Influence of different substrates on the evolution of morphology and life-history traits of azooxanthellate solitary corals (Scleractinia: Flabellidae)

Abstract

Sessile organisms are influenced considerably by their substrate conditions, and their adaptive strategies are key to understanding their morphologic evolution and traits of life history. The family Flabellidae (Cnidaria: Scleractinia) is composed of the representative azooxanthellate solitary corals that live on both soft and hard substrates using various adaptive strategies. We reconstructed the phylogenetic tree and ancestral character states of this family from the mitochondrial 16S and nuclear 28S ribosomal DNA sequences of ten flabellids aiming to infer the evolution of their adaptive strategies. The Javania lineage branched off first and adapted to hard substrates by using a tectura-reinforced base. The extant free-living flabellids, including Flabellum and Truncatoflabellum, invaded soft substrates and acquired the flabellate corallum morphology of their common ancestor, followed by a remarkable radiation with the exploitation of adaptive strategies, such as external soft tissue [e.g. Flabellum (Ulocyathus)], thecal edge spine, and transverse division (e.g. Placotrochus and Truncatoflabellum). Subsequently, the free-living ancestors of two genera (Rhizotrochus and Monomyces) invaded hard substrates independently by exploiting distinct attachment apparatuses such as tube-like and massive rootlets, respectively. In conclusion, flabellids developed various morphology and life-history traits according to the differences in substrate conditions during the course of their evolution. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 184–192.