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. However, few studies have systematically tested what ecological or life-history traits are associated with organisms' ecological flexibility. 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 analyzed data from 211 stony coral species to test if coral's geographic distribution, depth range, symbiont transmission mode, or colony morphology predict coral-algal flexibility. We report a novel positive correlation between coral-algal flexibility and coral species' geographic range. Symbiont transmission mode is also a predictor of flexibility, albeit the result is less robust against sampling bias. Coral depth range and morphology did not show significant effects. We discuss how host-symbiont dispersal abilities, interactions, and evolutionary history could contribute to the observed patterns and how this finding could inform conservation efforts.