Meeting Abstract
Scelaractinian corals, which form the basis of reef ecoystems, are declining due to stressors like disease. Corals are nutritionally dependent on symbiotic dinofagellates, Symbiodinium. Yet to establish and maintain symbiosis symbionts may suppress host immunity via the host’s transforming growth factorβ (TGFβ) pathway. To explore the relationship between symbiosis, host immunity and the TGFβ pathway, we conducted two experiments using the coral, Orbicella faveolata. First we examined the relationship between the TGFβ pathway and host immune response. Coral cores were pre-treated with exogenous TGFβ, anti-TGFβ, or a vehicle control, followed by an immune challenge. RNAseq analyses revealed few effects of TGFβ pathway manipulation without immune stimulation. In contrast, enhancement of the pathway with exogenous TGFβ resulted in reduction in immune response, whereas inhibition of the pathway preserved the immune response. Next, we used nutrient enrichment to experimentally manipulate symbiont density in coral cores. Gene expression analyses showed a negative effect of symbiont density on host immune gene expression. Comparison of the results from both studies revealed several genes that are affected similarly by TGFβ pathway manipulation and changes in symbiont density, indicating a potential link between TGFβ and symbiosis. Associated negative effects of symbiosis and TGFβ signaling suggest an ecological trade-off: increased symbiont density may provide energetic benefits to the host at the cost of reduced immunity. Further investigation of these relationships will increase understanding of how variation in symbiotic relationships shapes coral disease resistance.
