternation between morphologically different gametophytes and tetrasporophytes
and it seems that only filamentous tetrasporophytes (formerly described as a distinct
species
Trailliella
) are propagating, often growing as an epiphyte on native algae,
primarily
Corallina officinalis
and
Furcellaria fastigiata
.
B. hamifera
was coated
on surfaces to estimate settling success of native algal spores. Some field
experiments also tested whether this substance can be transferred among species
by placing exotic adjacent to native algae under simulated wave action. These
authors showed that at natural concentrations, 4-bromo-heptanone, the most abun-
dant brominated compounds in the alga, inhibits settlement of spores from native
algal species. Furthermore, the substance can be transferred from
B. hamifera
to the
native species. The mechanism of transferring 4-bromo-heptanone to other surfaces
might enable the algae to “reserve” space for future colonization, as native algae
cannot settle on the coated surfaces. This promising study is the first to show that
invasions by exotic algae are facilitated by allelopathy and that chemical defenses
can be transferred from exotic to native species (Svensson et al.
2009
; see also
Chap.
12
by Andreakis and Schaffelke). It is in agreement with the Novel Weapons
Hypothesis that predicts that exotic species will be successful if they possess
biochemicals unique to their new range (Callaway and Ridenour
2004
).
B
.
hamifera
is also found to be released from predators in the archipelago of Tj
€
arn
€
o (Enge et al.
