Ecological Speciation in Corals

The ocean is generally a homogenous environment with few geographic barriers that allow populations to connect over hundreds of kilometers, increasing gene flow and slowing down diversification and the formation of species. However, biodiversity in the ocean is vast across thousands of kilometers and even within single individuals (e.g., coral colonies). Species diversity peaks at coral reef ecosystems, which house at least one quarter of the marine biodiversity. Why are these systems so diverse? How do species differentiate despite rampant genetic connectivity? One possibility to explain biodiversity hotspots in the ocean, along with physical barriers, is through ecological factors. Populations can diverge if they specialize ecologically, reducing interbreeding, which can lead to reproductive isolation. We reviewed cases of speciation in coral reefs with emphasis on those driven by ecological factors. We find few studies in coral research using genomic approaches to understand the genetics of reproductive isolation. We propose the cases of the coral Orbicella spp. and the octocoral Eunicea spp. as ideal examples to study ecological speciation in corals.