Phylogeography of the sea urchin genus Echinothrix.

The sea urchins Echinothrix calamaris and E. diadema 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 E. diadema formed a single
trans-Indo-Pacific clade, but E. calamaris 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 E. calamaris was distributed across the entire Indo-Pacific
biogeographic region. A fossil calibrated phylogeny revealed that the
ancestor of E. diadema diverged from the ancestor of E. calamaris ~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 E. calamaris.
Colour variation was extensive in E. calamaris, but not clade or locality
specific. There was little colour polymorphism in E. diadema.