Biology Reference
In-Depth Information
the compounds have an antifouling role in the real ecological interaction with their
natural enemies (Steinberg et al.
2001
; Dworjanyn et al.
2006
). The metabolites
may have evolved in other contexts, e.g., as antiherbivory compounds, and their
antifouling properties may be artifacts generated by breaking up the cell structure
and exposing the compounds to fouling organisms. For example, in the red alga
Delesseria sanguinea
, crude extracts decrease settlement in assays where substrates
are coated with metabolites even though the intact alga does not inhibit settlement
(Nylund and Pavia
2003
).
Although the ecologically relevant examples of natural antifoulants are still few,
their number is increasing (Lane and Kubanek
2008
), indicating that chemical
characteristics of macroalgae do affect the epibiotic community. Further under-
standing of the ecology and evolution of macroalgal antifouling strategies has
become increasingly important (Callow and Callow
2011
). When a trait provides
resistance to biofoulers in nature, it is realistic to assume that the trait has evolved
under selection generated by the epibiotic organisms and such adaptation is suscep-
tible of inspiring biomimetic approaches to design new antifouling strategies.
11.5 Summary and Prospects
Altogether, the data described earlier indicate that marine plants are not passive
participants in epibiotic interactions and that they can actively alter their suscepti-
bility to various attackers. Macroalgae produce allelopathic metabolites that act
against sessile invertebrates, canopy-forming macroalgal competitors, and epibiotic
organisms in particular. Although a large body of evidence that shows that algae are
endowed with chemical defenses has been available for some time, the idea that
many of these defenses are induced following challenge by bioaggressors has
emerged only recently. Consequences of epi/endobiotism to the host alga depend
also on the community composition and, vice versa, epibiotism may modify the
susceptibility of the host to herbivory. However, relatively few studies have tested
the responses in ecologically relevant contexts. The scarcity of epidemiological
studies in natural populations of algal species is a major gap for the understanding
of naturally occurring mechanisms impacting ecosystem functioning. Hopefully,
metagenomics and qPCR approaches open the possibility of scoring the presence
and relative abundance of several epiphytes and pathogens in parallel, in order to
determine the global pressure acting on natural algal populations. A major chal-
lenge, which remains for further understanding, is to address whether fouling
pressure and pathogen attacks act as a selective force driving population diver-
gence. An approach that could be applied will be to compare the expression of
defense-responsive genes in natural populations experiencing different fouling
intensities or infectious diseases. Low cost and more accessible Next Generation
of Sequencing methods for monitoring gene expression (RNAseq) will help to
identify gene networks and the interplay of defense pathways in a growing number
of ecologically and/or economically relevant algal models in response to specific
