Phylogeography of the sea urchin genus Echinothrix.

<p><span>The sea urchins <i>Echinothrix calamaris</i> and<i> E. diadema</i> have sympatric distributions throughout the Indo-Pacific. Diverse colour variation is reported in both species. To reconstruct the phylogeny of the genus and assess gene flow across the Indo-Pacific we sequenced mitochondrial 16S rDNA, ATPase-6, and ATPase-8, and nuclear 28S rDNA and the Calpain-7 intron. Our analyses revealed that <i>E. diadema</i> formed a single trans-Indo-Pacific clade, but <i>E. calamaris</i> contained three discreet clades. One clade was endemic to the Red Sea and the Gulf of Oman. A second clade occurred from Malaysia in the West to Moorea in the East. A third clade of <i>E. calamaris</i> was distributed across the entire Indo-Pacific biogeographic region. A fossil calibrated phylogeny revealed that the ancestor of <i>E. diadema </i>diverged from the ancestor of <i>E. calamaris ~</i>16.8 million years ago (Ma), and that the ancestor of the trans-Indo-Pacific clade and Red Sea and Gulf of Oman clade split from the western and central Pacific clade ~9.8 Ma. Time since divergence and genetic distances suggested species level differentiation among clades of <i>E. calamaris</i>. Colour variation was extensive in <i>E. calamaris</i>, but not clade or locality specific. There was little colour polymorphism in <i>E. diadema</i>.</span></p>