Solving the coral species delimitation conundrum

Distinguishing coral species is not only crucial for physiological,
ecological and evolutionary studies, but also to enable effective
management of threatened reef ecosystems. However, traditional hypotheses
that delineate coral species based on morphological traits from the coral
skeleton are frequently at odds with tree-based molecular approaches.
Additionally, a dearth of species-level molecular markers has made species
delimitation particularly challenging in species-rich coral genera,
leading to the widespread assumption that inter-specific hybridization
might be responsible for this apparent conundrum. Here, we used three
lines of evidence – morphology, breeding trials and molecular approaches –
to identify species boundaries in a group of ecologically important
tabular Acropora corals. In contrast to previous studies, our
morphological analyses yielded groups that were congruent with
experimental crosses as well as with coalescent-based and allele
sharing-based multilocus approaches to species delimitation. Our results
suggest that species of the genus Acropora are reproductively isolated and
independently evolving units that can be distinguished morphologically.
These findings not only pave the way for a taxonomic revision of coral
species but also outline an approach that can provide a solid basis to
address species delimitation and provide conservation support to a wide
variety of keystone organisms.