Meeting Abstract
Photosymbiotic associations between invertebrate hosts and photosynthetic dinoflagellates are crucial to the trophic and structural integrity of tropical marine ecosystems. Although extensive efforts have been devoted to study the short-term ecological interactions between animal hosts and their symbionts, long-term evolutionary dynamics of photosymbiosis in many marine metazoans are less well understood. The marine bivalve family Cardiidae contains two lineages that include photosymbiotic taxa: the well-known giant clams (Subfamily Tridacninae) and the heart cockles (Subfamily Fraginae). Both groups host symbionts from the same genus (Symbiodinium), although several Fraginae species are non-symbiotic. To date, it is unclear whether the two bivalve lineages share a common photosymbiotic ancestor or evolved photosymbiosis independently. Morphologically, giant clams show relatively uniform shell forms whereas photosymbiotic taxa in the Fraginae exhibit a diverse suite of adaptations to photosymbiosis including greatly flattened, solar-panel-like shells and lens-like microstructural features. In this study, we established a backbone phylogeny for Cardiidae utilizing RNA-Seq-based transcriptomic data from five Tridacninae species, eight Fraginae taxa, and ten other cardiids. Phylogenomic approaches were used to resolve the relationship between Tridacninae and Fraginae, and to demonstrate how photosymbiosis evolved within the marine bivalve family Cardiidae. Our findings provide a solid foundation for understanding genomic evolution of photosymbiosis and long-term environmental influences (e.g., climate change) on photosymbiotic marine communities.
