Variation in symbiont uptake in the early ontogeny of the upside-down jellyfish, Cassiopea spp.

The upside-down jellyfish Cassiopea, like many cnidarians, form obligate symbioses with dinoflagellates belonging to the genus Symbiodinium (commonly known as zooxanthellae). In adult Cassiopea, the symbiosis is specific, with a given Cassiopea species hosting a particular symbiont phylotype throughout broad distributions. However multiple phylotypes of Symbiodinium can infect the scyphistoma (polyp) stage of development, making Cassiopea spp. an ideal model to study the effects of symbiont phylotype on host development and proliferation. To assess the flexibility of symbiont acquisition and to understand how symbiont identity affects the early stages of Cassiopea development, symbiont uptake and host developmental traits were monitored in two species of Cassiopea that were exposed to multiple symbiont phylotype in laboratory and field experiments. Scyphistomae of Cassiopea ornata and Cassiopea xamachana both demonstrated flexibility in their symbiosis at the scyphistoma stage during which they acquired a range of laboratory cultured Symbiodinium. The presence of symbionts in C. ornata increased planuloid production relative to uninfected controls, and the rate at which symbionts accumulated in the polyp tissues varied with symbiont phylotype. Laboratory infected C. xamachana polyps continued to take up novel/additional symbiont types when transferred to the field; however, novel uptake occurred significantly less frequently in polyps that harbored homologous (ITS type-A1) symbionts prior to field placement. Similarly, ephyrae of C. ornata were able to acquire additional symbiont types even when already infected with Symbiodinium ITS type C1. Our findings demonstrate that the symbiosis is flexible within the early ontogeny of Cassiopea, but that associating with the "right" symbiont may provide a developmental advantage for that host.