The very word infection brings to mind the arrival of a nasty pathogen countered by a host immune response, a battleground strewn with the carcasses of the losers. But how do you define infection? Is not the beginning of an endosymbiosis, even a mutually beneficial one, also an infection? Corals, anemones, and other Cnidarians have been infected for millions of years. They are among the numerous marine invertebrates that have established endosymbioses with photosynthetic partners, their partners being dinoflagellate algae of the genus Symbiodinium (commonly referred to as zooxanthellae, or zoox for short). While some Cnidarians pass their endosymbionts to their offspring, others have to be “infected” anew each generation. The intricacies of this relationship between Cnidarians and their dinoflagellates is the subject of an exhaustive review (424 cited references!) by Davy, Allemand, and Weis. Here you’ll find many questions to ponder, each presented as a mini-review that includes what is known, the research that provided those answers, and current hypotheses about the remaining questions. Here is a sampling of those questions.
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