Spawning times and breeding trials suggest no inbreeding occurs between Porites aff. lutea and P. cf cylindrica

Molecular approaches have advanced our understanding of reef coral biodiversity. However, in some taxa, they have yet to deliver a robust taxonomy that reflects differences in the ecology and biology of species. For example, Porites cf. cylindrica and P. aff. lutea, which have different morphologies and life histories, are clustered close together in a complex containing several other Porites species when analyzed using both single locus molecular markers and thousands of SNPs from ezRAD data. This suggests the possibility of recent or ongoing speciation and/or hybridization between these species. Here, we used the timing of gamete release and gamete compatibility to test reproductive boundaries between the two. At Orpheus Island (Australia), P. cf. cylindrica and P. aff. lutea spawned on the same night, while at Sesoko Island (Japan), they did not. Furthermore, when spawning occurred during in vitro breeding trials, the eggs did not cleave, suggesting that P. cf. cylindrica and P. aff. lutea are not interbreeding. Breeding trials can help resolve species identities in taxa for which molecular and morphological data provide unclear results.