Catalina Ramírez-Portilla and colleagues from Project Phoenix have just published a paper in Systematic Biology titled Solving the Coral Species Delimitation Conundrum.

In this case study, the authors focused on delineating tabular Acropora species in Okinawa (Japan) using morphology, cross-breeding trials and DNA sequences. Tabular Acropora spp. are notoriously difficult to identify, a phenomenon that is often attributed to morphological plasticity and a tendency to hybridize. The table species of Okinawa are no exception with much confusion on how many different species are present and uncertainty as to exactly which species they are.

The analyses revealed three morphologically distinct species that are reproductively isolated but share some haplotypes in a mitochondrial phylogeny.

Typically, this sort of discrepancy between morphology and molecules is taken as evidence for reticulate evolution in corals. However, Haploweb analyses of nuclear markers delimited the same three species as the morphological assessment and the breeding trials. Furthermore, there were no patterns suggestive of hybridization or introgression in the resulting nuclear-based conspecificity matrix. This highlights how a lack of monophyly and allele sharing in gene trees should not necessarily be taken as evidence for hybridization.

Catalina Ramírez-Portilla, Andrew H Baird, Peter F Cowman, Andrea M Quattrini, Saki Harii, Frederic Sinniger, Jean-François Flot. Solving the Coral Species Delimitation Conundrum, Systematic Biology, 2021;, syab077. DOI: 10.1093/sysbio/syab077.

Media release: Coral identity crisis – from ARC Centre of Excellence for Coral Reef Studies and James Cook University.