Early Evolution of the Montastraea “annularis” Species Complex (Anthozoa: Scleractinia): Evidence from the Mio-Pliocene of the Dominican Republic

Our understanding of species boundaries in reef corals has changed considerably over the past decade due to new discoveries in the areas of molecular phylogenetics, population genetics, and reproductive biology (Knowlton and Budd, 2001; Willis et al., 2006). Several species, long thought to be highly variable, have been found to be complexes of multiple species, similar to syngameons in plants. Within these species complexes, hybridization takes place most frequently in marginal habitats at the periphery of species ranges (Fukami et al., 2004a), and is believed to play an important role in range expansion, adaptation to changing environments, and evolutionary diversification (Willis et al., 2006). Nevertheless, due in part to disruptive selection (Wolstenholme et al., 2003; Willis et al., 2006), species are discrete and cohesive evolutionary entities with distinct ecological characteristics. Thus, despite occasional interspecific gene flow and reticulate evolution, species can be traced through geologic time (Budd and Klaus, 2001; Budd and Pandolfi, 2004). The patterns of speciation and extinction within any one complex over geologic time remain largely unexplored.