Antarctic marine chemical ecology: what is next?

Abstract

Antarctic ecosystems are exposed to unique environmental characteristics resulting in communities structured both by biotic interactions such as predation and competition, as well as abiotic factors such as seasonality and ice‐scouring. It is important to understand how ecological factors may trigger chemical mechanisms in marine Antarctic organisms as a response for survival. However, very little is known yet about the evolution of chemical compounds in Antarctic organisms. Investigations in chemical ecology have demonstrated over the last several years that defensive metabolites have evolved in numerous representative Antarctic species. This contradicts earlier theories concerning biogeographic variation in predation and chemical defenses. As reviewed here, a number of interesting natural products have been isolated from Antarctic organisms. However, we believe many more are still to be discovered. Currently, many groups such as microorganisms, planktonic organisms and deep‐sea fauna remain almost totally unknown regarding their natural products. Furthermore, for many described compounds, ecological roles have yet to be evaluated. In fact, much of the research carried out to date has been conducted in the laboratory, and only in a few cases in an ecologically relevant context. Therefore, there is a need to extend the experiments to the field, as done in tropical and temperate marine ecosystems, or at least, to test the activity of the chemicals in natural conditions and ecologically meaningful interactions. Defense against predators is always one of the main topics when talking about the roles of natural products in species interactions, but many other interesting aspects, such as competition, chemoattraction, fouling avoidance and ultraviolet (UV) protection, also deserve further attention. In our opinion, challenging future developments are to be expected for Antarctic marine chemical ecology in the years to come.

Deterrent activities in the crude lipophilic fractions of Antarctic benthic organisms: chemical defences against keystone predators

“…Further studies in progress will analyse other fractions. Differences in extraction protocols, bioassay methodologies (actual ingestion versus chemo-sensitive reactions in sea stars) and experimental predatory amphipod species, as well as the distance between collection sites, make it difficult to combine our results with those of other Antarctic studies in order to draw strong conclusions (for reviews see Avila et al 2008;McClintock et al 2010). Further studies should seek to fill in the gaps of understanding Antarctic chemical ecology.…”

“…Antarctic benthic ecosystems are considered stable but adapted to marked seasonalities of nutrient supply and composed of many defended sessile species with long lifespans subjected to intense generalist predation (Dayton et al 1974;Avila et al 2008). Most defensive deterrents do not totally prevent attacks, but they reduce the attractiveness of the organism compared to other coexisting prey, while generalist feeding mitigates possible toxicities of secondary metabolites and compensates for poor-quality diets (Bernays et al 1994;Stachowicz et al 2007;Sotka et al 2009).…”

“…The low deterrence we found in sponges conflicts with other published findings. Past studies, however, usually tested demosponge species, which are prolific sources of bioactive natural products and are presumably far better defended than the hexactinellids, which represent most of our Porifera (McClintock & Baker 2001;Avila et al 2008;McClintock et al 2010;Taboada et al 2012). When comparing the current study with parallel work testing the same fractions against the omnivore lyssianasid amphipod Cheirimedon femoratus (Nú ñ ez-Pons et al 2012), we observed that out of the 49 lipophilic extracts assessed in both bioassays, 22 (44.9%) were deterrent and five (10.2%) were suitable for both predators.…”

“…Odontaster validus is a predator commonly used in feeding acceptability studies (for review see Avila et al 2008). This asteroid is readily available, and its feeding response lends itself quite well to laboratory bioassays.…”

“…In Antarctic marine organisms, measures to deter consumption have been well documented by research using sea stars as model consumers; however, postingestion repulsive reactions have been scarcely tested (for reviews see Avila et al 2008;McClintock et al 2010;Taboada et al 2012). The current study evaluates the palatability of Antarctic benthic invertebrates and algae with respect to the sympatric asteroid predator, Odontaster validus.…”