Convergent Symbioses: Morphology, Life History, and Niche Specialization in Coral and Lichen Mutualisms

Corals and lichens represent some of the most diverse mutualistic symbioses in the marine and terrestrial ecosystems. Their evolutionary success is partly attributed to their association with internal, photosynthetic symbionts, which provide carbon and enable colonization of a wide-range of habitats. Although corals and lichens occupy fundamentally different ecosystems and are phylogenetically unrelated-corals are animals associated with dinoflagellates, while lichens are fungi associated with green algae/cyanobacteria-they share surprisingly many morphological, ecological, and life history traits. Here, we juxtapose morphology, reproduction, dispersal, symbiont acquisition strategies, and symbiont diversity in coral and lichen mutualisms, focusing mainly on the host and associated photobiont partner. We highlight how shared traits lead to convergent mechanisms of niche specialization, including adaptation to abiotic conditions through the formation of environment-specific host-symbiont combinations. The comparison enhances our understanding of evolutionary forces shaping these symbioses and provides a framework for evaluating their adaptive potential in a changing world.