Effect of Temperature Stress on Competition in Algal-Cnidarian Symbiosis
Open Access
- Author:
- Hewitt, Michael
- Area of Honors:
- Biology
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Todd C Lajeunesse, Thesis Supervisor
James Harold Marden, Thesis Honors Advisor - Keywords:
- symbiodiniaceae
coral
zooxanthellae
cnidarians
jellyfish
cassiopea
climate change
heat stress
temperature stress
competition - Abstract:
- Marine heatwaves associated with climate change and subsequent mass coral-bleachings have prompted decades of increased interest in the vital symbiosis between reef-building corals and mutualistic dinoflagellates in the family Symbiodiniaceae (zooxanthellae). The upside down jellyfish Cassiopea xamachana is a useful model system for studying symbiosis establishment, and competition between their potential symbionts. Previous studies have looked at competition between symbiont species in this system, however, none have looked at competition under heat stress. In some corals, thermotolerant symbionts may be more successful under high heat than their less tolerant counterparts. We ran competition experiments between three symbiont species known to establish symbiosis with C. xamachana; the jellyfish’s homologous symbiont Symbiodinium microadriaticum, and the heterologous symbionts Breviolum minutum, as well as the thermally tolerant Durusdinium trenchii. Each experiment paired species against one another, at different starting concentrations (25:75, 50:50, 75:25). The experiments were run under both control (27˚C) and heat-stressed (32˚C) conditions. Under control temperatures S. mic. and D. trenchii both competitively displaced B. min., but when competing against one another there was less of a clear winner in either direction. Under heat-stress, the polyps that were given heterologous symbionts did poorly; only two ephyrae established symbiosis and all polyps appeared bleached, however the polyps that were given the homologous symbiont continued strobilating throughout the experiment. Under heat stress, S. mic. dominated both of the other species. These results suggest that partner specificity in C. xamachana is somewhat strong and although the system can harbor heterologous symbionts, these foreign symbionts do not help the animal survive during heat stress even if the symbionts themselves are thermotolerant.