An ITS region phylogeny of Siderastrea (Cnidaria: Anthozoa): is S. glynni endangered or introduced?
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The genus Siderastrea contains only five extant species, including Siderastrea glynni, which is one of the few recognized species of endangered stony coral. Cloned sequences of the internal transcribed spacer (ITS) region had low levels of intragenomic nucleotide diversity, and few alignment ambiguities, which allowed for the first species-level phylogenetic analysis of the genus. Results indicated an unexpected deep divergence between the Western-Pacific and Atlantic species. ITS region sequences indicated that S. glynni is not derived from S. savignyana, as previously thought. Instead, S. glynni shared identical sequence types with S. siderea in the Caribbean. Given a range of previously published evolutionary rates for the ITS region, it is unlikely that S. glynni represents the remnants of a population that was divided by the closure of the Central American Seaway (approximately 3–3.8 MYA). It is more likely that S. glynni originated by a breach of the Isthmus (approximately 2 MYA), or a contemporary introduction by ship.