Abstract
The relationship between clownfishes and sea anemones is one of the most recognizable examples of symbioses on the planet. There are 30 described species of clownfishes, which have adaptively radiated to live with sea anemones, but only 10 nominal species of host anemones. Why does the diversity of clownfishes exceed that of the host anemones? Given the co-dependent nature of the mutualism, their broad geographic and ecological distribution, and that all 10 host species are only described morphologically, we hypothesize that many host anemone species are cryptic species complexes. We use the bubble-tip sea anemone Entacmaea quadricolor, the species that hosts the greatest number of clownfishes, as a case study to demonstrate the extent to which species level diversity in host anemones is likely underdescribed. Using samples spanning the entire geographic range of E. quadricolor, we take a molecular species delimitation approach using traditional and high-throughput sequencing to demonstrate that E. quadricolor harbors at least three cryptic species. These include an endemic species in the Red Sea, and lineages in the Indian and Pacific Oceans, respectively. Our slowly evolving Sanger sequence dataset recovers a fully supported (Red Sea, (Indian Ocean, Pacific Ocean)) topology, suggesting the E. quadricolor complex has an ancient Paratethyan origin that likely pre-dates the origin of the clownfish symbiosis. These are the first data that suggest the presence of cryptic host anemone diversity in the clownfish symbiosis. Our findings have important implications for our understanding of the evolution of the entire symbiosis