Species and population genomic differentiation in Pocillopora corals (Cnidaria, Hexacorallia).

Correctly delimiting species and populations is a prerequisite for studies of connectivity, adaptation and conservation. Genomic data are particularly useful to test species differentiation for organisms with few informative morphological characters or low discrimination of cytoplasmic markers, as in Scleractinians. Here we applied Restriction site Associated DNA sequencing (RAD-sequencing) to the study of species differentiation and genetic structure in populations of Pocillopora spp. from Oman and French Polynesia, with the objectives to test species hypotheses, and to study the genetic structure among sampling sites within species. We focused here on coral colonies morphologically similar to P. acuta (damicornis type β). We tested the impact of different filtering strategies on the stability of the results. The main genetic differentiation was observed between samples from Oman and French Polynesia. These samples corresponded to different previously defined primary species hypotheses (PSH), i.e., PSHs 12 and 13 in Oman, and PSH 5 in French Polynesia. In Oman, we did not observe any clear differentiation between the two putative species PSH 12 and 13, nor between sampling sites. In French Polynesia, where a single species hypothesis was studied, there was no differentiation between sites. Our analyses allowed the identification of clonal lineages in Oman and French Polynesia. The impact of clonality on genetic diversity is discussed in light of individual-based simulations.