Ribosomal Internal Transcribed Spacer (ITS) DNA Variation in Millepora

Abstract

Two main growth forms of Millepora (fire coral) are present around the islands of The Bahamas: one exhibits a strong, blade-like structure, Millepora complanata, and the other possesses a delicate branch-like structure, Millepora alcicornis. The phylogenetic relationship of these corals has been under considerable debate for over a century due to the existence of a wide-range of intermediate growth forms. Recent genetic analysis using ribosomal DNA (rDNA) suggests the existence of two distinct reproductively isolated cryptic clades that are independent of morphology (1). However, using repeated rDNA sequences for phylogenetic construction can lead to false phylogenies if repeated sequences have not undergone concerted evolution, a process involving homogenization of individual repeats of a multigene family. We analyzed twenty rDNA clones isolated from a single bladed Millepora colony and found that although variant rDNA sequences were present, rDNA appears to be largely homogenized.