Planktonic organisms are traditionally conceived as organisms that use sunlight for energy (phototrophs) or organisms that rely on the ingestion of prey for energy and nutrients (heterotrophs). Most food web studies work within these traditional descriptions of planktonic food-web transfers, examining inorganic nutrient uptake by phototrophic phytoplankton, prey ingestion by heterotrophic zooplankton and higher organisms, and recycling of non-living organic material by bacteria. However, many single-celled organisms called protists use “mixotrophy,” or the combination of phototrophy and heterotrophy. These species function at multiple trophic levels simultaneously, using their ability to ingest small prey (like bacteria and other protists) to supplement their photosynthetic abilities. As a result, mixotrophs often have a competitive advantage over strict phototrophs and heterotrophs at low light intensity, or when dissolved nutrients are limiting to the growth of strict phototrophs. In these multiple roles they can dominate areas important for fisheries production and in low nutrient systems (which cover the bulk of the oceans). Their unique flexibility for nutritional and energy acquisition also renders some mixotrophs supreme bloom-forming organisms—many produce toxins that can effect other members of the ecosystem. In this project, we are investigating how mixotrophs function on a cellular level and how environmental factors affect their ecology. As for many eukaryotic microbes, quantitative data about the roles and cellular capabilities of mixotrophs are lacking. We are using a combination of carefully controlled laboratory studies and high throughput sequencing technologies to test hypotheses related to ecological and molecular controls on three model mixotrophes. Each targeted organism exhibits complex and varied physiologies, and each falls differently within the spectrum of mixotrophic requirements, from mostly autotrophic to mostly heterotrophic.
We will determine specific genetic responses and ecological adaptation in different nutritional and physical conditions. This work will improve understanding specific functional properties, multi-scalar responses and interdependencies that connect microbial and abiotic ecosystem processes. We are also evaluating how the use of a combination of multiple strategies may exert additional costs and tradeoffs for building and utilizing dual cell machineries compared to specialized competitors. From these data, models that include the role of mixotrophy can be developed to gain more realistic insights about the nutritional factors that control or predict algal blooms and ecosystem impacts.
Caron, D. A. (2013). Towards a molecular taxonomy for protists: benefits, risks, and applications in plankton ecology. J Eukaryot Microbiol, 60(4), 407-413. doi: 10.1111/jeu.12044
Caron, D. A., P. D. Countway, A. C. Jones, D. Y. Kim, & A. Schnetzer. (2012). Marine Protistan Diversity. Ann Rev Mar Sci, 4(1), 467-493. doi: 10.1146/annurev-marine-120709-142802
Caron, D. A., & D. A. Hutchins. (2012). The effects of changing climate on microzooplankton grazing and community structure: drivers, predictions and knowledge gaps. J Plankton Res, 35(2), 235-252. doi: 10.1093/plankt/fbs091
Kim, D. Y., P. D. Countway, W. Yamashita, & D. A. Caron. (2012). A combined sequence-based and fragment-based characterization of microbial eukaryote assemblages provides taxonomic context for the Terminal Restriction Fragment Length Polymorphism (T-RFLP) method. J Microbiol Methods, 91(3), 527-536. doi: 10.1016/j.mimet.2012.09.026
Koid, A., W. C. Nelson, A. Mraz, & K. B. Heidelberg. (2012). Comparative analysis of eukaryotic marine microbial assemblages from 18S rRNA gene and gene transcript clone libraries by using different methods of extraction. Appl Environ Microbiol, 78(11), 3958-3965. doi: 10.1128/AEM.06941-11
Rose, J. M., E. Fitzpatrick, A. Wang, R. J. Gast, & D. A. Caron. (2013). Low temperature constrains growth rates but not short-term ingestion rates of Antarctic ciliates. Polar Biol, 36(5), 645-659. doi: 10.1007/s00300-013-1291-y
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