Environment and Symbiosis
Cnidarian Heat-Stress Response
The heat-stress response (HSR) is an evolutionarily conserved defense mechanism to environmental change. Its controlled by stress sensors and signal transduction pathways to offset deleterious effects of thermal stress . These mechanisms are well-characterized in bacteria, yeast and mammals, and is also sphingolipid-mediated (See Lipids and Symbiosis). In order to understand the breakdown of symbiosis in cnidarians, we first need to understand the series of orchestrated events involved in the HSR. My work on Aiptasia found two phases to the cnidarian HSR:
Phase I= acute stress; rapid loss of symbionts and upregulation of heat-shock proteins
Phase II= chronic stress; changes in gene expression, metabolism and membrane organization
Additional characterization is required in non-symbiotic cnidarians to refine the HSR model.
See Kitchen and Weis 2017, J. Exp Biol.
Onset of Symbiosis in Coral Larvae under Temperature Stress
Very few studies have examined the combined stress of symbiosis and elevated temperature on host-symbiont associations during early developmental life stages. Understanding the mechanisms that underlie the formation of coral-algal partnership is critical to predict how coral recruitment and resilience will change in periods of warmer seas forecasted with climate change. In this project, we examined larval health and survival, symbiont colonization, and gene transcriptional profiling under the combined stress of symbiosis and elevated temperature. We used Acropora digitifera, a coral model that is thermally sensitive and dominates reef in southern Japan.
We found that the combined stress decreased larval survival, and decreased symbiont colonization and symbiont density during two weeks of observation. Also, we identified novel transcriptional patterns in the coral molecular stress-response. Our data suggest that the physical environment and biotic pressures dramatically decreases larval health prior to settlement in A. digitifera.