| Summary: | Mutualistic symbioses between tropical cnidarian hosts and dinoflagellate symbionts are critical to the ecological success and function of coral reefs. Unfortunately, these symbioses are susceptible to climate change stressors, and extreme stress causes bleaching or the loss of symbionts from the host tissue. Thermal anomalies that cause bleaching are increasing in severity and frequency, and many studies have quantified the effects of extreme thermal stress on cnidarian symbioses. However, our understanding of how these relationships will acclimatize and adapt to future environmental conditions is lacking. My first experiment characterizes the physiological and molecular homeostasis reached by three asexual generations of Exaiptasia diaphana after 345 days of sublethal acidification and heating. Physiological acclimation was generation-specific, with later generations recovering or even improving function lost during acclimation in the first generation. However, asexual reproduction declined with acidification and heating in the first two generations suggesting that future environmental conditions could negatively affect anemone reproductive fitness. Unlike the generation-specific physiological response, anemone gene expression responded similarly to acidification and heating across generations. Acclimation to ocean acidification and heating required nuanced transcriptomic regulation that differed from patterns seen in acute stress experiments and were only identified using a novel analysis pipeline. Anemones in the acidification and heating treatment downregulated genes typically upregulated in response to acute stress, including immune signaling, protein folding, and programmed cell death, while upregulating genes associated with biogenesis and metabolism. Together this indicates that the sublethal stress treatment was sufficiently moderate to avoid the coral environmental stress response and suggests that elevated inorganic carbon availability and thermally-induced metabolic increases could support ...
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