High genetic differentiation and low connectivity in the coral Pocillopora damicornis type β at different spatial scales in the Southwestern Indian Ocean and the Tropical Southwestern Pacific

Abstract

Studying genetic connectivity in marine populations aims to understand the dispersal of an organism through the seascape and thus its gene flow. Here, we focused on one lineage of the recently revised coral Pocillopora damicornis complex, P. damicornis type β, corresponding to Primary Species Hypothesis PSH05 in Gelin et al. (Mol Phylogenet Evol 109:430–446, 2017b): it had been hypothesized that P. damicornis type β encompasses four distinct lineages, representing Secondary Species Hypotheses (SSH05a, SSH05b, SSH05c and SSH05d). The aim of the present study was to confirm this partition and to infer the genetic structuring and connectivity among 27 populations for this widespread and common scleractinian. For this, a total of 1418 colonies were hierarchically sampled from two marine provinces of the southern parts of its distribution range, which remain largely understudied: the Western Indian Ocean and the Tropical Southwestern Pacific. Using 13 microsatellite loci and assignment tests, our findings confirmed the partition into four SSHs, each SSH splitting into clusters, suggesting that P. damicornis type β may represent a complex of cryptic species. Moreover, within each SSH, clonal propagation was evidenced in almost every population, but clonal dispersal was mostly restricted to sampling site (except in Reunion Island and northern Madagascar, where clones were found in several populations approximately 50 km apart). Nevertheless, wherever the cursor of species level is placed (one or several species), populations were highly differentiated both within the Western Indian Ocean and the Tropical Southwestern Pacific, suggesting restricted gene flow at different spatial scales (marine province, ecoregions, islands/regions), leading to diverging lineages.