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7888896 
Journal Article 
Heat-evolved microalgal symbionts increase coral bleaching tolerance 
Buerger, P; Alvarez-Roa, C; Coppin, CW; Pearce, SL; Chakravarti, LJ; Oakeshott, JG; Edwards, R; Van Oppen, MJH 
2020 
1 
Science Advances
EISSN: 2375-2548 
6 
20 
32426508 
WOS:000533573300041 
Coral reefs worldwide are suffering mass mortalities from marine heat waves. With the aim of enhancing coral bleaching tolerance, we evolved 10 clonal strains of a common coral microalgal endosymbiont at elevated temperatures (31 degrees C) for 4 years in the laboratory. All 10 heat-evolved strains had expanded their thermal tolerance in vitro following laboratory evolution. After reintroduction into coral host larvae, 3 of the 10 heat-evolved endo-symbionts also increased the holobionts' bleaching tolerance. Although lower levels of secreted reactive oxygen species (ROS) accompanied thermal tolerance of the heat-evolved algae, reduced ROS secretion alone did not predict thermal tolerance in symbiosis. The more tolerant symbiosis exhibited additional higher constitutive expression of algal carbon fixation genes and coral heat tolerance genes. These findings demonstrate that coral stock with enhanced climate resilience can be developed through ex hospite laboratory evolution of their microalgal endosymbionts.