Unexpected cryptic species diversity in the widespread coral Seriatoporahystrix masks spatial-genetic patterns of connectivity

Mounting evidence of cryptic species in a wide range of taxa highlights the need for careful analyses of population genetic data sets to unravel within-species diversity from potential interspecies relationships. Here, we use microsatellite loci and hierarchical clustering analysis to investigate cryptic diversity in sympatric and allopatric (separated by 450km) populations of the widespread coral Seriatoporahystrix on the Great Barrier Reef. Structure analyses delimited unique genetic clusters that were confirmed by phylogenetic and extensive population-level analyses. Each of four sympatric yet distinct genetic clusters detected within S.hystrix demonstrated greater genetic cohesion across regional scales than between genetic clusters within regions (<10km). Moreover, the magnitude of genetic differentiation between different clusters (>0.620G(ST)) was similar to the difference between S.hystrix clusters and the congener S.caliendrum (mean G(ST) 0.720). Multiple lines of evidence, including differences in habitat specificity, mitochondrial identity, Symbiodinium associations and morphology, corroborate the nuclear genetic evidence that these distinct clusters constitute different species. Hierarchical clustering analysis combined with more traditional population genetic methods provides a powerful approach for delimiting species and should be regularly applied to ensure that ecological and evolutionary patterns interpreted for single species are not confounded by the presence of cryptic species.