Browsing by Author "Lane, Willa"
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Item SYMBIONT THERMAL HISTORY AND SENSITIVITY INFORM PHOTOCHEMICAL PERFORMANCE IN THE SEA ANEMONE EXAIPTASIA DIAPHANA DURING ACUTE HEATING(University of Delaware, 2023-05) Lane, WillaIncreasing seawater temperature due to global climate change is one of the largest threats to coral reefs. Excess heating often results in the host expelling the symbiotic algae, leading to a phenomenon commonly called coral bleaching. However, in some symbioses, these algae have the capacity to adjust to heating and can modulate this stress response. I examined how two genotypes of the symbiotic dinoflagellate Breviolum minutum responded to acute heat stress in the sea anemone Exaiptasia diaphana. Two phenotypes were tested for each genotype, one of which was thermally tolerant and previously exposed to gradual heating in free-living culture, and the other of which was thermally sensitive (i.e., wild-type) and naïve to heating. Anemones were acclimated to two different light levels to determine if photoacclimation differed by symbiont type, and if photoacclimation and symbiont type interacted to change the heat stress response. Anemones were then exposed to six hours of acute heating (from 24°C to 28, 32, 34, and 36°C), followed by a 16-hour recovery period at 28°C. At the end of acute heating, the maximum quantum yield of photosystem II (Fv/Fm) decreased with increasing temperature for all groups, but thermally selected algae exhibited less decline at low light levels. By the end of the recovery period, anemones exposed to 34°C showed some recovery in photochemistry, while Fv/Fm remained low in anemones exposed to 36°C. While Fv/Fm was sensitive to short-term heating, symbiont density and chlorophyll concentration remained similar to control values, and animal-based reactive oxygen species production did not increase with temperature. Overall, thermally selected symbionts did confer some tolerance to the host, and acute heat stress may predict the overall thermal tolerance of host-symbiont pairings. However, both the particular response variables and the time at which they are measured are critical for accurately determining short-term thermal responses in this symbiosis.