Abstract
BackgroundClassical morphological taxonomy places the approximately 1400 recognized species of Scleractinia (hard corals) into 27 families, but many aspects of coral evolution remain unclear despite the application of molecular phylogenetic methods. In part, this may be a consequence of such studies focusing on the reef-building (shallow water and zooxanthellate) Scleractinia, and largely ignoring the large number of deep-sea species. To better understand broad patterns of coral evolution, we generated molecular data for a broad and representative range of deep sea scleractinians collected off New Caledonia and Australia during the last decade, and conducted the most comprehensive molecular phylogenetic analysis to date of the order Scleractinia.MethodologyPartial (595 bp) sequences of the mitochondrial cytochrome oxidase subunit 1 (CO1) gene were determined for 65 deep-sea (azooxanthellate) scleractinians and 11 shallow-water species. These new data were aligned with 158 published sequences, generating a 234 taxon dataset representing 25 of the 27 currently recognized scleractinian families.Principal Findings/ConclusionsThere was a striking discrepancy between the taxonomic validity of coral families consisting predominantly of deep-sea or shallow-water species. Most families composed predominantly of deep-sea azooxanthellate species were monophyletic in both maximum likelihood and Bayesian analyses but, by contrast (and consistent with previous studies), most families composed predominantly of shallow-water zooxanthellate taxa were polyphyletic, although Acroporidae, Poritidae, Pocilloporidae, and Fungiidae were exceptions to this general pattern. One factor contributing to this inconsistency may be the greater environmental stability of deep-sea environments, effectively removing taxonomic “noise” contributed by phenotypic plasticity. Our phylogenetic analyses imply that the most basal extant scleractinians are azooxanthellate solitary corals from deep-water, their divergence predating that of the robust and complex corals. Deep-sea corals are likely to be critical to understanding anthozoan evolution and the origins of the Scleractinia.
Highlights
Principally known as the architects of coral reefs, the order Scleractinia, or stony corals, comprises two distinct ecological groups: the zooxanthellate species that live in symbiosis with a photosynthetic dinoflagellate occur in shallow tropical waters; and the azooxanthellate species, which are primarily associated with deeper and colder waters
The advantage of using cytochrome oxidase subunit 1 (CO1) sequence data for coral phylogeny is that, unlike the 16S rDNA, 12S rDNA, and 28S rDNA genes, the sequences are unambiguously alignable because they contain no indels
In addition to 234 scleractinian species, our analysis included representatives of each of the anthozoan subclasses with the exception of Ceriantharia
Summary
Principally known as the architects of coral reefs, the order Scleractinia, or stony corals, comprises two distinct ecological groups: the zooxanthellate species that live in symbiosis with a photosynthetic dinoflagellate occur in shallow tropical waters; and the azooxanthellate species, which are primarily associated with deeper and colder waters. Attempts to establish phylogenetic relationships within coral families based on skeletal characteristics have proved to be challenging, and as a consequence have been applied to date to only six of the 27 extant families – Fungiidae [15,16], Mussidae [17,18], Siderastreidae [17], Turbinoliidae [19], Acroporidae [20] and Dendrophylliidae [21]. Classical morphological taxonomy places the approximately 1400 recognized species of Scleractinia (hard corals) into 27 families, but many aspects of coral evolution remain unclear despite the application of molecular phylogenetic methods. In part, this may be a consequence of such studies focusing on the reef-building (shallow water and zooxanthellate) Scleractinia, and largely ignoring the large number of deep-sea species. To better understand broad patterns of coral evolution, we generated molecular data for a broad and representative range of deep sea scleractinians collected off New Caledonia and Australia during the last decade, and conducted the most comprehensive molecular phylogenetic analysis to date of the order Scleractinia
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