GBE Gene Expression Variation Resolves Species and Individual Strains among Coral-Associated Dinoflagellates within the Genus Symbiodinium John E. Parkinson1,*, Sebastian Baumgarten2, Craig T. Michell2, Iliana B. Baums1, Todd C. LaJeunesse1,and Christian R. Voolstra2,* 1Department of Biology, Pennsylvania State University 2Red Sea Research Center, Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia *Corresponding author: E-mail:
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[email protected]. Accepted: February 1, 2016 Data deposition: This project has been deposited at the NCBI Sequence Read Archive database under accession numbers PRJNA274852, PRJNA274854, PRJNA274855, and PRJNA274856, and the RNAseq transcriptomes at reefgenomics.org. Downloaded from Abstract Reef-building corals depend on symbiotic mutualisms with photosynthetic dinoflagellates in the genus Symbiodinium. This large http://gbe.oxfordjournals.org/ microalgal group comprises many highly divergent lineages (“Clades A–I”) and hundreds of undescribed species. Given their eco- logical importance, efforts have turned to genomic approaches to characterize the functional ecology of Symbiodinium. To date, investigators have only compared gene expression between representatives from separate clades—the equivalent of contrasting genera or families in other dinoflagellate groups—making it impossible to distinguish between clade-level and species-level functional differences. Here, we examined the transcriptomes of four species within one Symbiodinium clade (Clade B) at ~20,000 orthologous genes, as well as multiple isoclonal cell lines within species (i.e., cultured strains). These species span two major adaptive radiations within Clade B, each encompassing both host-specialized and ecologically cryptic taxa. Species-specific expression differences were consistently enriched for photosynthesis-related genes, likely reflecting selection pressures driving niche diversification.