In this two year postdoctoral research fellowship, the fellow will investigate how photosymbiotic associations shape marine biodiversification using the bivalve subfamily Fraginae as a study system. Research results will contribute to our fundamental knowledge of biodiversity, macroevolution and marine ecology. The project will be conducted under the mentorship of Dr. Colleen Cavanaugh at Harvard University. The project includes multi-level outreach activities that are specifically designed to broaden participation of underrepresented groups in ocean sciences.
Photosymbiotic associations between invertebrate hosts and photosynthetic dinoflagellates are crucial to the trophic and structural integrity of coral reef ecosystems. Although extensive efforts have been devoted to study the short-term ecological interactions between animal hosts and their symbionts, the effects of photosymbiosis on long-term evolutionary dynamics of marine metazoans are less well understood. This is partially because most marine photosymbiotic associations are ancient (e.g., arising more than 200 MYA for corals). The hosts' present diversities and genomes are highly modified by long, complex evolutionary histories; this makes it difficult to trace specific changes due to photosymbioses. The bivalve subfamily Fraginae is an apt system to address this topic because it contains an exclusive photosymbiotic lineage that diverged recently (7 MYA) from its non-symbiotic sister groups. Species in this group exhibit remarkable ecological and morphological adaptations to the photosymbiotic lifestyle. They occupy nutrient-deficient habitats where non-symbiotic species do not occur. Some species possess greatly flattened, solar-panel-like shells to enhance sunlight exposure to the symbionts, or bear microstructural shell features which function as light condensing lenses. To advance understanding of these photosymbiotic associations, the fellow will investigate evolutionary impacts of photosymbioses on Fraginae at two distinct levels. At a macroevolutionary level, patterns of lineage diversification and shell morphological evolution will be compared between the photosymbiotic and non-photosymbiotic lineages using phylogenetic comparative analyses. At a genomic level, comparative transcriptome analyses will be performed on twelve Fraginae species collected from the Indo-west Pacific and Atlantic oceans. Candidate genes involved in the establishment of photosymbioses will be identified and their functions in the hosts' physiological pathways and shell formations will be explored.
