Flexibility in coral-algal symbiosis is positively correlated with host geographic range

Generalists are thought to adapt to a broader breadth of ecological conditions compared to less flexible specialists who exhibit higher local fitness. However, few studies have systematically tested what ecological or life-history traits are associated with organisms’ ecological flexibility, particularly in mutualistic symbioses. Here, we used stony corals to test the relative effects of host traits and ecological factors on corals’ flexibility to form photosymbioses with algae. We used a meta-analysis of 211 stony coral species to test whether a coral’s geographic distribution, depth range, reproductive mode, colony morphology, or any combination of these factors predict coral-algal flexibility. We reported a novel positive correlation between coral-algal flexibility and coral species’ geographic range, while depth range, reproduction, and coral morphology did not show significant effects. We discussed how host-symbiont dispersal abilities, interactions, and evolutionary history could contribute to the observed patterns and how this finding could inform conservation efforts.