Project: Dimensions: Links Between Spectral Irradiance and Cryptophyte Biodiversity in Environments from Ponds to Oceans

In aquatic environments, microscopic algae known as phytoplankton are important primary producers. Through photosynthesis, these organisms fix carbon dioxide into the organic carbon molecules that fuel life in ponds, rivers, lakes and oceans. The color of light available for photosynthesis varies among environments, e.g., the deep blue ocean vs. a black water river. In order to live in a particular environment, phytoplankton must have photosynthetic pigments that are tuned to absorbing the colors of light available. This project focuses on the cryptophytes, a relatively uncharacterized group of phytoplankton, that are abundant in a wide range of aquatic habitats ranging from small ponds to oceans. Cryptophytes use phycobilin pigments to capture light energy; these pigments allow cryptophytes to photosynthesize in light environments that are poorly exploited by other types of algae. The project goals are: (1) to characterize the ecological distribution and taxonomic diversification of cryptophyte species, (2) to determine the effectiveness of their light capture in different light environments, and (3) to characterize the molecular evolutionary pathways of critical light capture genes. Understanding these links is important to predicting how changes in land-use (like deforestation and urbanization, both of which impact the color of light in downstream watersheds) will affect aquatic productivity. This project will provide training for a post-doc, 2-4 graduate students, and 10 undergraduates. Through a partnership with Morris College and other University of South Carolina programs, underrepresented minorities will be recruited into summer fellowships. Novel cryptophyte strains will be deposited in living culture collections for use by other researchers.

This project's central question is deceptively simple: How do functional, genetic, and phylogenetic diversity interact in the ecological diversification of cryptophytes with respect to light environment? The researchers will conduct an integrative research program on the biodiversity of cryptophytes to understand how environmental variation in spectral irradiance is associated with the physiological diversity of light capture in cryptophytes in the context of their historical diversification. This work integrates several components: (1) Field sampling in water bodies ranging from small ponds to oceans to identify the specific light environments in which strains live, to determine the pigments that cryptophytes produce in those habitats, and to identify novel species; (2) Phenotypic studies to determine how variation in spectral irradiance (light color) influences light capture, photosynthesis, and growth of diverse taxa. These will also determine spectral absorption of phycobilins in strains throughout the cryptophyta; (3) Construction of a well-supported phylogeny based on sequencing nucleomorph genomes of ~200 strains; (4) Analyses of molecular evolution of key light capture genes, in particular those that encode the alpha and beta subunits of the cryptophyte phycobiliproteins, and those involved in the phycobilin synthesis pathway; (5) Experimental evolution to test the ability of diverse strains of cryptophytes to evolve into new light niches; (6) Experimental transcriptomics to identify the functional responses of diverse strains to variation in spectral irradiance; and (7) Phylogenetically-informed tests of the associations between habitat, molecular evolution, organismal performance, and spectral absorbance. Ultimately, this work should be a transformative contribution to our understanding of the diversification of photosynthesis and the role of that diversification in the ecological distribution of cryptophytes.