Diverse chemical compounds play critical roles in the defenses of many marine organisms and can influence the community structure of entire ecosystems. This complexity reaches a peak on tropical coral reefs, which are well-known targets for prospecting biomedical agents. Although many marine natural products have been studied for biomedical activity, yielding important information about their biochemical effects and mechanisms of action, much less is known about predators' abilities to overcome these defenses. It is important to understand how predators cope with poisons in their diet (from prey biochemical defenses) and how these systems parallel human's ability to remove foreign chemicals that are encountered in their every day lives (drugs, pollutants, toxins, etc.) This project's use of herbivorous reef fish to define mechanisms of tolerance to chemically-rich diets will help fill important gaps: Fish that have evolved in (and depend on) chemically-rich coral-reef environments should be valuable models for studying mechanisms of xenobiotic tolerance. This knowledge will help to develop marine natural products as biomedical resources for humans; and, mechanisms of xenobiotic tolerance in herbivorous fish will provide fascinating and potentially insightful counterparts to mechanistic studies in well-studied terrestrial organisms such as insects. The vast majority of vertebrates are fishes, yet little is currently known about how fish tolerate their preys' biochemical defenses especially in tropical marine communities, where these mechanisms can be assumed to be highly developed. A state of the art genetic approach will characterize all genes expressed in the liver of S. spinus, a fish species that broadly represents chemically resistant tropical herbivorous fishes. These genes will be used to build a microarray chip to quantify changes in gene expression in response to differing environmental conditions. All gene sequences will be submitted to the National Center for Biological Information (available on www.ncbi.nlm.nih.gov/.) This work will provide an opportunity to define diet-driven adaptive mechanisms in tropical herbivorous vertebrates for the first time, and increase understanding of herbivore offense. Guam's island community has strong ties to the ocean, making marine science a valuable opportunity for presenting locally relevant scientific concepts and methods to a public to whom science often seems foreign. Public presentations and paid summer high-school research internships and the involvement of undergraduate and graduate biology majors will help to expand these opportunities. A better understanding of tropical fishes' mechanisms for coping with dietary xenotoxins can contribute to resource-management efforts to minimize impacts from nuisance species' of alga (e.g., cyanobacteria and other 'harmful algal blooms'; ciguatera poisoning). This project also has potential for initiating additional collaborative efforts towards ecologically relevant metabolomic and proteomic analyses of S. spinus. For people that depend on the ocean for food, understanding why some natural products persist in marine food chains can be equivalent to understanding the size and/or safety of their most important resource.

Project Report

The last three decades of research in marine chemical ecology have led to many great insights in our understanding of the ecological interactions between seaweeds and their herbivore predators. We now know that diverse chemical compounds play critical roles in the defenses of many marine organisms and can influence the community structure of entire ecosystems. This complexity reaches a peak on tropical coral reefs, which are well-known for seaweeds that produce a variety of chemical defenses. Yet, to date, very little knowledge exists on how herbivores tolerate and/or overcome these chemically-rich diets. Terrestrial organisms have adapted to consuming chemically defended plants through the evolution of behavioral, biochemical, and morphological countermeasures. It makes sense that marine organisms have done the same to increase the likelihood of obtaining the nutrients they need for survival and reproduction. Using a cross-disciplinary approach that melds field-sampling, laboratory-manipulations within a flow-through seawater system, molecular biology, next-generation transcriptomics (RNAseq), and computational analyses (bioinformatics) researchers at the University of Guam Marine Laboratory (UoGML) leveraged support from this Research Initiation Grant to Broaden Participation in Biology Program (RIGBP) to build a foundation for evaluating XME-expression plasticity in one culturally important reef fish, Siganus spinus, a strict herbivore who’s feeding preferences are not strongly affected by algal chemistry, and spark a decade of eco-biochemical analyses of diet-derived secondary metabolites. Although this work is in its infancy, over the course of these last three years a total of eighteen underrepresented minorities (eight graduate, three undergraduate, four high-school, and three middle-school students) have been trained in these diverse scientific disciplines. Together, they have isolated, sequenced, and annotated the S. spinus hepatic transcriptome, which encodes over 29,000 unique contigs. Further bio-informatic analyses of the genes expressed within these livers suggest that this species has the potential to produce over 130 gene products that, through comparisons with previously characterized genes in other organisms, have the potential to alter the fate of algal chemical defenses once consumed. We now know, using gene-expression analyses and dose/time-response experiments, that some of these genes have the ability to respond (via induction) to the presence of foreign substances within the fish’s body, including persistent organopollutants. These findings have important implications in terms of not only understanding how herbivorous fish deal with the natural chemical complexity within their world, but also how personal care and pharmaceutical products in the environment may complicate these interactions. Two major broader impacts are directs result of the knowledge and insights gained from this research initiation grant. First, the University of Guam has identified weaknesses within its research portfolio; these combined with our newly developed understanding of the power and utility of transcriptomics in investigating ecology, including how, when and why corals bleach, have become the foundation for a larger Experimental Program to Stimulate Competitive Research (EPSCoR) proposal that will change the very nature of UoG research. Second, on February 1, 2014, the 32nd Legislature of Guam passed Bill No. 190-32, creating the Research Corporation of the University of Guam (RCUoG), which enables UoG to institutionalize administrative and fiscal procedures dedicated to enhancing the feasibility and sustainability of 21st century research in the Western Pacific. Now, many more Pacific Islanders from Micronesian descent can aspire to research and work on the natural world which surrounds them.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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William E. Zamer
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University of Guam
United States
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