Transcriptome and metabolite responses to predation in a South pacific soft coral.

Sinularia polydactyla, a dioecious, abundant soft coral in the South Pacific, exhibits biochemical phenotypic plasticity in secondary metabolite production in relation to predation intensity. However, it is unclear to what extent changes in secondary metabolites, such as 11beta-acetoxypukalide, may result from specific, induced pathway activities at the level of gene expression. To investigate both chemical changes and differences in mRNA diversity in response to predation stress, artificial predation experiments were conducted in situ on colonies of S. polydactyla. Multivariate statistical analyses of coral biochemical metabolites and our kinetic transcriptome profiling technique indicate that that the induction of 11beta-acetoxypukalide by predation stress likely results from the upregulation of either one dominant transcript or a very small set of transcripts, indicative of a targeted upregulation rather than a generalized, genetic stress response. Overall, this work establishes a routine method for integrating high-throughput transcriptome and metabolome data sets to allow for the identification of metabolites whose intracellular concentrations can be readily linked to gene expression events in response to specific treatments in non-model organisms.

Isolation of two polyketide synthase gene fragments from the uncultured microbial symbiont of the marine bryozoan Bugula neritina.

"Candidatus Endobugula sertula," the uncultured microbial symbiont of the bryozoan Bugula neritina, produces ecologically and biomedically important polyketide metabolites called bryostatins. We isolated two gene fragments from B. neritina larvae that have high levels of similarity to polyketide synthase genes. These gene fragments are clearly associated with the symbiont and not with the host.

Chemical attractants in horseshoe crab, Limulus polyphemus, eggs: the potential for an artificial bait.

Horseshoe crabs, Limulus polyphemus, are the preferred bait in the eel and conch fisheries along the east coast of the United States. However, recent management measures have restricted the availability of horseshoe crabs to commercial fisheries, creating the need for sustainable, alternative bait sources. In this study, we examined the chemistry underlying the predator-prey attraction to determine if specific, isolable attractant metabolites from the horseshoe crab could be identified and characterized for incorporation into an artifical bait. Initial assays with the mud snail, Hyanassa obsoleta, suggested that the chemoattractants were concentrated in L. polyphemus eggs. Chemical analyses and biological assays of the egg extract indicated the primary cue was a heat-stable, proteinaceous compound (>10 kDa). A carbohydrate-rich fraction of low molecular mass (< 10 kDa) also enhanced mud snail chemotaxis. Analysis of egg digests with SDS-PAGE confirmed the presence of glycoproteins or carbohydrate-binding proteins in the horseshoe crab egg extract. Because the attractant appears to be a complex protein or glycoprotein, conventional chemical synthesis is unlikely. However, the tools of modem biotechnology offer the potential to produce this attractant in a system independent of the horseshoe crab. Such an attractant could be incorporated into an artificial bait, providing an ecologically sound alternative for commercial eel and whelk fisheries.

Marine tannins: the importance of a mechanistic framework for predicting ecological roles.

Since chemical ecology emerged as a field of marine science, it has been strongly influenced by studies of chemically mediated interactions in land-based systems. Marine chemical ecologists, like their terrestrial counterparts, initially focused on identifying natural products and evaluating the potential ecological roles of these products as defenses, attractants, or other cues. Now, like our land-based colleagues, we must increase our focus on the physiological and biochemical mechanisms that underlie the chemical interactions, paying particular attention to regulation of biosynthetic pathways, within-plant and between-plant signaling cues, and comparative and functional genomics. Here, we review the current state of knowledge regarding a heterogenous group of macrophyte natural products, the marine tannins and simple phenolics, to illustrate how such information is critical to future attempts to predict their ecological roles.

Tropical marine herbivore assimilation of phenolic-rich plants.

Phenolics in marine brown algae have been thought to follow a latitudinal gradient with high phenolic species in high latitudes and low phenolic species in low latitudes. However, tropical brown algae from the western Caribbean have been shown to be high in phlorotannin concentration, indicating that latitude alone is not a reasonable predictor of marine plant phenolic concentrations. This study shows that the range of high phenolic phaeophytes is not limited to the western Caribbean but encompasses the western tropical Atlantic, including Bermuda and the Caribbean, where algal phlorotannin concentrations can be as high as 25% dry weight (DW). Assimilation efficiencies (AEs) of phenolic-rich and phenolic-poor plants were examined in three tropical marine herbivores (the parrotfish, Sparisoma radians, and the brachyuran crab, Mithrax sculptus, from Belize and the parrotfish, Sparisoma chrysopterum, from Bermuda). AEs of phenolic-rich food by each of the three herbivore species were uniformly high, suggesting that high plant phenolic concentrations did not affect AEs in these species. This is in contrast to some temperate marine herbivores where phenolic concentrations of 10% DW have been shown to drastically reduce AE. The apparent contradiction is discussed in light of the effects of specific herbivore gut characteristics on successful herbivory of high phenolic brown algae.

Biogeographic comparisons of marine algal polyphenolics: evidence against a latitudinal trend.

Marine allelochemicals generally are present in greater quantity and diversity in tropical than in temperate regions. Marine algal polyphenolics have been reported as an apparent exception to this biogeographic trend, with literature values for phenolic concentrations significantly higher in temperate than in tropical brown algae. In contrast, our results, the first reported for Caribbean brown algae (orders Dictyotales and Fucales), show that many species have high phenolic levels. In addition, both our study and previous studies with north temperate and tropical species demonstrate that there is marked variation in algal phenolic levels within species from different locations. We conclude that high phenolic concentrations occur in species from both temperate and tropical regions, indicating that latitude alone is not a reasonable predictor of plant phenolic concentrations.