Cryptic genetic divergence within threatened species of Acropora coral from the Indian and Pacific Oceans

Abstract

Most hard corals have broad distributions, and historically this was attributed to their capability for extensive dispersal leading to high evolutionary and demographic inter-dependence among regions. More recently there has been a paradigm shift in the understanding of coral dispersal, driven largely by genetic evidence, which has put greater emphasis on self-recruitment and larval retention. There is now a growing body of evidence that morphologically cryptic species exist within many recognized ‘species’ of stony corals. Here, we characterise levels of genetic divergence within and between five species of Acropora sampled from disparate populations spanning the Indo-Pacific Oceans. We find that strong regional genetic differentiation corresponding to the separation of the Indian and Pacific Ocean basins is a consistent pattern in three of the five species examined. Furthermore, the extent of allopatric divergence within species is similar to that observed between species, implying negligible contemporary gene flow between regions in four of the five species examined. This is consistent with the presence of numerous morphologically cryptic allopatric subspecies or incipient Acropora species. If this is confirmed, the conservation status of several species, which are already demonstrably threatened, would require re-evaluation so that risks including silent extinctions and inappropriate translocations are properly managed.